**5. Conclusions**

The introduction of the Climate Based Daylight Modelling (CBDM) concept has questioned the robustness of the traditional practice of relying on static (i.e., fixed) sky conditions to appraise daylight levels within buildings. This paper advanced the knowledge about the use of recently developed CBDM metrics by proposing a detailed daylight analysis of a school building located in Agira (Italy), a town that experiences sunny and clear-sky conditions for most of the year.

Hourly simulations, run using the Radiance-based DIVA software for a calibrated daylight model, allowed to identify the main issues of rooms presenting different orientation, shape, function, and furniture, and helped to inform the design of the required shading and re-directing devices.

More in detail, the calculation of the spatial Daylight Autonomy (*sDA*) metrics revealed good daylight availability for all of the rooms analysed (with values always higher than 90%), but on the other hand the Annual Sunlight Exposure (*ASE*) calculation evidenced a risk of glare occurrence especially for the gym (*ASE* = 68.2%). This happens because of the large glazed surfaces that are oriented due to both west and east, since they expose the room to direct sunlight in the morning (from east) and in the afternoon (from west). Glare risks have been confirmed by the calculation of the simplified Daylight Glare Probability (*DGPs*) metrics for some observers' position and by the number of hours when the Useful Daylight Illuminance (*UDI*) metric is above the upper threshold of 2000 lux (which happens for around 23% of the occupied hours in the standard and computer classrooms).

Based on these outcomes, retrofit solutions that are aimed at reducing and re-directing direct sunlight, such as external overhangs, light shelves, louvers, and reflective ceilings, have been designed and their efficacy tested by calculating all of the static and dynamic metrics again. The results showed that, despite a reduction in daylight levels in proximity of the windows, as shown by lower *sDA* values than in the base case, higher illuminance values were expected at the bottom of the rooms.

In this way, the useful *UDI* metrics keeps above 90% in all rooms, the *ASE* metrics is close to the threshold of acceptability of 10% (except for the computer classroom) and the *UR* significantly improves in all rooms.

However, it must be pointed out that a design that was carried out using CBDM metrics appears in contrast with what would be suggested if considering the average Daylight Factor (*aDF*) metrics alone, as it is usually done in common design practice. In fact, all of the proposed design solutions lower the *aDF* values if compared to the existing scenario, which are already below the minimum threshold, as prescribed by the Italian regulations for classrooms. This would likely suggest a designer to bring in more daylight by increasing the glazed surfaces; however, such a choice would actually be wrong in relation to the sunny hours, which are much more frequent than cloudy hours in Southern Italy.

These outcomes rebate the need of performing more accurate and dynamic daylight simulations using recorded (i.e., varying) rather than fixed sky conditions to correctly inform the design process.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/2071-1050/10/8/2653/s1, Figure S1: Hourly luminance distribution for a typical user of the standard classroom, computer classroom and gym, respectively, during 7 December from 7 a.m. to 5:30 p.m.

**Author Contributions:** Conceptualization, Methodology and Writing, V.C.; Writing—review and editing and Data Curation, G.E.; Supervision and Resources, L.M.; Investigation and Visualization, F.P.N.

**Acknowledgments:** The authors would like to warmly thank all the teachers and pupils of the 'Guglielmo Marconi' elementary school in Agira (Italy) for their kind support throughout the measurement campaign.

**Conflicts of Interest:** The authors declare no conflict of interest.


**4. Discussion**

A total of 124 studies were systematically reviewed to identify relevant dimensions of family functioning associated with children's and adolescents' happiness. Four themes emerged from a review of these studies: (1) family dimensions and happiness; (2) global family functioning (i.e., family functioning and family relationships), environmental variables and happiness; (3) parental differences; (4) longitudinal studies.

Regarding the first theme, 91 studies examined the relationship between family dimensions (i.e., family cohesion and adaptability, family satisfaction and communication, and family conflict) and children's and adolescents' happiness. The results highlighted that family cohesion significantly predicted changes in happiness, life satisfaction, and positive affect over time [77,113,117,175]. In other words, increased family cohesion and adaptability were associated with higher levels of happiness in children and adolescents [20,110,122]. Thus, positive family dimensions may contribute directly to children's and adolescents' sense of happiness, contentment, and general life satisfaction [111,121].

Furthermore, in both boys and girls, positive communication with the mother and the father and high family satisfaction were directly associated with increased happiness [25,138,170,174]. The possibility to express oneself freely at home (i.e., to speak openly about any subject) was associated with greater life satisfaction for adolescents [114]. Adolescents who communicated effectively with their families probably felt that they could share their points of view and feelings openly and sincerely with their parents, and they may have interpreted this communication as a sign of parental support, trust, and closeness [30,140]. This may be especially true for girls, for whom the influence of family communication on happiness was slightly greater [27,171], possibly due to gender differences in cultural norms and socialization. Different parental socialization styles based on child gender [204] may also explain why communication tends to be more open between mothers and daughters and between fathers and sons [140].

On the other hand, communication problems and higher levels of family conflict were associated with lower happiness for children and adolescents [126,128,139]. When communication was open and trouble-free, children and adolescents were more likely to report satisfaction with their families, positive affect, and low levels of conflict, relative to children and adolescents who reported less communication with parents [30]. This finding suggests that family relationships which are perceived to be good may help children and adolescents develop feelings of freedom, love, and happiness [172], underlining that family dimensions play an essential role in influencing children's and adolescents' happiness [46].

As regards the second theme, 39 studies examined the association between global family functioning (i.e., family functioning and family relationships), family environment variables, and children's and adolescents' happiness. Specifically, a more positive perception of family functioning was related to better emotional well-being in children and adolescents [184,185,191,203]. Furthermore, regardless of the cultural background, children's family relationships influenced their levels of happiness [1,196] more significantly than any other variable. Bad parent–child relationships were usually accompanied by lower levels of family satisfaction and happiness [145]. Thus, feeling happy at home may contribute to both boys' and girls' happiness [174].

The reported studies provided support for the association between global family functioning and happiness during adolescence, even though adolescents consolidate new social relationships with friends and partners during this developmental period [36]. The family is the context in which the first emotional relationships develop, and where children learn to respect and establish positive relationships of love and respect for others [194]. Parents in a well-functioning family can provide emotional support to children, allowing them to express their emotions. A warm and open family communicates happiness to children [185], giving them a sense of security, emotional connection, and trust [178].

A subtheme of environmental factors associated with happiness concerned differences in sociodemographic variables. Some family factors predicted individual differences in happiness and life satisfaction during adolescence. In particular, more positive family environments were associated with greater happiness [191,197]. Furthermore, the findings supported both stability and change in perceived levels, and the relevance of certain life satisfaction domains, among children and adolescents. Young people who perceived a higher quality parent–child relationship had elevated and stable life satisfaction from middle adolescence (i.e., aged 14–16 years) to late adolescence (i.e., aged 17–18 years) [197].

Other studies found that young people's life satisfaction was negatively correlated with age in all global and life (i.e., family satisfaction) domains [48,146]. The decrease in happiness levels during this period suggests that pre-adolescence may be a stressful phase of development, during which cognitive, physical, and emotional changes strongly influence young people's overall sense of happiness [27]; family members may play an essential role in accompanying them through these changes. In particular, the decline in both family cohesion and happiness during early and middle adolescence (i.e., aged 12–16 years) may be explained by both the multiple challenges that adolescents face and the more significant conflict that they tend to experience with parents, which tend to result in less participation in family activities; this may reduce adolescents' perceived family cohesion and life satisfaction [117].

Regarding the third theme identified, 17 studies explored parental gender differences in the association between happiness and family functioning. The selected studies produced contradictory results: a single study reported that a positive mother–child relationship, but not a father–child relationship, was associated with greater happiness in children [43]. However, six studies found significant correlations with the father–child relationship and not the mother–child relationship [12,73,129,177,178,201]. These results suggest that relationships with both mothers and fathers are relevant to children's and adolescents' happiness.

However, the reviewed studies found that the father–child relationship was more closely related to indicators of happiness in adolescents than the mother–child relationship [12,73,129]. Indeed, the father–child relationship, father–child cohesion, and father– child conflict predicted children's life satisfaction, while no equivalent associations were

found for the mother [129,177,178]. These results suggest that the effect of father–child proximity on children's and adolescents' development is not related to mother–child proximity [178].

However, these studies, which suggest that fathers have the most significant impact on children's and adolescents' well-being, contradict the literature showing that mothers tend to be more significant in determining child developmental outcomes. While fathers tend to spend less time with children relative to mothers [205], they may be more committed and dedicated to children when they do spend time together, focusing on the specific situation at hand. Children may perceive their father's behavior as an essential aspect of their relationship that increases their happiness over the long term [73]. Future studies should investigate the differences between mothers and fathers and the different perspectives between parents and children, to better understand these aspects.

Finally, the last theme that emerged (13 studies) highlighted the importance of evaluating the relation between happiness and family functioning over time, from a predictive perspective. Several studies showed that, regardless of the informant (i.e., father, mother, or child) and the sequence of data collection (i.e., simultaneously vs. longitudinally), children's happiness was correlated with family functioning [89,181]. The results of both the simultaneous and longitudinal studies consistently showed that the cognitive component of happiness (i.e., life satisfaction) was significantly associated with family functioning and family relationships [22,43,199]. In addition, the longitudinal studies suggested that the relation between perceived family functioning and adolescents' happiness may be bidirectional [24]; therefore, it is not possible to confirm a univocal causal link between these factors.

Regarding subdimensions of family functioning, studies found that family cohesion [110,175], family communication [176], and parent–adolescent conflict [89,129] significantly predicted changes in adolescent happiness over time: more significant parent– adolescent conflict at Time 1 tended to be associated with a decline in adolescent life satisfaction at Time 2 [89], and greater family cohesion and open communication with parents tended to be associated with increased life satisfaction over time [117,176]. Also, concerning family conflict, the data showed that the relation between parent–adolescent conflict and adolescent emotional well-being could be bidirectional [89]. Future studies should further investigate the causal links between individual and family variables.

In conclusion, the findings of this study suggest that family dimensions may influence the affective and cognitive components of children's and adolescents' happiness [30,46,77,110–112,124,125,135]. In particular, the reviewed findings demonstrate the significance of family bonds and support for adolescents, indicating that, when family members provide help, affection, and understanding, children and adolescents experience multiple benefits that undoubtedly affect their development of positive psychological experiences [145,200].

#### *Limitations and Strengths of the Studies, and Future Research Directions*

Despite increasing research interest in the relation between happiness and family functioning (as evidenced by the growing number of publications in recent years), the investigated studies suffered from some methodological limitations. First, the use of selfreport measures may have exposed the research to social desirability bias. Future studies should employ a multi-informant and multi-method methodology combining qualitative measures (i.e., structured or semi-structured interviews and observational measures) or multi-informant questionnaires (i.e., parent and teacher reports) with self-reports. Second, the use of cross-sectional designs did not enable causal links to be drawn between variables. Thus, future studies should implement longitudinal procedures to better understand the factors that contribute to the happiness of children and adolescents. Furthermore, the heterogeneity of the samples (with respect to, e.g., geographical scope, size, and age range) limit the generalizability of the results.

The lack of a coherent theoretical model to define the construct of happiness represents a significant gap in the literature. This may explain the variety in both measurement tools and operationalizations of the construct in the investigated studies. Compounding this, some of the investigated studies did not clearly define happiness, positive affect, or life satisfaction. Therefore, future research should explicitly make the psychological construct operational. Additionally, future research should explore the association between attachment styles and children's and adolescents' happiness during development.

A further limitation of the present research is the possibility that methodological biases may have affected the study selection, due to the arbitrariness of the constructs and the interpretation of the reviewers. However, two independent evaluators excluded all articles that deviated from a precise definition of happiness or that analyzed family factors other than family functioning. Thus, attempts were made to target the constructs of interest.

A future research direction might be to examine overall effect sizes, which were not addressed in the present study. Moreover, as the present work focused on the relation between happiness and family functioning in non-clinical samples, an equivalent analysis in clinical samples may provide important new insights. Finally, the present review suggests the relevance of the father–child relationship, father–child cohesion, and father–child conflict in predicting children's and adolescents' happiness. Future research should further investigate the differences between fathers and mothers, using multi-informant and mixedmethods procedures and a longitudinal approach.

However, the present work also has significant strengths, including compliance with a rigorous systematic review protocol with clearly-defined inclusion and exclusion criteria. Indeed, a careful research strategy carried out by two independent evaluators was employed to acquire all relevant articles. Another strength is the high reviewer reliability during the screening process, reflecting a transparent selection methodology. Uniquely, the review represents the first study to synthesize the literature on happiness in the family context during development, filling a significant gap in the literature pertaining to the possible impact of family functioning on children's and adolescents' happiness. Finally, the review identified heterogeneous measurements of happiness and family functioning during development, suggesting that future studies should develop a more standardized approach to obtain more consistent results.


**Hsp90 Structure, Mechanism and Disease**

Editor

**Chrisostomos Prodromou**

Basel • Beijing • Wuhan • Barcelona • Belgrade • Novi Sad • Cluj • Manchester

*Editor* Chrisostomos Prodromou Biochemistry and Biomedicine University of Sussex Brighton United Kingdom

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This is a reprint of articles from the Special Issue published online in the open access journal *Biomolecules* (ISSN 2218-273X) (available at: https://www.mdpi.com/journal/biomolecules/special issues/Hsp90 Structure Mechanism Disease).

For citation purposes, cite each article independently as indicated on the article page online and as indicated below:

Lastname, A.A.; Lastname, B.B. Article Title. *Journal Name* **Year**, *Volume Number*, Page Range.

**ISBN 978-3-0365-9714-0 (Hbk) ISBN 978-3-0365-9715-7 (PDF) doi.org/10.3390/books978-3-0365-9715-7**

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© 2023 by the authors. Articles in this book are Open Access and distributed under the Creative Commons Attribution (CC BY) license. The book as a whole is distributed by MDPI under the terms and conditions of the Creative Commons Attribution-NonCommercial-NoDerivs (CC BY-NC-ND) license.


**Abstract**

The paper describes illegal substance abuse by inmates in prisons in the Czech Republic and gives the readers information about the results of initial research on this hardly avoidable issue. The paper brings interesting findings in this field and describes new ways of prevention and treatment, which is dealt with by prison directorates not only in the Czech Republic.

**Keywords:** prisons, detoxification units, illegal substance, drug policy, therapeutic communities


1. Introduction

Ring opening metathesis polymerization (ROMP) is a process of one or more cyclic olefins transformation to polymer catalyzed by metal carbene compounds. Indeed, the number of

© 2018 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited.

double bonds both in polymer and in monomer is equal [1–4]. As well as in any other type of polymerization, ROMP can be divided into several stages (Scheme 1).

The initiation begins with the coordination of the cycloolefins' double bond with the metalcarbene complex. The next step is a formation of a metal-cyclobutane intermediate. This process occurs in each act of addition of the monomer during the chain growth. The intermediate decomposes to form a new metal-carbene complex, with the growing chain being a ligand attached to the metal via a double bond.

The polymerization continues until the monomer is completely reacted or an equilibrium state is reached or the reaction is terminated by the addition of a special reagent that blocks the catalyst.

Living polymerization with ring opening metathesis is terminated by removing the transition metal from the end of the growing chain and its further deactivation. Deactivation in this case involves the formation of a complex unable to initiate polymerization [5]. Ethyl vinyl ether is an effective stopper for most ruthenium catalysts. It forms a very stable complex of the [Ru]=CHOEt type and ensures the functionalization of the polymer end-group. Acrylate derivatives of 2-butene-1,4-diol, succinic anhydride or butyl acrylate can also stop the growth of the macromolecule [6].

ROMP, as well as most metathesis reactions, is reversible, so the described transformations can proceed both in the forward and backward directions. The direction of the reaction can be predicted using the Gibbs energy:

Scheme 1. Stages of ROMP.

$$
\Delta G = -RT \cdot \ln K\_{\text{pann}} = \Delta H - T \cdot \Delta S \tag{1}
$$

The enthalpy factor makes an essential contribution to ROMP's Gibbs energy. This fact is explained by a high strain energy of cyclic unsaturated compounds participating in the polymerization [7]. The cycle strain energy of most cycloalkenes is more than 20 kJ/mole. For example, norbornene has an energy of about 100 kJ/mole [8]. The strain energy of the cycle releasing during the decomposition of the metal-cyclobutane complex and maintaining the forward direction of the reaction. However, if the deformation energy of cycle is low, the contribution of the entropy factor into the Gibbs energy becomes more significant in comparison with a smaller enthalpy factor. In this case, the entropy factor must be properly reduced in order to implement the direct process by increasing the monomer concentration or decreasing the temperature of the process [9].

double bonds both in polymer and in monomer is equal [1–4]. As well as in any other type of

The initiation begins with the coordination of the cycloolefins' double bond with the metalcarbene complex. The next step is a formation of a metal-cyclobutane intermediate. This process occurs in each act of addition of the monomer during the chain growth. The intermediate decomposes to form a new metal-carbene complex, with the growing chain being a

The polymerization continues until the monomer is completely reacted or an equilibrium state is reached or the reaction is terminated by the addition of a special reagent that blocks the

Living polymerization with ring opening metathesis is terminated by removing the transition metal from the end of the growing chain and its further deactivation. Deactivation in this case involves the formation of a complex unable to initiate polymerization [5]. Ethyl vinyl ether is an effective stopper for most ruthenium catalysts. It forms a very stable complex of the [Ru]=CHOEt type and ensures the functionalization of the polymer end-group. Acrylate derivatives of 2-butene-1,4-diol, succinic anhydride or butyl acrylate can also stop the growth of the

ROMP, as well as most metathesis reactions, is reversible, so the described transformations can proceed both in the forward and backward directions. The direction of the reaction can be

polymerization, ROMP can be divided into several stages (Scheme 1).

ligand attached to the metal via a double bond.

catalyst.

macromolecule [6].

16 Recent Research in Polymerization

Scheme 1. Stages of ROMP.

predicted using the Gibbs energy:

Secondary metathesis reactions can occur in addition to the main described reactions during the polymerization process. Intermolecular and intramolecular chain transfers are two main side reactions of ROMP (Scheme 2).

During the intermolecular transferring, the active metal-carbene complex located at the end of one macromolecule interacts with the double bond of the adjoined macromolecule, which leads to fragment exchange process. The reaction proceeds simultaneously in two directions. One of them provides two polymer chains with the active ruthenium on both. The second leads to one inactive chain and one chain with two active centers.

At the intramolecular chain transferring, the active metal-carbene complex reacts with the double bond of the same macromolecule led to a cyclization of the polymer chain. The listed side reactions, eventually, lead to a broadening of the molecular mass distribution (MMD) and a decrease in a molecular weight of the polymer [10].

The chain transfer as well as the spontaneous termination of the growing chain is highly improbable, so ROMP is a living polymerization. ROMP polymers are characterized by high molecular weights and a narrow MMD, as well as for products of other living polymerizations [11].

Scheme 2. Intermolecular and intramolecular chain transfers in ROMP.


**Author details**

patient safety is a "team sport" [111, 112]. Consequently, active participation of all stakeholders is required to optimize patient outcomes. This involves active involvement of all those who directly or indirectly participate in IVT—providers, patients, and families. Our *Clinical Vignette* demonstrates the dangers inherently associated with increasingly complex systems, where transitions of care occur frequently and where several different teams care for the same patient over a period of just several hours. In such environments, even the smallest mistake

In this chapter, we outlined key considerations around two primary types of PVCAEs—local and systemic. We also discussed intra-arterial PIV catheter placement and the rare but devastating scenario involving the "forgotten tourniquet." Each topic was presented in a clinically relevant fashion, incorporating a brief description, diagnosis, management, and finally prevention. Clinical approach to preventing PVCAEs is multipronged and includes a broad variety of considerations, such as checklists, knowledge of procedures and equipment, proper sterile technique, and the maintenance of appropriate PIV site cleanliness. Providers must also be aware of subtle clinical signs of PVCAEs, including PIV site erythema, IVT-related tissue injury, manifestations of air embolization, and signs of PIV catheter occlusion [2, 113]. In addition, each of the sections outlined specific strategies to prevent PVCAEs and PIV catheter failure. With growing numbers of patients needing vascular access for a range IVTs, providers need to show an understanding of the broad range of vascular access devices and corresponding clinical management aspects, including specific indications for various device types. Finally, providers need to be aware of patient needs, preferences, and concerns. After all, for many patients it is not the procedure that is of maximum concern but rather the clinician's communication skills, competence, and appropriate selection of PIV insertion site [114]. Patients and their families may be greatly untapped allies in preventing, monitoring, and

In summary, PVCAEs continue to be quite common and can lead to substantial patient discomfort, unnecessary or prolonged hospitalization, increased costs, and additional downstream morbidity. To improve patient outcomes, enhance patient safety, and reduce healthcare costs, there has been a substantial interest to implement measures aimed at reducing the incidence of PVCAEs [2]. Efforts to prevent PVCAEs should involve thorough provider education, clinical vigilance by all involved healthcare providers, as well as the proactive participation of all

The authors would like to thank Dr. Stanislaw P. Stawicki for providing generous assistance

can result in catastrophic sequelae.

128 Vignettes in Patient Safety - Volume 4

reporting adverse events [101].

stakeholders, including patients and their families.

and input regarding this chapter and its scientific content.

**10. Conclusion**

**Acknowledgements**

Parampreet Kaur1 \*, Claire Rickard2,3,4, Gregory S. Domer5 and Kevin R. Glover6

\*Address all correspondence to<EMAIL_ADDRESS>
1 Department of Research and Innovation, St. Luke's University Health Network, Bethlehem, Pennsylvania, United States

2 National Centre of Research Excellence in Nursing Interventions, Alliance for Vascular Access Teaching and Research (AVATAR), Menzies Health Institute Queensland, Griffith University, Australia

3 Centre for Clinical Nursing, Royal Brisbane and Women's Hospital, Australia

4 Princess Alexandra Hospital, Woolloongabba, Australia

5 Department of Surgery, Division of Vascular Surgery, St. Luke's University Health Network, Bethlehem, Pennsylvania, United States

6 B. Braun Medical, Inc., Bethlehem, Pennsylvania, USA


**1. Introduction**

Evolution of repair techniques of mitral valve has taken a concurrent route along with that of cardiac surgery itself. From the concept of replacement to repair and now from respect rather than resect approach to the current non resectional method has been due to a better understanding of the dynamic nature of the valve. Stress pattern studies that have currently received a boost with technological advancements [1]. While "resection" techniques are associated with good results, reparability rates stood at around 60–70% for the last decade. We are presenting a new technique based on latest stress and dynamic updates on the valve, which would facilitate near to 100% reparability rates in future. All current studies support our view of adopting a completely nonresectional method in mitral valve repair – or the dynamic Indian Correction as we call it.


3. Quantitative phase imaging for sperm analysis

#### 3.1. Basic principles of quantitative phase microscopy

stress and corroborated the findings using an established assay and an alternative but complementary spectroscopic technique (Fourier-transform infrared (FTIR) spectroscopy). The results of this last work confirm that RS is able to reveal different levels of oxidative DNA fragmentation, especially associated to alterations within the 1050–1095 cm�1 spectral range (Raman spectra in the box 2 of Figure 2), which includes the band associated with the DNA phosphate backbone, changes that were confirmed by similar shifts in the corresponding FTIR peaks (not shown) [25]. Also, the Raman bands associated to protein and lipid content (1400–1600 cm�1

solely on the presence of differing spectra [24].

224 Spermatozoa - Facts and Perspectives

Figure 2. Overview of the most representative studies on Raman spectroscopy and imaging for the label-free analysis of sperm cells. Box 1: the highlighted variations in peak intensities in the Raman spectra correspond to different sperm head shapes [21]. Box 2: the peaks at 1095 and 1050 cm�1 represent biomarkers of fragmented DNA in the sperm nucleus [24, 25]. Box 3: panel A shows the chemical Raman reconstruction of distinct sperm regions [23]; panels B–Y represent the biochemical composition of individual immobilized, living human sperm cells [26]; and panel Z shows the efficiency of Raman imaging in revealing small irregularities in the sperm head such as vacuoles (yellow circles) distinguishable based

showed some alterations induced by UV radiation, consistent with protein denaturation and lipid peroxidation that are well-known markers of oxidative damage [27]. Raman-based identification of DNA-damaged sperm cells linearly correlated with the findings from the flow

)

Quantitative phase microscopy (QPM) is a label-free imaging technique, which allows reconstructing both the amplitude and the phase information of an optical field that passes through the sample, and it is particularly interesting in case of transparent biological cells. Respect to differential interference contrast (DIC) microscopy [29] or Nomarski/Zernike's phase contrast [30], the QPM gives a quantitative measure of the optical path difference (OPD) at each point in the sample. OPD in each position (x, y) of the acquisition plane is defined as the refractive index variation across the cell thickness, t(x, y):

$$\text{OPD}(\mathbf{x}, \mathbf{y}) = t(\mathbf{x}, \mathbf{y})(n\_c - n\_s) \tag{2}$$

where nc and ns are the refractive index of the cell and the surrounding medium (assumed to be homogeneous), respectively. The resulting OPD map of the cell is reconstructed by recording the interference fringes pattern, the so called "hologram," of two superimposed coherent beams, one that interacts with an object under test and another that does not come in contact with the object and acts as a reference beam, and calculating the phase difference between them [31]. If the hologram is acquired by a digital sensor array, typically a charge-coupled device (CCD) or a complementary metal-oxide semiconductor (CMOS) device, digital holographic microscopy (DHM) technique is implemented. A typical interferometric setup for DHM is reported in Figure 3.

The acquired hologram is then mathematically analyzed, allowing obtaining the complex field of the object beam that can be reconstructed at different distances, too. Therefore, numerical refocusing of a digital hologram, that is a 2D image, at different object planes, without any zscan of the optical system, allows to retrieve a 3D quantitative imaging [31]. This makes digital holography a very powerful method for metrology applications, particularly attractive in the field of biology as it is noninvasive, noncontact, and label-free, allowing the characterization of live specimen.

Intensity and phase distributions can be reconstructed by Sprop(m, n) according to the following

Ipropð Þ¼ m; n Spropð Þ m; n

The phase φprop(m, n) includes information about the morphological profile of the object under

λ

Digital holography (DH) allows retrieving a fully 3D image of the sample, thus offering new prospects for the analysis of sperm cells in a noninvasive, quantitative, and label-free way. Sperm cells were acquired by a digital holographic microscope for the first time in 2008 by

The potential of applying this technique for label-free sperm assessment was recently confirmed by Shaked's group. Indeed, they demonstrated that DHM allows obtaining equivalent information about key morphological parameters of fixed human spermatozoa to that

Additionally, the opportunity to have information about the third dimension in the sperm analysis can offer a better understanding of this kind of cell and of male infertility [40]. Furthermore, since this technique allows obtaining quantitative information and numerical analysis, estimation area or profiles in a given direction may be carried out. Such kind of analysis can help to study the male infertility and its possible relation with the abnormal

DH has been mainly employed to study the morphology of human sperm cells in order to verify the integrity of their structures and to evaluate their kinematic parameters and concentration. This approach allows to visualize the morphology of abnormal sperm and to analyze in 3D some typical defects such as cytoplasmic droplet along the tail, bent tail, and acrosome

Additionally, a quantitative study of vacuoles has been performed by DH. In particular, it was demonstrated that the profile of the normal spermatozoon results higher than that of the spermatozoon with vacuoles, whereas their 2D dimensions (such as area and axes length) are similar [43]. The difference in height denotes a reduced volume in spermatozoon with vacuoles respect to the normal spermatozoon; this difference could be ascribed to a modification of the

inner structure of the sperm head with loss of material (see box 1 in Figure 4).

φpropð Þ¼ m; n arctan

OPD mð Þ¼ ; n

The relation between the OPD and the thickness of the cell t is given by Eq. (2).

obtained by bright field microscopy (BFM) imaging of stained sperm cells [39].

3.2. Digital holography microscopy for sperm cells assessment

investigation; in fact, it is related to the OPD:

 2

Advanced Label-Free Optical Methods for Spermatozoa Quality Assessment and Selection

Im Spropð Þ m; n

; (5)

http://dx.doi.org/10.5772/intechopen.71028

227

Re Spropð Þ m; n : (6)

2πφpropð Þ m; n : (7)

equations:

Mico et al. [38].

morphology [41, 42].

broken, as reported in the box 1 of Figure 4 [42].

Figure 3. Typical interferometric setup for digital holography microscopy. BS: beam splitter, M: mirror. Reference and object beams are highlighted.

In DHM, in addition to the hologram of the sample under investigation, a second hologram is acquired on a reference region near to the object in order to numerically compensate all the aberrations due to the optical components, comprising the defocusing due to the microscope objective. An "off-axis" configuration is generally adopted to avoid a spatial overlapping of the real and conjugate images due to the holographic reconstruction, leading to the separation of first diffraction order from the entire spatial frequency spectrum. Thus, the spectrum of the sample (object field defined as S(x, y)=|S(x, y)|e iφ(x, y) , with |S(x, y)| and φ(x, y) amplitude and phase, respectively) can be retrieved except for a constant [32]. Then, it is possible to propagate the optical wavefront at different distances from the plane of acquisition applying the Fourier formulation of the Fresnel-Kirchhoff diffraction formula [33, 34]. This reconstruction can be obtained by means of the operator algebra proposed by J. Shamir [35], where Fresnel diffraction is described by replacing the Fresnel-Kirchhoff integral, the lens transfer factor, and other operations by operators. The resulting propagated object field Sprop(ξ, η) is expressed as a function of the initial object field S(x, y) and can be written as [36, 37]:

$$\mathcal{S}\_{\text{pr}\mathfrak{p}}(\nu,\mu) = \exp\left(\text{ikd}\right) \times \left\{ \Im^{-1} \left[ \exp\left(-\frac{\text{ik} d\lambda^2}{2} \left(p^2 + q^2\right)\right) \right] \Im(\mathbf{S}(\mathbf{x},y)) \right\} \tag{3}$$

being I½ � f xð Þ the Fourier transform of the function f(x), k ¼ 2πn λ (with n refractive index of the medium), p and q spatial frequencies defined as p ¼ ν λd and q ¼ μ λd, and d the reconstruction distance. For digital reconstruction, Eq. (3) is applied in a discrete form:

$$\mathcal{S}\_{prop}(m,n) = \exp\left(i\hbar d\right) \left\{ \mathfrak{I}\_D^{-1} \left[ -\frac{i\hbar d\lambda^2}{2N^2 d^2} (\mathcal{U}^2 + V^2) \right] \mathfrak{I}\_D(S(h,j)) \right\} \tag{4}$$

where N is the number of pixels in both directions and m, n, U, V, h, and j are integer numbers varying from 0 to N � 1.

Intensity and phase distributions can be reconstructed by Sprop(m, n) according to the following equations:

$$I\_{prop}(m,n) = \left| S\_{prop}(m,n) \right|^2; \tag{5}$$

$$\varphi\_{prop}(m,n) = \arctan \frac{\text{Im}\left[\mathcal{S}\_{prop}(m,n)\right]}{\text{Re}\left[\mathcal{S}\_{prop}(m,n)\right]}.\tag{6}$$

The phase φprop(m, n) includes information about the morphological profile of the object under investigation; in fact, it is related to the OPD:

$$\text{OPD}(m,n) = \frac{\lambda}{2\pi} \varphi\_{pmp}(m,n). \tag{7}$$

The relation between the OPD and the thickness of the cell t is given by Eq. (2).

#### 3.2. Digital holography microscopy for sperm cells assessment

In DHM, in addition to the hologram of the sample under investigation, a second hologram is acquired on a reference region near to the object in order to numerically compensate all the aberrations due to the optical components, comprising the defocusing due to the microscope objective. An "off-axis" configuration is generally adopted to avoid a spatial overlapping of the real and conjugate images due to the holographic reconstruction, leading to the separation of first diffraction order from the entire spatial frequency spectrum. Thus, the spectrum of the

Figure 3. Typical interferometric setup for digital holography microscopy. BS: beam splitter, M: mirror. Reference and

iφ(x, y)

2 p2 þ q2

d2 U2 þ V2

λd and q ¼ μ

phase, respectively) can be retrieved except for a constant [32]. Then, it is possible to propagate the optical wavefront at different distances from the plane of acquisition applying the Fourier formulation of the Fresnel-Kirchhoff diffraction formula [33, 34]. This reconstruction can be obtained by means of the operator algebra proposed by J. Shamir [35], where Fresnel diffraction is described by replacing the Fresnel-Kirchhoff integral, the lens transfer factor, and other operations by operators. The resulting propagated object field Sprop(ξ, η) is expressed as a

> D � ikdλ2 2N2

where N is the number of pixels in both directions and m, n, U, V, h, and j are integer numbers

, with |S(x, y)| and φ(x, y) amplitude and

∙Ið Þ S xð Þ ; y

∙IDð Þ S hð Þ ; j

λ (with n refractive index of the

λd, and d the reconstruction

(3)

(4)

sample (object field defined as S(x, y)=|S(x, y)|e

object beams are highlighted.

226 Spermatozoa - Facts and Perspectives

function of the initial object field S(x, y) and can be written as [36, 37]:

Sprop ν; μ ¼ exp ð Þ� ikd I�1 exp � ikdλ2

distance. For digital reconstruction, Eq. (3) is applied in a discrete form:

being I½ � f xð Þ the Fourier transform of the function f(x), k ¼ 2πn

Spropð Þ¼ m; n exp ð Þ ikd I�1

medium), p and q spatial frequencies defined as p ¼ ν

varying from 0 to N � 1.

Digital holography (DH) allows retrieving a fully 3D image of the sample, thus offering new prospects for the analysis of sperm cells in a noninvasive, quantitative, and label-free way. Sperm cells were acquired by a digital holographic microscope for the first time in 2008 by Mico et al. [38].

The potential of applying this technique for label-free sperm assessment was recently confirmed by Shaked's group. Indeed, they demonstrated that DHM allows obtaining equivalent information about key morphological parameters of fixed human spermatozoa to that obtained by bright field microscopy (BFM) imaging of stained sperm cells [39].

Additionally, the opportunity to have information about the third dimension in the sperm analysis can offer a better understanding of this kind of cell and of male infertility [40]. Furthermore, since this technique allows obtaining quantitative information and numerical analysis, estimation area or profiles in a given direction may be carried out. Such kind of analysis can help to study the male infertility and its possible relation with the abnormal morphology [41, 42].

DH has been mainly employed to study the morphology of human sperm cells in order to verify the integrity of their structures and to evaluate their kinematic parameters and concentration. This approach allows to visualize the morphology of abnormal sperm and to analyze in 3D some typical defects such as cytoplasmic droplet along the tail, bent tail, and acrosome broken, as reported in the box 1 of Figure 4 [42].

Additionally, a quantitative study of vacuoles has been performed by DH. In particular, it was demonstrated that the profile of the normal spermatozoon results higher than that of the spermatozoon with vacuoles, whereas their 2D dimensions (such as area and axes length) are similar [43]. The difference in height denotes a reduced volume in spermatozoon with vacuoles respect to the normal spermatozoon; this difference could be ascribed to a modification of the inner structure of the sperm head with loss of material (see box 1 in Figure 4).

the OPD of the cell linearly depends on the axially averaged refractive index of the cell relative to the surrounding medium, for a given thickness t [45]. Thus, considering that the human spermatozoa head can be divided in the cell nucleus and the acrosome, which differ in the composition and concentration of proteins, nucleic acids, and other components, Balberg et al. evaluated the dry mass of the cell by starting by the knowledge of the OPD [31]. In particular, the authors measured the dry mass of separate cellular compartments in the OPD maps of

Advanced Label-Free Optical Methods for Spermatozoa Quality Assessment and Selection

http://dx.doi.org/10.5772/intechopen.71028

229

Finally, the movements of living spermatozoa have been tracked applying an automatic 4D tracking (movements in the 3D spatial directions over time) of the swimming samples in [46]. The results are showed in the box 3 of Figure 4, where an anomalous spermatozoa behavior, known as "bent tail," is highlighted. A collection of several holograms at a fixed distance between the sample and the microscope objective was acquired. In order to simultaneously track multiple spermatozoa, a proximity criterion has been included into the algorithm. In particular, by means of this approach, the position in the (n + 1)th frame has been searched in a

Therefore, DH could be seen as a breakthrough that can renew the sperm analysis in the spermatology laboratories, encouraging researchers in the field of sperm cell biology to con-

As seen in the previous sections, Raman spectroscopy and quantitative phase microscopies have been separately developed for assessing spermatozoa from a biochemical and morphological perspective, respectively. The two photonic techniques, employing intrinsic contrast mechanisms, allow noninvasively selecting the fertile spermatozoon according to its normal morphology as well as its DNA integrity. Kang et al. [47] first proposed a combined system where quantitative phase microscopy and Raman imaging allowed correlating morphological parameters with molecular information, i.e. the red blood cell thickness was correlated to the hemoglobin distribution. Huang and colleagues in 2014 published a study that evaluated the possibility to combine micro-Raman spectroscopy with image analysis for label-free identification of normal spermatozoa [48]. Recently, our group proposed a similar system, which combines Raman spectroscopy/imaging and digital holography microscopy as a potential tool

The setup used in our works for the simultaneous Raman and holographic analysis essentially consists of a Raman microscope coupled to an interferometer (Figure 5) [36, 49, 50]. We used two different laser sources: a green laser at 532 nm for the Raman excitation and a long coherence (>100 m) red laser at 660 nm for the holographic experiments. The red laser beam was split into two beams: the object beam passing through the sample and the reference beam

4. Combined optical approach for the noninvasive analysis of single

unlabeled human spermatozoa, as reported in the box 2 of Figure 4.

sider using DH as a standard method for their characterization studies.

to rapidly and objectively identify the healthy spermatozoa [36, 49, 50].

reasonable neighborhood of the nth frame position.

spermatozoa

4.1. The optical setup

Figure 4. Some potentialities of DHM. Box 1: morphological analysis of semen carried out by DHM; top panels: sperm cells with distinct morphological defects; center and bottom panels: difference in height denotes a reduced volume in spermatozoon head with vacuoles respect to the normal spermatozoon [41, 43]. Box 2: examples of some physical parameters obtained by DHM [31, 44]. Box 3: 4D tracking of clinical sperm samples [45].

In 2013, Merola et al. [44] provided an evaluation of the biovolume of spermatozoa (about 55 μm3 ). The authors used optical tweezers to trap and rotate the cells; meanwhile, they flow through a microchannel, enabling recording digital holograms of the sperm at different angles and the production of a tomographic 3D model, as showed in the box 2 of Figure 4.

Another important semen parameter, the dry mass of the cell (i.e. the average mass of the proteins, carbohydrates, lipids, and so on within the cell), can be obtained by DHM. Indeed, the OPD of the cell linearly depends on the axially averaged refractive index of the cell relative to the surrounding medium, for a given thickness t [45]. Thus, considering that the human spermatozoa head can be divided in the cell nucleus and the acrosome, which differ in the composition and concentration of proteins, nucleic acids, and other components, Balberg et al. evaluated the dry mass of the cell by starting by the knowledge of the OPD [31]. In particular, the authors measured the dry mass of separate cellular compartments in the OPD maps of unlabeled human spermatozoa, as reported in the box 2 of Figure 4.

Finally, the movements of living spermatozoa have been tracked applying an automatic 4D tracking (movements in the 3D spatial directions over time) of the swimming samples in [46]. The results are showed in the box 3 of Figure 4, where an anomalous spermatozoa behavior, known as "bent tail," is highlighted. A collection of several holograms at a fixed distance between the sample and the microscope objective was acquired. In order to simultaneously track multiple spermatozoa, a proximity criterion has been included into the algorithm. In particular, by means of this approach, the position in the (n + 1)th frame has been searched in a reasonable neighborhood of the nth frame position.

Therefore, DH could be seen as a breakthrough that can renew the sperm analysis in the spermatology laboratories, encouraging researchers in the field of sperm cell biology to consider using DH as a standard method for their characterization studies.


**3. Results**

#### *3.1. Sociodemographic and Occupation Characteristics*

The servants that responded to the comorbidity survey (n = 447) were predominantly male (52.7%), married/stable union (69.1%), and a mean age above 46 years. Table 1 shows the sociodemographic details of the participants.

**Table 1.** Sociodemographic and occupation characteristics of the participants.

1 Mean (Standard deviation).


2.2 RMP impact on the edge impurity radiation and stability of detached plasma

The large helical device, LHD, is a heliotron-type fusion machine, in which the magnetic field is produced by superconducting coils with poloidal and toroidal

#### Figure 1.

The pattern of the connection length LC in the edge stochastic layer of LHD (a); the tomographic reconstruction of the emission from carbon ions CII (514 nm) (b) and CIV (466 nm) (c), recorded just before the detachment onset, at line averaged plasma density ne = 5 1019 m3 .

winding numbers l = 2 and n = 10, respectively [23]. Figure 2(b) displays a poloidal cut of the calculated magnetic field structure in the edge region and the distribution of connection length LC. The magnetic field in helical devices is completely generated by currents in external coils and has a broad spectrum of Fourier harmonics of different mode numbers m and n. Each of those generates magnetic islands, and by overlapping of the islands, the magnetic field structure becomes stochastic. The divertor legs, named left and right legs, are connected to the L and R divertor plates, respectively, rotating helically by moving in the toroidal direction. The lower half of the Figure 2 presents the LC distribution with RMP of m/n = 1/1, where the remnant island structure embedded into the stochastic layer is visible.

Figure 3 shows the time evolution of several plasma parameters in discharges with and without RMP where the density ramp up was performed without auxiliary impurity seeding, and the edge radiation was coming mainly from carbon impurity sputtered from the divertor target plates. On the one hand, without RMP (blue lines), the growth of the density leads to a sudden increase of the radiated power, see Figure 3(b), and, finally, to the radiation collapse of the whole plasma. On the other hand, with the RMP application (red lines), the radiated power is saturated at a higher level and the state with the plasma detached from the divertor targets is sustained during the whole later phase of the discharge. This is demonstrated in Figure 3(a) by the evolution of the heat load onto the divertor target. The strong cooling of the edge plasma by impurity radiation leads to the decrease of the plasma column effective radius a99 displayed in Figure 3(d).

Figure 4 shows the radial profiles of the electron temperature Te, density ne, and pressure in the edge region along the LHD mid-plane, in the attached and detached discharge phases [24]. With the RMP application, a clear flattening of the Te profile due to the magnetic island is observed at the outboard, R = 4.60–4.75 m, in the attached phase. The increase in the density leads to the lowering of Te, and during the detached phase,Te inside the island is sustained at 20 eV. It is also interesting to note that with the growing ne, the width of the region with the profile flattening becomes slightly narrower, and at the same time, a region with the flattening appears

#### Figure 2.

Top view of the LHD torus with the position of divertor probe arrays at the inboard, indicated by numbers and letters "L"& "R" (a); LC distribution in the edge region of LHD, without (upper half) and with (lower half) RMP application (b). The right and left legs, indicated in the figure, are connected to L and R divertor arrays, respectively.

Experimental Studies of and Theoretical Models for Detachment in Helical Fusion Devices DOI: http://dx.doi.org/10.5772/intechopen.87130

#### Figure 3.

Time evolution of plasma parameters in the LHD density ramp-up discharges, with (red) and without (blue) the RMP application: The power load onto divertor targets measured by probes (a), the radiated power measured by AXUV (b), line averaged density (c), and the effective plasma minor radius a99 defined as that of the flux surface, containing 99% of the total plasma energy (d).

#### Figure 4.

Radial profiles of the plasma parameters in the LHD edge region: electron temperature (a, d, g), density (b, e, h), and pressure (c, f, i); the panels (a–f) correspond to discharges with RMP, (g–i)—without RMP. The region of the Te flattening caused by the magnetic island is indicated by yellow patch [24].

at the inboard, R = 3.1–3.2 m. This is interpreted as a result of the plasma response to the external RMP field. Indeed, the measurements with a saddle loop coil indicate the reduction of the total field perturbation by RMP induced by the currents in the plasma under the attached conditions and its amplification during the detached phase [20, 25, 26]. A similar flattening appears in the pressure profiles, while density is relatively flat in the entire edge region with some modulations around the magnetic island. Without RMP application, there is no such flattening except for a small modulation due to the inherent small remnant islands of higher mode numbers.

The edge impurity radiation profiles are estimated using the Te and ne profiles presented in Figure 4 and by assuming a concentration of carbon of 1% with respect to ne. Figure 5 shows the temporal evolution of the radiation profiles together with LC distributions [24]. Without RMP, Figure 5(b), the impurity radiation starts to peak around the X-point of the divertor leg, at R 4.8 m, and later moves gradually radially inward due to the decrease in the temperature as the density increases; the X-point of the divertor leg should be distinguished from that of the magnetic island created by the RMP. Finally, the radiation penetrates into the confinement region at t = 4 sec, leading to the radiation collapse, as shown in Figure 3. With the RMP application, Figure 5(a), a bundle of flux tubes of long connection length appears at the edge, as a remnant island. The radiation starts to peak at the X-point of the divertor leg and moves radially inward, similarly to the case without RMP. It is, however, stopped at the periphery of the edge of the island, R 4.75 m, without penetrating into the confinement region at the detachment transition, t 2.9 sec. Then, the discharge is sustained until the end of NBI heating due to the stabilization of the radiation profile by the island.

Radiation profile measurements have been performed to capture the change of the global structure of impurity emission due to RMP and are compared with numerical transport simulations with the code EMC3-EIRENE [20–22]. Figure 6 shows the calculated impurity radiation distribution, with and without RMP, and

#### Figure 5.

The calculated LC distribution in the outboard edge region (upper panels); time evolution of the carbon radiation estimated from Te and ne profiles as shown in Figure 4, by assuming 1% carbon concentration and noncoronal cooling rate at neτ = 1017 m3 s (lower panels), with (a) and without (b) RMP [24].

Experimental Studies of and Theoretical Models for Detachment in Helical Fusion Devices DOI: http://dx.doi.org/10.5772/intechopen.87130

Figure 6.

Carbon impurity radiation distribution calculated by EMC3-EIRENE at poloidal cross section, together with line-integrated profile of the simulation and measurements by AXUV, on the right panel, without (a) and with (b) RMP [20].

the radiation profile measured by the AXUV diagnostics [20]. Without the RMP application, the impurity radiation is enhanced at the inboard as it is demonstrated in Figure 6(a). The line integrated radiation profile found both in the measurements and in simulations are shown in the right panel. Both profiles have maxima at the center channels, which pass through the enhanced radiation at the inboard location. With the RMP, the peak of the radiation moves to the bottom of the plasma, where the X-point of the m/n = 1/1 island is located (note that the toroidal angle positions of the cross sections are different in Figures 2(b) and 6). The simulation also shows a peak at the bottom channel in accordance with the measurement. The measurements by imaging bolometer also indicate enhanced radiation around X-point in agreement with the numerical simulation [21].

The impact of RMP on the impurity emission intensity was also investigated in the VUV range with the diagnostic equipment [22], viewing the entire plasma toroidal cross section. Density dependence of the radiated power measured by the resistive bolometer, together with emissions from different charge states, CIII (C2+), CIV (C3+), CV (C4+), and CVI (C5+), measured with the spectrometer [27] is plotted in Figure 7. Here, the plasma density is normalized to the density limit in helical devices, nsudo [28]. It is seen that without RMP, the radiated power shows rapid increase around the density limit, that is, ∂ Pbolo ∂ ne without RMP! . This means that any small density perturbation leads to a significant change in the radiation; that is, the system in question is becoming unstable. With RMP, the radiation is enhanced in the low-density range even in the attached phase. The increase of the radiation with RMP is interpreted due to the enlarged volume inside the edge magnetic island with a low Te, of 10–20 eV where the radiation of low charged carbon ions approaches its maximum. After the detachment transition, there appears a region where the radiation is insensitive to the density, that is, ∂ Pbolo ∂ ne with RMP!0. This provides a possibility to the radiation level control and, thereby, the detachment stability. One can see that the "flat" region extends slightly beyond the density limit, which results in an extension of density operation range for the case with RMP. Very similar density dependence as for the bolometer measurement is observed in the emission of CIII and CIV species, being the dominant radiating charge states, see Figure 7(b) and (c). As it is analyzed in Ref. [16], CIV is providing the largest contribution to the total radiated power. On contrary, with RMP, the radiation of CV and CVI ions increases monotonically with the plasma density, and is larger than without RMP. Since the ionization energies of CV and CVI ions, 392 and 490 eV, respectively, are much higher than the Te inside the magnetic island, the higher emission intensity might indicate enhanced penetration of impurity toward the core boundary. The contribution of CV and CVI to the total radiated power is, however, small compared to the states of lower charges [16].

#### Figure 7.

Density dependence of the radiated power measured by the bolometer (a), the emissivity of CIII (b), CIV (c), CV (d), and CVI (e) species measured by VUV spectrometer without (triangles) and with (circles) RMP. The density is normalized to the density limit in helical devices, nsudo [27].

The results above clearly show the difference of edge impurity radiation and transport with and without RMP. This is of high importance for the detachment stabilization in the former situation. The mechanism of the stabilization of the radiation layer is under investigation by taking into account the magnetic geometry, the particle, and the energy transport, both parallel and perpendicular to the field lines within and out of the magnetic island. Similar observations of the detached plasma stabilization with large island were also found in W7-AS [29]. The recent results on the successful detachment control in W7-X with the island divertor also suggest an important role of the edge magnetic island for the detached plasma stability [30].

#### 2.3 Change of divertor footprint with RMP application

The toroidal variation of the particle fluxes onto divertor plates with RMP has been investigated with Langmuir probe array installed around the mid-plane of the targets at the inboard side [17, 31]. It has been found that the time evolution of the divertor particle flux exhibits substantial difference between toroidal locations, that is, some plates are becoming detached earlier than others; at some plates, the flux even increases after detachment [27]. The summary of this behavior is shown in Figure 8, where the divertor particle flux normalized to its value without RMP is plotted for different toroidal sections. In the attached case, there is an n = 1 mode structure for both left (L) and right (R) divertor arrays, which are connected to the left and right legs, respectively, as indicated in Figure 2. In the detached phase, the n = 1 structure remains, but the toroidal phase is shifted by one section. The relation between the divertor flux and LC profiles is presented in Figure 9 for several toroidal cross sections [27]. At the section 6L (Figure 9(a) and (b)), a bundle of flux tubes of 6.5 mm width is connected to the divertor plate. By applying RMP, the footprint shifts toward the right side with increased LC. The measured particle flux increases in the absolute values due to the longer LC, as seen also in Figure 9(a).

Experimental Studies of and Theoretical Models for Detachment in Helical Fusion Devices DOI: http://dx.doi.org/10.5772/intechopen.87130

#### Figure 8.

The toroidal distributions of the particle flux onto divertor targets with RMP normalized by the values without RMP on attached (a) and detached (b) discharge phases. Red circles correspond to the left divertor and blue diamonds to the right divertor arrays, as it is indicated in Figure 2 by the toroidal section number [27].

The flux profile becomes more asymmetric with respect to the central peak, being increased at the right side, which reflects the right shift of the LC footprint. On the other hand, the 2R plate shows decrease of the particle flux with the RMP application, as seen in Figure 9(c). This is interpreted by the decrease in LC, as shown in the figure, where the long LC bundle at the central region almost disappears with RMP, and thus, the particle flux decreases as well. These results show that, to a certain extent, the particle transport is well correlated with the LC distribution calculated in the vacuum approximation, i.e., without a plasma response to RMP, and thus can be controlled by the RMP application in the attached phase. In the detached phase, the particle flux both at 6L and 2R decreases in the entire region with respect to the case without RMP, as shown in Figure 9(b) and (d).

In Figure 9(e) and (f), the observations in section 2L are presented. By applying RMP, the particle flux becomes smaller in the attached phase with respect to the reference case without RMP. The flux, however, increases at the detached phase, as shown in Figure 9(f). At this plate, the fraction of long flux tubes with LC > 100 m decreases, but those with LC 30 m increases with RMP. The reduction of the flux at the attached phase may be due to the reduction of the contribution from the tubes with LC > 100 m. On the other hand, in the detached phase, the increases of the flux could be attributed to the change of the particle transport channel from long, LC > 100 m, to the medium, LC 30 m, flux tubes. This effect has to be investigated by analyzing in detail the relation between the magnetic field structure and the ionization front. It has to be taken into account that there is a significant

Figure 9.

LC (solid lines) and divertor particle flux (dashed lines with circles) profiles along the divertor probe pins, with (red) and without (black) RMP. (a and b) 6L, (c and d) 2R, and (e and f) 2L toroidal section, respectively [27].

plasma response to the RMP, which is different in the attached and detached phases, as mentioned above.

During the detached phase, there are large oscillation in both divertor particle flux and radiation. Figure 10 presents the time traces of the particle flux to the divertor targets and of the radiation losses measured by AXUV during the detached phase, where oscillation with 60–90 Hz is visible. The particle flux and radiation are oscillating in phase. Similar behavior was also observed in the particle flux to the first wall [32]. The mechanism of the oscillation is discussed later in this chapter.