of comb-like discharges in Fig. 1(b) and in additional photos and video in the supplementary material.

![ Circuit details of the Marx coil apparatus. (a) Component wiring for operation with the solenoid, as in Fig. 1(a). CT denotes a current transformer. (b) Modification to operate without the solenoid, as in Fig. 1(d). (c) Inductors (red) and capacitor (blue) for one Marx stage. (d) Spark gaps. (e) Power supply. The variac was set to 140 V$_\text{rms}$ for all data shown. Additional details are in the supplementary material. []{data-label="fig2"}](Fig2_McGuyer_MarxCoil){width="8.5cm"}

![ Output during operation with the solenoid. (a) Like a SGTT, the Marx coil produced pulses at a roughly 120 Hz rate, which appear as under-sampled lines in the solenoid current $I_s$ measured by a current transformer. (b) Current $I_s$ and inferred voltage $V_t \approx - L_s \, d I_s/dt$ during a pulse. The decaying exponential oscillation of an RLC circuit fits $I_s$ well, but allowing time-varying RLC parameters improves the fit (see supplementary material). Inset shows representative spark discharge for this data, which used a larger terminal and a different breakout point than shown in Fig. 1(a). []{data-label="fig3"}](Fig3_McGuyer_MarxCoil){width="8.5cm"}

While the secondary solenoid of a classic SGTT has no components inside, here the 