said magnets alternating in polarity so that each adjacent pair of magnets have two inside pole surfaces of respectively opposite polarities facing said central axis, and two outside pole surfaces of respectively opposite polarities attached to said inside surface of said case, the inside surface of said cylindrical case having {HEAD ~ a corresponding plurality} of recesses, said outside pole surfaces of {TAIL ~ said plurality} of magnets being positioned in said recesses, 
said magnets alternating in polarity so that each adjacent pair of magnets have two inside pole surfaces of respectively opposite polarities facing said central axis , and two outside pole surfaces of respectively opposite polarities attached to said inside surface of said case , the inside surface of said cylindrical case having { HEAD ~ a corresponding plurality } of recesses , said outside pole surfaces of { TAIL ~ said plurality } of magnets being positioned in said recesses ,
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