One interrupter structure comprises a plurality of longitudinally spaced interrupter elements mounted on a core rod, each element comprising a plurality of blade like members each of {HEAD ~ at least approximately spherical segment profile} in {TAIL ~ side elevation}, the members extending mutually radially outward relative to one another to touch or nearly touch the said surface or surfaces adjacent the elements 
One interrupter structure comprises a plurality of longitudinally spaced interrupter elements mounted on a core rod , each element comprising a plurality of blade like members each of { HEAD ~ at least approximately spherical segment profile } in { TAIL ~ side elevation } , the members extending mutually radially outward relative to one another to touch or nearly touch the said surface or surfaces adjacent the elements
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