Gas fuelling of Rf-sustained tandem mirror end plugs

The possibility of fuelling pure RF-powered tandem mirror end plugs by gas puffing is considered. It is shown experimentally that gas puffing can lead to significant increases in plug density and that the details of the plug density buildup depended on the antenna locations relative to the central cell and the plug midplane. Large charge-exchange energy loss resulting from the puff gas makes it an inefficient technique for fuelling high-temperature end plugs. The possibility of employing gas puffing for building up high-density end plugs composed of relatively cold ions is also considered as a means of achieving electrostatic confinement for an ICRF-stabilized central cell. Experimental enhancement of the central-cell density, which shows no significant cooling of the central cell by the colder plug plasmas, is demonstrated. The RF power requirements for refuelling an ICRF-powered end plug to a given density and temperature are estimated.