Density Buildup Experiments

Recent experiments on CTIX have greatly increased density and kinetic energy density over previous values. These improved compact toroids are produced by injecting neutral gas, typically helium, into the acceleration region approximately 1 ms before CT formation and acceleration. Simple models predict that in most cases, virtually all injected gas is ionized and incorporated into the CT, resulting in density increases of one or more orders of magnitude. The most recent experiments have demonstrated that at sufficiently high accelerator voltage (<= 13 kV, well within normal CTIX operating limits), CT internal magnetic field strength is maintained (> 6 kG) during gas puffing, and CT velocity is only moderately reduced (> 100 km/sec). The result is a CT with a normal ratio of toroidal to poloidal field of approximately unity, and increased kinetic energy compared to non-gas-puffed shots at comparable operating conditions. Capacitor energy is converted to plasma kinetic energy with >20% efficiency in the best gas-puffing shots. Forthcoming modification to the nonlinear inductor used to control accelerator-region timing are expected to considerably reduce inductive energy storage, further increasing CT energy and energy efficiency. The goal is to obtain the maximum CT energy density available with the existing CTIX capacitor system. The density addition results are summarized in the plot below.


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