A Time-of-Flight Neutral Particle Detector for the Irvine FRC

A time-of-flight neutral particle detector\footnote{D. E. Voss and S. A. Cohen, Rev. Sci. Instrum. 53, 1696 (1982).} has been constructed to diagnose the ion contribution to the current in the Irvine FRC. Charge exchange neutrals are chopped by a slotted disk which then collide with a Channeltron electron multiplier. The 22cm diameter slotted disk has a rotation frequency of 30,000 RPM and a chopping frequency of 80kHz. This rotation frequency and a slot thickness of 152$\mu$m allow a snapshot of 0.8$\mu$s to be taken and spread out over a 1.5m streaming length. With these parameters, the time-dependent ion velocity distribution can be measured with 12.5$\mu$s time resolution.