E∥B end-loss-ion analyzer for Tandem-Mirror Experiment-Upgrade

Abstract

We are constructing and testing a diagnostic instrument to investigate, in detail, ions emanating along magnetic field lines from the plasma region of the TMX-U tandem-mirror experiment. This analyzer (of Tokamak Fusion Test Reactor design) contains parallel electric and magnetic fields, which yield ion mass and energy spatial separation, respectively. A two-dimensional array of 128 copper collector plates detects the particles. The entering ion flux is first well collimated and then focused onto the detector plane during the 180° bending in the magnetic field. This instrument is designed to measure higher particle energies than the present gridded end-loss analyzers as well as determine the energy spectra more accurately. Tandem-mirror plasma parameters to be investigated with this analyzer include end-plug potential, average central-cell-ion energy, and plasma potential in the thermal barrier and nearby regions. We plan a time resolution of up to 2 kHz for each detector.

Contemporary Instrumentation and Application of Charge Exchange Neutral Particle Diagnostics in Magnetic Fusion Experiments

“…The superimposed E||B spectrometers constructed and calibrated at PPPL have been applied to charge exchange neutral particle measurements on ATF [43], LHD [44], NSTX [45] and MAST [46]. A similar instrument was developed for TMX-U [47].…”

E∥B energy-mass spectrograph for measurement of ions and neutral atoms

“…For example, Fig. 2 shows the exit charge state distributions of H, D, 3 He, 4 He, and C as a function of incident energy per nucleon. The dominant charge states observed for Eр20 keV are Ϫ1, 0, and ϩ1.…”

“…The relative abundance of fusion fuel and products, for example, H, D, T, 3 He, and 4 He, are required to understand the temporal evolution of fusion experiments and their neutron yields. For example, in the divertor region of an ignited tokomak, the abundance of He will need careful monitoring to assure adequate 4 He and 3 He ash removal.…”

“…For example, in the divertor region of an ignited tokomak, the abundance of He will need careful monitoring to assure adequate 4 He and 3 He ash removal. Measurement of contaminants present in the plasma such as Li, Be, B, and C is also important to provide a measure of the erosion rate of the first wall surfaces or divertor regions.…”

Spectroscopic analysis of low Z impurities in the Tandem Mirror Experiment-upgrade

“…Previous measurements from RGA 72 titanium-gettering of the walls, there were still an appreciable amount of hydrogen gas in the machine even though the plasma was directly fueled with deuterium; the abundance of hydrogen gas decreased with each day of plasma operation. Recent results from end loss ion spectrometer 73 showed that during the first few titanium-gettered shots, the fraction of hydrogen plasma ions may be as high as 30%. This fraction decreased to an unmeasureable level after several plasma shots with gettering which might have removed water in the unbaked TMX-U vacuum vessel.…”