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The development of an Omegratron plasma ion mass spectrometer for Alcator C-Mod [electronic resource].

Published
Washington, D.C. : United States. Dept. of Energy, 1993.
Oak Ridge, Tenn. : Distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy.
Physical Description
117 pages : digital, PDF file
Additional Creators
Massachusetts Institute of Technology, United States. Department of Energy, and United States. Department of Energy. Office of Scientific and Technical Information
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Summary
A new diagnostic device, the Omegatron Probe, has been developed to investigate relative impurity levels and impurity charge state distribution in the Alcator C-Mod Tokamak edge plasma. The Omegatron probe consists of two principal components, a ``front-end`` of independently biased grids, arranged in a gridded energy analyzer fashion and a large collection cavity. Particles enter the probe in a thin ``ribbon`` through a knife-edge slit. The grids provide a means to measure and control the parallel energy distribution of the ions. In the collection cavity, an oscillating electric field is applied perpendicularly to the ambient magnetic field. Ions whose cyclotron frequencies are resonant with this electric field oscillation will gain perpendicular energy and be collected. In this way, the probe can be operated in two modes: first, by fixing the potentials on the grids and sweeping frequencies to obtain a `` Z/m spectrum`` of ion species and second, by fixing the frequency and sweeping the grid potentials to obtain the distribution function of an individual impurity species. The Omegatron probe performed successfully in tests on a Hollow Cathode Discharge (HCD) linear plasma column. It obtained measurements of T{sub e} ≈ 5 eV, T{sub i} (H⁺) ≈ 2.0 ± 0.2 eV, n₀ ≈ 9 × 10¹⁵ m{sup −3}, RMS potential fluctuation levels of ∼ 0.5 ± 0.05 ± T{sub e}, and obtained ``Z/m`` spectra for the plasma ions (H⁺, H₂⁺, He⁺). Additional experiments confirmed the theoretical scalings of the f/δf resolution with the applied electric field and magnetic field strengths. The instrument yielded an absolute level of resolution, f/δf, of approximately 2.5 to 3 times the theoretical values. Finally, the results from the HCD are used to project operation on Alcator C-Mod.
Report Numbers
E 1.99:doe/et/51013--t248
E 1.99: pfc/rr--93-3
pfc/rr--93-3
doe/et/51013--t248
Subject(s)
Other Subject(s)
Dissertation Note
Thesis (M.S.); PBD: May 1993
Note
Published through SciTech Connect.
05/01/1993.
"doe/et/51013--t248"
" pfc/rr--93-3"
"DE93017617"
Thomas, E.E. Jr.
Funding Information
AC02-78ET51013
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