The development of an Omegratron plasma ion mass spectrometer for Alcator C-Mod

Thesis/Dissertation · Sat May 01 00:00:00 EDT 1993

DOI:https://doi.org/10.2172/10174738· OSTI ID:10174738

Thomas, Jr., Edward E. ^[1]

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1. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)

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_e ~ 5 eV, T_i (H⁺) ~ 2.0 ± 0.2 eV, n₀ ~ 9 x 10¹⁵ m^-3, RMS potential fluctuation levels of ~ 0.5 ± 0.05 ± T_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.

• Research Organization: Massachusetts Inst. of Tech., Cambridge, MA (United States). Plasma Fusion Center
• Sponsoring Organization: USDOE
• DOE Contract Number: AC02-78ET51013
• OSTI ID: 10174738
• Report Number(s): DOE/ET/51013-T248; PFC/RR-93-3; ON: DE93017617
• Resource Relation: Other Information: TH: Thesis (M.S.); PBD: May 1993
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
47 OTHER INSTRUMENTATION
MASS SPECTROMETERS
DESIGN
ALCATOR DEVICE
PLASMA DIAGNOSTICS
PROBES
PLASMA IMPURITIES
FLUCTUATIONS
ELECTRONIC CIRCUITS
DATA ANALYSIS
PERFORMANCE
700320
440800
PLASMA DIAGNOSTIC TECHNIQUES AND INSTRUMENTATION
MISCELLANEOUS INSTRUMENTATION