Measurement of the current density profile in the Alcator C tokamak using lithium pellets

Journal Article · Fri Dec 01 04:00:00 EST 1989 · Review of Scientific Instruments; (USA)

DOI:https://doi.org/10.1063/1.1140485· OSTI ID:7264826

Marmar, E S; Terry, J L; Lipschultz, B; Rice, J E ^[1]

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1. MIT Plasma Fusion Center, Massachusetts Institute of Technology, 175 Albany Street, Cambridge, Massachusetts, 02139 (US)

High-speed lithium pellets have been injected into Alcator C tokamak plasmas in order to measure the internal magnetic field, and thus current density profiles. In the pellet ablation cloud, intense visible line radiation from the Li{sup +} ion ({lambda}{approx}5485 A, 1{ital s}2{ital s} {sup 3}{ital S}{minus}1{ital s}2{ital p} {sup 3}{ital P}) is polarized due to the Zeeman effect, and measurement of the polarization angle yields the direction of the total local magnetic field. A snap shot'' of the {ital q} profile is obtained as the pellet penetrates from the edge into the center of the discharge, in a time of about 300 {mu}s. The spatial resolution of the measurement is about 1 cm. At a toroidal field of {ital B}{sub {ital T}}=10 T, the emission in the unshifted {pi} component of the Zeeman triplet is more than 80% polarized, and {ital q} profiles have been obtained. The pellets are perturbative ({l angle}{Delta}{ital n}{sub {ital e}}{r angle}/{l angle}{ital n}{sub {ital e}}{r angle}{approx}1), but the total pellet penetration time is at least a factor of 1000 smaller than the classical skin time. It can thus be anticipated that the current density profile should not be perturbed significantly during the time of the measurement. With some relatively straightforward modifications and refinements, precision approaching 10% for the measurement of {ital q} profiles should be achievable. The technique appears viable, using Li, as long as the toroidal field is {approx gt}4 T.

• OSTI ID: 7264826
• Journal Information: Review of Scientific Instruments; (USA), Journal Name: Review of Scientific Instruments; (USA) Vol. 60:12; ISSN RSINA; ISSN 0034-6748
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
700102* -- Fusion Energy-- Plasma Research-- Diagnostics
ALCATOR DEVICE
ALKALI METALS
CLOSED PLASMA DEVICES
CURRENT DENSITY
ELEMENTS
LINE BROADENING
LITHIUM
MAGNETIC FIELDS
MEASURING METHODS
METALS
PELLET INJECTION
PLASMA DIAGNOSTICS
POLARIZATION
THERMONUCLEAR DEVICES
TOKAMAK DEVICES