Newsgroups: sci.physics.plasma
From WOLFE@CMOD2.PFC.MIT.EDU Mon Jan 16 15:32:46 1995
From: WOLFE@CMOD2.PFC.MIT.EDU
Organization: MIT
Subject: Alcator C-MOD Weekly Highlights

Alcator C-MOD Weekly Highlights
Jan 17,1995

Operation continued on Alcator C-MOD this week. Four runs were scheduled and
completed. Principal experiments included studies of divertor detachment and
ICRF antenna conditioning and heating.

The TFTR-type Neutral Particle Analyzer (PCX) at F-port was calibrated using a
series of reproducible discharges. The mass discrimination was explored using
varying concentrations of H minority in D plasmas, with cross-calibration to
the U. Md. Spectroscopic diagnostic. Calibration data were also obtained for
the K-port tangential charge exchange (TCX) system. During this run several
piggy-back experiments were also conducted, including Li pellet injection,
conditioning of the E-port ICRF antenna, and a vertical scan of the ECE
system.

Experiments on the effect of increasing radiation on divertor detachment
(MP#043) were carried out using Neon puffing into standard 800kA lower SN
discharges. The plasma density was ramped from about 1 to 3e20/m3 with varying
amounts of Neon injection. The power conducted through the LCFS varied from
800kW to less than 200kW. Detailed data were obtained for the upstream SOL
using the fast scanning probe as well as at the target plate. Strikepoint
control was used to keep the outer strike position at its nominal location.

Conditioning of the E-port dipole ICRF antenna (MP#054) was completed, and
heating studies (MP#059) using this antenna begun. Target plasmas were 800kA
lower SN with a small outer gap, with typical density around 2e20/m3. Up to
1.75 MW was coupled through the antenna. Heating was found to be comparable to
that observed previously using the D-port antenna; for 1.6MW the plasma stored
energy increased by about 25kJ in L-mode. Several shots were run with Li
pellet injection just prior to the turn-on of the RF. These showed good
heating, up to 40kJ increase in the diamagnetic stored energy. Several
ELM-free H-modes were also obtained in the high-density post-pellet RF-heated
phase.

A second piggy-back experiment on this run was an investigation of magnetic
dipole (M1) lines of Ti-like Xenon and Tungsten (MP#072),which are of interest
for ITER ion temperature diagnostics. Xe injection was successfully carried
out, however the predicted forbidden line at 4139A was not observed. Divertor
detachment was obtained on several shots; these results provide additional
data for the detachment studies carried out earlier in the week. Radiation
properties for Xe and W in the main plasma were measured.

Analysis of confinement data is continuing. This week we contributed 190
time-slices to be included in the ITER L-mode database. Examination of our
growing H-mode database indicates that the outer gap may be a significant
parameter in determining the H-mode threshold, at least in the ohmic cases.