From: WOLFE@PSFC.MIT.EDU
Reply-To: WOLFE@PSFC.MIT.EDU
Subject: Alcator C-Mod Weekly Highlights
Newsgroups: sci.physics.plasma
Organization: MIT


Alcator C-Mod Weekly Highlights
April 3, 2000


Plasma operation at Alcator C-Mod resumed last week. Four run days were
scheduled and completed. All runs were devoted to machine startup and
conditioning activities. In order to minimize time devoted to startup
development for "reverse-field" operation later in the campaign, this first
week of plasma runs was carried out with current and toroidal field in the
reverse, i.e. positive, direction. A total of 31 plasma shots were produced,
out of 69 attempts.

Operationally, the machine performance was similar to previous startup
weeks. Breakdown was readily obtained, with very minor adjustments from
control settings used during the last campaign. The main difficulty was in
machine cleanup (conditioning) which requires a significant number of tokamak
discharges. The startup scenario in reverse field was improved by adjusting
the vertical field ramp rate, and by the end of the week appeared to be
satisfactorily robust. Full length (>1.6 sec) discharges at 5.4T and 800kA
were produced. At the end of Friday's run, the walls were still not fully
conditioned, as evidenced by the rate of gas evolution from the walls, the
high H/D ratio, and the relatively high loop voltage.

A partial flux loop, F28, which had been repaired during the last vent, failed
early in the week, apparently due to disruption forces. The PCS control
algorithms were modified to use a nearly redundant loop, F27, and operation
was resumed.

The bus work is being re-configured for normal (negative) field and current
operation. This week will also be a plasma startup week, devoted to additional
conditioning discharges.

Physics:
--------

The Thomson scattering diagnostic is ready for the run. Over the last weekend
the laser beam was aligned, laser tuned up and tested, both core and edge
spectrometers tested, and the diagnostic calibrated using Raman scattering in
D2.

ICRF:
-----

Work on the transmitters has focused on operational safety and diagnostics. We
have recently imported FPA and Driver tube models from C. Brunkhorst (PPPL).
Currently, the measured data and model predictions significantly disagree. We
have re-calibrated the anode voltage and current instrumentation on the Driver
and FPA. We have re-calibrated the RF power measurements of the IPA, Driver,
and FPA stages. Currently the transmitters produce 1.8 - 2.4 MW into dummy
load. We plan to document the working status of the transmitters and compare
them with the models. The PLC system has been investigated for FMIT#1.
Programming modifications were implemented to improve the information required
for operations. Future work is scheduled to transfer these improvements to
FMIT#2-#4. A gas barrier in E-port's matched line section has failed and
needs to be replaced. This work will begin this week.

Lower Hybrid System Fabrication:
--------------------------------

The first klystron has been installed in the test stand. The filament power
supply has been tested successfully, and emission current measured in the
tube.

Diagnostic Neutral Beam
------------------------

We continued the conditioning of the beam and were able to operate in the
45 to 48 kV range with few arc downs. There are some problems with the
plasma arc power supply. The connections in the oil tank appear to be
intermittent. We tightened them, which appeared to result in temporary
remediation, but the problem persists and will be addressed this week. We
successfully tested the software that we use to fire conditioning shots
between C-Mod shots. The software also detects the preparation for C-Mod
shots and then synchs the beam with them. The software was demonstrated
to work.


Travel and Visitors:
--------------------

John Rice attended the Atomic Processes in Plasmas Meeting in Reno Mar. 19-23
and presented a poster on Satellites to the Hign n Rydberg Series in Ar, Cl
and S from Alcator C-Mod Plasmas.

Amanda Hubbard attended a Workshop on Core and Edge Transport Barriers, held
at JAERI in Tokai, Japan, and presented a talk on 'Conditions for EDA H-mode'.
She also discussed with Drs. Kamada and Hatae ideas for comparing this regime
with the 'grassy ELM' regime on JT60U.

Yongkyoon In attended the Sherwood Fusion theory meeting, which was held in
Los Angeles from March 27 through 29.

Perry Phillips from the Fusion Research Center has been at MIT for the past
week installing the high resolution ECE system. He will be here for another
week to finish the installation.

Norton Bretz was at PPPL this week working on MSE software and preparing final
hardware adjustments. He will be back at C-Mod the week of 4/3. Gerd
Schilling also spent the week at PPPL, tidying up remaining FWP issues,
collecting fiber optic telemetry for the C-Mod ICRF transmitters, working on
obtaining a replacement to man the MSE diagnostic next year, and trying to
arrange for further and additional rf engineering help to finish off the
remaining problems of the ICRF transmitters.