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


Alcator C-Mod Weekly Highlights
Feb 01, 1999

Operations
-----------
The C-Mod startup campaign continued this week, with four run days scheduled
and completed. Considerable progress was made in cleaning up the machine this
week. By Friday, full length limiter and divertor discharges were being
run. The plasma current was increased to 750kA. Startup reliability increased
to over 75%. The machine condition is now adequate for most diagnostic and
auxiliary system commissioning activities.

Between-shot Electron Cyclotron Discharge Cleaning (ECDC) in helium was
employed on Friday in an attempt to reduce the recovery time and increase
startup reliability after plasma shots. This technique seemed to be helpful.

This week will be devoted to continuation of the cleanup campaign, alignment
and calibration of various diagnostics, and conditioning of the D- and E-port
ICRF antennas. We also plan initial plasma experiments with the divertor
bypass flappers.

RF
--
Antennas D and E-port have been conditioned to 40 kV into
vacuum. Remaining conditioning and testing require plasmas which will
begin this week.

The new 2274 vacuum tube, on loan from PPPL, has been successfully
installed into FMIT#4. The remote control system was tested
successfully and tuning to 78 MHz was begun and low power output has
been achieved.

We received the remaining 6" coax needs for J-port (two 30" lengths,
two crosses, two 6", and one tee). We began testing the J-port loops
and the calculations appear to be within a few percent. We are
working closely with PPPL to finish these loops. The two 9" coax
lengths yet required to complete the power feed have been ordered and
assembly of the final 9" coax run has begun.

DNB
---
Diagnostics and controls for the DNB continued to move ahead. Preparations
for running the accelerator supply into a dummy load were completed. The
supply local controls were tested with power, the nitrogen blankets to
maintain the transformer oil conditioning are now in place and running off
the lab N2 supply rather than individual bottles, and the dummy load was
prepared for 50 kV at 2A. Work continued on the new Mod/Reg tube control
electronics. Ron Bravenec of UT-FRC continued his visit to prepare the
BES system. The required fiber optics arrived from PPPL and are now being
terminated.


Physics:
--------

The spectrograph which is dedicated to H/D ratio measurements using Balmer alpha
emission is operating reliably. The time histories of the H/D ratio are
automatically written to the tree after each discharge. During the present
cleanup phase, wall fueling is an important particle source, and the levels of
hydrogen and deuterium in the recycling gases are approximately equal.

The location of peak electron heating due to mode conversion of the
injected RF wave is directly related to how much minority ion species is
present. To improve efforts in estimating the Helium-3 fraction in D(3He)
plasmas, the predictions of such peak heating from TORIC, a full wave code
including temperature effects were compared with a cold plasma model. The
comparison indicates that the simpler cold plasma model is adequate for
concentrations above about 15%, but differs from TORIC by up to 1.2 cm
(out of a 22 cm minor radius) for lower concentrations.

The edge x-ray diagnostics measure chord integrals of the soft x-ray
emissivity in the edge of the plasma. Improvements have been made to the edge
x-ray inversion algorithm. Most of the CPU time involved in this routine was
previously spent on mapping pixels to their flux surfaces (and then to the
midplane). A routine has been developed which performs this mapping roughly 6
times faster. This improvement allows us to invert data from both edge arrays
in between shots. In addition, the inversion algorithm has been changed to
eliminate a numerical problem which previously limited the spatial resolution
to 1.7 mm. Inversions can now be performed routinely with a spatial resolution
of 1.2 mm. This improvement is particularly important for ELM-free H-modes,
where the pedestal width is very narrow.

Travel,Visits:
--------------

Dr. Nakanishi, Dr. Yamaguchi, Dr. Ohsuna, and Dr. Emoto from NIFS in
Japan visited Josh Stillerman and Tom Fredian last week to learn about
the MDSplus data system and evaluate its possible use on the LHD
experiment.

Dr. Mamiko Sasao, from NIFS, visited last week. She discussed various
diagnostics, with an emphasis on those based on neutral beams, with E. Marmar,
J. Rice, W. Rowan, E. Eisner, and J. Terry.

Ron Bravenec has been at C-Mod since Jan 22 working on the BES diagnostic.

Bruce Lipschultz visited Columbia Friday and presented a talk - 'Exploring the
synergism between atomic and plasma physics in Alcator C-Mod'.

Miklos Porkolab attended the Fusion Power Associates Meeting in Marina del
Ray, California, on Jan. 25-27, and presented a paper with the title:
"Requirements and Development Path for the Advanced Tokamak Concept". He also
attended the FPA Board Meeting on 1/25/99.