Newsgroups: sci.physics.plasma
From WOLFE@CMOD2.PFC.MIT.EDU Wed Jan 17 12:31:58 1996
From: WOLFE@CMOD2.PFC.MIT.EDU
Organization: MIT
Subject: Alcator C-MOD Weekly Highlights

Alcator C-MOD Weekly Highlights
Jan 16, 1996

Alcator C-MOD operation resumed last week after completion of boronization
wall conditioning. Boronization has been successful in terms of
reducing molybdenum radiation, and increasing the confinement time in H-mode.
New record values (for C-MOD) of stored energy, H-factor, and neutron rate
have been obtained.

Boronization of C-Mod was carried out on Jan 7, 9,10 using ECDC to decompose
the diborane gas in the vessel. The total number of boron atoms injected was
~2e23, corresponding to a layer 100 nm thick if it were uniformly distributed.
Helium ECDC was then carried out overnight on Wednesday and during the day and
overnight on Thursday, in preparation for Friday's run.

On Friday, we carried out a series of standard 800kA fiducial shots, followed
by a density and partial RF power scan, similar to the the pre-boronization
run of 960105. The boronization has reduced the Mo in the ohmic phase to
background level. Distinctive Mo peaks are there during RF but they are down
almost an order of magnitude , from a brightness of ~8e15 photons/ster/cm2/s
before boronization to a value of 1.5e15 photons/ster/cm2/s after
boronization. The Mo level continued to fall slightly during the run to
~8e14 photons/ster/cm2/s. A strong boron II line at 345.1 nm was seen on the
Chromex spectrometer and did not change brightness significantly throughout
the run. The spatial distribution of the boron (BII, 411 nm) seemed peaked at
the inner nose like all the other impurities we have looked at. The CII
monitor was down but by less than a factor 2. The OI monitor is down almost a
factor of 2. The fraction of the total power radiated has fallen
significantly, to less than 30%.

Good H-modes were obtained over most of the parameter range covered in this
run, with H-factors higher than previously obtained on C-MOD with RF, up to
1.8 times ITER89-P. Threshold powers were about the same, or slightly lower,
than for the pre-boronization runs, with P/nBS values around .018. The low
density limit for H-mode was observed at essentially the same value as
previously, ~0.8e20/m3. The only negative impact of the boronization seems to
be a somewhat less robust startup behavior.

Operation continued on Tuesday, with higher RF powers, up to 3MW, and plasma
current up to 1MA. Stored energy above 0.2MJ was achieved, with H-factors
above 2 relative to ITER89-P, and above 1.5 relative to ITER93H ELM-free
H-mode scaling. These values are much better than any obtained on C-MOD
prior to boronization. Neutron rates above 10^14/sec were also obtained for
the first time.

Operation is continuing, and we will continue to monitor the evolution of the
boronization layer and improved performance during the remainder of this week.

Earl Marmar is participating in the meeting of the FEAC Strategy and Science
Sub-panels in Washington D.C. this week.