Alcator C-Mod Weekly Highlights

			Nov. 28, 2005

FY2006 weeks of research operations:
   Planned: 12 weeks (tentative)
   Completed: 2.5 weeks

Operations
----------

Research operations continued at Alcator C-Mod last week. Three run days were
scheduled and completed. A total of 51 plasma discharges were produced, with a
startup reliability of 65%. Experiments were carried out in support of 
research under the RF Physics, Divertor/Edge, and Operations topics.

Experimental time on Monday was reduced by two hours while a power supply 
fault was diagnosed and repaired.

The second turbo-molecular pump on the main torus pumping station had to be
taken out of service prior to Tuesday's run. Operation continued with the
replacement TMP#1 which was installed last week. The two failed turbo-pumps
had been in service for several years and exhibited similar symptoms. A
replacement for TMP#2 is being installed. Operation with a single pump did not
significantly impact plasma operation, although a modification of the
boronization procedure was required on Wednesday.

Plasma operations are planned to continue this week.

Physics
--------

Monday's run was devoted to MP#440, "Erosion of boronization under different
conditions". This experiment is designed to employ ohmic H-modes to evaluate
the status of boronization conditioning following localized between-shot
boronization. During this run the 1.2MA, 5.4T ohmic H-mode shot was developed
and pre-boronization baseline conditions established. A between-shot
boronization was carried out with the ECDC resonance located between
.75<R<.85m. The first full-length post-boronization discharge showed marked
improvement in performance: the rate of increase of radiated power following
the L-H transition was reduced by a factor of 3, and the H-mode duration was
extended. Molybdenum radiation during the H-mode was very low and the Mo
source rate was undetectable at the inner- and outer- limiter locations.

On Tuesday we continued experiments in support of MP#438, "Evaluation of
J-antenna without Faraday screen". Comparison of upper and lower null
discharges indicated that the J-port antenna strap interaction observed on
upper null discharges is not apparent for LSN target equilibria. H-modes
obtained in lower null discharges using the J-port antenna had lower
performance than those obtained with D- and E-port antennas. This effect was
more apparent at higher plasma current.

Wednesday's run continued the series of experiments described in MP#409 "Phase
Space of the SOL". The old-style Mo probe head had been re-installed on the
A-side scanning probe drive, and performed nominally. Parallel and
perpendicular flows were documented in standard upper and lower null 800kA,
5.4T discharges with a two-point density scan, to verify consistent operation
of the diagnostics. We then began an investigation of ohmic H-mode plasmas,
looking at the behavior of parallel and perpendicular flows during the
ELM-free phase following the transition. One between-shot boronization was
carried out, using parameters similar to those employed during Monday's run,
modified to account for lower pumping speed. Initial observations indicate
that there is a spatial compression of the velocity shear layer in H-mode
relative to L-mode. Detailed analysis of these data is proceeding.

ICRF System
------------

An intermittent high voltage interlock fault on FMIT#3 prevented operation of
J-port on a number of shots last week. The fault appears coincident with C-Mod
pulses, and does not occur between shots or on test pulses. Instrumentation
has been added to the interlock chain and trouble-shooting of the problem is
proceeding.


Long Pulse Diagnostic Neutral Beam System
------------------------------------------

The DNB had an up-to-air event over the weekend, and required a long rough
down to remove the resultant contaminant loading from the de-frosted cryo
pumps. Rough down was slow but uneventful, and the beam vacuum is now in the
high 10(-6) Torr range and dropping. The cryo system was left warm through
the Thanksgiving holiday.

LH System
----------

We are working with a local vendor to produce ultrasonic images of the coupler
windows.  Initial tests with an early rejected coupler indicate that high
resolution images of faults in the alumina windows can be made.  We plan to
have all four of the production couplers tested prior to installation.

Work continued on the klystron body current sensor installation. All the
circuit boards and chassis are tested, assembled, and ready to be bolted into
the carts. The shield boxes have been assembled and installed into the
carts. Wiring is nearly complete.

All probe detector diodes and blocks have now been installed on the patch
panel and are ready for connection.

Calibration of the coupler protection system (CPS) intermediate diode circuits
is proceeding.



------------------------------------------------------------------------

    * Previous message: [Cmod_weekly] Alcator C-Mod Weekly Highlights
      <000073.html>
    * *Messages sorted by:* [ date ] <date.html#74> [ thread ]
      <thread.html#74> [ subject ] <subject.html#74> [ author ]
      <author.html#74>

------------------------------------------------------------------------
More information about the Cmod_weekly mailing list 
<http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly>