Alcator C-Mod Weekly Highlights
			June 26, 2006

FY2006 weeks of research operations:
   Planned: 14 weeks
   Completed: 14.4 weeks

Operations
----------

Plasma operations continued at Alcator C-Mod last week. Four run days were
scheduled and three and a half were completed. Experiments were carried out in
support of research in ICRF Physics, MHD, and Wall Conditioning optimization.
A total of 74 plasma discharges were produced with a reliability of 90%.

C-Mod has now accomplished 14.4 weeks of Research Operations during fiscal
year 2006, satisfying the OFES Operational (JOULE) Target of 14 Weeks.

Last week's runs complete the 50MHz ICRF experiments for the present campaign.
Next week will be a maintenance week with no plasma operations scheduled.
Plasma operations are planned to resume in July, with the J-port ICRF system
set for 70MHz operation.

Run Details
-----------

The runs on Tuesday and Friday were concerned with Mode Conversion Current
Drive, aimed at generating localized current using mode converted 50MHz waves
in D(He3) plasmas. Data were obtained for two MiniProposals MP#356 "Mode
Conversion Current Drive Experiments" and MP#447 "MCCD experiments during
current ramp-up". These experiments comprise part of the thesis research of an
MIT graduate student.

Wednesday's run concerned the comparison of boronization erosion with D(He3)
and D(H) minority heating scenarios. Previous results had shown indications
that the lower single pass absorption D(He3) scheme resulted in faster
degradation of the beneficial effects of between-shot boronization. The
experiments on Wednesday, employing 80MHz RF from the D- and E-port antennas
for D(H) and 50MHz from J-port for D(He3), at a field of 5.1T, did not support
this conclusion. There were in fact some indications that the D(He3) cases
showed slower degradation. There were observations indicating a stronger edge
interaction with D(He3), including larger D-alpha increases and higher
radiated power in the L-mode phase.

Thursday's run was in support of MP#450 "Disruption mitigation using
high-pressure gas-mixture injection", submitted by M. Bakhtiari (U. Wisconsin)
in collaboration with the C-Mod MHD Group. Disruption mitigation experiments
were carried out using pure helium and mixtures of helium (>50%) and argon
(<50%). For all mixture cases the halo current was less than 120 kA while for
those with pure helium injection we got I_halo=138 and 157 kA.  The current
quench time with mixtures was about 1 ms while it was more than 2.5 ms with
pure helium.  When the fraction of argon is small the mixture approaches the
plasma almost as fast as a pure helium gas, while as we mentioned above the
current quench is faster and halo current is lower with mixtures.  The density
increment with mixtures, when the fraction of argon is small, was comparable
with that in pure helium cases, which is advantageous from the standpoint of
runaway avoidance.

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

The capacitance across the DC breaks in the J-port transmission line was
increased in an effort to correct the pickup observed on the magnetics and
other diagnostics during 50MHz operation in the previous week. No recurrence
of the pickup was observed during last week's experiments.  All four
transmitters were successfully employed when needed during experiments last
week.

Long Pulse DNB System
---------------------

The DNB source repair continued last week.  Replacement ceramic spacer rings
are now in-house.  Budker Institute has shipped replacement first and second
diaphragms and new seal rings. A leak test fixture to test the assembled
source cathode and arc channel has been machined and has successfully passed a
leak test.

Lower Hybrid System
--------------------

The Lower Hybrid system klystrons are being conditioned to higher voltages as
we prepare for higher power current drive experiments.  This work will
continue this week, followed by period of calibrations at the high power
levels.


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

Earl Marmar, Miklos Porkolab, Jerry Hughes, Joe Snipes, Dennis Whyte (invited
talk), Olaf Grulke, John Wright, and Marco Brambilla presented results related
to C-Mod Research at the European Physical Society Conference on Plasma
Physics in Rome last week.

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