From:
irby@PSFC.MIT.EDU
Reply-To: IRBY@PSFC.MIT.EDU
Subject: Alcator C-Mod
Weekly Highlights
Newsgroups: sci.physics.plasma
Organization:
MIT
Alcator C-Mod Weekly Highlights
September 8, 2003
We continued work on Lower
Hybrid and ICRF systems last week.
We
expect completion of the alternator inspection early this week,
but we
are discussing additional tests on the stator windings.
Physics
-------
Robert
Granetz has continued the analysis of the deuterium DNB
experiment, with
the goal of learning more about the confinement of
the ICRF-generated
hydrogen minority tail ions. The focus
is now on
the absolute neutron rates measured in a variety of plasma
conditions.
Any significant prompt loss of fast deuterons will show up as
a
reduction in the measured 2.45 MeV neutron rates compared to the
calculated
expected rates. Simplified calculations
show that the
measured neutron signal turns out to be 25%-75% of the
calculated
rate, and that this ratio has a dependence on density. The effect of
Zeff on the deuterium
plasma density has been included in these
calculations, but profile
effects and beam penetration effects have
not, and they could, in
principle, explain the deficit and its density
dependence. Therefore the simplified calculations show that
to within
an order of magnitude, prompt losses are small or non-existent,
but in
order to get better than a factor of ~2 accuracy, TRANSP runs will
be
required, and are indeed planned.
Alternator
----------
All
UT tests of the alternator rotor have been completed. The rotor
end rings have been replaced, and the rotor is
ready for DC hi-pot
tests early this week. DC hi-pot tests performed last month of the
stator showed
low leakage and polarization currents on all windings,
which would usually
be considered a very good result.
However, we had
questions about the shape of the hi-pot I-V curves
that we asked GE,
the vendor doing the inspection, and outside
consultants, to help us
understand.
The interpretation and correctness of these curves weigh
heavily on
our decision about whether or not a rewind of the stator is
required, and
in any decision to put the alternator back into service
now, as has been
recommended by GE. At the
recommendation of GE, and
one of our consultants, we have repeated the DC
hi-pot tests with
results consistent with those found during several
inspections ranging
back to 1977.
These tests indicate a stator in very good condition
that is ready
for a return-to-service. However, we
are still
investigating the unusual results obtained from the first DC
hi-pot,
and we may require GE to do an additional AC hi-pot as a
final
guarantee of the stator condition.
Lower
Hybrid
------------
A meeting between PPPL and MIT personnel
was held at MIT on 9/3 for
discussions on finite-element modeling of the
lower hybrid coupler
windows.
Initial measurements of the coefficient of thermal expansion
have
been performed both for the titanium and the alumina that is used
for the
couplers, and the results are being evaluated and compared
against published
values. The vendor has started braze
alloy
selection tests and will subsequently braze coupler prototypes. The
upper Forward Wave Guide has been
reassembled, and is ready for
shipment to MIT for high power RF
testing. The lower FWG is in the
process
of reassembly bolting sequence optimization prior to low power
RF testing
at PPPL.
Two SFOL receivers are complete and ready for testing. We continue to
develop PLC control and
display software for the launcher.
ICRF
----
We
continued design of the 50 MHz matching system. There are ongoing
discussions with the vendor for the
prototype fast ferrite tuner
system to gather the information needed to
prepare it for testing.
Travel and Visits
-----------------
Doug
Loesser and Irving Zatz, both from PPPL, visited last week for
discussions
on the lower hybrid coupler.
Clyde Maughan, Maughan Engineering
Consultants, visited last Friday to
inspect the stator and give advice on
our alternator.
E3-I:
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