Alcator C-Mod Weekly Highlights
			Oct 21, 2002

Physics operations continued at Alcator C-Mod last week. Three run days were
scheduled and completed. Experiments were carried out in support of the
Transport and Advanced Tokamak Studies programs. Progress also continued on
the Lower Hybrid Fabrication project, and in the implementation of DNB-based
diagnostic systems. Plasma operations are scheduled to continue next week.

Operations
----------

Plasma operations were conducted Wednesday through Friday last week. A total of
79 plasma discharges were produced with a startup reliability over 90%.  

The run on Wednesday was in support of MP#312, a study of toroidal rotation
profiles in ohmic H-mode discharges. This experiment, which comprises part of
the doctoral research project of an MIT graduate student, addresses issues of
momentum transport and generation in ohmic tokamak plasmas. The results are to
be compared with related phenomena in the presence of ICRF heating. The
experiment on Wednesday included documentation of rotation profiles in H-mode
discharges with and without internal transport barriers (ITB).

Thursday's run was primarily devoted to an assessment of the CXRS diagnostic,
one of the new beam-based diagnostic capabilities being developed at Alcator
C-Mod. The goal of the day's run was to acquire CXRS spectral data in
quiescent discharges to determine limits of present diagnostic
configuration.The questions to be answered were: How far into the plasma can
measurements be made?  What is the signal attenuation with increasing plasma
density?  Are the Ti inferences reasonable?  Series of reproducible ohmic
shots were produced at several densities, 0.8<nebar<1.8 e20/m3. Beam-induced
CXRS spectra were measured in the outer third of the plasma radius.  These
signals were observed to diminish at the higher end of the density scan.  This
data will be used with penetration and emission estimates to determine the
density limit for the measurement.  The spectra are of sufficient quality so
that a line shape model can be developed and Ti measured. This run was also of
use for MSE as it provided an excellent opportunity to evaluate the
shot-to-shot reproducibility of the MSE pitch-angle measurement.

Friday's run continued the program of MP#317 to improve the documentation and
establish the physics of ITB formation associated with off-axis ICRF
heating. The target plasmas for this experiment were 800kA<Ip<1MA discharges
at toroidal fields 6.2<Bt<6.5 tesla, with ICRF proton minority heating at a
frequency of 80MHz, which places the resonance on the low-field side. As in
previous experiments at lower field and 70MHz, ITB formation was observed,
developing out of an EDA H-mode, at fields above 6.4T. These were the highest
fields at which the off-axis ICRF-generated ITB's have been obtained. The
quality and duration of the ITB's in these experiments was limited,
however. Profiles of density, temperature, and rotation were obtained for
future analysis. 


ICRF Systems
------------

D- and E-port dipole antennas were employed for ICRF heating at 80MHz during
the C-Mod experiment on Friday.  Up to 2 MW was delivered to the plasma, as
called for in the run plan. 

During operation on Friday, Oct 11, a fault in the FMIT #4 screen supply
resulted in arcing in the FPA input cavity. The input cavity was disassembled
and evidence for the arcing found at the input loading capacitor.  The
capacitor is being repaired.  Cavity dimensions are being verified while the
unit is disassemled so that a spare cavity can be built.

While transmitter #4 is out of service, the feed to the four-strap J-port
antenna is being reconfigured to allow the two central straps to be driven as
a dipole using transmitter #3 alone.

Lower Hybrid MIE Project
------------------------

The design of the waveguide support structure is proceeding.  The material for
most of the structure has been ordered.

The parts for the HVPS crowbar have been received from the vendor, and
preparations for installation are underway.

Good progress continues to be made on the Lower Hybrid launcher 
fabrication.  The ceramic windows for the fourth coupler have been 
brazed and tested vacuum tight.  All four couplers needed for the 
laucher are now having final machining performed prior to cleanup and 
plating.  A spare coupler will be brazed later in the week.

DNB Systems
-----------

The DNB ran reliably through the week; data were collected during the H-mode
and ITB experiments, as well as for the dedicated CXRS experiment on Thursday.
The beam component mix was improved to [E, E/2, E/3, E/18] =
[0.33,0.12,0.36,0.19] by increasing the rep rate and running the beam before
the C-Mod run began.  This improvement represents a reduction in the E/18
component, but essentially no improvement in the main energy component.  This
returns the beam to essentially the component mix that was measured after
commissioning earlier in the year.

The apparent magnetic pitch-angle has been evaluated from MSE data in roughly
50-70 discharges comprising about 15 sets of plasmas with 2-10 shots of nearly
identical plasma conditions.  Assuming that the q-profile is nearly the same
for all shots in a given set, this provides a direct measurement of the
statistical uncertainty in the measured angle.  Initial results are consistent
with expected behavior:
   1.  The shot-to-shot scatter is smallest in the outer radial 
channels, for which beam attenuation is weak.
   2.  At the outermost radial channel, the scatter increases because 
the density is low.
   3.  As the plasma density is increased beyond a vertical 
line-integral of about 1.e20, the shot-to-shot scatter in the core 
measurement increases significantly.  As the density is increased 
still further, the core region over which the scatter exceeds 1 degree 
grows in size.


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

A number of C-Mod physicists attended the 19th IAEA Fusion Energy Conference
in Lyon last week. Papers presented on C-Mod Results included:
	Earl Marmar,"Overview of Recent Alcator C-Mod Research"
	Brian Labombard, "Density Limit and Cross-Field Edge Transport Scaling
		in AlcatorC-Mod"
	Dmitri Mossessian, "H-Mode EdgeStability of Alcator C-Modd Plasmas"
	John Rice, "Double Transport Barrier Plasmas in Alcator C-Mod"
	James Terry,""Experimental/Theoretical Comparisons of the Turbulence in the
		Scrape-Off-Layers of Alcator C-mod, DIII-D, and NSTX"
		(presented by G. McKee of DIII-D)
	Steve Wukitch,"Performance of a Compact Four-Strap Fast Wave
		Antenna"
	David Mikkelsen (PPPL), "Nonlinear Simulations of Drift-Wave
		Turbulence in Alcator C-Mod"
In addition, Joe Snipes presented a paper on behalf of the ITPA Threshold
Working Group entitled "Multi-Machine Global Confinement and H-mode Threshold
Analysis".
Ron Parker, Miklos Porkolab, and Bruce Lipschultz also participated in the
meeting. 

At the IAEA meeting in Lyon, there were a series of meetings on
U.S. bilateral collaborative agreements. Miklos Porkolab participated in the
US/EU and US/Japan meetings. Earl Marmar participated in the US/Korea and US/PRC
meetings; in addition, he participated in the ASDEX IEA Executive Committee
Meeting.