From: IRBY@CMOD.PFC.MIT.EDU
Date: Tue, 21 Apr 1998 21:08:55 -0400
Reply-To: IRBY@PSFC.MIT.EDU
Message-ID: <980421210855.22a6473f@CMOD.PFC.MIT.EDU>
Subject: Alcator C-Mod Weekly Highlights
Organization: MIT Plasma Fusion Center
Newsgroups: sci.physics.plasma


Alcator C-Mod Weekly Highlights
April 20, 1998


We continue preparations for the repair of the TF magnet. The
hydraulic soldering fixture required to attach the feltmetal to the magnet
finger joints has been setup and is in operation. New laser cut feltmetal is
in-house and will be used for soldering tests over the next couple
of days. The machining of the new TF vertical leg plates is complete,
and work on the new TF horizontal arm plates will begin shortly. Detailed
analysis of the forces and thermal effects at the finger joints during
high field shots has made good progress.
We continue to debug the crowbar problem on FMIT#4 which is
limiting the power at 78 MHz to about 500 kW. It is uncertain at this point
whether the problem is in the crowbar circuit itself or if it indicates a
real fault in the RF section of the transmitter (tube for example). PPPL has
extended the services of an RF engineer, Chris Brunkhorst, to work with us
on this problem. Progress was made last week on testing the control boards
for the new transmitters. A group of 12 boards need to be tested before we
can begin full operation with the new antenna. The 9" coax installation has
progressed as far as it can until the DC breaks have been modified to limit
RF leakage, and the new modification tested.
Last week we reported that the 4-strap antenna Faraday shield
rods had developed a cracking problem around the threaded ends.
PPPL has investigated further by pull and shock testing the rods. A single
Faraday rod is made of three pieces: one straight piece with a threaded
end (center post) and two bent rods with threaded ends. The three
pieces are brazed together. All rods passed the pull test, but the bent
rods failed the shock test. The failures show no signs of ductile
deformation before breaking which suggests the material is brittle at
room temperature. The proposed short term solution is to remove the
threaded TZM and replace it with Inconel. In parallel PPPL is also
investigating replacement of the TZM rods with copper coated inconel.
PPPL has continued to prepare the RF test stand for antenna electrical
characterization and testing. Gerd Schilling (PPPL) has continued to
develop a resonant loop model for the new antenna.
Conditioning of the oil in the DNB Mod/Reg isolation transformer
continued after observing a test breakdown of 35 kV. On the arc/filament
/snubber supply, we made progress on the circuit design for the interface
to the master control logic (MCL) unit. The required number of fiber optic
transmitter boards was completed, some fiber optic transmitters and receivers
were installed, and associated fiber optic links were routed and connected.
Work on fault circuitry calibration for the arc/filament/snubber voltage
feedback and monitoring systems continued. The hardware and software
for the CAMAC timing of the DNB during the plasma discharge was completed
and tested under software control through the output of the CAMAC modules.
Attention here has now shifted to distribution of other control functions
between PLC and CAMAC. The modified clock board was installed in the MCL
and the input connectors for the new timing signals to the existing chassis
and interconnecting wiring were completed.
Larry Owen and Ben Carreras of ORNL were here much of the week
assembling data and running models with the goal of calculating the neutral
profiles in C-Mod, in particular prior to the L-H transition.
We forgot to mention in a previous weekly report that on April 2nd
Miklos Porkolab visited the Magnetic and Laser Fusion Groups at LANL
and gave a seminar on the MIT PSFC Programs. He also discussed collaborations
with LANL personnel, particularly in the MHD modeling area where they are
completing a new nonlinear MHD code, called NIMROD, under the leadership
of Allen Glasser.