Alcator C-Mod Weekly Highlights August 17, 1998 Engineering: Plating of the TF core is approximately 30% complete. This process has become the machine assembly critical path issue. The vendor doing the electroplating expects to have two platers on-site completing this work this week. In preparation for machine assembly we began checking out magnets, insulation, thermocouples, heaters, flux loops, and other machine systems last week. A careful cleanup followed by borescope inspections of the magnet pockets will follow over the next few days. Tests of the new feltmetal revealed a sintering problem that has already been resolved with the manufacturer. Properly sintered material will be available early this week. This problem will delay somewhat soldering of the TF arms but is as yet not delaying machine assembly. Feltmetal samples have now been tested to 20,000 cycles at 9000 A/cm^2. This current density is well above what is needed for high field operation. A very good electroforming run was finished over the weekend. We hope this run will complete the electroforming stage of the TF core finger repair. We are now in the process of cleaning up and inspecting the finger. Depending on the amount of material still required to be plated, we will either have to electroform a final copper layer, or brush plate. The latter is the simpler and most likely process. The alternator has been brought up to full speed to verify that changes to the drive motor alignment were done properly. We are also making preparations for running the alternator during the full scale TF joint tests. A two month long upgrade in air and oil handling systems for the alternator is nearly complete. These changes will allow better control of water and particulate content in the alternator oil supply. We continued work on the DNB accelerator supply. Installation and wiring of one control panel has begun. A second is still under construction. Hardware for testing the controls on the bench was tested and calibration is complete. Work continued on the fast control logic for the accelerator supply and on construction of the F-Port flange. The initial fitup of the J-port antenna was done with the help of several PPPL collaborators (Les Gereg, Dave Cylinder, Randy Wilson, Gerd Schilling). The antenna fit inside the port once the planned modifications to internal magnetic probes near J-port were made. Remaining installation steps include: the antenna feed straps need to be modified slightly to avoid internal conduits; the flange design and assembly procedure needs to be finalized; approximately 40 components need to be silver plated; and the boronization gas conduit needs to be moved outboard about an inch. Physics: We plan to measure disruption induced distortions in the C-Mod vacuum vessel inner wall during our next run period. These measurements are needed to help model the inner wall as we plan upgrades to the divertor for high field, high current operation. A prototype diagnostic for making this measurement has been built in collaboration with Carlos III University and is being tested. The system relies upon retro-reflectors installed on the inner wall returning the 0th and 1st order beams from a diode laser after its beam has passed through a Bragg cell. The returning beams are combined with a beamsplitter, and the relative phase difference between the two beams is measured. Several retro-reflectors along the inner wall will allow maps of relative motion to be made on very fast timescales during disruptions. This technique avoids the need to make absolute position measurements relative to some external reference. Tests so far indicate the diagnostic can easily measure 2 to 3 mm relative motions with a 0.69 um resolution (a laser wavelength). Also in collaboration with Carlos III University, we are continuing to develop the tangential interferometer which we expect to use to make high spatial resolution density measurements of the plasma edge. We are exploring both the possibility of simply expanding the prototype to more channels, and the development of a differential interferometer that measures dNL/dR rather than NL (NL is the line density). The gradient in the line density is what is required to perform the Abel inversion, not the line density. The differential measurement is not sensitive to vibrations and allows diode arrays with high spatial resolution to be used as the detector. We have begun bench tests of our 5 channel AM reflectometer to uncover the cause of some unusual results from the last run campaign in which calibrations derived from inner wall measurements could not be used to produce density profiles. Preliminary tests results indicate that spurious reflections from flange components and the outer wall at the edge of the ports caused this problem. Sensitivity of the overmoded waveguide to vibrations may also have contributed. The Alcator C-Mod Ideas Forum will be held this week at MIT, August 19-20, 8:30 to 5:30, in room NW17-218 at the Plasma Science and Fusion Center. There will be 118 talks this year, about a 50% increase over the 1997 Forum; fifty authors submitted ideas. The agenda has been posted on the Web at http://www.pfc.mit.edu/cmod/agenda_98.html For those of you interested in the C-Mod forum but unable to attend, note that it will be broadcast over the MBone. Instructions can be found at http://www.pfc.mit.edu/cmod/forum_mbone.html As mentioned in previous reports, the general forum announcement is at http://www.pfc.mit.edu/cmod/forum98.html Visits and Travel: Joaquin Sanchez, Asociacion EURATOM-CIEMAT, is visiting for approximately 4 weeks to learn how to run the 2-D reflectometry code developed here at MIT. He will also work with us on hardware issues involving the C-Mod AM reflectometer. Les Gereg, Dave Cylinder, Randy Wilson, and Gerd Schilling were visiting from PPPL working on the new antenna fitup.