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.