Alcator C-Mod Weekly HIghlights Apr 5, 1999 Alcator C-Mod resumed plasma operations last week. Three runs were scheduled, but only one was completed. The scheduled runs were primarily dedicated to check-out and conditioing of the ICRF systems. During the run on Wednesday, it was determined that an arc had occurred in the E-port transmission line, as described below, and the Thursday and Friday runs were cancelled so that the line could be repaired. Aside from this arcing problem, the run on Wednesday was successful and productive. This was the first day of plasma operations following several weeks of maintenance activities, during which a "clean" vent of the vacuum system was performed. The machine condition was good. Startup reproducibility was high, and impurity levels, including Mo, were low. EDA H-modes were readily obtained at about 1MW of RF power. The RF power was brought up to 1.7MW, mostly from the D-port antenna. Several piggyback experiments were carried out. The FSP fast scanning probe was observed on the video system, in preparation for plume imaging experiments. Ron Bravenec (U. Tx) completed installation and first operation of the BES system by observing continuum emission to the red of D-alpha. All eight channels produced signal with low noise. Edge-peaked fluctuations were observed above 50 kHz. Data was obtained on the Omegatron edge plasma diagnostic, which had been aligned during the maintenance period. This probe combines a gridded energy analyzer and an ion mass spectrometer. Analysis of these data is proceeding. Physics & Analysis: ------------------- First results from the new Kaiser spectrometer have been obtained. The Kaiser system consists of 14 spatial chords looking tangentially at the plasma boundary (spatial resolution ~ 3 mm). In addition to observing Halpha and B II profiles, the spectrometer views three He I lines emanating from a helium gas jet which is fixed to the side of the AB split limiter. Using the ratio of the three He lines, it is possible to derive the local ne and Te profiles. This work is in collaboration with PPPL (which has loaned the spectrometer) and TEXTOR (which has supplied the theoretical line ratios). First ne and Te profiles are very encouraging. Full profiles from several centimeters outside the separatrix to approx 1 cm inside have been obtained. There is reasonable quantitative agreement with the ASP (probe at approximately the same location), particularly with respect to the density profile. We will continue to obtain data with the new system and hope to provide some scalings for separatrix values of ne, Te and their gradients. ICRF Systems: ------------- Initial testing into plasma indicated an arc in the E-port transmission line between the transmitter and stub tuner that prevented increasing the power beyond ~400 kW. The initial damage was probably done during testing with an improper switch set ting. Upon disassembly, an elbow assembly was found to have arced. The elbows were replaced with spare elbows and tested under matched and unmatched vacuum conditions. To avoid a repeat of this problem, a proceedure will be put in place requiring visual inspection of switch positions. A lockout and monitoring system will also be implemented. On FMIT#1 and #2, the FPA screen current limit was changed from 4 A to 7.2 A (recommended screen current limit). This change should eliminate some screen overcurrent crowbars that occurred during the last campaign. With the help of Chris Brunkhorst and Gary D'Amico (PPPL), a general survey of FMIT#1 and #2 were conducted to establish documentation of present system and to identify systems that limit output power. The J-port 9" coax has been reassembled, including the phase shifter #3. The phase shifter required reconditioning of the push/pull rod connection. The system was evacuated and is currently pressurized to 5 psi N2 (15 psi will be the initial operating value). All the Mega coax elbows have been inspected and those that failed were modified. Vacuum tuning and testing will begin shortly. Travel and Visits ------------------ Gary Taylor returned from PPPL to work on the 19-channel grating polychromator. He modified the filters on the fast channels, which gave improved signal to noise. During the maintenance break, he completed analysis of electron power deposition in some previous RF modulation experiments, which showed good agreement with TORIC and other RF codes. Tom Fredian has returned from his trip to the Australia National University in Canberra, Australia, March 8-19 to install MDSplus for use on the H-1 Heliac experiment.