Alcator C-Mod Weekly Highlights September 14, 1998 Engineering: We continued feltmetal soldering of the upper arms last week. We have completed soldering on all arms except for the five upper ones that are being rebuilt. We also completed an extensive survey of all the feltmetal pads and will soon begin peel tests and resoldering of a few pads that did not meet specs. Trimming of the feltmetal pad edges has also begun as has a general cleanup of the arms. Cleanup of the TF core was finished over the weekend. We continue to bake the core and OH coils to dry them out and prepare them for hi-pot tests. Fabrication of the welding fixture for the new spring plate design was completed. This fixture allows both the 4 pack and 2 pack spring plate assembles to be welded. Lifetime tests of the spring plates will be run as soon as we have some welded samples. A packet of information about the new spring plates has been sent to Peter Bonanos at PPPL for an outside opinion. We will also have an internal review in the next few days as more test data becomes available. The FMIT#4 transmitter remote control system is partially operational. Tests of the digital input signals have been completed. Tests of the output signals will begin shortly. The transmitter can be remotely turned on but faults can not as yet be reset. The J-port antenna 9" power feed design has been completed. Antenna parts which were sent out for replating have been received at PPPL. These components were tested and have been accepted by PPPL. One of our 2274 final amplifier tubes has been tested at EIMAC. They confirmed that the tube would support static voltage but not RF. We continued the development of the DNB for C-Mod. Testing of the power supply control panels for the HV accelerator supply continued. Modifications to the control system for the vacuum oil dryer were completed, extraneous hardware installed during testing removed, and vent valves were added. Construction of the F-Port flange continued along with design for an analog signal conditioning board for the HV supply. Construction drawings for the required modifications to the diagnostic stand near F-port, for in-cell installation of the near-beam power conditioning equipment, and for the HV terminations in the cell were completed. Work continued this week on the design of the laser rangefinder under development in collaboration with Carlos III University. Design of invessel components required to hold the retro-reflectors has begun. Modifications will be required of the inner divertor tiles, and support and wedge plates. Physics: J. Snipes compared the Low Particle Confinement H-mode (LPCH) (Bures, et al, Nucl. Fus., Vol. 32 (1992) 539.) observed on JET with the Enhanced D alpha H-mode (EDA H-mode) (Snipes, et. al, 24th EPS Conference Berchtesgaden, Vol. 21A Part II (1997) 565.) observed on C-Mod. At least in the case of strong gas puffing into the X point of JET (before they had a divertor), the LPCH-mode and the EDA H-mode do appear to be quite similar. They are both obtained with high gas puffing. There is increased D alpha emission and main chamber recycling. The particle confinement is reduced relative to ELM-free H-mode with taup (LPCH/EDA) = 1/3 taup(ELM-free). The energy confinement is only 20% lower than in ELM-free H-mode. In the case of JET, the magnetic configuration was double null with Ip = 3 MA, Bt = 2.8 T, kappa = 1.8, delta =0.54, D(H) ICRF heating with P_RF < 10 MW, nebar = 5-6 x 10^19 m^-3, and T_i =T_e. There was no divertor and the walls were mostly carbon with some beryllium. In the case of C-Mod, the EDA is regularly obtained in a single null X point configuration with Ip < 1.4 MA, Bt = 5.3 T, kappa = 1.6, delta = 0.5, D(H) ICRF < 3.5 MW, nebar = 4 x 10^20 m^-3, and T_i = T_e. In C-Mod, however, there is a very closed divertor and there are molybdenum walls. Both regimes are at relatively low betan < 2 . Both P. Lomas and J. Jacquinot have expressed interest in trying to reproduce this regime on JET, but there may be some difficultly in reaching these triangularities in JET with the present divertor configuration. There is also interest on DIII-D to try to reproduce this regime, though the ICRF there may be limited to relatively low power. C-Mod intends to collaborate with both machines to attempt to reproduce the LPCH/EDA regime, which may prove to be the most reactor relevant regime observed to date. By comparing the results in the same regime on all three machines, we should be able to obtain an improved understanding of the physics of this interesting regime. Topical focus groups have been formed to follow up on the prioritization of run time for experiments proposed at the C-Mod Ideas Forum in August. A total of fourteen groups are meeting to refine and develop the relevant ideas into a conceptual list of experiments, and assign relative priority to each experiment according to its importance to the development of a particular physics topic. On average, each idea presented at the Forum is being considered by two focus groups, due to overlaps in the physics or techniques involved.