Alcator C-Mod Weekly Highlights November 2, 1998 Engineering: Reassembly of Alcator C-Mod continued last week with the installation of the upper TF arms. The arms have been carefully aligned and shimmed into position, and installation of the upper spring plates is now underway. Application of G10 plates that support the load between the arms and the cylinder has also begun. Feltmetal soldering of the legs is nearing completion, with only two legs remaining to be soldered. A qualification process, which includes ultrasonic cleaning, hi-pots, checkout of voltage taps and thermocouples, and a careful inspection of the solder joints and plated surfaces has begun. DNB development continues. Completed wall mounts required for in-vessel installation of the CXRS optics were shipped from U. Texas so that they would be available for installation when mounting studs are installed. The F-port flange was thoroughly cleaned in preparation for leak testing, and detailed as-built measurements were begun. Oil conditioning on the arc/filament/bias power supply tank is complete, and a gas purge system for maintaining the oil conditioning was installed. Of the last two boards for the accelerator supply local control, the analog signal conditioning board is under construction, and the fast fault logic board design and associated chassis wiring diagram were completed. The Omegatron diagnostic, which combines a gridded energy analyzer and an ion mass spectrometer, has been reassembled, and detailed checkout of the electrical characteristics is underway. Last week the Omegatron was leak-checked, and it is being baked in preparation for installation on C-Mod. Final machining of the parts necessary to complete the Fast MHD pick-up coils is underway. These 65 new poloidal field pick-up coils will be mounted on the two outboard limiters. The new coils have been designed with a factor of two improvement in poloidal spatial resolution and a factor of five improvement in toroidal spatial resolution to determine high m and n numbers associated with Alfven eigenmodes, ELM pre-cursors, and Fast Edge Modes. The improved spatial resolution will also allow us to determine if the turbulence spectrum peaks along a field line as suggested by previous measurements. Other invessel activity continued last week on projects in various stages of completion from design to installation. A partial list includes work on the bolometer box, z-meter array, 2Pi bolometer, impurity injector, changes to the outboard limiters and installation of new diode arrays, TTCI mirror and retro-reflector array, rangefinder retro-reflectors, scanning mirror and shutter system for new VUV views of the divertor, new probes to be mounted on the AB limiter, modifications to the D and E-port antenna tiles, and helium probe gas injector. General vacuum related work still in progress includes changes to B, F, G, H, J, and K horizontal ports. Installation of the lower teardrop adapters needed to mount the large diagnostic flanges on the vertical ports was begun. We also continued work on the magnet power supplies, RF camac system, and heater and cryo systems last week. Our collaborators from INEEL/Lockheed Martin, W.J. Carmack and S.V. Gorman, have written a report on the dust collected in Alcator C-Mod in April of 1998. Details of particle composition and size distributions are discussed in great detail. Physics: Modeling of the edge plasma of C-Mod with the multi-fluid code UEDGE has progressed. This code solves the steady state Braginskii equations for ions and electrons and the Navier-Stokes equation for the neutrals in the real geometry of the edge plasma. The anomalous transport is adjusted to match experimental profiles of plasma density and temperature in the SOL. It has been shown in the modeling that, if the radial particle transport in the SOL is modeled as j=-D grad n, then a spatially constant D does not match the experimental SOL density profiles as given by scanning probe data. However using a D profile which grows rapidly towards the wall results in a good match to the density profile. Such spatially non-uniform radial particle transport can be also represented by a uniform D combined with a radially inward pinch, or a radially outward "anti-pinch". A spatially constant anomalous heat diffusivity is sufficient to model the T profiles. Reasonably good matches with experimental plasma density and temperature profiles, mid-plane gas pressure and the flow velocity was achieved in the code for two modeled shots by adjusting the anomalous transport. The input power Psol was taken from the experiment. One of the modeled shots had high mid-plane gas pressure Pmid and the other one had low Pmid. Comparing the 'effective diffusion coefficient' D in these two cases, one could see that the general shape of the radial D profile is the same, however the magnitude of D is much larger in the high Pmid case. This is consistent with the ideas that high Pmid reflects a high level of particle transport from the core. According to the modeling in the low Pmid case, neutrals come mostly from the divertor, while in the high Pmid case the main chamber wall itself becomes a significant source of gas, providing 50% and more of neutrals. Since mid-plane pressure grows with the core density, it appears that it is the high density of C-Mod plasmas that makes C-Mod a special case with quite high transport from the core. Analyses of the radial heat flux in the SOL for the two modeled shots show that in the high Pmid case heat convection by the radial particle flux and heat conduction by CX neutrals can account for a significant fraction of Psol (20-50%). These two "classical" mechanisms of heat transport dominate the heat far in the SOL (rho ~ 5mm and more), even in the low Pmid case. Travel and Visits: John Rice was at LHD in Toki, Japan last week. Bruce Lipschultz attended the ITER Divertor meeting at the Naka site (JAERI). He also visited the Tokai site to see JFT-2M and the ITER vacuum vessel sector. Bob Granetz attended the ITER MHD/Control/Disruptions expert group meeting also at the Naka site.