Alcator C-Mod Weekly Highlights August 24, 1998 Engineering: ----------- Copper plating of the TF core sliding joints is nearly 100% complete and silver plating is now 50% complete. The electroforming of copper into the one broken core finger was successfully completed last week. The problem with the sintering of the new feltmetal which was reported last week has been solved and the soldering of the feltmetal pads to the lower horizontal magnet arms is underway. At this point, six arms are complete and production soldering is proceeding on schedule with the remainder of the lower magnet arms. Material for manufacture of new springs for the TF sliding joints is in house and the receiving inspection has been completed. Overall progress to date is consistent with the scheduled completion of magnet re-work as presented at the last quarterly review. We continued work on the DNB accelerator supply. Installation and wiring of the power supply control panels continued. The control chassis for the HV supply power bus wiring was completed. Work continued on the fast control logic for the accelerator supply and on construction of the F-Port flange. The RF group finished conditioning the EIMAC 2274 (final amplifier tube) in FMIT#4 and resumed testing. The maximum power obtained was about 1 MW at 78 MHz. The tube however was unreliable and it finally failed late in the week (an open filament). We began swapping the 2274 with a lower power 8973 tube (~1.25 MW output with a tungsten filament). We had hoped to finish testing FMIT#4 with the 2274. Because the characteristics of the two tubes may be significantly different, this testing is not the most direct but is the best we can do until one of the two broken 2274's is fixed. The first tube we sent back to EIMAC tested fine under static voltages which is the same result we obtained here. It is currently awaiting RF testing in the test transmitter. The other tube is being sent back and should be fixed within 60 days. The DC breaks for the J-port transmission line were finished. The visible break was shielded with 1/16" copper to reduce RF leakage fields while maintaining 10 kV voltage capability. Further measurements were made regarding the J-port antenna. A single strap and backplane assembly were placed invessel. The only problem was minor: additional clearance is needed for the magnetics on strap 1 and 4. The antenna parts were then removed and sent back with Gerd Schilling to Princeton. We discussed further the modifications required on the vacuum flange. The presently preferred option is to weld four 20" long, 4" diameter extensions directly to the flange. This would put the helicoflex seals beyond the cowling and igloo making the bolts easily accessible on both the machine and feedthroughs flanges. With this arrangement, the feedthroughs can be put on and leak tested on the bench top before putting them on the machine. A mock-up (made of plastic and aluminum) is being made at PPPL to test the configuration. Physics: ------- Nearly fifty shots at 7.9 T with a D(3He) plasma have been analyzed to investigate the balance between direct electron heating through mode- converted ion Bernstein waves and He-3 minority ion heating. Electron power absorption profiles were calculated from the break-in-slope of electron temperature at times of RF power transitions. The location of peak power absorption was compared with a cold plasma model to estimate the He-3 concentration present in the bulk plasma. The resulting relationship of power to electrons vs. He-3 concentration was compared with the full-wave code TORIC, with which it agrees qualitatively. The 1998 Alcator C-Mod Ideas Forum was held on Wednesday and Thursday last week. There were a total of 117 presentations of ideas for experiments to be carried out on C-Mod during the next campaign. The Ideas, presented by about fifty principal authors from eight institutions, covered topics including divertor flows, impurity transport, neutral effects, RF heating and current drive, advanced tokamak studies, internal transport barrier physics, turbulence, testing of theoretical transport models, toroidal rotation, similarity scaling, divertor detachment, recombination, RI-mode experiments, H-mode and edge-barrier physics, SOL transport, MHD stability, high-performance plasma experiments, and support for burning plasma initiatives. The Ideas Forum sessions at MIT were well-attended, including a significant presence by representatives from collaborating institutions. In addition, the proceedings were broadcast (audio and video) on the MBone, allowing participation from off-site. Initial feedback on the broadcast has been favorable. Computation and Data Acquisition: -------------------------------- The final step in upgrading the alpha workstations to the latest version of the OpenVMS operating system was completed last Friday. The previous version of the operating system was removed from the main disk server and replaced with the latest version. During this upgrade an additional 4 gigabytes of disk space was added for user files. A significant ESnet connectivity milestone was reached last Thursday when the following long-awaited events occurred: ESnet-MITnet peering was established, with a dedicated 100Mbps link between the ESnet and MITnet routers. This made it possible for the ESnet network to become the preferred path for communication between any MITnet node and any node at an ESnet site. Routing support was enabled for a block of ESnet IP addresses for the use of the PSFC. This block of ESnet addresses is routed as a primary ESnet site. All of these changes will contribute to a vast improvement in network performance for communication between C-Mod/PSFC computers and our off-site collaborators. Along with this new address space came the ability to start moving nodes from the pfc.mit.edu domain (or namespace) into the psfc.mit.edu domain. Visits and Travel: ----------------- Ron Bravenec of UT-FRC visited to discuss modeling and collect examples of edge deuterium emission that will form the background emission for BES measurements. Perry Phillips and Romik Chatterjee visited to discuss integration of C-Mod turbulence diagnostics with those to be supplied by UT-FRC. All three also participated in the C-Mod Ideas Forum. Ian Hutchinson attended the Editors meeting of the New Journal of Physics, to be launched in October. The journal is targeted as a high-calibre, all-electronic, fully refereed physics journal, freely available on the web and taking advantage of its new media opportunities. Ian hopes that plasma physics will be strongly represented in the journal's papers.