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The DIII-D ECH system includes three launcher assemblies each of which can accommodate the RF beams from two gyrotrons. The launchers use four different designs for the mirrors which focus and direct the beams into the tokamak. The designs use molybdenum brazed to graphite, thin Glidcop or variable thickness Glidcop. A fourth design with laminated Glidcop/stainless steel construction has been operated, but no thermal data are available. All the mirrors operate without active cooling. This paper presents preliminary analyses and measurements of the thermal performance of the three designs for which data have been obtained.

The DIII-D toroidal field [TF] belt bus system provides an electrical connection between adjacent TF-coil bundles to form a continuous current path for the TF-coil system. There is also a return path which is electrically isolated from the belt bus. The function of the system is to carry TF-coil current while minimizing the TF-coil error field in accordance with physics requirements. The system is currently capable of handling 5 s of operation with a peak current of 127 kA in the TF-coil. Future requirements for the system are the capability to support 10 s operation with 10 min cooldown periods in between shots. Experiments have been carried out which describe the physical parameters of the system, such as the contact resistance across the bus bar joints. Additionally, using an optical fiber-based temperature monitoring unit, the temperature response of the system to operations was determined. Based on these characterizations of the system, a 3-D thermal model was built to predict the behavior of the system for 10 s operations. The limitation of the system is the maximum allowable temperature of approximately 150/spl deg/C for the G11 insulators. The model was constructed full scale per engineering drawings using Solidworks, meshed, and then exported to Cosmos for analysis. Once good correlation was achieved with the observed responses to 5 s pulses, the behavior of the system for 10 s pulses was predicted. Various design modifications, such as water cooled bolts, were simulated in order to estimate their impact on creating a system that meets the 10 s criteria.

Each GA ECH launcher mirrors is used to transmit 800 kW of power to the plasma. Until 2000, the pulse length for use of these mirrors was limited to 2 s due to temperatures of the mirrors resulting from 1) a high ratcheted bulk temperature and 2) a large increase in temperature of the mirror during the pulse. A new design was proposed and implemented which has extended the capability of the mirror to 10 s with passive cooling. The important features of the new design are 1) increase in the passive heat transfer rate during cooling and 2) a modified shape of the mirror. The analysis shows that, the new mirrors can be used for 10 s pulses. The new mirrors have been installed in DIII-D, they have been used for up to 2 s pulses.

The radiative divertor program of DIII-D is in its final phase with the installation of the cryopump and baffle structure (Phase 1B Divertor) in the upper inner radius of the DIII-D vacuum vessel at the end of this calendar year. This divertor, in conjunction with the Advanced Divertor and the Phase 1A Divertor, located in the lower and upper outer radius of the DIII-D vacuum vessel respectively, provides pumping for density control of the plasma while minimizing the effects on the core confinement. Each divertor consists of a cryo/helium cooling ring and a shielded protective structure. The cryo/helium-cooled pumps of all three diverters exhaust helium from the plasma. The protective shielded structure or baffle structure, in the case of the diverters located at the top of the vacuum vessel, provides baffling of neutral charged particles and minimize the flow of impurities back into the core of the plasma.