110 GHz Gyrotron System on DIII-D: Gyrotron Tests and Physics Results

摘要

The DIII-D tokamak has installed a system with three gyrotrons at the 1 MW level211u001eoperating at 110 GHz. Physics experiments on electron cyclotron current drive, 211u001eheating, and transport have been performed. Good efficiency has been achieved 211u001eboth for on-axis and off-axis current drive with relevance for control of the 211u001ecurrent density profile leading to advanced regimes of tokamak operation, 211u001ealthough there is a difference between off-axis ECCD efficiency inside and 211u001eoutside the magnetic axis. Heating efficiency is excellent and electron 211u001etemperatures up to 10 keV have been achieved. The gyrotron system is versatile, 211u001ewith poloidal scan and control of the polarization of the injected rf beam. Phase 211u001ecorrecting mirrors form a Gaussian beam and focus it into the waveguide. Both 211u001eperpendicular and oblique launch into the tokamak have been used. Three different 211u001egyrotron designs are installed and therefore unique problems specific to each 211u001ehave been encountered, including parasitic oscillations, mode hops during 211u001emodulation and polarization control problems. Two of the gyrotrons suffered 211u001edamage during operations, one due to filament failure and one due to a vacuum 211u001eleak. The repairs and subsequent testing will be described. The transmission 211u001esystem uses evacuated, windowless waveguide and the three gyrotrons have output 211u001ewindows of three different materials. One gyrotron uses a diamond window and 211u001egenerates a Gaussian beam directly. The development of the system and specific 211u001etests and results from each of the gyrotrons will be presented. The DIII-D 211u001eproject has committed to an upgrade of the system, which will add three gyrotrons 211u001ein the 1 MW class, all using diamond output windows, to permit operation at up to 211u001eten seconds per pulse at one megawatt output for each gyrotron.