Abstract. This paper summarizes highlights of research results from the Alcator C-Mod tokamak covering the period 2006 through 2008. Active flow drive, using mode converted waves in the ion cyclotron range of frequencies (ICRF), has been observed for the first time in a tokamak plasma, using a mix of D and 3He ion species; toroidal and poloidal flows are driven near the location of the mode conversion layer. ICRF induced edge sheaths are implicated in both the erosion of thin boron coatings and the generation of metallic impurities. Lower Hybrid RF has been used for efficient current drive, current profile modification, and toroidal flow drive. In addition, LHRF has been used to modify the H-mode pedestal, increasing temperature, decreasing density, and lowering the pedestal collisionality. Studies of hydrogen isotope retention in solid metallic plasma facing components reveal significantly higher retention than expected from ex-situ laboratory studies; a model to explain the results, based on plasma/neutral induced lattice damage has been developed and tested. During gaspuff mitigation of disruptions, induced MHD causes the magnetic field to become stochastic, resulting in reduction of halo currents, spreading of plasma power loading, and loss of run-away electrons before they cause damage. Detailed pedestal rotation profile measurements have been used to infer ER profiles, and correlation with global H-mode confinement. An improved L-mode regime, obtained at q 95 ≤3 with ion drift away from the active x-point, shows very good confinement without a strong density pedestal, and no evidence of particle or impurity accumulation without the need for ELMs or any other edge density regulation mechanism.
A multipactor discharge is a resonant condition for electrons in an alternating electric field.This discharge can be disruptive to radio frequency (RF) circuits, cavities, and resonators. The Coaxial Multipactor Experiment (CMX) investigates these discharges in parallel plate and coaxial transmission line geometries at frequencies from 40 to 150 MHz with goals of measuring the electron energy distributions. CMX has a unique experimental setup which allows the transmission line to pass continuously through a short vacuum region. Retarding potential analyzers with secondary electron suppression measure the electron current as a function of bias voltage. Both parallel plate and coaxial multipactor experiments provide the first detailed measurements of the electron energy distributions under a variety of RF frequencies and electrode materials.
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