Effective sputtering yield for deuterium on molybdenum, deuterium with 1% boron+3 on molybdenum, and deuterium with 1% boron+3 and molybdenum+3 on molybdenum. 16,17 Note that around 100 V, the sputtering yield increases dramatically because deuterium is capable of sputtering molybdenum whereas below 100 V the sputtering is dominated by impurities.
Schematic of the outer tokamak wall showing the location of the antennas, limiters, and diagnostics. The field aligned antenna is aligned to the total field and the conventional, toroidally aligned antenna has only its Faraday screen bars aligned to the total field. Representative field lines show the mapping of the diagnostics to each antenna. The emissive probe maps to regions that are expected to have lower integrated E|| than the gas puff imaging. By fortuitous coincidence, the gas puff imaging maps to regions of both antennas that are expected to have maximum integrated E||.
Field aligned and conventional toroidally aligned ICRF antenna installed in C-Mod. The field aligned antenna is aligned to a 10° field pitch such that the current straps and antenna box structure are perpendicular to the total magnetic field and the FS rods are parallel to the total magnetic field. The toroidally aligned antennas have their current straps and antenna structure perpendicular to the toroidal magnetic field and the FS rods are parallel to the total magnetic field.
The integrated E|| field 1 cm in front of the Faraday screen along field lines that extend beyond the antenna sufficiently such that the E|| contribution is vanishing at the ends of the field line. The poloidal coordinate is perpendicular to the total field for the field aligned antenna and vertical for the toroidally aligned antenna. The bottom of the antenna box is at −0.25 m and the top of the antenna box is at 0.25 for the toroidally aligned antenna. The field aligned antenna monopole phase has the lowest integrated E|| and the field aligned dipole phase is 2–3 times lower at the antenna end compared to the toroidally aligned.
The scrape of layer plasma potential profile is estimated from GPI measurements of the poloidal phase velocity assuming the turbulence is E × B convected and integrating the radial electric field profile referencing to the typical 3Te potential. (a) The poloidal phase velocity profile in ohmic portion of discharge compared to the profile obtained with ICRF applied. (b) Plasma potential profile derived from integrating the radial electric field profile referenced to 3Te.
The plasma response to 2.5 MW of applied RF power from the field aligned antenna is superior to the response from the toroidally aligned antenna. The stored plasma energy is higher and the radiated power and molybdenum contamination is lower for the field aligned antenna than the toroidally aligned antenna.
In H-mode, the molybdenum contamination and the radiated power are lower for the field aligned antenna than the toroidally aligned antenna.
(a) Spectroscopic view (molybdenum I) of the toroidally aligned antenna shows strong correlation with RF power from the toroidally aligned antenna and a weak response with RF power from the field aligned antenna. (b) Spectroscopic view of the toroidally aligned antenna shows strong correlation with RF power from the toroidally aligned antenna and a weak response with RF power from the field aligned antenna.
Radial electric field profile derived from gas puff imaging (GPI—blue points) and the emissive probe (red line) shows a strong reversal at the RF limiter radius when the RF antenna is energized and the GPI and probe map to the energized antenna.
The measured plasma potential as a function of RF power for the toroidally aligned and field aligned are not significantly different.
Plasma response to dipole and monopole phasing of the field aligned antenna shows that dipole phasing heats more effectively than monopole phasing. A significant decrease in plasma temperature suggests a large influx of impurities cooling the plasma.
The maximum plasma potential for monopole and dipole phasing as a function of power shows that monopole phasing has significantly higher plasma potential than dipole phasing despite the model prediction that monopole phasing has the lowest integrated E||.
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