The geometry of the ICRF-induced wave–SOL interaction. A multi-machine experimental review in view of the ITER operation

Abstract

As part of ITPA-Integrated Operational Scenario activities, this contribution reviews recent experimental characterizations of radio-frequency (RF)-induced scrape-off layer (SOL) modifications of various tokamaks worldwide and of the LArge Plasma Device at UCLA. The phenomenology, as observed using a large variety of measurement techniques, is consistent with expectations from RF sheath rectification. Emphasis is then put on the complex three-dimensional (3D) spatial patterns of the RF–SOL interaction, in relation to the magnetic topology and the spatial distribution of RF currents over the metallic structures surrounding the RF wave launchers. Dependence on the local plasma parameters in the antenna vicinity is also briefly addressed. The final part discusses implications for future devices.

Operating a full tungsten actively cooled tokamak: overview of WEST first phase of operation

“…It has to be noted that the five antennas are equipped with W coated side limiters. Interestingly, the fraction of radiated power is very similar when operating LHCD or ICRH, despite ion acceleration in front of the ICRH antennas favouring W sputtering [29]. Discharges lasting more than 30 s were routinely carried out with LHCD alone using the actively cooled upper divertor and a discharge duration close to 1 min was obtained with 3 MW of LHCD (figure 9) [30].…”

On the origin of high harmonic fast wave edge losses in NSTX

“…The RF waves launched by the antenna cause sheath rectification [18,32]. An enhanced DC potential develops on the plasma-facing components on which the RF waves are incident (usually the antenna surface itself, but in NSTX we must consider the possibility that this happens on the divertor), which causes a DC current to flow mostly along the field lines, the direction along which the magnetized plasma conducts current most easily.…”

“…usually from the active ICRF antenna to the divertor [38]. Perkins deduced the direction of the DC currents from the sign of the floating potential on Langmuir probes, and found that DC currents in NSTX flow in the opposite direction [32], as if the current is mainly driven by divertor sheath rectification.…”

WEST actively cooled load resilient ion cyclotron resonance heating system results

“…As the toroidal phase decreases from dipole (Δφ = 180 • ) to 80 • , the brightness on the right limiter increased by a factor 1.5. Although the coupled power decreases by a factor of 2 as the antenna departs from its matching point, applying a factor √ P ICRF (homogeneous to the antenna electric fields which are a proxy to RF sheath amplitudes [43]) to compensate for lower RF power leads to a normalized brightness increases by around 1.8.…”