Temporal evolution of confined fast-ion velocity distributions measured by collective Thomson scattering in TEXTOR.

Fast ions created in the fusion processes will provide up to 70% of the heating in ITER. To optimize heating and current drive in magnetically confined plasmas insight into fast-ion dynamics is important. First measurements of such dynamics by collective Thomson scattering (CTS) were recently reported [Bindslev, Phys. Rev. Lett. 97, 205005 2006]. Here we extend the discussion of these results which were obtained at the TEXTOR tokamak. The fast ions are generated by neutral-beam injection and ion-cyclotron resonance heating. The CTS system uses 100-150kW of 110-GHz gyrotron probing radiation which scatters off the collective plasma fluctuations driven by the fast-ion motion. The technique measures the projected one-dimensional velocity distribution of confined fast ions in the scattering volume where the probe and receiver beams cross. By shifting the scattering volume a number of scattering locations and different resolved velocity components can be measured. The temporal resolution is 4ms while the spatial resolution is approximately 10cm depending on the scattering geometry. Fast-ion velocity distributions in a variety of scenarios are measured, including the evolution of the velocity distribution after turnoff of the ion heating. These results are in close agreement with numerical simulations.

Fast-ion dynamics in the TEXTOR tokamak measured by collective Thomson scattering.

Here we present the first measurements by collective Thomson scattering of the evolution of fast-ion populations in a magnetically confined fusion plasma. 150 kW and 110 Ghz radiation from a gyrotron were scattered in the TEXTOR tokamak plasma with energetic ions generated by neutral beam injection and ion cyclotron resonance heating. The temporal behavior of the spatially resolved fast-ion velocity distribution is inferred from the received scattered radiation. The fast-ion dynamics at sawteeth and the slowdown after switch off of auxiliary heating is resolved in time. The latter is shown to be in close agreement with modeling results.

Effect of an internal rotating current on low-frequency inductively coupled plasmas.

The effect of an internal low-frequency rotating current on inductively coupled plasmas in cylindrical chambers is studied. The electromagnetic field structure, power density distribution, the plasma density, and the operating regimes of the discharge are investigated using electrodynamic, power, and particle balance equations. It is shown that the rotating current sheet can dramatically improve the uniformity of the electromagnetic fields and the power transferred to the plasma electrons from that of conventional low-frequency inductively coupled plasma sources with external flat spiral inductive coils.