Interaction of fast waves with ions

To fully utilize the available power sources in DIII-D (FW, NBI, ECH), understanding of the synergism between the heating mechanisms is important. In this paper the ion distribution, under simultaneous application of NBI and FW, is calculated from Fokker-Planck code CQL3D coupled to ray-tracing code CURRAY. It is found that interaction between energetic ions and FW can be minimized or maximized by adjusting various parameters such as magnetic field, density, beam energy, and FW frequency. Specifically, in DIII-D, the authors find negligible interactions above 1.8 T and above 80 MHz, while the interaction increases at lower fields and frequencies. The results are compared with experiments in DIII-D including the calculated neutron rate. Energetic ion orbit losses may play an important role in the ion distribution, and this effect is being investigated

Advantages of Traveling Wave Resonant Antennas for Fast Wave Heating Systems

The resilience of a maximally flat externally coupled traveling wave antenna (TWA) is contrasted with the sensitivity of a simple directly driven resonant loop array to vacuum and plasma conditions in DIII-D. We find a unique synergy between standing and traveling wave resonant TWA components. This synergy extends TWA operation to several passbands between 60 and 120 MHZ, provides 60{degrees}- 120{degrees} tunability between elements within a 1-2 MHZ bandwidth and permits efficient and continuous operation during ELMing H-mode

Plasma rotation and rf heating in DIII-D

In a variety of discharge conditions on DIII-D it is observed that rf electron heating reduces the toroidal rotation speed and core ion temperature. The rf heating can be with either fast wave or electron cyclotron heating and this effect is insensitive to the details of the launched toroidal wavenumber spectrum. To date all target discharges have rotation first established with co-directed neutral beam injection. A possible cause is enhanced ion momentum and thermal diffusivity due to electron heating effectively creating greater anomalous viscosity. Another is that a counter directed toroidal force is applied to the bulk plasma via rf driven radial current

Plasma mass density, species mix and fluctuation diagnostics using fast Alfven wave

The authors propose to employ a fast Alfven wave interferometer and reflectometer as a tokamak diagnostic to measure the plasma mass density, D-T species mix profile, and density fluctuations. Utilize the property that the phase velocity of the fast wave propagating across the magnetic field is the Alfven speed with thermal correction, this fast wave interferometer on the DIII-D tokamak was successfully used to obtain the line integrated density. Since the position of the ion-ion hybrid cut-off in tokamaks is uniquely determined by the species mix ratio and the wave frequency, the reflectometer arrangement finds the species mix profile. The inversion method of reflectometry is discussed. The multiple chord interferometer also measures the mass density fluctuation profile

Collective modes and correlations in one-component plasmas

The static and time-dependent potential and surface charge correlations in a plasma with a boundary are computed for different shapes of the boundary. The case of a spheroidal or spherical one-component plasma is studied in detail because experimental results are available for such systems. Also, since there is some knowlegde both experimental and theoretical about the electrostatic collective modes of these plasmas, the time-dependent correlations are computed using a method involving these modes.Comment: 20 pages, plain TeX, submitted to Phys. Rev.

Improved tuning and matching of ion cyclotron systems

Future fusion devices will require delivery of ion cyclotron heating and current drive power during plasma changes (e.g., L-H transition, ELMs). The use of a passive circuit (``ELM dump``) to protect the RF sources during transients has been demonstrated on DIII-D, and the results are applied to the ITER ion cyclotron system in this analysis. In addition, the use of frequency shifting to compensate for plasma load changes is illustrated for a possible ITER tuning and matching system

Pedestal bifurcation and resonant field penetration at the threshold of edge-localized mode suppression in the DIII-D tokamak

Rapid bifurcations in the plasma response to slowly varying n=2 magnetic fields are observed as the plasma transitions into and out of edge-localized mode (ELM) suppression. The rapid transition to ELM suppression is characterized by an increase in the toroidal rotation and a reduction in the electron pressure gradient at the top of the pedestal that reduces the perpendicular electron flow there to near zero. These events occur simultaneously with an increase in the inner-wall magnetic response. These observations are consistent with strong resonant field penetration of n=2 fields at the onset of ELM suppression, based on extended MHD simulations using measured plasma profiles. Spontaneous transitions into (and out of) ELM suppression with a static applied n=2 field indicate competing mechanisms of screening and penetration of resonant fields near threshold conditions. Magnetic measurements reveal evidence for the unlocking and rotation of tearinglike structures as the plasma transitions out of ELM suppression.This work is supported by the U.S. Department of Energy under Awards No. DE-FC02-04ER54698, No. DE-AC02-09CH11466, No. DE-FG02-07ER54917, No. DE-FG02-89ER53296, No. DE-FG02-08ER54999, No. DE-FG02-08ER54984, No. DE-AC05-00OR22725, No. DE-FG02-86ER53218, and No. DE-FG02- 92ER54139