Einar Tennfors

Ion temperature, heating and scaling relations at the Extrap-T1 reversed-field pinch

Investigations of the temperatures of the in situ impurity ions , , , and have been performed at the Extrap-T1 reversed-field pinch (RFP) via measurements of the Doppler broadening of emission lines in the near-UV wavelength region. Ion temperatures of the high ionization stages are found to be of the order of the electron temperature. This means that ion heating can be connected with RFP dynamo activity giving rise to the non-Spitzer part of the power input. Power input to the ions of the order of the non-Spitzer part of the total power input is required to explain the high ion temperatures. MHD effects could be responsible for this heating. We present scaling of the observed ion temperatures with plasma current , electron density , pinch parameter and magnetic fluctuations. We also present an empirical scaling law in which the ion temperature can be expressed as . Keeping constant, this gives a constant ion beta poloidal .

Anisotropy of ion temperature in a reversed-field-pinch plasma

Anomalous heating of ions has been observed in the EXTRAP-T2 reversed-field-pinch (RFP) plasma. Ions are heated primarily in the parallel direction (with respect to the magnetic field), resulting in an appreciable anisotropy of the ion temperature. This observation suggests that the magnetohydrodynamic fluctuations are dissipated primarily by the ion viscosity.

Localized global ICRF eigenmodes and conversion zones in a two-ion species tokamak

The location of the slow - fast wave conversion zones is analysed for a tokamak in ICRF. The obtained dispersion relation which determines the surfaces of wave conversion describes the cases of weak and strong mode coupling as well as the intermediate one. Using the same approach, the localized global eigenmodes are studied. With respect to their nature, they are separated into two types. The first is the TLE - TAE-like eigenmode. Like the TAE it is the result of mode coupling. The second one is the single-mode eigenmodes. This type is represented by two eigenmodes. One is the extension of the GAE (global Alfven eigenmode) to the two-ion species plasma. The other one is OHE (original hybrid eigenmode) which exists in the case of strong mode coupling. The field structure and dispersion of these waves are discussed.

A limitation of RF electric fields in a partially ionized blanket

It is suggested that Alfvens critical ionization velocity phenomenon limits the RF electric field in a partially ionized blanket. The frequency range in which the phenomenon can occur is discussed and expressions for the limiting -field are given.

Ionization, heating and stabilization by currents along a poloidal magnetic field

Abstract The ionization and heating effects of induced low frequency poloidal currents in the internal ring device F IV A have been studied. The start-up process is more efficient and works at lower filling pressures than without poloidal currents. The plasma temperature is increased due to ohmic heating. Rotating plasmas with a density of 1.5 × 10 21 m −3 were obtained for a filling pressure of 6 m Torr. Fluctuations are stabilized already at low power poloidal currents. The stabilizing effect seems to be related to the applied toroidal magnetic field rather than the induced poloidal current. At the lowest filling pressures (0.2 mTorr) a nonrotating plasma, sustained only by the poloidal current, with a density of 1.5 × 10 20 m −3 and a temperature of 7 eV was produced. At this low density, the plasma is permeable to neutral gas, as opposed to the impermeable plasmas in the earlier experiments with this device.

ON THE LIMITATION OF RF FIELDS BY ALFVÉN'S CRITICAL IONIZATION VELOCITY PHENOMENON

ABSTRACT Alfvens critical ionization velocity hyphotesis and some of the numerous experiments supporting it are briefly reviewed. The critical velocity is associated with a critical electric field, which may limit the transfer of RF power through a cold partially ionized blanket. The underlying mechanism is not fully understood at present, but experimental observations indicate the parameter and frequency ranges in which the phenomenon occurs. The upper frequency limit seems to be higher than the ion cyclotron frequency. For frequencies below the ion-neutral collision frequency, the field limitation becomes less severe.