Measurement of the radial electric field in the ASDEX tokamak
The radial electric field (E(tau)) at the plasma periphery is determined by measuring the drift velocities of low-Z impurity ions (BIV, CIII and HeII). The measurements are performed with a scannable mirror system which allows the determination of the poloidal, perpendicular (to B) and toroidal components of the drift velocities from the differential Doppler shift of visible line emission observed along opposing viewing directions. It is shown that for radially localised emission shells a line of sight exists, perpendicular to B, along which E(tau) may be inferred directly from the observed Doppler shift of the line emission. Along such a line of sight the net contribution to the shift from the diamagnetic drift and the radial gradient of the excitation probability is negligible. During the ohmic and L-phases, the perpendicular drift velocity of the BIV ions is small (less than 2 km/s) and in the ion diamagnetic drift direction. At the L to H-mode transition, it changes sign and begins to increase. It is inferred that a strong negative radial electric field exists in the H-mode, just inside the separatrix. The dependence of the drift velocity of the BIV ions and E(tau), on the NBI-heating power and the magnitude and direction of the plasma current and magnetic field are investigated.
Bibliographic Reference: Report: IPP III/165 EN (1990)
Availability: Available from Max-Planck-Institut für Plasmaphysik, 8046 Garching bei München (DE)
Record Number: 199110509 / Last updated on: 1994-12-02
Original language: en
Available languages: en