Tomographic analysis of the nonthermal x-ray bursts during disruption instability in the T-10 tokamak.

Non-thermal x-ray radiation (Eγ up to 150 keV) is measured in the T-10 tokamaks during disruption instability using two sets of CdTe detectors (10 vertical and 7 horizontal view detectors). Special narrow cupper tubes collimators with lead screening and CdTe detectors integrated with amplifiers inside metallic containers provides enhanced spatial resolution of the system (r ∼ 3 cm) and assures protection from the parasitic hard x-ray (Eγ up to 1.5 MeV) and electromagnetic loads during disruption. Spatial localization of the nonthermal x-ray emissivity is reconstructed using tomographic Cormack technique with SVD matrix inversion. Analysis indicated appearance of an intensive non-thermal x-ray bursts during initial stage of the disruptions at high density. The bursts are characterized by repetitive spikes (2-3 kHz) of the x-ray emissivity from the plasma core area. Analysis indicated that the spikes can be connected with acceleration of the non-thermal electrons in enhanced longitudinal electric fields induced during energy quench at the disruption instability.

Movable magnetic probe system in the T-10 tokamak.

New magnetic probe system is installed on the T-10 tokamak to investigate fast-scale magnetic perturbations (f up to 2 MHz). The system is based on vertical and horizontal magnetic probes made by nickel wire in glass enamel isolation (effective area 20-250 cm(2)) separated from the support structures by ceramic spacers (5-10 mm). The probe system is mounted on the top of movable rode allowing positioning along vertical axis close to the plasma boundary at the low field side of the torus. Additional positioning system allows rotation of the probes around the vertical axis on pulse-to-pulse basis. The probes are directly connected to the analog-to-digital converter (ADC) module (acquisition rate 60 MHz) through short (~4 m) coaxial cables. The system allowed identification of the fast-scale magnetic oscillations (0.2-0.5 MHz) during energy quench phase of the disruption instability in plasma with high density. Amplitude of the fast-scale magnetic oscillations decays with distance from the plasma boundary 2-10 times faster than one of the standard magnetohydrodynamic modes.

Quasicoherent oscillations induced by nonthermal electrons during magnetic reconnection in the T-10 tokamak.

Small-scale quasicoherent oscillations of the x-ray emissivity and magnetic field perturbations are observed in the T-10 tokamak during abrupt growth of the m=2, n=1 magnetohydrodynamic modes at the density limit disruption. Analysis indicates a possible link between the small-scale oscillations and nonthermal electron beams induced around the X points of the m=2, n=1 magnetic island during reconnection of magnetic field lines at the disruption instability.

Generation of suprathermal electrons during magnetic reconnection at the sawtooth crash and disruption instability in the T-10 tokamak.

Evidence for excitation of suprathermal electrons ( E(gamma) approximately 20-100 keV) during magnetic reconnection in the T-10 tokamak is presented through analysis of the x-ray measurements with enhanced spatial and time resolution. A toroidally viewing x-ray imaging system and a fast hard x-ray detector placed inside the tokamak vessel allow identification of bursts of the nonthermal x-ray radiation around X points of the m = 1 and m = 2 magnetic islands during the sawtooth crash and prior to the energy quench at the density limit disruption.