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211 records were found.

We have investigated the effect of edge localized modes (ELMs) on the total plasma current in JET tokamak plasmas using the earth leakage current detection circuit connected to the in-vessel saddle coils. These measurements, and the geometry of the saddle coil circuit, indicate that, in typical H-mode plasmas, up to similar to 300 A (corresponding to a maximum of similar to 150 A per MA of plasma current) can be deposited at each ELM in regions rather far away (similar to 50 cm) from the strike point position and divertor target plates. These current losses decrease with increasing ELM frequency (f(ELM)), being practically below or around the detection limit for f(ELM) > 60 Hz, and show some saturation for increasing diamagnetic energy losses for 'slow' Type-l ELMs at f(ELM) < 10Hz. The measurements reported here are consistent with th...
We have investigated the effect of different ion cyclotron resonance frequency (ICRF) heating schemes, of error field modes, of the plasma shape and edge magnetic shear, and of the ion delB drift direction on the stability of Alfven eigenmodes (AEs). The use of multi-frequency or 2nd harmonic minority ICRF heating at high plasma density gives rise to a lower fast ion pressure gradient in the plasma core and to a reduced mode activity in the Alfven frequency range. Externally excited low-amplitude error fields lead to a much larger AE instability threshold, which we attribute to a moderate radial redistribution of the fast ions. The edge plasma shape has a clear stabilizing effect on high-n, radially localized AEs. The damping rate of n = 1 toroidal AEs is a factor 3 higher when the ion VB drift is directed towards the divertor. These r...
The mechanisms of nonlinear interaction of external helical fields with a rotating plasma are investigated analyzing the results of recent systematic experiments on the Joint European Torus (JET) [A. Gibson , Phys. Plasmas 5, 1839 (1998)] that widen the previous data base collected on Compass-D [T. C. Hender , Nucl. Fusion 32, 2091 (1992)], Doublet III-D [R. J. La Haye , Nucl. Fusion 32, 2119 (1992)] and JET. The empirical scaling laws governing the onset of "error field" locked modes are re-assessed and interpreted in terms of existing driven reconnection theories and with new models. In particular the important mechanisms of plasma rotation braking, and spin up, associated with error fields are analyzed in detail and interpreted. (C) 2002 American Institute of Physics.
The results concerning the theoretical evaluation of the small-angle Bhabha Scattering cross section obtained during the Workshop on Physics at LEP2 (CERN, Geneva, Switzerland, 1995) by the Working Group ``Event Generators for Bhabha Scattering'' are summarized. The estimate of the theoretical error on the cross section in the luminometry region is updated.
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