X-ray tomography of hot electrons in the barrier region of the tandem mirror GAMMA 10

Publisher Website
Google Scholar
Abstract
Tomographic reconstructions of x‐ray emission from hot electrons have been carried out in the thermal barrier region of the GAMMA 10 plasmas. Here, the first application of two sets of the 50‐channel microchannel plates have been performed using their detailed calibration data as a function of x‐ray energy and incident angle [Rev. Sci. Instrum. 5 9, 256 (1988); 5 9, 2453 (1988); 6 0, 368 (1989)]. The x‐ray reconstructed signals under standard thermal barrier operating conditions indicate a good axisymmetric radial profile peaked on the magnetic axis. This symmetric profile is important for preventing the formation of a local anisotropic electric field, which may cause particle confinement degradation, and its peaking profile is desirable for thermal barrier potential formation in the core plasma region. When we have relocated the second‐harmonic electron cyclotron layers (ω=2Ωe) in two different ways (moving them out radially, or axially away from the midplane), tomographic reconstructions show hollow x‐ray profiles in both cases. These may be formed due to the E×B rotations of the hot electrons produced near ω=2Ωe . These applications of x‐ray tomography to two‐dimensional radial profile observations along with the axial x‐ray profile measurement give information that the production mechanism of these hot electrons is ascribed to second‐harmonic electron cyclotron heating.