Magnetic Diagnostics of Magnetic Island in LHD

Characteristics of magnetic islands are investigated by magnetic diagnostics in the Large Helical Device (LHD). The structure of the magnetic island with m/n = 1/1 (where, m and n are poloidal and toroidal mode number, respectively) can be estimated from the perturbed magnetic field appearing when a magnetic island changes. To measure the toroidal profile of the perturbed magnetic field δb1 originating from the plasma, a toroidal array of magnetic flux loops is set up in the LHD. The toroidal profile of δb1 is then spatially Fourier decomposed to determine the amplitude of the n = 1 component, δb1n=1 and its phase, φn=1 which correspond the change of the island width and the toroidal position of the X-point of the island, respectively. Therefore, the information about the magnetic island structure can be obtained from δb1n=1 and φn=1. In case the island width becomes larger than the seed island, measurements show that δb1n=1 is non-zero and φn=1 is temporally constant. A non-zero δb1n=1 can also be observed when the island width becomes smaller than the seed island. In this case, the angle φn=1 shifts by about π[rad] compared with the increasing case and the δb1n=1 is limited to a certain value which corresponding to the magnetic field suppressing the seed island

THERMAL-WAVE MEASUREMENTS OF MULTI-LAYER SUPERINSULATION FOILS

Abstract Thermal wave measurements rely on modulated laser heating and IR detection of the thermal response, using a MCT detector with IR optics and lock-in amplifier. Both, the amplitude and the phase retardation of the thermal wave response with respect to the heating modu-lation, provide information on the effective thermal transport properties of the measured samples. Here we apply this method to determine the shielding properties of multilayer superinsulation foils, used for the thermal insulation of superconducting magnetic coils in particle accelerators, e.g. in LHC at CERN. The measurements, performed at ambient temperature and ambient and reduced pressure, have been interpreted using a theoreti-cal model, including both conductive and radiative heat transport. The results show that the radiative heat transport can be well identified, although the conductive heat transport is dominant across multi-layer samples. At reduced pressures, the conductive heat transport decrea-ses considerably and, depending on the number of spacer layers, the radiative heat transport can become dominant. Applying this new photothermal technique, the shielding efficiencies of multi-layer superinsulation foils have been compared in this work for the first time