High Power Density Beam Measurement of a Single Beamlet Multi-Grid Prototype H^- Negative Ion Accelerator

Abstract

Beam optics of the ITER prototype accelerator with 88 mm acceleration gap length has been examined through H- beam acceleration tests at the ITER target beam perveance. The beam optics has been examined for beam energies up to 790 keV under the ITER target perveance. The total grid heat load was successfully reduced to 10 %, which was lower than the allowable value of 15 %. The beam emittance of the ITER perveance has been measured for the first time by using newly developed emittance measurement system consisting of carbon-fiber-composite (CFC) plate with pin-holes. The emittance of 790 keV H- beam shows the divergence angle of the beam core is satisfied with the ITER requirement of <7 mrad. Measurement at the beam periphery was made possible by modifying the pin-hole size of pepper-pot apertures, and the observed divergent components were 20 mrad. The ratio of the diverged beam became lower with the increase of the beam energy. This result contributes the design of the ITER accelerator and the beam line components.

Beam Optics Study during Long-Pulse MeV-Class Beam Operation for the ITER HNB

“…Figure 1 shows the cross-sectional schematic of MTF. Two one-dimensional CFC tiles, which have anisotropic thermal conductivity in the thickness direction and other directions, are installed at 1770 mm and 2400 mm downstream from a grounded grid (GRG) with IR cameras, respectively [4]. For this experiment, upper CFC tile was used for obtaining the footprint of beamlets.…”

Beam divergence of RF negative hydrogen ion sources for fusion

“…the ratio of acceleration to extraction voltage has not been optimized), thus the divergences are generally rather high. The usage of 1D Carbon Fiber reinforced Carbon (CFC) calorimeters, in which the bers are aligned in one dimension along the beam direction and thus heat conductivity in this direction is up to 20x higher compared to the perpendicular directions, are common tools in the NNBI community to determine properties of an individual beamlets [13,14]. The beam footprint is observed via IR cameras either from the front or the backside of the CFC tile.…”