Beam calorimetry at the large negative ion source test facility ELISE: Experimental setup and latest results

Abstract

The test facility ELISE is the first step within the European roadmap for the development of the ITER NBI system. ELISE is equipped with a 1 x 0.9 m 2 Radio Frequency negative ion source (half the ITER source size) and an ITER-like 3-grid extraction system which can extract an Hor Dbeam for 10 s every 3 minutes (limited by available power supplies) with a total acceleration voltage of up to 60 kV. In the beam line of ELISE several beam diagnostic tools have been installed with the aim to evaluate beam intensity, divergence and uniformity. A copper diagnostic calorimeter gives the possibility to measure the beam power density profile with high resolution. The measurements are performed by an IR micro-bolometer camera and 48 thermocouples embedded in the calorimeter. A gaussian fit procedure has been implemented in order to characterize the large negative ion beam produced by ELISE. The latest results obtained from the beam calorimetry at ELISE show that the average beamlet group inhomogeneity is maximum 13%. The measured beam divergence agrees with the one measured by beam emission spectroscopy within 30%.

Achievement of the ITER NBI ion source parameters for hydrogen at the test facility ELISE and present Status for deuterium

“…The current measured on the GG is assumed to be caused by stripped and secondary electrons; negative ions with high divergence can contribute as well. The accelerated current (negative ions and neutralized particles) is measured by the diagnostic calorimeter installed 3.5 m downstream of the grid system [14].…”

“…The magnetic filter field of the ITER NBI source differs in some aspects from the field at ELISE and will be tested at MITICA (part of the NBTF) representing the prototype of the ITER beamline. The magnetic filter field is generated by the current through the PG (as at ELISE) with the boundary condition to have a fixed value of the magnetic field in front of the grid of 3 mT and a weak long-range field of 0.5 mT (at the exit of the accelerator) to deflect secondary and stripped electrons out of the beam [14]. For that purpose additional side conductors are placed beside the source in the PG plane and two remote return conductors are positioned about 1 m behind the source.…”