Simulation of extracted ion current distributions from mini-STRIKE beam profiles

The present report presents the work performed in 2015 concerning the characterisation of the BATMAN beam by mini-STRIKE accompanied by the simulation of the beam acceleration. These simultaneous activities allow the obtainment of extraction current density distributions compatible with the measured beam profile. The work is summarised by a Bachelor thesis in Physics and by a paper presented at the ICIS 2015; as the former is written in Italian, only the ICIS paper is annexed. The Radio Frequency (RF) negative hydrogen ion source prototype has been chosen for the ITER neutral beam injectors due to its optimal performances and easier maintenance demonstrated at Max- Planck-Institut für Plasmaphysik, Garching in hydrogen and deuterium. One of the key information to better understand the operating behavior of the RF ion sources is the extracted negative ion current density distribution. This distribution--influenced by several factors like source geometry, particle drifts inside the source, cesium distribution, and layout of cesium ovens--is not straightforward to be evaluated. The main outcome of the present contribution is the development of a minimization method to estimate the extracted current distribution using the footprint of the beam recorded with mini-STRIKE (Short-Time Retractable Instrumented Kalorimeter). To accomplish this, a series of four computational models have been set up, where the output of a model is the input of the following one. These models compute the optics of the ion beam, evaluate the distribution of the heat deposited on the mini-STRIKE diagnostic calorimeter, and finally give an estimate of the temperature distribution on the back of mini-STRIKE. Several iterations with different extracted current profiles are necessary to give an estimate of the profile most compatible with the experimental data. A first test of the application of the method to the BAvarian Test Machine for Negative ions beam is given.