Design study of radio frequency knockout slow extraction for the MedAustron synchrotron

Abstract

MedAustron is a state-of-the-art ion therapy facility in Wiener Neustadt with the aim to treat cancer patients with ion beams. The extraction of the accelerated particles with the desired energy from the synchrotron to the treatment rooms is one of the critical steps of the process. A stable beam of five seconds with a constant intensity is mandatory to achieve high quality patient treatment. To reach such long extraction times, third order resonant slow extraction is used. At MedAustron, slow extraction is currently driven by a betatron core, which increases the particle momentum to move the beam slowly into the resonance condition. However, current ripples on synchrotron components (especially quadrupoles) have got a negative impact on the quality of the extracted spill. Additionally, a fast change of the beam energy via multi energy extraction is not possible with betatron core driven extraction. To address these problems, the slow extraction mechanism could be changed to a slow extraction driven by Radio Frequency Knockout (RF KO). This method increases the transverse amplitude of the particles by applying an RF voltage to a transverse kicker. The current is modulated with a frequency corresponding to the revolution frequency times the horizontal tune of the particles. The design of such a mechanism is the goal of this Master thesis, which is undertaken by simulations of the extraction process with MAD-X and Python. Firstly, the Steinbach diagram of the extraction is re-constructed via simulations and the behaviour under parameter variation is studied. Secondly, the basic principle of RF KO is tested and the optimal choice of the lattice parameters such as horizontal tune QH and horizontal chromaticity QH′ is determined in order to maximize beam intensity and quality after extraction. Thirdly, promising candidates for RF KO are investigated more closely and a comparison to the betatron core-driven extraction is drawn.