Commissioning and Operation of the MedAustron Injector: Results and Future Outlook

Abstract

The MedAustron facility [1, 2] is a synchrotron-driven hadron therapy and research center presently under construction in Wiener Neustadt, Austria. In its final outline, the facility will provide H beams with kinetic energies ≤250MeV and C beams of ≤400MeV/u for clinical applications, and H of up to 800MeV for nonclinical applications. At a later stage of the project, beams of other species can be generated with similar optics. First patient treatment is foreseen for the end of 2015. This contribution presents the results of commissioning and operation of the injector of the MedAustron accelerator. A comparison with the baseline optics and with the design error studies is given alongside with an overview on the operational experience, with emphasis on the system reliability, stability and reproducibility. THE MEDAUSTRON INJECTOR The layout of the MedAustron injector, as commissioned, is presented in Figure 1. Figure 1: The MedAustron injector. The primary particle beams (H3, C) are generated in continuous mode at 8keV/u by two ECR ion sources (one for each particle type). A third ion source is used as backup and can be tuned for both ion species, and at a later stage for other light ions. All three ion sources are connected by individual transport lines to a common LEBT comprising a fast electrostatic deflector for beam pulse length adjustment. From there, they are transported to the RFQ for acceleration to 400keV/u. An inter-tank matching section (IMS), encompassing a Buncher (BU) RF cavity, two quadrupole doublets, and two steerers, matches the beam to the entrance plane of an IH-mode DTL (KONUS) that accelerates the particles to 7MeV/u before they are stripped to, respectively, H and C, debunched and transported to the injection plane of the synchrotron. The Linac RF system is operated with 10Hz repetition rate and a maximum pulse length of 500μs. A beam dump located after the stripping foil allows operating the source lines, LEBT and the Linac even when installation works are taking place inside the synchrotron hall, which increases availability for beam commissioning. The beam diagnostic (BD) devices available for beam characterisation in the Injector involve [3]: profile grids (PGX), wire scanners (WSX; only in the source lines and LEBT, where the beam is continuous) and slits (SLX) for transverse profile and emittance measurements, current transformers (CTAs) and Faraday Cups (FCs) to measure the beam current, Phase Probes (PHPs) for beam energy measurements, and a four-button probe to determine the beam position at the entrance plane of the IH-tank. The injector commissioning was started in 2012/12 using the H beam from ion source 1 (IS1). First H beam was seen on the injection plane of the synchrotron in 2014/03. INJECTOR COMMISSIONING STRATEGY The injector of the MedAustron accelerator has been commissioned in a stepwise process in order to fully characterize the beam for each section of the injector, by making use also of two temporary installations of beam diagnostics. Due to the tight time constraints, the commissioning strategy was optimized to allow the acquisition of sufficient data with only one ion beam species (H3), from one ion source (S1). Based on this commissioning data, the injector can be commissioned for any new beam, even though the temporary test benches are no longer available. The commissioning stages are described in the following. Ion Sources The MedAustron ion sources have several operational parameters that affect directly the emittance and the Twiss parameters of the generated beam. The commissioning goal was to find at least a set of source parameters providing a beam within the specified requirements [4] and to identify on which beam property each ion source parameter is acting on. A notable dependence, integrated into the strategy of the next commissioning stages, is the possibility to tune THPME001 Proceedings of IPAC2014, Dresden, Germany ISBN 978-3-95450-132-8 3202 C op yr ig ht © 20 14 C C -B Y3. 0 an d by th e re sp ec tiv e au th or s 04 Hadron Accelerators A08 Linear Accelerators the Twiss parameters of the beam after the spectrometer magnet via the electrical potential on the middle extraction electrode of the ion source (“Focus” electrode). The dependence of α and β in the horizontal plane is presented in Figure 2; in the vertical plane, the influence on α and β is considerably weaker. Figure 2: Dependence of the horizontal Twiss parameters after the spectrometer on the potential of the Focus electrode.