Abstract
In the framework of the program on medical applications a compact 750 MHz RFQ has been designed and built to be used as an injector for a hadron therapy linac. This RFQ was designed to accelerate protons to an energy of 5 MeV within only 2 m length. It is divided into four segments and equipped with 32 tuners in total. The length of the RFQ corresponds to $5\ensuremath{\lambda}$ which is considered to be close to the limit for field adjustment using only piston tuners. Moreover the high frequency, which is about double the frequency of existing RFQs, results in a sensitive structure and requires careful tuning. In this paper we present the tuning algorithm, the tuning procedure and rf measurements of the RFQ.
Highlights
The high frequency RFQ (HF-RFQ), shown in Fig. 1, for medical applications will be used as an injector for the LIGHT project, a linac based proton therapy facility [1,2]
Beam dynamics parameters have been chosen in order to minimise beam losses above 1 MeV and to meet the requirements as an injector for facilities working at 3 GHz [3]
The field tuning plays an important role in order to deliver the longitudinal voltage distribution as required from the beam dynamics design
Summary
The high frequency RFQ (HF-RFQ), shown in Fig. 1, for medical applications will be used as an injector for the LIGHT project, a linac based proton therapy facility [1,2]. In general many tuner algorithms for accelerator cavities are based on equivalent circuit models [5,6,7] This is the case for RFQs, where the measurable field errors, usually obtained using the standard bead-pulling technique, are described as elements of the circuit [8,9,10]. Problems like inverting a nonsquare and illconditioned matrix in this case have been solved by using singular values decomposition (SVD) of the matrix as discussed in this paper This leads to a simple and powerful tuning algorithm that allowed a fast field tuning of the RFQ. This is followed by a description of the tuning procedure paying special attention to the use of different obtained solutions for tuner settings by the algorithm in order to avoid remeasuring the response matrix and to speed up the tuning process
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