Proposed Linac Upgrade with a SLED Cavity at the Australian Synchrotron, SLSA

The Australian Synchrotron Light Source has been operating successfully since 2007 and in top-up mode since 2012, while additionally being gradually upgraded to reach a beam availability exceeding 99 %. Considering the ageing of the equipment, effort is required in order to maintain the reliability at this level. The proposed upgrade of the linac with a SLED cavity has been chosen to mitigate the risks of single point of failure and lack of spare parts. The linac is normally fed from two independent klystrons to reach 100 MeV beam energy, and can be operated in single (SBM) or multi-bunch mode (MBM). The SLED cavity upgrade will allow remote selection of single klystron operation in SBM and possibly limited MBM without degradation of beam energy and reduce down time in case of a klystron failure. The proposal for the SLED cavity upgrade is shown and the linac designs are detailed. INTRODUCTION The injector comprises a 100 MeV linac and a 3 GeV booster to enable full energy beam injection into the storage ring. The injector was upgraded later from decay to top-up mode operation to keep the storage ring at 200 mA current. Top-up has been continually running since then with an MBM injection of 0.5 mA every few minutes compared to a reinjection every 12 hours in decay mode. Alongside top-up came the need to improve reliability and mean down time for the entire facility. Improvements on the injector were more cost effective to target mean down time due to the increase in wear on the system, single point of failure and the limited lifespan of devices such as the electron tubes. Improvements on the linac were necessary with two klystrons required for operation, and a failure could take weeks, depending on missing critical spare parts. The waveguide radio frequency (RF) distribution system for the linac was modified in the first stage in 2010, to test single klystron operation to power the whole linac; albeit at a reduced final beam energy. Booster injection was successful, but booster ramping remained unsolved as a lack of control in fine field adjustments at low energy levels from below 100 MeV. The increase in klystron trips operating at higher power levels was also not satisfactory. The next stage is to add a SLED cavity to overcome the current deficiencies. This paper will outline the proposed upgrade and benefits. LINAC OVERVIEW General Specifications The 100 MeV 3 GHz linac structure is made of a 90 keV thermionic electron gun (GUN), a 500 MHz subharmonic prebuncher unit (SPB), preliminimary buncher (PBU), final buncher (FBU), and two 5 m accelerating structures. The structures are powered by two 35 MW pulsed klystrons supplied from a pulse forming network (PFN). The low level electronics include two pulsed 400W S band amplifiers to drive the klystrons, and two 500W UHF amplifiers for the GUN and SPB. The linac is based on the SLS/DLS design and was delivered by Research Instruments, formerly ACCEL, the modulators subcontracted to PPT-Ampegon, and the waveguide to SPINNER. The linac overview is shown in Figure 1, a summary of the general specifications listed in Table 1 and more details referenced to [1]. KLYSTRON 1 POS: 00000