IMPROVEMENT OF THE SPS MACHINE PERFORMANCE Saroj Rujirawat a,b , Nuanwan Sanguansak a *, Supagorn Rugmai a,b , George Garnet Hoyes a , Ruttakarn Apiwatwaja a , Somjai Chuenjareon a , Chanita Kaewpraset a , Goro Isoyama a,c , Weerapong Pairsuwan a,b and Takehiko Ishii a,b a National Synchrotron Research Center, Technopolis, 111 University Avenue, Muang District, Nakhon Ratchasima 30000, Thailand b School of Physics, Suranaree University of Technology, Nakhonratchasima, Thailand c Institute of Scientific and Industrial Research, Osaka University, Osaka 567-0047, Japan Abstract Ever since the first successful storage of electron beam, work for improving the machine performance has been performed on the Siam Photon Source (SPS), the modified SORTEC machine. The majority of the problems to be overcome are inherent in a used machine. Apparent features were unstable operation of the machine control system caused by electrical noise, the energy fluctuation of the linac electron beam, low injection efficiency to the storage ring, the frequent strong beam instability of the storage ring, large COD and the nonuniform distribution of the betatron function with anomalously large values at some quadrupole magnets. Noise has been removed. The origin of the serious beam instability is the short circuit in some of the quadrupole magnets. Renewal of four very defective coils significantly improved the machine performance. A maximum stored current of 216 mA and the beam lifetime of 6 hrs at 100 mA have been attained. We are writing a program for the easier setting of the required operating points. INTRODUCTION The Siam Photon Source has been built using the components of a used machine, SORTEC. The machine components were transferred from the SORTEC Laboratory to the National Synchrotron Research Center (NSRC). The accelerator complex comprises a 40 MeV injector linac of the re-entrant type, a 1 GeV booster synchrotron of the FODO lattice and a light source storage ring of the DBA Double Bend Achromat) lattice [1]. The LBT (Low energy Beam Transport) line connects the linac and the synchrotron. The HBT (high energy beam transport) line connects the synchrotron and the storage ring. In the Siam Photon Source, the linac, the synchrotron and the LBT line of the original SORTEC machines were used without modification. The storage ring and HBT line were rebuilt and modified to have a more advance structure for the utilization of synchrotron radiation. The work of the machine reassembly, the commissioning and the performance improvement included a lot of repairing. The machine control system is described elsewhere [2, 3]. The first electron storage was achieved in December 2001. BEAM INSTABILITY PROBLEM Many defects have been found. They were caused by the degradation of various components in electrical power supplies and controllers [1-7]. Ever since the first storage of the electron beam in the storage ring, efforts to improve the machine performance have been carried out. The problems we had to solve were the low injection efficiency, short lifetime and the beam instability. They are related to each other to some extent. We have spent almost two years to settle the serious parts of the problems. In this report, the problems described above and their cures are presented. They appear to be quite distinctive of the accelerator complex of the Siam Photon Source. MEASUREMENS OF MACHINE PARAMETERS In the early stage, most of the efforts of the machine performance improvement were focused on the removal of noise [6-7]. The power supplies of the linac and the synchrotron are great sources of noise. The noise affects various parts of the control system, power supplies and controllers. The details of the noise trouble-shooting are not described here. Serious noise has been removed up to the present. The beam instability is defined as the change of the beam intensity and the beam location. The beam instability of the storage ring had long been puzzling, since long-lasting investigations provedthat there was no defect in the power supplies and controllers of magnets and the microwave system for the RF acceleration. We eventually measured the machine parameters such as the tunes, the betatron functions, the dispersion function and momentum compaction factors. Among others, the measured data of the distribution of the betatron functions along the electron orbit is very astonishing. The betatron functions at the quadrupole positions have been measured. The functions can be obtained by measuring the tune shift, as the magnetic field is charged [8]. Figure 1 shows the measured values of the betatron functions. The x- axis indicates the position of quadrupole magnets along the central orbit. The points show the values obtained by the measurements. The lines connecting the measured points are the calculated betatron functions obtained by the data fitting. The program, Beam Optics, was used in the. ___________________________________________ * Corresponding author Tel.: +66-44-217040 ext. 651 E-mail: nuanwan@nsrc.or.th Proceedings of APAC 2004, Gyeongju, Korea 601