Vacuum System Design and Research for the Super Sor

The Super SOR is a third-generation VUV and soft Xray light source that is being designed at the University of Tokyo. Eight insertion devices (ID) including a 27-m long undulator will be installed in the ring. Since the ring has a very narrow acceptance for beam loss by collision with residual gases, the vacuum system is required to achieve operation pressure of 10 Pa range in order to guarantee a long beam lifetime. According to the designed lattice, the pump location and pressure distribution was examined by a simple calculation. Beam chambers should be equipped with high pumping speed, especially in arc sections. The chambers for arc sections and insertion devices have been designed. Some vacuum components were manufactured for trial and examined. 1 PRESSURE AND BEAM LIFETIME The beam lifetime of the ring is determined by the Touschek effect and pressure. Because ID chambers having a narrow aperture (16mm) will be installed in the section where the beta function is rather high (16m), the vacuum lifetime is very short. Figure 1 shows expected lifetimes in 1.0-GeV and 1.6-GeV operations as a function of the CO equivalent pressure. In order to guarantee a long beam lifetime, 1 Ah for example, the operating pressure of about 1 × 10 Pa is required in 1.0GeV operation. A longer lifetime is expected in the 1.6GeV operation because of the higher beam energy though the pressure increases approximately by 1.6 under same pumping condition. General description and machine parameters of the ring are given in this proceedings [1]. 0 .0 0 .2 0 .4 0 .6 0 .8 1 .0 1 .2 1 .4 1 .6 1 .8 2 .0 2 .2 2 .4 2 .6 2 .8 1 .E-10 1 .E-09 1 .E-08 1 .E-07 1 .E-06 PRESSURE [CO eq. Pa] B E A M L IF E T IM E [ A * h ] B E A M L IF E T IM E [ A * h ] B E A M L IF E T IM E [ A * h ] B E A M L IF E T IM E [ A * h ] 1 .0 GeV 1 .6 GeV Figure 1: Expected beam lifetime in the Super SOR as a function of pressure. 2 PUMPING SPEED AND LOCATION Dominant outgassing process in the ring is photon stimulated desorption (PSD). The pressure is principally determined by outgassing rate and pumping speed. To evacuate the gas efficiently and to achieve the required pressure, pumping speeds should be located according to the distribution of the incident photon flux on beam chamber wall. However, the pump space is restricted by magnet. The location of pumping speed and pressure distribution of the ring was examined and optimised by a simple calculation. Figure 2 shows a typical example of a proposed distribution of the pumping speed with the designed lattice. In the calculation the beam chamber has uniform aperture of φ60 and the PSD yield is uniformly 1 × 10 molecules/photon. Additionally minimum outgassing rate is assumed as 1 × 10 Pa·m/s/m, which corresponds to the thermal outgas at the long straight sections suffer no serious photon-irradiation. The pumping speeds and their locations by which the required pressure can be obtained were searched against the magnet arrangement. As the result, every unit cell in the arc section should have the speed more than 1300 l/s. To obtain the high pumping speed we plan to make the pumping space in the quadrupole magnets. Also 250 l/s is located every 3 m in the long-straight sections and total pumping speed of 40000 l/s is needed in the proposal. Under above conditions the average pressure lower than 1 × 10 Pa is expected at 1.0 GeV-200 mA storage, from which the beam lifetime more than 5 h must be resulted. 3 DESIGN OF BEAM CHAMBERS According to the magnet arrangement and required pumping speeds, beam chambers have been designed. Figure 3 shows a conceptual design of a beam chamber in a typical arc section. Aluminium alloy is used as main material and stainless steel is used for bellows. There is only one flange-connection a unit cell because beam position monitor, pumping port and bellows should be installed in the narrow space limited by many magnets. The length of the chamber is about 5.3 m. Main pumps are titanium sublimation pumps (TSP) and ion sputter pumps (SIP). Photon absorbers are installed just at the downstream of the bending magnet and first quadrupole magnet, and the pumping speed is concentrated in this region so that the outgas by PSD is efficiently pumped. The pumping space for TSP is made in the quadrupole magnet as well as in the bend chamber. _____________________________________________________________________________ *Present affiliation is the KEK 0-7803-7191-7/01/$10.00 ©2001 IEEE. 2415 Proceedings of the 2001 Particle Accelerator Conference, Chicago