• S. An, Y.D. Joo, H.-S. Kang, C.D. Park, I.S. Park, Y.U. Sohn
  PAL, Pohang, Kyungbuk

In the PLS-II storage ring, the available length of a long straight section for RF system is 6.28 m, which is from quadrupole magnet to quadrupole magnet beam-pipe valves with an elliptical transverse cross section. In this room, two beam-pipe transitions from elliptical to circle cross section, two commercial cryomodules with a circle transverse cross section, three bellows for adjusting cryomodule length and four vacuum valves could need to be installed. Two commercial cryomodules are too long to be installed into this section. In order to install two cryomodules into this section, we need to modify the tapers for reducing the total length of these parts. In this paper, the HOM damping effects for different taper shapes has been studied. The beam loss factor influence and broad-band impedance change due to taper shape changes have been estimated.

• Y.U. Sohn, S. An, M.-H. Chun, Y.D. Joo, H.-S. Kang, H.-G. Kim, K.R. Kim, C.D. Park, H.J. Park, I.S. Park, I.H. Yu
  PAL, Pohang, Kyungbuk

The RF system for PLS-II upgrade, of which beam current and emittance are 400 mA and 5.6 nmrad at 3 GeV, becomes much more important compared to PLS. To reduce the HOM intensity in RF cavities for stable beam, a superconducting RF cavity is selected for the PLS-II. The RF system has to compensate beam loss power of 663 kW from 24 bending magnets, 20 insertion devices and other losses by RF HOM and broadband losses along vacuum chambers. For sufficient energy acceptance and lifetime the design RF voltage is 4.5 MV. Three 500 MHz superconducting cavities will be operated from October 2012, following successful commissioning with PLS NC cavities from July 2011. For the 3 SRF cryomodules, a 700 W class He cryogenic system will be prepared in 2011. The design of PLS-II SRF system including cryogenic system will be reported in the paper.

• Y.D. Joo, T. Ha, C. Kim, C.D. Park, S.J. Park
  PAL, Pohang, Kyungbuk

A superconducting RF cavity is used in the storage ring of the Pohang Light Source (PLS) upgrade project (PLS-II) at Pohang Accelerator Laboratory (PAL) for increasing the electron beam current and energy from 2.5GeV/200mA to 3.0GeV/400mA. In order to meet the requirement of lower beam emittance and higher photon energies, as well as more straight sections for insertion devices, the vacuum chambers in the storage ring need to be reconstructed. To control the spurious harmonic resonances' effect to beam position monitors (BPMs) in the PLS and PLS-II storage ring vacuum chamber, the TE mode distribution in vacuum chambers has been analyzed by both numerical simulation and experiment. Based on this analysis, the proper method to control the strength of TE mode at the position of BPMs is suggested.