J.R. Chen

An overview of the insertion device development at SRRC

Abstract Five high performance insertion devices, namely W20, U10, U5, U9 and EPU5.6, have been constructed and installed in the storage ring of the Synchrotron Radiation Research Center (SRRC). Among them, the 2-m-long conventional undulator U10 and the 4-m-long elliptically polarized undulator EPU5.6 were designed and built in-house. These two devices have achieved high magnetic field quality and high spectral performance. To facilitate hard-X-ray experiments, the project of building a superconducting wavelength shifter (SWLS) and a superconducting multi-pole wiggler (SMPW) is ongoing. These two superconducting insertion devices were designed to be cryogen-free.

The pilot-runs of the helium cryogenic system for the TLS superconducting cavity

At NSRRC the installation of a helium cryogenic system, which is tailor-made for the cooling of TLS superconducting cavity, was finished at the end of October 2002. The cryogenic system had finished its first phase commission work at the end of March 2003. This paper presents the first measurement result of the cryogenic system.

Collective Effects in the TLS Storage Ring after the Installation of Superconducting RF Cavity

A superconducting (SC) rf cavity designed by Cornell University [1] was installed in the storage ring at Taiwan Light Source (TLS) in December of 2004. The purpose of rf system upgrade is to increase the stored beam current without collective instabilities caused by higher-order-modes (HOM) of rf cavity. Beam measurements related to collective effects are performed. Results are compared with those measured prior to the rf system upgrade. Theoretical studies on collective effects after the rf upgrade are also presented.

Effects of magnets with non-unit magnetic permeability on an elliptically polarizing undulator.

This study employs the three-dimensional magnetostatic code TOSCA to assess numerically the effects of NdFeB magnets with non-unit magnetic permeability on an elliptically polarizing undulator. A reduction of a few percent of the on-axis magnetic field strength is predicted. In addition, a deviation of +/-100 G cm uncompensated dipole steering is predicted in a phase shift of 180 degrees for the elliptically polarizing undulator EPU5.6 (having a period length of 56 mm) at the minimum gap of 18 mm, which is related primarily to the configuration of the device end scheme. Results presented herein demonstrate that implementing an active compensation mechanism is a prerequisite for minimizing the orbit distortion during phase-shift adjustment, particularly for operating such a polarizing undulator in a third-generation machine having a median energy similar to that of the 1.5 GeV storage ring at SRRC.

Recent developments of the Synchrotron Light source at NSRRC

1) The storage ring operation energy was raised to 1.5 GeV, the maximum value limited by dipole magnets, to improve electron beam lifetime and to extend its spectrum to higher energies in 1996. 2) Five permanent-magnet insertion devices have been constructed and installed, as listed in Table I, by the end of 1999 to provide synchrotron radiation with higher brightness and energies. In 2003, the U10 undulator was removed and loaned to ANKA, Germany. 3) The booster energy was increased from 1.3 to 1.5 GeV. With this accomplishment, the facility can perform full energy injection and reduces the transient behavior between shifts, opening the possibility of top-up injection mode. 4) The stability of electron beam has been improved. With the raise of electron beam position monitors (EBPM) resolution to better than 1μm, the reduction of both air and cooling water temperature fluctuations to less than ±0.1 , and the °C implementation of the global feedback system, the beam orbit stability of ~ 1μm with a drift of ~ 5μm in a single shift is routinely achievable now.

Design of cryogenic system for several superconducting modules at National Synchrotron Radiation Research Center

National Synchrotron Radiation Research Center (NSRRC) is planning to install two 500 MHz superconducting radio frequency (SRF) cavities and six superconducting magnet (SM) modules. For the cryogenic requirements, we are presently constructing a helium cryogenic system. The cryostat properties of the SRF cavities and the SM modules are so different that in our design the cryogenic system has two cryogenic plants (465 W or 110 liters per hour @ 4.5 K for every plant), one is for the SRF cavities and the other is for the SM modules. The two plants are independent in normal operation. However, when the cryogenic plant for the SRF cavities shuts down, the other one can be transferred to supply the SRF cavities, and we design a distribution valve box to carry out the transformation.

Spectral properties of the polarizing devices at SRRC

User requirements at SRRC for high-brilliance synchrotron light in various polarization states will be fulfilled in the near future by the implementation of two types of polarizing devices in the storage ring: the elliptically polarizing undulator (EPU) and the elliptically polarized bending magnet (EPBM). The EPBM provides a broadband polarized spectrum up to the soft X-ray range with rapid alternation of the left and right helicities. The EPU, which has a magnetic period length of 56 mm, generates a high-brilliance harmonic spectral intensity in the range 80-1400 eV with abundant polarization states, including circular ones. The optimal merit flux is evaluated for the operation of these two polarizing devices in the SRRC 1.5 GeV storage ring. The available polarization states are also surveyed.