S.S. Chang

Successful Operation of the 500 MHz SRF Module at TLS

A project to replace two existing room-temperature radio frequency (RF) cavities by one CESR-III 500 MHz superconducting radio frequency (SRF) module was initiated for the Taiwan Light Source (TLS) synchrotron ring in 1999. The goals are to double the photon flux of the synchrotron light by doubling the electron beam current and to increase the stability of the electron beam by taking the advantage of the ultra-weak high-order modes (HOM) of the SRF cavity. The SRF module has been routinely operated since February 2005. The NSRRC users have benefited from a very high photon flux stability (Δ I0/I0∼ 0.05%) that had never been achieved previously. Here, we report the initial operational experience of the SRF system.

Stabilization of the spectral intensity fluctuations with the higher order mode frequency tuners

A strong excitation of the longitudinal coupled-bunch instabilities, which is suspected to be driven by the TM/sub 011/-like mode of the DORIS-I cavities, was observed at the higher electron beam current in the storage ring of SRRC. Such instability leads to heavy fluctuations of the photon beam intensity in the horizontal plane and therefore restricted the maximal useful beam current for the user experiments. This restriction has been released by replacing the damping antennae with the additional tuners. Here, we report our experiences after one-year routine operations of the main RF cavities with the second tuners at SRRC.

Cryogenic‐related Performance of an SRF Cavity Module in NSRRC

A superconducting 500‐MHz cavity module has been installed into the electron storage ring of NSRRC. This SRF module is tested on both the RF and cryogenic performances, before and after installation into the electron ring. Calibrations and measurements on its cryogenic load at different operating helium bath pressures are described and concluded. The test results of unloaded quality factor are reported. Meanwhile the excellent regulation on helium bath pressure is so advantageous to all these measurements. During normal operation with RF power, fluctuations of the helium bath pressure and liquid helium level are +/− 1.38 mbar (0.02 psi) and +/−0.2%, respectively.

On the mechanical design of a 1.5 GHz Landau cavity

A third harmonic Landau cavity with the fundamental mode of about 1.5 GHz is under development at SRRC. The cavity consists of inner copper layer and outer stainless steel layer. The vacuum-brazing process is adopted for cavity construction. The maximal power flow density on the cavity surface will be about 52.19 W/cm/sup 2/, as the total thermal loading of 32 kW. To verify the cooling capacity, the finite element method is adopted to perform the thermal and stress analyses. Under 15 m/sup 3//hr water flow rate, the temperature rise on the cavity body will be less than 14/spl deg/C, and the maximal equivalent stress on the copper layer of 29.75 N/mm/sup 2/(MPa) is achieved, which is much less than the yielding stress of copper.

Operation of the Superconducting RF System at TLS

The Taiwan Light Source (TLS) is the first dedicated synchrotron light source facility that used a superconducting RF cavity to upgrade its existing RF system. More then one year has passed since the superconducting RF cavity was successfully integrated with the existing RF subsystem for routine operation. The operating status shows that the superconducting RF (SRF) system has effectively suppressed the instabilities of the beam that are caused by the interaction of the electron beam with the higher‐order‐modes of the cavity. The original goal of doubling the photon intensity has been reached by applying top‐up mode injection at the beam current of 300 mA. However, compared to the original RF system, the beam loading is much higher, and the frequency of the superconducting cavity is also more easily perturbed by the mechanical vibrations. Those make the operation of the SRF system facing the challenge on the machine reliability, especially for a dedicated synchrotron light source facility. Here we report ...

Upgrade issues of the TLS storage ring RF system

To achieve the goals in the TLS storage ring performance upgrade plan, the necessity of adding the third RF station to the storage ring for radiation loss compensation at 1.5 GeV/350 mA operation and lifetime improvement are analyzed. We estimated the RF power required to compensate the radiation losses by bending magnets and various insertion devices. Effects of the proposed passive Landau cavity on power consumption is also studied.