W.K. Lau

Study of longitudinal coupled-bunch instabilities in the SRRC storage ring

Longitudinal coupled-bunch instabilities in the SRRC 1.3 GeV storage ring have been studied by analyzing the signals picked up from the stripline electrodes and rf power reflected from the cavities. The current dependence of the instability strengths was measured. As a cross check, the bunch phase jitters as a function of beam current has also been measured by using sampling optical oscilloscope. Threshold currents of a few milliamperes have been determined from both measurements. They agree with each other very well. It is also found that the strength of the instabilities can be reduced significantly by randomly distributing electron bunches around the ring.

A high brightness, X-band photoinjector for the production of coherent synchrotron radiation

Linear colliders, future electron acceleration concepts, and short pulse, ultrawideband millimeter-wave sources all require bright electron beams. Photoinjectors have demonstrated the ability to produce relativistic electron beams with low emittance and energy spread. The system described herein combines state-of-the-art capabilities in the laser and rf systems, advanced photocathode materials, and new concepts for synchronization. Phase jitter has been measured in detail, and schemes for alleviating this problem have undergone initial proof-of-principle testing. Direct mode locking of a multiple quantum well Al:GaAs solid-state laser oscillator by an rf signal sampled from within a high-power rf accelerator cavity was demonstrated for the first time. Characterization of the electron beam produced by the system is presented. The linear electron accelerator system is comprised of a 1.5 cell side-wall coupled standing wave accelerator structure, driven by a 20 MW Stanford Linear Accelerator Center (SLAC) Kl...

The design and fabrication of an X-Band RF gun

A recently proposed 1 high brightness, high repetition rate, multibunch photoinjector project has reached the high power construction stage. The accelerator structure consists of a 1-1/2 cell, side wall coupled, X-Band (8.548 GHz) standing wave cavity, driven by a 20 MW SLAC Klystron, and a GHz repetition rate (burst mode) rf modelocked AlGaAs laser diode oscillator and Chirped Pulse Amplification (CPA) Ti:Al2O3 multipass amplifier. The photocathode gun will be used to accelerate a train of one hundred, 0.1–1 nC electron bunches to an energy in the range of 5 MeV. A joint collaboration between the UC Davis Department of Applied Science (DAS), and the Synchrotron Radiation Research Center (SRRC) has been established to expedite the construction and characterization of the accelerator structure. A prototype copper cavity has been fabricated and characterized. The results of the low power rf measurements are presented, as well as a description of the high power cavity design. The solenoid focusing system des...

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.

Design of a third harmonic Landau cavity for the SRRC storage ring

We present here our design of the SRRC third-harmonic Landau cavity to be operated on the first stage in a passive mode for bunch lengthening so as to increase the Touschek life-time. Its implementation will also be helpful for suppression of the longitudinal coupled-bunch instabilities observed in the storage ring of SRRC. The cavity profile was optimized with the 2D code URMEL with the following criteria: (1) maximization of the shunt impedance; (2) minimization of the maximal power flow density on the cavity surface; (3) feasibility of the mechanical constructions. A prototype is now under construction.

Effects of the Landau cavity on the electron beam

This paper presents the procedure and the formulas to analyze the effects of Landau cavity on the electron beam while the main RF system is operated on the compensated condition. It is shown that the maximal available current, determined by the phase instability limit, is reduced with Landau cavity. The model of potential energy is used for the calculations of the bunch length and the synchrotron frequency of the storage ring with double RF system. It is shown that the bunch length can be manipulated by tuning the resonance frequency of the passive Landau cavity, and the spread of synchrotron frequency can be induced by the addition of a Landau cavity.

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.

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.

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.