Superconducting RF Cavity Frequency and Field Distribution Sensitivity Simulation
Frequency and electromagnetic field distribution sensitivity of a superconducting RF (SRF) cavity are the fundamental phyical paramethers in cavity and tuner design. At low temperature, the frequency sensitivity can be obtained by measuring prototype cavity, but it is not easy to test the filed distribution sensitivity. This paper presents and describes a simulation method combining ANSYS and SUPERFISH to calculate the cavity frequency and field distribution variation due to cavity’s small deformation caused by mechanical force, radiation force, thermal expansion etc.. As an example, the simulation results of the frequency and field flatness sensitivity on the SNS cavities were confirmed by their test results.
THE RF SYSTEM OF INFRARED FREE ELECTRON LASER FACILITY AT NSRL
An infrared free electron laser light source (IRFEL) is being constructed at National Synchrotron Radiation Laboratory, which could be used in the study of far infrared detection, light dissociation and light excitation. The accelerator of IRFEL deliver an average current 300 mA electron beam at 15~60 MeV, the energy spread is less than 240 keV, and the emittance is less than 30 mm*mrad. IRFEL is consisted of two optical resonator system, which could create 2.5~50 um, 40~200um infrared laser respectively. The design of IRFEL RF system is introduced, the recent progress of prebuncher, buncher, frequency distribution, accelerator and DLLRF system are also present in this paper. INTRODUCTION RF system is main part of IRFEL linac, which is used to compress and accelerate the electron beam. The IRFEL linac is composed of prebuncher, buncher and two accelerating sections. The prebuncher is a single resonant cavity, and the buncher is a 1-meter travelling wave accelerating construct. The accelerating section is 2-meter constant gradient travelling wave accelerators. The pulse length of electron beam is 1 ns from the electron gun, and the charge quantity is 1.5 nC. At the end of linac, the pulse length is compressed to 10 ps, and the beam energy reaches 60 MeV. The layout of IRFEL RF system is shown in Figure 1. Figure 1: Layout of IRFEL RF system. DESIGN OF IRFEL RF SYSTEM Each section is fed by Toshiba E3729 klystron, which could offer 35 MW output power. The power for prebuncher is much less than buncher and accelerating section, so a 10 kW solid state amplifier is used as the power supply for prebuncher. The output of first klystron is divided into two-branch, one provides 8 MW for buncher, the other branch is 20 MW, which supplies power for the first accelerating section. According to this design, the energy of electron gain 30 MeV, by passing each accelerating section.476 MHz reference signal is produced by Keysight N5181B source. The frequency convertor system creates several signals, such as the clock signal, local signal, IF signal and excitation signal. The digital down conversion and acquisition is achieved by digital low level system. It also completes the complex feedback calculation, in order to maintain amplitude and phase in high stability. Prebuncher and Accelerator The prebuncher is a standing wave resonant cavity. Due to the high current, the beam loading effect is quite strongly. For purpose of reducing beam loading effect, lower Q factor and shunt impedance R is designed. Therefore stainless steel is used as cavity material. The simulation result of electric field in the cavity is obtained using CST code, as shown in Fig. 2. The cavity resonant frequency is 476.0031MHz, Q factor is approximately 3000, and shunt impedance is 440 kΩ. The dimension parameter of prebuncher is list in Table 1. Figure 2: Simulation of E-field distribution in prebuncher. Accelerator
Optical rotatory dispersion and absolute configuration—III
Abstract Optical rotatory dispersion measurements on pyrrolidine, piperidine, and tetrahydro-isoquinoline alkaloids indicate that the absolute configuration of the α-asymmetric center may be assigned directly from the dispersion curve, provided either that the nitrogen atom is not protonated, or that the compound contains a chromophore absorbing above 200 mμ.