Shuxin Zheng

Mode Analysis of High-Power Microwave Generation in the Inward-Emitting Coaxial Vircator Based on Computer Simulation

A mode analysis is carried out with the MAFIA TS3 module to study the high-power microwave generation in the inward-emitting coaxial vircator with two opposed nonaxisymmetric emitting surfaces. The central angle thetas of the emittors, and the axial distance D between the cathode and anode reflector, are verified to have a large influence on the mode component. For a fixed diode voltage of 250 kV, the coaxial diode current is 13.7 kA when the beam injection is axisymmetric (thetas = 180deg). In this situation, the simulation gives the highest efficiency of 8.3% for D = 5.0 cm and 10.9% for D = 10.0 cm , comparing with the nonaxisymmetric beam injection. For the case of two opposed nonaxisymmetric emitting surfaces with central angle thetas, there exists a range for thetas to acquire a rather pure output of the TE11 mode (80% of the total power), which is 80deg < thetas < 160deg. However, the efficiency decreases with smaller thetas. The polarized direction of the main TE11 mode is consistent with the directional layout of the two opposed emitters. FFT transformation shows that the dominant frequency for thetas < 80deg can be estimated by the equations derived from the 2-D theoretical analysis of the symmetric coaxial vircator.

A Three-Cell Superconducting Deflecting Cavity Design for the ALS at LBNL

Deflecting RF cavities may be used to generate subpicosecond x-rays by creating correlations between longitudinal and transverse phase space in electron bunches in radiation devices. Up to 2-MV defecting voltage at 1.5-GHz is required for 1.9-GeV electron beam at the Advanced Light Source (ALS) of Lawrence Berkeley National Laboratory (LBNL). In this paper, we present a conceptual design for a 1.5-GHz three-cell superconducting RF cavity and its couplers. The cavity geometry and its shunt impedance at the deflecting mode are optimized using MAFIA code. The cavity impedances from lower and higher order modes (LOMs and HOMs) are computed as well. Possible schemes for damping most harmful LOM and HOM modes are discussed and simulated.

A Resistive BPM for Mini-LIA

A prototype of resistive BPM (Beam Position Monitor) was designed and built for Mini-LIA. The design parameters and bench test results are presented. A beam displacement nearly 1mm off-axis can be observed. The relationship between the signal amplitude and decay time constant to current rising time was studied. In conclusion, some factors and phenomenon in the experiment are analyzed.

Experiment on the cold test model of a 2-cell superconducting deflecting cavity for ALS at LBNL

Deflecting cavities are proposed for ALS at LBNL to generate sub-picosecond X-ray pulses. A 2-cell structure has been simulated to achieve required deflecting voltage and damping waveguide is attached on beam pipe to get low impedance. To demonstrate the simulation, we made an aluminum cold test model. Detailed configuration of the experiments measuring the field distribution and Qs with/without waveguide loaded are presented. Calculated (R/Q)s and waveguide damping are compared with simulation.

Design of a compact ring for proton radiation applications

This paper presents the design of a compact proton synchrotron, including lattice structure, injection system and extraction system, for radiation applications. The lattice is based on a DBFO cell and shows good properties like small βmax and decent kick arm. Radiation applications require relative strong and continuous beam, so we propose strip injection and resonance extraction for the design. A phase space painting scheme is designed and simulated by ORBIT. The scheme achieves good uniformity in phase space. The extraction system is designed and optimized by multi-particle tracking.

Study of Achieving Low Energy Beam by Energy Degradation and Direct Resonance Extraction in a Compact Ring

We have designed a compact proton synchrotron (7∼230 MeV) for applications like proton therapy and space environment study. These applications require slow extraction from 10∼230 MeV. Traditionally, the low energy beam (10∼60 MeV) is achieved by energy degradation from high energy beam which may cause beam lose and energy spread increase, because the beam quality may suffer from magnetic remanence, power ripple and strong space charge effects in low energy stage. To achieve high quality beam directly from resonance extraction, we study these effects by multiparticle simulation. Methods of improving beam quality are discussed.

Cold and High Power Test of Large Size Magnetic Alloy Core for XiPAF's Synchrotron

A compact magnetic alloy (MA) loaded cavity is under development for XiPAF’s synchrotron. The cavity contains 6 large size MA cores, each is independently coupled with solid state power amplifier. Two types of MA core are proposed for the project. We have developed a single core model cavity to verify the impedance model and to test the properties of MA cores under high power state. The high power test results are presented and discussed.