Weimin Pan

Development of a 325 MHz β=0.12 superconducting single spoke cavity for China-ADS

Twelve very low Beta superconducting single spoke cavities, whose Beta is only 0.12 (Spoke012) when operating at 325 MHz, are adopted in Injector I for China-ADS linac. This type of spoke cavity is believed to be one of the key challenges for its very low geometric Beta. So far, in collaboration with Peking University and Harbin Institute of Technology, IHEP has successfully designed, fabricated, and tested the Spoke012 prototype cavity. This paper presents the details of the design, fabrication and test results for Spoke012 prototype cavity.

A tuning system for BEPC II

The tuning system plays a very important role when a superconducting cavity is in operation. It cooperates with other control loops to adjust the cavity frequency with high precision, reduce the reflection power, guarantee the stability of beam, and ensure the safety of the superconducting cavity. This paper focuses mainly on the tuning system working principle, the working state and problems that Beijing Electron Positron Collider (BEPC II) has encountered during operation.

Design and test of frequency tuner for a CAEP high power THz free-electron laser

Peking University is developing a 1.3 GHz superconducting accelerating section highpower THz free-electron laser for the China Academy of Engineering Physics (CAEP). A compact fast/slow tuner has been developed by the Institute of High Energy Physics (IHEP) for the accelerating section to control Lorentz detuning, compensate for beam loading effect, microphonics and liquid helium pressure fluctuations. The tuner design, warm test and cold test of the first prototype are presented, which has a guiding significance for the manufacture of the formal tuner and cryomodule assembly.Peking University is developing a 1.3 GHz superconducting accelerating section highpower THz freeelectron laser for the China Academy of Engineering Physics(CAEP). A compact fast/slow tuner has been developed by the Institute of High Energy Physics(IHEP) for the accelerating section to control Lorentz detuning, compensate for beam loading effect, microphonics and liquid helium pressure fluctuations. The tuner design, warm test and cold test of the first prototype are presented, which has a guiding significance for the manufacture of the formal tuner and cryomodule assembly.

Some experiences with BEPCII SRF system operation

The Superconducting Radio Frequency (SRF) system of the upgrade project of the Beijing Electron Positron Collider (BEPCII) has been in operation for almost 8 years. During operation, many problems have been encountered, such as excessive heating of the power couplers, frequent beam trips during high intensity colliding, false arc interlock trigger and so on. Among them, some has been solved successfully, some have been alleviated. This paper will describe some experiences with BEPCII SRF system operation, including the symptoms, causes and solutions of problems.

Design of a 325 MHz half wave resonator prototype at IHEP

A 325 MHz β = 0.14 superconducting half-wave resonator prototype has been developed at the Institute of High Energy Physics, Beijing, which can be applied in the low energy section of continuous wave high current proton linear accelerators. The electromagnetic design, multipacting simulation, mechanical optimization and fabrication are introduced in detail. Test results at room temperature and 4.2 K, and a comparison between measured and simulated results, are analyzed in this paper.

Study and design of RF coupler for Chinese ADS HWR superconducting cavity

An RF power coupler is a key component of the superconducting accelerating system in Chinese ADS proton linac injector I, which is used to transmit 15 kW RF power from the power source to the superconducting HWR cavity. According to the requirement of working frequency, power level, transmission capability and cooling condition, the physics design of coupler has been finished, which includes RF structure optimization, thermal simulation, thermal stress analysis and so on. Based on this design, the prototype of HWR coupler has been fabricated, and it has successfully passed the high power test.

Development of fundamental power coupler for C-ADS superconducting elliptical cavities

5-cell elliptical cavities have been selected for the main linac of the China Accelerator Driven sub-critical System (C-ADS) in the medium energy section. According to the design, each cavity should be driven with radio frequency (RF) energy up to 150 kW by a fundamental power coupler (FPC). As the cavities work with high quality factor and high accelerating gradient, the coupler should keep the cavity from contamination in the assembly procedure. To fulfil the requirements, a single-window coaxial type coupler was designed with the capabilities of handling high RF power, class 10 clean room assembly, and heat load control. This paper presents the coupler design and gives details of RF design, heat load optimization and thermal analysis as well as multipacting simulations. In addition, a primary high power test has been performed and is described in this paper.

High accuracy amplitude and phase measurements based on a double heterodyne architecture

In the digital low level RF (LLRF) system of a circular (particle) accelerator, the RF field signal is usually down converted to a fixed intermediate frequency (IF). The ratio of IF and sampling frequency determines the processing required, and differs in various LLRF systems. It is generally desirable to design a universally compatible architecture for different IFs with no change to the sampling frequency and algorithm. A new RF detection method based on a double heterodyne architecture for wide IF range has been developed, which achieves the high accuracy requirement of modern LLRF. In this paper, the relation of IF and phase error is systematically analyzed for the first time and verified by experiments. The effects of temperature drift for 16 h IF detection are inhibited by the amplitude and phase calibrations.

1.3 GHz SRF Technology R&D Progress of IHEP

IHEP started the 1.3 GHz SRF technology R&D in 2006 and recently enters the stage of integration and industrialization. After successfully making several single cell and 9-cell cavities of different shape and material, we designed and assembled a short cryomodule containing one large grain low-loss shape 9-cell cavity with an input coupler and a tuner etc. This module will perform horizontal test in 2016 with the newly commissioned 1.3 GHz 5 MW klystron and the 2 K cryogenic system. Beam test with a DC photocathode gun is also foreseen in the near future. We report here the problems, key findings and improvements in cavity dressing, clean room assembly, cryomodule assembly and the liquid nitrogen cool down test. A fine grain TESLA 9-cell cavity is also under fabrication in a company as the industrialization study.

Design of a 325 MHz SC Spoke040 cavity at IHEP

A spoke cavity is a TEM-class superconducting resonator with particular advantages: compact structure and high shunt impedance. The 325 MHz beta=0.40 (beta=v/c, v is the velocity of particle and c is the velocity of light) single spoke cavity (Spoke040) is adopted for the Chinese ADS (Accelerator Driven Sub-critical System) project. The physics and mechanical design has been accomplished, and the fabrication of a prototype is currently in progress. In this paper, the optimization processes for the main radio frequency (RF) and mechanical parameters are analyzed in detail. Two kinds of cavity end-walls (flat and convex) are compared. The convex end-wall is preferred in order to improve mechanical performance of the cavity. Two prototypes of the Spoke040 cavity are in the machining stage, and should be finished in early 2014. Vertical testing is also under preparation.