Liu Ke-Xin

Stable Operation of the 2 K Cryogenic System for the Superconducting Accelerator at Peking University

A superconducting energy recovery linac test facility (PKU-SETF) was built at Peking University, and a 2K cryogenic system, which is the first closed-loop 2K cryogenic system for a superconducting accelerator in China, was constructed for the 1.3 GHz 3+1/2 cell dc-SRF injector. The main accelerator consists of two nine-cell TESLA-type superconducting cavities of the PKU-SETF The commissioning and stable operation of this 2 K cryogenic system was carried out. A helium pressure stability of better than ±0.1 mbar and a total refrigeration capacity of 65 W at a temperature of 2K was reached.

Multi-pass, multi-bunch beam breakup for 9-cell Tesla cavities in the ERL

Generally, Energy Recovery Linac (ERL) needs special designed high current superconducting RF cavities. In this paper, the threshold current of BBU for compact ERL facilities with 9-cell Tesla type cavities are investigated. The results show that it is feasible to adopt 9-cell Tesla cavity for compact ERL test facilities with just a few cavities and beam current around tens mA.

Theoretical Design of a 104 MHz Ladder Type IH-RFQ Accelerator

Beam dynamics and rf designs of a 104 MHz ladder type IH-RFQ (L-IH-RFQ) accelerator are finished at Peking University for the acceleration of 14C+ from 40keV to 500keV. As a specific feature, the output beam energy spread is as low as 0.6% achieved with the internal discrete bunching method, which makes potential applications of RFQ feasible, such as accelerator mass spectrometry and ion implantation. Tolerances of the beam dynamics design are studied by means of changing the input beam parameters, and the results are quite satisfying. On the other hand, the L-IH-RFQ structure is employed, taking advantage of its mechanical stability and the absence of inter-electrode voltage asymmetry. Radio-frequency properties are studied and optimized for reducing power loss with Microwave Studio (MWS). Tuning of the field flatness and frequency is investigated in principle.

Design of triode extraction system for a dual hollow cathode ion source

A triode extraction system is designed for a dual hollow cathode ion source being developed at the Institute of Heavy Ion Physics, Peking University. Basic parameters of the plasma are selected after examining the operation principle of the ion source, then the triode extraction system is designed and optimized by using software PBGUNS (for Particle Beam GUN Simulations). The physical design of the system is given in this paper.

Design of a low level radio frequency control system for the direct current-superconductive photocathode injector at Peking University

A digital low level radio frequency (LLRF) control system based on a high precision field-programmable gate array (FPGA) is being developed for the stable operation of the upgraded direct current-superconductive (DC-SC) photocathode injector at Peking University The design of this LLRF control system is described, including both the hardware and the internal algorithm. Analysis of disturbances shows that the system can achieve the requirement of ±0.1% for amplitude stability and ±0.1° for phase stability. Through experiments, preliminary results are presented in the paper.

Applications of AMS radiocarbon dating in Chinese archaeological studies

Over the past three years we have applied the AMS 14C technology to a variety of areas in Chinese archaeology. This paper outlines cases of dating archaeological sites and ancient human bones. We also describe some evidence of the beginning of pottery. Some dating results of Miaoyan and Yuchanyan sites are presented. The data show that the ages of potsherds are about 15.6 Ka and 14.4 Ka BP, respectively, and these potsherds might be the earliest pottery products discovered in the world.Over the past three years we have applied the AMS 14C technology to a variety of areas in Chinese archaeology. This paper outlines cases of dating archaeological sites and ancient human bones. We also describe some evidence of the beginning of pottery. Some dating results of Miaoyan and Yuchanyan sites are presented. The data show that the ages of potsherds are about 15.6 Ka and 14.4 Ka BP, respectively, and these potsherds might be the earliest pottery products discovered in the world.

Beam breakup simulation study for a high energy ERL

The maximum beam current that can be accelerated in an energy recovery linac (ERL) can be severely limited by the transverse multi-pass beam breakup instability (BBU), especially in future ERL light sources with multi-GeV high energy beam energy and more than 100 mA average current. In this paper, the multi-pass BBU of such a high energy ERL is studied based on the simulation of a 3-GeV ERL light source that is proposed by KEK. This work is expected to provide a reference for future high energy ERL projects.

Preliminary design and multipacting simulation of a SRF quarter wave electron gun at Peking University

Peking University is designing a new SRF gun that is composed of a quarter wave resonator (QWR) and an elliptical cavity. Compared to the elliptical cavity, the QWR is sufficiently compact at the same frequency and its electric field is quasi-DC. The RF parameters are determined by optimization of QWR cavity structure and the possible multipacting locations are analyzed by 2D MP simulation. The simulation results show that multipacting is not a critical issue for our optimized cavity structure.

Cold RF test and associated mechanical features correlation of a TESLA-style 9-cell superconducting niobium cavity built in China

The RF performance of a 1.3 GHz 9-cell superconducting niobium cavity was evaluated at cryogenic temperatures following surface processing by using the standard ILC-style recipe. The cavity is a TESLA-style 9-cell superconducting niobium cavity, with complete end group components including a higher order mode coupler, built in China for practical applications. An accelerating gradient of 28.6 MV/m was achieved at an unloaded quality factor of 4 × 109. The morphological property of mechanical features on the RF surface of this cavity was characterized through optical inspection. Correlation between the observed mechanical features and the RF performance of the cavity is attempted.

The design of a five-cell high-current superconducting cavity

Energy recovery linacs are promising for achieving high average current with superior beam quality. The key component for accelerating such high-current beams is the superconducting radio-frequency cavity. The design of a 1.3 GHz five-cell high-current superconducting cavity has been carried out under cooperation between Peking University and the Argonne National Laboratory. The radio-frequency properties, damping of the higher order modes, multipacting and mechanical features of this cavity have been discussed and the final design is presented.