Jiankui Hao

Peking university superconducting accelerator facility for free electron laser

Peking University Superconducting Accelerator Facility (PKU-SCAF) is to generate high-quality electron beams with high average current. It is mainly composed of a DC-SC photocathode injector and a superconducting accelerator. It will operate in CW mode. The energy of the electrons is 20–35 MeV and the emittance is o15p mm mrad. PKUSCAF will be used for Free Electron Lasers. r 2002 Elsevier Science B.V. All rights reserved. PACS: 41.85.Ar; 41.60.Cr

Researches on new photocathode for RF electron gun

Abstract Semiconductor photocathode and metal photocathode have different properties. To consider the properties of both, we studied a new type of photocathode – ion implanted photocathode. Cesium ions are implanted into a metal substrate. A photocathode preparation chamber is set up to make this photocathode. A cesium ion source is attached to the common photocathode preparation chamber. In the past two years, we finished making this photocathode and did research on its properties. A series of experiments have been done with different metal substrates, implanting dosages and implanting energies, in order to get a kind of photocathode material with high quantum efficiency and good stability. An increase of quantum efficiency after implantation has been observed. A more interesting result is that the emission spectrum becomes broader.

Ultrafast electron diffraction with megahertz MeV electron pulses from a superconducting radio-frequency photoinjector

We report ultrafast relativistic electron diffraction operating at the megahertz repetition rate where the electron beam is produced in a superconducting radio-frequency (rf) photoinjector. We show that the beam quality is sufficiently high to provide clear diffraction patterns from gold and aluminium samples. With the number of electrons, several orders of magnitude higher than that from a normal conducting photocathode rf gun, such high repetition rate ultrafast MeV electron diffraction may open up many new opportunities in ultrafast science.

Research and experiments on niobium-sputtered superconducting QWR in Peking University

R&D on SC quarter wave resonators (QWRs) for heavy ion linacs were initiated in China several years ago. A DC bias-voltage sputtering technology was developed in Peking University for niobium-coated copper QWR. A niobium-sputtered copper QWR with good niobium films was successfully made in October 1999. Low temperature experiments were carried out from November 1999 to September 2000. The accelerating gradient of 5/spl sim/6 MV/m can be obtained with no beam load at 4.2 K. The QWR is installed after the 2/spl times/6 MV tandem and is used to accelerate proton beams. The accelerating gradient of 3 MV/m was obtained with a proton beam load.

Electron Bunch Train Excited Higher-Order Modes in a Superconducting RF Cavity

Higher-order mode (HOM) based intra-cavity beam diagnostics has been proved effectively and conveniently in superconducting radio-frequency (SRF) accelerators. Our recent research shows that the beam harmonics in the bunch train excited HOM spectrum, which have much higher signal-to-noise ratio than the intrinsic HOM peaks, may also be useful for beam diagnostics. In this paper, we will present our study on bunch train excited HOMs, including the theoretic model and recent experiments carried out based on the DC-SRF photoinjector and SRF linac at Peking University.

A 1.3 GHz Cryomodule with 2x9-Cell Cavity for SETF at Peking University

The straight beam line of SETF at Peking University is under construction, which consists of a DC-SRF photoinjector and a superconducting linac with two 9-cell cavities. Stable operation of the DC-SRF photoinjector has been realized and the design, manufacture and assembly of the cryomodule with two 9-cell cavities have been completed. Improved capacitive coupling RF power coupler and fast tuner with piezo are adopted.

DC-SC Photoinjector with Low Emittance at Peking Univeristy

High average power Free Electron Lasers require the high average current electron beams with the low emittance. The DC-SC photoinjector developed at Peking University, directly combining a DC Pierce gun with an SRF cavity, can produce the high brightness beam with moderate bunch charge and high duty factor. In order to optimize the transverse emittance which sharply increases at the beginning of the DC gun, a carefully design for the DC gap and the cavity shape is needed. In this paper, the simulation of an upgraded design has been performed. This photoinjector, consisting of a DC gap and a 2+1/2 cell SRF cavity, can produce 4.2 MeV electron beams with 100 pC per bunch and 1.1 μm normalized emittance.

Research on Peking University Superconducting Accelerator Facility (PKU-SCAF)

Peking University Superconducting Accelerator Facility (PKU-SCAF) is under development now. This facility is mainly composed of a DC-SC photocathode injector and a main accelerator with 9-cell cavity. It will provide high quality electron beams with 1 mA average current and 20 MeV energy.