Dao Xiang

First principle measurements of thermal emittance for copper and magnesium

There are growing interests in generation, preservation and applications of high brightness electron beam. With the rapid development in the techniques for emittance compensation, laser shaping and generation of ellipsoidal beam, we are approaching the limit--the uncorrelated thermal emittance. In this paper, we describe the design of the angle-resolved photoemission spectroscopy for measurements of thermal emittance for Cu and Mg. The measurement is conducted in a field-free region. The energy spectrum and angular distribution of the electrons will be measured immediately after its emission and further used to reconstruct the initial phase space and the corresponding thermal emittance. We also show how cathode surface roughness and laser incidence angle as well as its polarization state affect the quantum efficiency and thermal emittance.

High power beam test and measurement of emittance evolution of a 1.6-cell photocathode RF gun at Pohang accelerator laboratory

A Brookhaven National Laboratory (BNL) GUN-IV type photocathode rf gun has been fabricated to use in femtosecond electron diffraction (FED), femtosecond far infrared radiation (fs-FIR) facility, and X-ray free electron laser (XFEL) facilities at the Pohang Accelerator Laboratory (PAL). The gun consists of a 1.6-cell cavity with a copper cathode, a solenoid magnet, beam diagnostic components and auxiliary systems. We report here the measurement of the basic beam parameters which confirm a successful fabrication of the photocathode RF gun system. The emittance evolution is measured by an emittance meter and compared with the PARMELA simulation, which shows a good agreement.

Multiple parameter characterizations for electron beam with diffraction radiation

There are growing interests in developing non-intercepting method for real-time monitoring electron beam parameters for international linear collider (ILC) and X-ray free electron lasers (XFEL). In this paper we briefly review the theories on using optical and coherent diffraction radiation (ODR and CDR) to measure electron beam profile, divergence, emittance and bunch length. We focus on using ODR to direct image electron beam profile. A new method for bunch length measurement with diffraction radiation deflector is introduced. We also report the preliminary study on radiation spectrum distortion that generally occurs when using CDR to measure bunch length with Martin-Puplett or Michelson interferometers.

Status of the photocathode RF gun at tsinghua university

A photocathode RF gun system was built to develop the electron source for the Thomson scattering X-ray source at Accelerator laboratory of Tsinghua University. The system consists of a BNL/ATF type 1.6 cell S-band RF cavity, a solenoid for emittance compensation, a laser system and some simple equipments for beam diagnosis. The status of the system is introduced in this paper, and the first beam measurements of the photocathode RF gun, including the dark current, transverse beam profile, charge and quantum efficiency is also reported.

Experimental approaches for the beam dynamics study in the PC RF gun at the PAL

A high-brightness electron beam is emitted from a photo-cathode (PC) RF gun for use in the FIR (Far Infrared) facility being built at the Pohang Accelerator Laboratory (PAL). The beam dynamics study for the PAL XFEL injector is essential to generate low emittance electron beam from the PC RF gun. The XFEL injector requires 1 nC beam with short bunch length and low emittance. These conditions are simulated with PARMELA code and then are realized on experimental conditions. The experimental conditions for the XFEL injector are measured with beam diagnostic devices such as ICT and Faraday cup for charge measurement, a spectrometer for beam energy measurement. In this article, we present the experimental approaches of the beam dynamics study for the XFEL injector.