About NSRRC / Organization

Light Source Division > High Brightness Injector Group

High brightness beams are streams of high intensity charged particles of low emittance. Emittance is the figure-of-merit of a charged particle beam in a particle accelerator. It is a measure for the average spread of particle coordinates in six-dimensional position-momentum phase space. It has the dimension of length times angle (i.e. meter-radians). A beam of smaller emittance implies a beam of better quality. The beam emittance produced by the current advanced high-brightness beam technology can be much smaller than 10 mm-mrad. High brightness electron beam injector is the key technology of next generation light sources such as X-ray free electron lasers and inverse Compton scattering etc. In-house development of a laser-driven photocathode microwave electron gun system was started in 2006. In the past several years, we have accumulated experiences on high energy ultrafast lasers, high power microwaves, low emittance electron sources and high-brightness electron beam design. Operation of the first photocathode rf gun system in the country has been successful in delivering high brightness electron beam since March 2013. The NSRRC High Brightness Injector Group has been set up in April 2014. Our efforts have been focused on the continuous improvement of the photocathode rf gun system performance. We also pursue for a high brightness linac system that can be used for novel light source R&D aggressively. This linac system is now being installed in the accelerator test area (ATA) at NSRRC.

Coherent THz radiations driven by the high brightness photoinjector

Generation of a low-emittance electron beam from the laser-driven photoinjector has been carried out by the High Brightness Injector Group. An ultrashort electron bunch of ~ 500 fs bunch length and few tens MeV beam energy has been produced from the photoinjector linac in which the beam is accelerated and compressed simultaneously via the velocity bunching mechanism in the rf linac. Tunable, high-energy and narrow-band coherent THz radiation has been be generated from a U100 planar undulator when it is driven by such beam. In the meantime, broadband, single-cycle coherent THz transition radiation can also be generated by passing this beam through an Al foil.

Table 1 Specifications of the high brightness photoinjector
beam charge (pC) 100
beam energy (MeV) 62
bunch length (ps, 1σ) 1.27
normalized emittance (mm-mrad) 10
repetition rate (Hz) 10


Table 2 Specifications of coherent THz sources
parameters coherent transition radiation coherent undulator radiation
beam charge (pC) 210 280
beam energy (MeV) 17.7 17.7
bunch length (fs, rms) 490 490
central frequency (THz) -- 0.62
bandwidth -- 15%
output energy (μJ) 6.7 26.4
repetition rate (Hz) 10 10
average power 67 μW 264 μW
peak power 9.4 MW 530 kW
photocadthode rf gun and pulsed Klystron system
high energy ultrafast laser system
high brightness photoinjector and setup of coherent THz sources
English NameJob Responsibilities
Wai-Keung Lau
  • High brightness linear accelerator R&D
An-ping Lee*
  • High brightness linac maintenance and upgrade, linac-based light source R&D
Hsin-Pai Hsueh
  • Design and manufacturing for electron diagnostic and monitor system on vacuum system
Jiing-Yi Hwang
  • High power microwave system maintenance and upgrade
Ming-Chang Chou
  • Ultrafast laser system maintenance and upgrade, studies of laser-beam interaction in accelerators
* Group Leader