Emittance measurement &amp; optimization for the photocathode RF gun with laser profile shaping

LIU Sheng-Guang; Masafumi Fukuda; Sakae Araki; Nobuhiro Terunuma; Junji Urakawa

doi:10.1088/1674-1137/34/5/014

Chinese Physics C> 2010, Vol. 34> Issue(5) : 584-588 DOI: 10.1088/1674-1137/34/5/014

Emittance measurement & optimization for the photocathode RF gun with laser profile shaping

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Abstract：
The Laser Undulator Compact X-ray source (LUCX) is a test bench for a compact high brightness X-ray generator, based on inverse Compton Scattering at KEK, which requires high intensity multi-bunch trains with low transverse emittance. A photocathode RF gun with emittance compensation solenoid is used as an electron source. Much endeavor has been made to increase the beam intensity in the multi-bunch trains. The cavity of the RF gun is tuned into an unbalanced field in order to reduce space charge effects, so that the field gradient on the cathode surface is relatively higher when the forward RF power into gun cavity is not high enough. A laser profile shaper is employed to convert the driving laser profile from Gaussian into uniform. In this research we seek to find the optimized operational conditions for the decrease of the transverse emittance. With the uniform driving laser and the unbalanced RF gun, the RMS transverse emittance of a 1 nC bunch has been improved effectively from 5.46 πmm・mrad to 3.66 πmm・mrad.

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LIU Sheng-Guang, Masafumi Fukuda, Sakae Araki, Nobuhiro Terunuma and Junji Urakawa. Emittance measurement & optimization for the photocathode RF gun with laser profile shaping[J]. Chinese Physics C, 2010, 34(5): 584-588. doi: 10.1088/1674-1137/34/5/014

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Received: 2009-07-13
Revised: 2009-09-29

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沈阳化工大学材料科学与工程学院沈阳 110142

Emittance measurement & optimization for the photocathode RF gun with laser profile shaping

Corresponding author: LIU Sheng-Guang,

Received Date: 2009-07-13
Accepted Date: 2009-09-29
Available Online: 2010-05-05

Abstract:

The Laser Undulator Compact X-ray source (LUCX) is a test bench for a compact high brightness X-ray generator, based on inverse Compton Scattering at KEK, which requires high intensity multi-bunch trains with low transverse emittance. A photocathode RF gun with emittance compensation solenoid is used as an electron source. Much endeavor has been made to increase the beam intensity in the multi-bunch trains. The cavity of the RF gun is tuned into an unbalanced field in order to reduce space charge effects, so that the field gradient on the cathode surface is relatively higher when the forward RF power into gun cavity is not high enough. A laser profile shaper is employed to convert the driving laser profile from Gaussian into uniform. In this research we seek to find the optimized operational conditions for the decrease of the transverse emittance. With the uniform driving laser and the unbalanced RF gun, the RMS transverse emittance of a 1 nC bunch has been improved effectively from 5.46 πmm・mrad to 3.66 πmm・mrad.