IPAC2011 - List of Authors (Qian, H.J.)

Paper	Title	Page
MOPC022	Development of a Compact C-band Photocathode RF Gun	116
	X.H. Liu, H. Chen, W.-H. Huang, H.J. Qian, C.-X. Tang, Z. Zhang TUB, Beijing, People's Republic of China
	Funding: This work is supported by National Natural Science Foundation of China and National Basic Research Program of China (973 Program). A C-band photocathode RF gun for a compact electron diffraction facility is developed in Tsinghua University, which is designed to work at the frequency of 5.712GHz. This paper presents the physics and structure design of this C-band RF gun, and the comparison on beam dynamics of S-band and C-band photoinjector has been done. Some new structure design will be adopted in this gun, including the optimized cavity length and elliptical iris, which is helpful to achieve lower emittance and larger mode separation.

THPC120	Experimental Investigation of Photocathode Thermal Emittance Components with a Copper Cathode*	3167
	H.J. Qian, Y.-C. Du, Hua, J.F. Hua, W.-H. Huang, C. Li, C.-X. Tang, L.X. Yan TUB, Beijing, People's Republic of China
	With progress of photocathode RF gun technology, thermal emittance has become the primary limitation of electron beam brightness. Extensive efforts have been devoted to study thermal emittance, but experiment results diverge between research groups and few can be well interpreted. One possibility is the undefined online cathode surface conditions, which may cause difference of work functions, field enhancement factor and surface roughness, and lead to thermal emittance divergence. In this paper, we report an experiment of characterizing online photocathode work function, field enhancement factor and surface roughness effect by measuring electric field dependence of photoemission quantum efficiency (QE) and thermal emittance in a Cu-cathode RF gun. Preliminary experiment results reveal huge thermal emittance contributed by surface roughness for the first time, and are in reasonable consistency with theoretical model prediction*. Ivan V. Bazarov et al., Phys. Rev. Lett. 10², 104801(2009) D.H. Dowell et al, Nucl. Instrum. Methods Phys. Res., Sect. A 622, 685 (2010). *D. Xinag et al, PAC’07, 10⁴⁹ (2007)

THPC121	Design and Cold Tests of a Prototype photocathode RF Gun for Shanghai SXFEL Facility	3170
	H.J. Qian, H. Chen, Y.-C. Du, W.-H. Huang, C. Li, X.H. Liu, X. H. Lu, C.-X. Tang TUB, Beijing, People's Republic of China
	A soft X-ray (~9 nm) FEL (SXFEL) facility is going to be constructed in Shanghai, China, which requires high charge (>500 pC) electron beam with low transverse emittance (<1.5 mm-mrad) at photoinjector exit. One of the keys to achieve a low emittance with high charge is high gradient on the photocathode, so an S-band photocathode RF gun modified from BNL type gun is designed, which aims running 100 MV/m peak gradient at 10 Hz. By changing the cathode seal technique, removing the insertion RF tuner, and reducing the peak surface field, RF breakdown possibility is reduced. Besides, RF pulse width is also considered to be reduced to lower the RF breakdown possibility. Since zero mode and multipole field degrades the beam emittance, they are also suppressed in the new gun design. Design details and cold testing results are presented in this paper.

Paper

Title

Page

Development of a Compact C-band Photocathode RF Gun

116

X.H. Liu, H. Chen, W.-H. Huang, H.J. Qian, C.-X. Tang, Z. Zhang
TUB, Beijing, People's Republic of China

Funding: This work is supported by National Natural Science Foundation of China and National Basic Research Program of China (973 Program).
A C-band photocathode RF gun for a compact electron diffraction facility is developed in Tsinghua University, which is designed to work at the frequency of 5.712GHz. This paper presents the physics and structure design of this C-band RF gun, and the comparison on beam dynamics of S-band and C-band photoinjector has been done. Some new structure design will be adopted in this gun, including the optimized cavity length and elliptical iris, which is helpful to achieve lower emittance and larger mode separation.

THPC120

Experimental Investigation of Photocathode Thermal Emittance Components with a Copper Cathode*

3167

H.J. Qian, Y.-C. Du, Hua, J.F. Hua, W.-H. Huang, C. Li, C.-X. Tang, L.X. Yan
TUB, Beijing, People's Republic of China

With progress of photocathode RF gun technology, thermal emittance has become the primary limitation of electron beam brightness*. Extensive efforts have been devoted to study thermal emittance, but experiment results diverge between research groups and few can be well interpreted**. One possibility is the undefined online cathode surface conditions, which may cause difference of work functions, field enhancement factor and surface roughness, and lead to thermal emittance divergence. In this paper, we report an experiment of characterizing online photocathode work function, field enhancement factor and surface roughness effect by measuring electric field dependence of photoemission quantum efficiency (QE) and thermal emittance in a Cu-cathode RF gun. Preliminary experiment results reveal huge thermal emittance contributed by surface roughness for the first time, and are in reasonable consistency with theoretical model prediction***.
*Ivan V. Bazarov et al., Phys. Rev. Lett. 10², 104801(2009)
** D.H. Dowell et al, Nucl. Instrum. Methods Phys. Res., Sect. A 622, 685 (2010).
***D. Xinag et al, PAC’07, 10⁴⁹ (2007)

THPC121

Design and Cold Tests of a Prototype photocathode RF Gun for Shanghai SXFEL Facility

3170

H.J. Qian, H. Chen, Y.-C. Du, W.-H. Huang, C. Li, X.H. Liu, X. H. Lu, C.-X. Tang
TUB, Beijing, People's Republic of China

A soft X-ray (~9 nm) FEL (SXFEL) facility is going to be constructed in Shanghai, China, which requires high charge (>500 pC) electron beam with low transverse emittance (<1.5 mm-mrad) at photoinjector exit. One of the keys to achieve a low emittance with high charge is high gradient on the photocathode, so an S-band photocathode RF gun modified from BNL type gun is designed, which aims running 100 MV/m peak gradient at 10 Hz. By changing the cathode seal technique, removing the insertion RF tuner, and reducing the peak surface field, RF breakdown possibility is reduced. Besides, RF pulse width is also considered to be reduced to lower the RF breakdown possibility. Since zero mode and multipole field degrades the beam emittance, they are also suppressed in the new gun design. Design details and cold testing results are presented in this paper.