| Paper | Title | Page |
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| TUPC109 | Electron Bunch Slice Emittance Measurement with the Space Charge Effects* | 1272 |
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Funding: supported by the National Natural Science Foundation of China (Grant Nos. 10735050, 10805031, 10875070 and 10925523), and the National Basic Research Program of China (Grant No. 2007CB815102). Since slice transverse emittance of the electron beam is critical to a high-gain short-wavelength FEL, its characterization is very important. For space charge dominated electron beam, conventional emittance measurement techniques, such as solenoid scanning and quadruple scanning, without considering space charge forces lead to large errors of emittance evaluations. This essay introduces a modified solenoid-scan method of slice emittance measurement for space charge dominated beam, and simulations show that the new method brings the emittance evaluations much closer to actual values. |
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| TUPC110 | Ultrashort Bunch Train Longitudinal Diagnostics using RF Deflecting Structure | 1275 |
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| Ultrashort electron bunch train has been produced using UV laser stacking in Tsinghua University. With an S-band deflecting cavity inserted into the Tsinghua Thomson Scattering beamline, it is possible to characterize the bunch train longitudinal property. This paper briefly introduced the measurement layout in our lab and reported the recent experiment results, including bunch train profile measurement and longitudinal phase space. The main sources of error are also discussed. | ||
| THPC120 | Experimental Investigation of Photocathode Thermal Emittance Components with a Copper Cathode* | 3167 |
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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) |
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| THPC121 | Design and Cold Tests of a Prototype photocathode RF Gun for Shanghai SXFEL Facility | 3170 |
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| 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. | ||