Author: Du, Y.-C.
Paper Title Page
TUPC109 Electron Bunch Slice Emittance Measurement with the Space Charge Effects* 1272
 
  • C. Li, Y.-C. Du, W.-H. Huang, C.-X. Tang, L.X. Yan
    TUB, Beijing, People's Republic of China
  
  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. 		 
 
TUPC110 Ultrashort Bunch Train Longitudinal Diagnostics using RF Deflecting Structure 1275
 
  • Y. Yang, H. Chen, Y.-C. Du, W.-H. Huang, C. Li, L.X. Yan
    TUB, Beijing, People's Republic of China
  
  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
 
  • 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.