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Minimized emittance for high charge with multi cell superconducting guns and solenoidal focusing

This study explores the optimization of transverse emittance in multi-cell superconducting guns with solenoidal focusing using a simplex minimization routine. The results show a decrease in emittance with RF focusing and the impact of solenoid distance on emittance.

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Minimized emittance for high charge with multi cell superconducting guns and solenoidal focusing

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  1. Minimized emittance for high charge with multi cell superconducting guns and solenoidal focusing D. Lipka, BESSY

  2. Setup and goal for the simulation solenoid ½ n= 1 2 3 … one module with 8 cavities TESLA cavity superconducting gun without RF focusing Minimize transverse emittance at the end of the module by vary injector parameters with simplex minimization routine D. Lipka, BESSY

  3. Tool for the optimization • Beam dynamic simulation with Astra • ROOT program calls Astra and reads the result • Implemented Simplex minimization routine in ROOT changes the parameters to find the minimum transverse emittance (multi dimensional minimization routine) D. Lipka, BESSY

  4. Simplex n = 1 n = 2 NELDER and MEAD D. Lipka, BESSY

  5. Basic simplex n = 2 D. Lipka, BESSY

  6. Simplex reflection stretching n = 2 flattening contraction D. Lipka, BESSY

  7. Parameters of the simulation • Fixed parameters • Q = 2.5 nC (BESSY FEL mode) • Fall and rise time of Flat Top laser distribution = 4 ps • Emax,gun = 60 MV/m • Emax, last 4 TESLA cavities = 32 MV/m • Distance peak solenoid field to cathode (magnetic field at full cell lower than 3 mT): • n = 1: 0.6 m • n = 2: 0.7 m • n = 3: 1.0 m • Varied parameters • RMS transverse laser size (thermal emittance scaled accordingly): 0.1 – 3 mm • FWHM laser duration: 15 – 100 ps • Bmax: 0 – 0.4 T • Distance cathode to middle of first TESLA cavity (complete module is moved accordingly): 1 – 7 m • Each Emax of first 4 TESLA cavities: 5 – 33 MV/m  8 parameters D. Lipka, BESSY

  8. Result: beam size n = 1 n = 2 n = 3 D. Lipka, BESSY

  9. Result: transverse emittance Difference between n = 1,2 and n = 3 caused by larger solenoid distance D. Lipka, BESSY

  10. Result: RF focusing of 3 ½ cell gun beam size transverse emittance with RF focusing decrease of transverse emittance D. Lipka, BESSY

  11. Summary • developed tool to minimize transverse emittance with Astra and ROOT • investigated n ½ superconducting cell guns (n = 1, 2, 3) without RF focusing with 8 parameters • solenoid has certain distance to cathode to keep superconductivity • n = 3 gives larger emittance • with RF focusing transverse emittance decreased D. Lipka, BESSY

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