DEFLECTING CAVITY OPTIONS FOR RF BEAM SPREADER IN LCLS II December 4th, 2013

RF Spreader System Requirements CDR CHAPTER 7: ELECTRON COMPRESSION AND TRANSPORT 3-Way Beam Spreader Vertical Beam Separation Parameter Value Unit Electron energy 4.0 GeV Angle of deflection (θdef) 0.75 / 1.0 mrad Transverse voltage (VT) 3.0 / 4.0 MV RF frequency (f) 325 MHz Three rf cavity design options Superconducting rf-dipole cavity Normal conducting rf-dipole cavity Normal conducting 4-rod cavity

Superconducting RF-Dipole Cavity RF-Dipole Design RF Fields and Surface Fields Beam aperture of 40 mm Considering cavity processing Low wakefield impedance budget Any dimensional constraints ? Cavity Length = 70 cm Bar length = 41 cm Bar height = 4.4 cm θ Angle = 50 deg Cavity diameter = 34 cm SC RFD Cavity Units Frequency 325 MHz Nearest HOM 508 VT* 0.46 MV Ep* 2.6 MV/m Bp* 3.6 mT Bp*/Ep* 1.4 mT/ (MV/m) U* 0.049 J [R/Q]T 2133 Ω Geometrical Factor 91.5 RTRS 1.95×105 Ω2 At ET* = 1 MV/m Electric field Magnetic field

Superconducting RF-Dipole Cavity Required deflection can be achieved by one cavity Compensation for beam loading Only fundamental deflecting mode is considered At a beam offset of 5 mm with a transverse voltage variation of δVT = 0.002VT Average beam current of 0.02 mA Multipacting is expected to be processed easily No lower order modes Widely separated HOMs Reduced field non-uniformity with increased bar height VT 4.0 MV Ep 23 MV/m Bp 32 mT Operating Temperature 2.0 / 4.2 K Surface Resistance (RS) [Rres = 10 nΩ] 10.9 / 58.7 nΩ Q0 8.4 / 1.6 ×109 Power Dissipation (Pdiss) 0.9 / 4.8 W QL 5.5×106 Loaded Bandwidth 59 Hz Compensation for beam loading 1.4 kW 183 MHz

Field Non-Uniformity Shaped loading elements To reduce filed non-uniformity across the beam aperture Suppress higher order multipole components Voltage deviation at 20 mm Horizontal: 5.0%  0.2% Vertical: 5.5%  2.4% (A) (B)

Current RF-Dipole Cavities 499 MHz Deflecting Cavity for Jefferson Lab 12 GeV Upgrade 400 MHz Crabbing Cavity for LHC High Luminosity Upgrade Deflecting voltage – 3.8 MV Total crabbing voltage – 13.4 MV per beam per side Per cavity – 3.4 MV 750 MHz Crabbing Cavity for MEIC* Crabbing voltage Electron beam – 1.5 MV Proton beam – 8.0 MV *A. Castilla et.al., in Proceedings of the 3rd IPAC, New Orleans, Louisiana (2012), p. 2447.

Properties of RF-Dipole Cavity Designs 499 MHz Deflecting Cavity for Jefferson Lab 12 GeV Upgrade Frequency 499.0 400.0 750.0 MHz Aperture Diameter (d) 40.0 84.0 60.0 mm d/(λ/2) 0.133 0.224 0.3 LOM None Nearest HOM 777.0 589.5 1062.5 Ep* 2.86 3.9 4.29 MV/m Bp* 4.38 7.13 9.3 mT Bp*/Ep* 1.53 1.83 2.16 mT/ (MV/m) [R/Q]T 982.5 287.0 125.0 Ω Geometrical Factor (G) 105.9 140.9 136.0 RTRS 1.0×105 4.0×104 1.7×104 Ω2 At ET* = 1 MV/m 24 cm 44 cm 400 MHz Crabbing Cavity for LHC High Luminosity Upgrade 34 cm 53 cm 750 MHz Crabbing Cavity for MEIC at Jefferson Lab* 19 cm 35 cm *A. Castilla et.al., in Proceedings of the 3rd IPAC, New Orleans, Louisiana (2012), p. 2447.

499 MHz RF-Dipole Cavity Multipacting was easily processed during the 4.2 K rf test Design requirement of 3.78 MV can be achieved with 1 cavities Achieved fields at 2.0 K ET = 14 MV/m VT = 4.2 MV EP = 40 MV/m BP = 61.3 mT Quench 3.78

400 MHz RF-Dipole Cavity Multipacting levels were easily processed Achieved fields at 4.2 K ET = 11.6 MV/m VT = 4.35 MV EP = 47 MV/m BP = 82 mT Limited by rf power at 4.2 K Achieved fields at 2.0 K ET = 18.6 MV/m VT = 7.0 MV EP = 75 MV/m BP = 131 mT 3.4 5.0 Quench Limited by rf power Multipacting levels observed below 2.5 MV Design goal – 10 MV Multipacting levels observed below 2.5 MV

Normal Conducting RF-Dipole Cavity RF-Dipole Design * RF Fields and Surface Fields Beam aperture of 25 mm Due to the dependence on transverse shunt impedance (RT) Considering cavity processing Bar length = 31 cm Cavity length = 37 cm Cavity height = 26 cm Bar height = 1.5 cm Bar width = 6 cm Cavity width = 15 cm NC RFD Cavity Units Frequency 325 MHz Nearest HOM 518 VT* 0.46 MV Ep* 3.2 MV/m Bp* 3.8 mT [R/Q]T 8367 Ω Geometrical Factor 48.3 RTRS 4.0×105 Ω2 At ET* = 1 MV/m Electric field Magnetic field * T. Luo, D. Summers, D. Li, “Design of a Normal Conducting RF-dipole Deflecting Cavity”, in Proceedings of the 2013 International Particle Accelerator Conference, Shanghai, China, WEPFI091

Normal Conducting RF-Dipole Cavity Total Power Requirement VT 4.0 MV Ep 28 MV/m Bp 33 mT Surface Resistance (RS) 4.7 mΩ Shunt Impedance (RT) 86 MΩ Q0 1.03×104 Power Dissipation (Pdiss) 186 kW Peak dPdiss/dA 158 W/cm2 Per Cavity Power Requirement VT per cavity 0.67 MV Ep 4.7 MV/m Bp 5.5 mT Q0 1.03×104 No. of Cavities 6 Power Dissipation (Pdiss) per cavity 5.2 kW Peak dPdiss/dA per cavity 4.4 W/cm2 Total deflection can be achieved by 6 cavities Surface heating at the loading elements are reduced by curving and requires cooling RF properties can be further improved with reduced beam aperture

Normal Conducting 4-Rod Cavity 4-Rod Design * RF Fields and Surface Fields Beam aperture of 25 mm Due to strong relation with shunt impedance (RT) Cavity diameter = 45 cm Cavity length = 45 cm Rod diameter = 3.1 cm Rod length = 21 cm Rod gap = 2 cm NC RFD Cavity Units Frequency 325 MHz Nearest HOM 518 LOM 226 VT* 0.46 MV Ep* 3.4 MV/m Bp* 7.2 mT [R/Q]T 1.9×104 Ω Geometrical Factor 37.3 RTRS 7.2×105 Ω2 At ET* = 1 MV/m Magnetic field Electric field * C.W. Leemann, C. G. Yao, “A Highly Effective Deflecting Structure” in Proceedings of the 1990 Linear Accelerator Conference, Albuquerque, New Mexico, p. 232

Normal Conducting 4-Rod Cavity Total Power Requirement VT 4.0 MV Ep 29 MV/m Bp 63 mT Surface Resistance (RS) 4.7 mΩ Shunt Impedance (RT) 153 MΩ Q0 8.0×103 Power Dissipation (Pdiss) 104.4 kW Peak dPdiss/dA 583 W/cm2 Per Cavity Power Requirement VT per cavity 1.0 MV Ep 7.3 MV/m Bp 15.8 mT Q0 8.0×103 No. of Cavities 4 Power Dissipation (Pdiss) per cavity 6.5 kW Peak dPdiss/dA per cavity 36 W/cm2 Total deflection can be achieved by 4 cavities Localized surface magnetic field has higher cooling requirements per cavity Surface heating at the end of the rods requires cooling RF properties can be substantially improved with reduced beam aperture, compared to NC RFD cavity

499 MHz Normal Conducting 4-Rod Cavity 499 MHz 2-cell 4-rod cavity* Cu coated stainless steel can Uses parallel cooling mechanism RF power coupled using magnetic coupling at the end of the cavity Maximum reached rf power = 5.2 kW Limited by the cooling of rf power coupler 2-cell 4-rod cavity Frequency 499 MHz Shunt Impedance (RT) 210 MΩ QL 2.5×103 Q0 5.0×103 VT ~ 0.75 MV Max Power Dissipation (Pdiss) per cavity 5.2 kW * C. Hovater, G. Arnold, J. Fugitt, L. Harwood, R. Kazimi, G. Lahti, J. Mammosser, R. Nelson, C. Piller, L. Turlington, “The CEBAF RF Separator System”, in Proceedings of the 1996 Linear Accelerator Conference, Geneva, Switzerland, p. 77.

Summary Total deflection of 4.0 MV can be achieved by one cavity using the SC RF-Dipole Cavity Considering the distance between rf spreader system and end of linac needs to look into liquid He supply by A transfer line A separate refrigerator NC RFD requires 6 cavities and has low rf power requirements NC 4-Rod cavity requires 4 cavities Similar rf cavity is currently being used successfully at Jefferson Lab rf separator system SC RFD NC RFD NC 4-Rod Units Frequency 325 MHz LOM - None Nearest HOM 508 518 349 VT* 0.46 MV Ep* 2.6 3.2 3.4 MV/m Bp* 3.6 3.8 7.2 mT RTRS 1.95×105 4.0×105 7.2×105 Ω2 No. of cavities 1 6 4 VT per cavity 4.0 0.67 1.0 Pdiss per caivty 4.8 (At 4.2 K) 5.2×103 6.5×103 W At ET* = 1 MV/m