Optimization of CLIC-G structure & Design of CLIC open structure Hao Zha, Alexej Grudiev (CERN) Valery Dolgashev (SLAC) 27/01/2015

Optimization of CLIC-G structure CLIC-G design : current base line design Magnetic field is determined by geometry of wall and waveguide Beam axis b c ac=eow*bc bc iw/2 w/2 ldw 45 o rdw Frequency11.994GHz Cells26+2 coupler Active length230mm Iris aperture2.35~3.15mm

Width=11mm Opening=8mm Study on waveguide geometry Width↓, damping ↑, H-field↓, Opening↓, damping ↓, H-field↓, => Width↓, Opening↓, same damping, H-field↓↓.

Optimum waveguide geometry There is optimum (on H-field) solution of width and opening. Damping effect keep same. CellsOptimized width & opening Widthopening First9.9mm7.98mm Middle9.8mm7.94mm Last9.7mm7.90mm

New CLIC-G design ParametersCLIC-GCLIC-G-New waveguide Maximum electric field235MV/m236MV/m Maximum Sc5.58MW/mm25.48MW/mm2↓ Maximum Pulse T-rise47.1 K44.6 K↓ Peak power61.3MW60.3MW↓ Filling time67ns65ns↓

safety distance Compact waveguides Large safety distance reduce power penetration at the RF loads. Original safety distance: 50~55mm New design : 35~40mm Diameter decrease: 3cm ~15mm

Wall rounding > Large rounding may reduce manufacturing cost significantly*. > However, pulse ΔT increase. > No conclusion now. CLIC-G original By optimized on waveguide R = 0.5mmR = 2.5mm *Courtesy of Nuria Catalan Lasheras

Wall shape optimization Elliptical Polynomial

Wall shape optimization ParametersCLIC-GCLIC-G-New waveguide CLIC-G-New waveguide Polynomial wall shape Maximum electric field235MV/m236MV/m238MV/m↑ Maximum Sc5.58MW/mm25.48MW/mm2↓5.42MW/mm2↓↓ Maximum Pulse T-rise47.1 K44.6 K↓41.6K↓↓ Peak power61.3MW60.3MW↓59.8MW↓↓ Filling time67ns65ns66ns CLIC-G Polynomial wall shape

Conclusion & future plan We optimized the waveguide shape to gain lower pulse T-rise and more compact waveguide design. Need more investigate on the rounding and polynomial wall shape. Future: optimize on the tapering of iris aperture. Goal: Lower cost, lower input power, lower surface field.

CLIC open structure

Gap and rounding Gap will cut off fields, but still some electric field near the iris gap. This may cause multi-pacting. Elliptical rounding has identical profile to that of iris: easier manufacturing. Regular rounding Elliptical rounding Electric field in the gap

Gap and rounding Small gap has lower field, but has risk of multipacting. We took 1mm as current design. Elliptical rounding has lower field (except for a little bit higher H- field)

Race track cell Due to limitation of milling head, there is a flat section in the cell profile => race track cells (like muffin-tin cells) Milling head

race track cell Optimum solution: Fx = 4mm, Fy = 1.2mm (minimum value).

Full structure ParametersCLIC-G undamped CLIC-G open Shunt impedance86/103116/150107/137 Vg [%c]1.66/ / /1.06 Maximum Es field [MV/m] Maximum Sc[MW/mm2] Maximum Pulse T [K] Peak power [MW] Filling time [ns]

Conclusion & Future plan We designed a open un-damped X-band accelerating structure for CLIC. We optimized on the gap dimension, geometry of rounding and cell profile, to get lower surface field. We design coupler and full structure, which had been already manufactured. Cold test and brazing are still undergoing in SLAC. In future prototype will be delivered to CERN for high power test.

Thanks!