Electric Field Amplitude (MV/m) The RF System of the Probe Beam Linac in CTF3 Franck Peauger, Alban Mosnier, Daniel Bogard, Gilles Dispau, Wilfrid Farabolini, Patrick Girardot, Jean Luc Jannin, CEA/DSM/DAPNIA, 91191 Gif-sur-Yvette Cedex, France Alexej Grudiev, Gerard Mcmonagle, Jean Mourier, CERN, Geneva, Switzerland Probe Beam Linac Parameters Schematic layout of CTF3 The probe beam linac aims at simulating the main beam of CLIC in order to measure precisely the performances of the 30 GHz accelerating structures Abstract: The probe beam Linac in CTF3 will simulate the main beam of CLIC in order to measure precisely the performances of the 30 GHz accelerating structures. The poster shows a layout of the probe beam linac and its RF system. Three important points are described in details: the use of a RF pulse compression cavity to increase the RF power, the development of a high power phase shifter to control the bunch length and transient simulations of the accelerating field in the RF structure to determine the best RF pulse shape to be provided. Introduction: The Compact Linear Collider (CLIC) is a study of a linear multi TeV collider. The test facility CTF3 will demonstrate the RF power generation scheme. This 30 GHz high power RF is exacted from a drive beam, running parallel to the main beam. The probe beam Linac in CTF3 will simulate the main beam in order to measure precisely the performances of the CLIC 30 GHz accelerating structures. The RF power of the probe beam linac is produced by a single 45 MW klystron working at 3 GHz. A pulse compression system increased the power up to 90 MW and a distibution network divides the power into four arms. Schematic layout of the probe beam linac (CALIFES) Parameters Specifications Observations Energy 200 Mev Avoid beam disruption in high RF fields Norm. rms emittance < 20 π mm mrad Fit in 30 GHz structure acceptance Energy spread <  2 % Measurement resolution Bunch charge Bunch spacing 0.2 nC 0.33 ns ~ CLIC Parameters Number of bunches 1 – 64 Measure 30 GHz structure transients Rms bunchlength < 0.75 ps Acceleration with 30 GHz 0.33 ns 3 GHz Bunch length < 0.75 ps DAPNIA / IN2P3 / CERN Collaboration 30 GHz 33 ps RF Gun Layout of the RF System Power phase shifter TE10□ E Field H Field RF Generator 2.99855 GHz Slow Phase Shifter 360 ° Fast Phase Shifter 180 ° Solid State Pre-amplifier The Power Phase Shifter is a 3 GHz scaling of the one studied at SLAC at 11.4 GHz and consists of a circular waveguide operating on the TE01 mode and two wrap-around mode converter The circular waveguide has an area with an expanded diameter, inducing a reduction of the waveguide length. The length of this widened guide can be varied to produce a phase variation. PFN (25 cells) 320 kV – 360 A 7.6 µs – 5 Hz 300 W – 3 GHz TE01○  0.25% ripple during 5.5 µs 45 MW – 3 GHz Klystron DC Power Supply + - Thyratron 21.5kV Pulse Transformer SF6 1:15 45 MW – 5.5 µs BOC Cavity Klystron Gallery Beam Tunnel Parameters Specifications Peak RF Power 25 MW Sensitivity 1° / mm Maximum course 200 mm Precision 0.5 ° Stability 0.1 ° Bandwidth |S11| < 27 MHz @ -30 dB 90 MW 90 MW – 1.4 µs 4.5 dB Splitter W Electric field simulation (HFSS) The RF components operates mainly under a vacuum of 10-9 mbar. Losses in rectangular waveguides are 0.02 dB/m (WR284 in Copper) 4.5 dB Splitter Circ 3 dB Splitter SF6 Ampl Phase adjustment by length of waveguides Power Phase Shifter F Taking into account the losses in RF components, a total power of approximately 70 MW is delivered to the linac, W F = - 90° F = 0 ° F = 0 ° Electric field superposition for two positions 7 MW 15 MW 25 MW 22 MW TW Acceleration TW Acceleration SW Gun TW bunching bellows 3D mechanical model Surface = 1535 x 400 mm, Heigth = 508 mm Weight = 270 kg 2D mechanical drawing Pulse compressor cavity Transient calculation in traveling wave section E Field A specific code, based on the coupled resonator model has been developed to study the transient effects in the traveling wave sections Kn-1 Kn H Field The Pulse compressor system is based on a high Q0 storage cavity working on a “whispering gallery” mode TM10, 1, 1 Q0 = 197 800 (calculated with HFSS) f0 = 2.9985 GHz β = Qx / Q0 = 6 n-1 n n+1 The LIL section is a quasi constant gradient structure, composed of 9 constant impedance families linked by 4 linearly tapered transition cells Vn-1 Vn Vn+1 Yn Lkn-1 Lkn Lkn+1 Vg Vr Good directivity provided by λg/4 multi-hole coupler Equivalent circuit differential equation relative to cell n Φg(t) ic(t) 1 Forward wave Vg vg(t) vc(t) G C L Backward wave Vr = Vc - Vg Differential equation For a phase step of 57°, and a phase variation until 180° over the total pulse length, Filling time Reflection coefficient Electric Field Amplitude (MV/m) Approximations : Sinusoidal voltage A flat top pulse is obtained : - Voltage amplification factor = 1.45 - Power amplification factor = 2.1 - Vg varies slowly compared to Time (s) Cell number - High Q0 factor franck.peauger@cea.fr