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R.F.AND HIGH VOLTAGE SYSTEMS FOR IR-FEL (CUTE FEL) IN INDIA Umesh Kale Beam Physics & FEL Lab Raja Ramanna Centre for Advanced Technology, Indore 452 013 INJECTOR For CUTE FEL Pre-buncher @ 476MHz Pulser + Power supplies 50kW , 476MHz RF Source buncher @ 2856MHz PWT @ 2856MHz 10MW,2856MHz RF system LLRF & HPM Undulator Pulsed thermionic GUN Terahertz FEL Wave length region : 80 um , 10ps pulses Peak power : 1MW, Average power 1W Beam Energy : 10MeV Already made Under way MODULATOR Beam Dump INJECTOR For CUTE FEL Pre-buncher @ 476MHz Pulser + Power supplies 50kW , 476MHz RF Source buncher @ 2856MHz PWT @ 2856MHz 10MW,2856MHz RF system LLRF & HPM Undulator Pulsed thermionic GUN Terahertz FEL Wave length region : 80 um , 10ps pulses Peak power : 1MW, Average power 1W Beam Energy : 10MeV MODULATOR Beam Dump •PWT LINAC: 2856MHz •BUNCHER : 2856MHz •PRE BUNCHER :476MHZ •GUN : 36.6 MHz Pre - Buncher • A single cell re-entrant type pill box cavity with nose cone at 476MHz. It prebunches the beam to minimize current loss. • RF power for the pre-buncher : ~ 30kW @ 476MHz •Cavity developed put in the beam line. • Procurement of Planner triode based multistage amplifier is underway. (JPAW,USA) Buncher • A 4-cell PWT ( Plane wave transformer) LINAC developed indigenously . • Around 3MW RF power @ 2856MHz for ~4MeV energy gain. • 10MW RF system @ 2856MHz delivers power to both Buncher & Accelerator. Accelerator •A 8-cell PWT ( Plane wave transformer) LINAC developed indigenously . • Around 8MW RF power @ 2856MHz for 7.5MeV energy gain. • RF system for Buncher & Accelerator ready. PULSED THERMIONIC GUN ( CCR, USA InC.) • Thermionic gun with grided dispenser cathode • Beam energy : 90keV , Charge : 1nC & Pulse width : 1ns FWHM •Pulse separation : 27.3 ns ( @ 36.615MHz) dictated by the one round trip time of the optical pulse in 4.1m long optical cavity. •Normalized emittance : 15 pi-mm-mrad ( rms) & Energy spread : <1% • Macro-pulse duration : 10us @ 10Hz ( Max) • Operating cathode voltage is -90kV, grid is negatively biased with -150V and a fast pulser applies 200V to drive 1A peak micro pulse current. • Spellman make -130kV,0.1mA HVDC power supply with 1nF intermediate energy storage capacitor bank supply 1A peak current. •A isolation transformer supply power to Filament P/S , BIASING P/s & pulser floating at -90kV . • Employed a crow bar system for the protection Gun in events of arcing. (maximum energy that can be dumped in the event of arc is 1J ). But stored energy is 4J. • COMMISSIONING IS UNDERWAY. LLRF ( Low level RF ) • Synchronized operation of GUN , modulator & low power RF • SG1 operated with internal in-built 10MHz source & SG-2 operated from SG-1 externally. •SRS delay generator triggers the SG-1 ,gun controller & modulator. • Pulse modulation of 2856MHz done internally in SG-1. • Pulse modulated low power RF pulse is set inside the high voltage pulse in flat portion to avoid false triggering, any phase change. • Complete system is operated remotely. TTL, 10us @ 1-10Hz SG-1 VA1 2856MHz 36.615MHz GUN controller SG-2 TTL, 10us @ 1-10Hz DG 535 90kV thermionic gun ( procured from CCR Inc. ,USA) Modulator TTL, 10us @ 1-10Hz Low power RF line for present set up ( pre-buncher is not energized) RF System & Modulator Specification of 10MW klystron Specification of 25MW line type modulator Circulator High power RF • WR284 based transport line. •Presently RF transport line is pressurized with N2 at 4 bar. • Circulator has provision for installing arc detector. (AFT make) • Each line has one circulator , phase shifter and dual directional coupler for protection,phase adjustment and power measurement. Chiller Micro -controller Analog/Digital control High power RF line L2 L1 30H D1 L3 L3 L3 R3 C3 R 1 0 2 Y 1 0 2 B 1 2 U4 HVDC P/S, EHT xmer, 12 pulse rectifier + LC filter R1 C3 C1 R2 C2 N 0 Interlocked for Low flow Droor interlock Scram Ref 0-10V 0 TTL from SRS delay generator Driver 0 0 TX4 0 Reservior Heater Core bias P/s Filament Heater Micro -controller Analog/Digital control Modulator Block diagram Filament P/s Features • Line type modulator , PFN with mutual inductance • Resonant charging through charging inductor . • 15kV, 1A HVDC power supply , reg. <1%, Ripple <1% • HVDC power supply has two 6 pulse rectifier in series forming 12 pulse rectifier with LC filter. • 15 section PFN with mutually coupled inductors of 6 Ohm characteristic impedance. Total capacitance : 0.8 uF • E2V make 40kV, 10kA thyratron switch ( CX2609) used for discharging PFN. • Pulse transformer ( ratio 1:6 ) with reset core employed. • Provision to power filament through transformer secondaries. • Remotely operated using distributed control architecture 8 bit micro controllers placed locally using supervisory PCs in control room. • Lab-view based GUI •Interlocks for experimental hall door ,Vacuum of klystron, wave guide arcing, scram, low flow provided. All safety interlocks are relay based. • PFN voltage, klystron filament current, HVDC voltage are monitored remotely. • Modulator tested with klystron and dummy water load up to 7MW peak power. Modulator is operational since 2002. • Preliminary acceleration trials with 4-cell PWT performed. Electron beam form 2us,40keV DC thermionic gun accelerated up to 3.5MeV consuming ~ 4MW of RF power. Typical wave shape across the klystron Using the existing set up we have done the following experiments Conditioning of 4 cell buncher. Acceleration up to 4MeV using 4 cell PWT and a 2us DC thermionic gun. Transmission through undulator experiment. ( 60 % transmission measured) Problems encountered during commissioning Ringing on flat top of pulse due to stray inductance, capacitance. ( eliminated by putting an RC network across Pulse Transformer. However rise time affected) Damaging spikes through ground path. ( all components insulated from cabinet then grounded to ensure single point grounding), used MOVs, filters , faraday shield transformer for the electronics) Cabinet door with RF contact fingers helped in reduction of EMI generated noise. Tuning of PFN is difficult with this design. • These power supplies are basically SMPS buck converters with 100ppm stability developed in RRCAT Some photographs Pulse transformer 25MW Pulse Modulator Brazed components of PWT3 GUN THANKS