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sLHC A magnetron solution for proton drivers Amos Dexter Simulation Using Tech-X’s VORPAL e.m. code SPL11 sLHC Collaborations Lancaster Richard Carter, Graeme Burt, Ben Hall, Chris Lingwood JLab Haipeng Wang, Robert Rimmer CEERI Shivendra Maurya, VVP Singh, Vishnu Srivastava TechX Jonathan Smith CERN ? ESS ? SPL11 sLHC The Reflection Amplifier • Linacs require accurate phase control • Phase control requires an amplifier Cavity • Magnetrons can be operated as reflection amplifiers Compared to Klystrons, in general Magnetrons Magnetron Load Circulator Injection Source - are smaller - more efficient - can use permanent magnets (at 704 MHz) - utilise lower d.c. voltage but higher current - are easier to manufacture Consequently they are much cheaper to purchase and operate J. Kline “The magnetron as a negative-resistance amplifier,” IRE Transactions on Electron Devices, vol. ED-8, Nov 1961 H.L. Thal and R.G. Lock, “Locking of magnetrons by an injected r.f. signal”, IEEE Trans. MTT, vol. 13, 1965 SPL11 sLHC Proof of principle Demonstration of CW 2.45 GHz magnetron driving a specially manufactured superconducting cavity in a VTF at JLab and the control of phase in the presence of microphonics was successful. Double Balance Mixer Phase shifter Spectrum Analyzer 1 Stub Tuner 2 Load 3 Loop Coupler Circulator 3 Oscilloscope Spectrum Analyzer 2 Stub Tuner 1 Loop Coupler 2.45 GHz Panasonic 2M137 1.2 kW Magnetron Phase shifter 1W Amplifier IQ Modulator (Amplitude & phase shifter) DAC DAC Digital Signal Processor Circulator 2 Load 2 Cathode heater control Load Oscilloscope ADC Digital Phase Detector HMC439 ÷2 LP Filter 8 kHz cut-off High Voltage Transformer ÷2 42 kHz Chopper Agilent E4428 signal generator providing 2.45 GHz 300 V DC +5% 120 Hz ripple Control voltage Pulse Width Modulator SG 2525 1.2 kW Power Supply SPL11 sLHC SCRF cavity powered with magnetron 0 0 Injection but magnetron off Power spectral density (dB) -20 Injection + magnetron on + control -10 Power spectral density (dB) -10 -30 -40 -50 -60 -70 -80 -90 -100 -20 -30 -40 -50 -60 -70 -80 -90 -110 -120 -500 -250 0 Frequency offset (Hz) 250 500 Power spectral density (dB) Cavity phase error (degrees) 0 Injection + magnetron on -10 -20 -30 -40 -50 -60 -70 -80 -250 0 Frequency offset (Hz) 250 -250 0 Frequency offset (Hz) 250 500 45 Control on 35 Control off 25 15 5 -5 -15 0.00 -90 -100 -500 -100 -500 0.01 500 SPL11 0.02 0.03 Time (seconds) 0.04 0.05 sLHC Next Steps • Development of a 704MHz Magnetron (440kW – 880kW ) Collaboration with CEERI, Pilani, India • Procure standard modulator Hope to use klystron modulator with different pulse transformer however rate of voltage rise is tightly defined. Need to deal with impedance change on start up. The CI have a suitable 3 MW magnetron modulator for short pulses up to 5 micro-seconds and could be used for characterisation • Establish test station with Television IOT as the drive amplifier Could be used for conditioning SPL and ESS components • • • • • Understand locking characteristics of new magnetron Commission advanced modulator with in-pulse current control Establish minimum locking power Establish two magnetron test stand Develop LLRF for simultaneous phase and amplitude control SPL11 sLHC Layout using one magnetron per cavity Permits fast phase control but only slow, full range amplitude control Cavity Standard Modulator Pulse to pulse amplitude can be varied 880 kW Magnetron Slow tuner ~ -13 dB to -17 dB needed for locking i.e. between 18 kW and 44kW hence between 42 kW and 16 kW available for fast amplitude control Load 4 Port Circulator LLRF 60 kW IOT Could fill cavity with IOT then pulse magnetron when beam arrives SPL11 sLHC Layout using two magnetrons per cavity Phasor diagram output of magnetron 1 Permits fast full range phase and amplitude control output of magnetron 2 Cavity combiner / magic tee Advanced Modulator 440 kW Magnetron Fast magnetron tune by varying output current 440 kW Load 440 W ~ -30 dB needed for locking Magnetron 440 W LLRF SPL11 Advanced Modulator Fast magnetron tune by varying output current sLHC Reflection Amplifier Controllability 1. Phase of output follows the phase of the input signal 2. 3. Phase shift through magnetron depends on difference between input frequency and the magnetrons natural frequency Output power has minimal dependence on input signal power 4. Phase shift through magnetron depends on input signal power 5. There is a time constant associated with the output phase following the input phase Anode Voltage 10kW 915MH z 30kW 20kW 916MHz 40kW 12.0 kV 3.00A 11.5 kV 2.92A Magnetron frequency and output vary together as a consequence of 1. Varying the magnetic field 2. Varying the anode current (pushing) 3. Varying the reflected power (pulling) 0o Arcing Power supply load 11.0 kV line towards magnetron Moding 2.85A 900 W 800 W 700 W 2.78A 10.5 kV 2 270o 2.70A 10.0 kV 1 2 3 4 5 VSWR 3 4 6 90o +5MHz Magnetic field coil current +2.5MHz -5MHz Anode Current Amps -2.5MHz SPL11 +0MHz 180o sLHC CEERI Collaboration Dr Shivendra Maurya of the Microwave Tube Division, CEERI, PILANI, India visited Lancaster University from 1st August to 31st November to start work on the design of a suitable magnetron. This visit has been funded by the Royal Academy of Engineering. If there is sufficient interest CEERI will seek funding to manufacture the magnetron. CEERI already manufacture a range of tubes mainly for use in India. 5 MW (pk), 5kW(avg) S-band Klystron as RF amplifier for injector microtron in Synchrotron Radiation Source at RRCAT, Indore S-band, 3.1 MW Pulse Tunable Magnetron for Accelerator SPL11 sLHC Specification of initial device Frequency Power Pulse length Max average power Efficiency Magnet External Q Mechanical Tunability Cathode heating 704 MHz 200 kW to 1 MW 5ms to 5 ms (for max power) 100 kW > 90% above 500 kW NyFeB (< 0.5 T) ~ 50 (for ease of locking) ~ 5 MHz indirect and controllable SPL11 sLHC Approximate Calculations Using standard theory one can estimate Magnetic field, anode and cathode radii from requirement data (frequency 704 MHz, efficiency >90% and power Power output Overall efficiency target DC power DC impedance Anode voltage Anode current Cathode plus circuit losses electronic efficiency V anode over V threshold V threshold Modified Slater factor Number of Vanes Anode radius Cathode radius Anode height Cathode current density Electric field Voltage field product B W W Ohms V m m m A/m^2 V/m kV/mm^2 T 5.26E+05 0.9066 5.80E+05 1615 30611 18.954 4.00% 94.66% 1.25 24488 1.96 14 0.02400 0.01775 0.05536 3070 9.79E+06 299.6 0.30477 1.00E+06 0.9210 1.09E+06 1615 41876 25.930 4.00% 96.10% 1.25 33501 2 14 0.02401 0.01774 0.05536 4202 1.34E+07 559.8 0.41331 Given Assumed Derived Guessed Derived Derived Estimated Derived Assumed Derived Assumed Assumed Calculated Calculated Assumed Derived Derived Derived Calculated Should be able to use same block for efficient generation at both the 500 KW and 1 MW level SPL11 e B 0.5Bo B 1.5Bo Bo 4 m rf 1 e N 1 rc ra 2 2 2m rf 2 Vo ra e N Vth B 2 1 Vo Bo r r V SF a c N 1 Vc ra rc B Vc Vo Bo 2 sLHC Expected operating range Threshold for moding Short circuit regime VORPAL simulations SPL11 sLHC Take VORPAL Predictions at 30 kV Amps Anode current (A) B = 0.3 T, Va = 32 kV, Ic = 60 A time (s) Volts Predict Ianode = 19 A, Efficiency = 92%, Cathode voltage (V) Power = 560 kW Z = 1684 W time (s) Watts Output power (W) time (s) SPL11 sLHC Volts Moding Issues Voltage in magnetron Excitation in the mode at 1060 MHz might be a problem. We think the coarse mesh or other issues with the simulation might exacerbate the issue. time (s) Volts time (s) FFT (dB) time (s) SPL11 sLHC MWS modes p mode at 702 MHz p1 mode at 1060 MHz p1 mode at 1063 MHz SPL11 0.010 sLHC Efficient Orbits 0.005 An efficient orbit should have no loop -0.025 -0.020 -0.015 -0.010 0.000 -0.005 0.000 0.005 -0.005 -0.010 -0.015 -0.020 -0.025 -0.030 SPL11 0.010 0.015 0.020 0.025 sLHC Magnetron Size air cooling for cathode 704 MHz water cooling for anode Magnets dg dm dg ~ 360 mm dm ~ 165 mm hm ~ 650 mm cost £8000 hm If magnetron design is similar to industrial design with similar tolerances and can be made on same production line then cost may not be much more air cooling input for dome SPL11 sLHC High Efficiency Klystrons • Design of high efficiency klystrons for ESS in collaboration with CLIC – Similar Klystrons (704.4 MHz, 1.5 MW, 70% efficiency) allow synergetic activities with CLIC. – Focus on understanding of bunching process and space charge in the output cavity. – Using evolutionary algorithms to improve optimisation – New design concepts to achieve optimum beam modulation – Single and Multiple beams investigated Images courtesy of Thales Electron Devices SPL11