Ben Woolley CLIC Workshop 2016 (LCWS16) CERN, Switzerland 18/01/2016 X-Band test-stand operation: LLRF, controls, conditioning and operational algorithms, stability, XBox3 schedule Ben Woolley CLIC Workshop 2016 (LCWS16) CERN, Switzerland 18/01/2016

Outline General test stand specifications Control systems ≤ 250 ns pulse, 50 MW, ≥ 50 Hz pulse repetition rate. Adequate diagnostics. E.g Xbox-2. Control systems Down mixing and digitization. LLRF signal generation and up mixing. Safety and interlocks. PXI crate. Automation algorithms Power control: Pressure and BDR. Pulse compressor tuning. System stability Xbox-1. Xbox-2. Xbox-3 Layout. LLRF crates. Schedule. B. Woolley 18/01/2016

Test Stand Specification For most CLIC accelerating structure designs the required input power to achieve an average unloaded accelerating gradient is 40-45 MW. The CLIC pulse shape has a 160 ns flat top with a ~70 ns ramp. However for conditioning of the structures a flat pulse ≤ 250 ns can be used. Recent studies suggest that it is the number of pulses that dictates the speed at which a structure conditions, therefore high pulse repetition rates are preferred ≥ 50 Hz. Use of a single 50 MW klystron and pulse compressor can be used to test one or more structures (Xbox-1/2). Or 2+ klystrons can be combined (Xbox-3 or nextef). B. Woolley – CLICWS 2016 18/01/2016

Diagnostics of the DUT RF Load Dipole Device under test Magnet Incident Power Reflected Power Uppsala Dark Current Spectrometer 60 dB directional coupler RF Load Transmitted Power RF In From Pulse Compressor WR90 Waveguide Ion gauge readout Ion gauge readout Input coupler Output coupler Screen Dipole Device under test Beam-pipe Beam-pipe Magnet Upstream Faraday cup signal Radiation Monitor Downstream Faraday cup signal Collimator Readout B. Woolley – CLICWS 2016 18/01/2016

Example: Xbox-2 Scandinova Modulator Klystron (50MW, 1.5us pulse) For Crab cavity test: SLAC XL5 klystron Pulse compressor (250ns, ratio ~3) Stainless steel load B. Woolley – CLICWS 2016 03/11/2015

Down-mixing and Digitization RF Input 1 Amp 400 MHz LPF splitter IF output 1 2.9 GHz PLL RF Input 2 Amp 400 MHz LPF X4 freq. IF output 2 RF Input 3 Amp 400 MHz LPF IF output 3 RF Input 4 Amp 400 MHz LPF IF output 4 12 GHz signals are sent to a mixing crate containing a CERN built 2.9 GHz PLL (Stephane Rey). x4 multipliers are used to produce 11.6 GHz. This is used to down-mix the signals to 400MHz IF. NI 5772 digitizer module samples at 1.6GSPS and FPGA IQ demodulation is used to obtain amplitude and phase. B. Woolley – CLICWS 2016 18/01/2016

LLRF Generation and Up-mixing To TWT Amp 12 GHz BPF 2.4 GHz input from PXI IQ modulator 2.4 GHz PLL X4 freq. splitter splitter To Reference input 12 GHz BPF NI 5793 IQ modulator with 200MHz bandwidth and 250MSPS IQ voltage generator is used to produce an arbitrary signal which can be varied in amplitude and phase at 2.4GHz. The signal is mixed up to 12 GHz using a mixer with a 9.6GHz input. A reference 12GHz signal is also crated which is locked to the signal generated by the IQ modulator. B. Woolley – CLICWS 2016 18/01/2016

Safety, Interlocks and control Algorithms Main personal safety issue is X-ray radiation during operation. Interlocks on the bunker door and klystron/modulator access doors stop modulator pulsing if opened. Modulator interlocked is radiation levels are too high inside or outside of the bunker. Machine protection issue is from high vacuum and reflected power to the klystron. Double interlocking of the vacuum; 10-5 mbar interlocks the modulator and 10-7 mbar interlocks the LLRF driver. Reflected power is monitored by log detectors which stop the LLRF output if a certain level is breached. Interlock hardware Modulator control system is used for radiation and access interlocks. NI 6583 module attached directly to an FPGA in the PXI crate is the main trigger and interlock module at Xbox-2&3. This is used for all other interlocks; vacuum, RF, high temperatures, etc. B. Woolley – CLICWS 2016 18/01/2016

PXI Crate Allows up to 17 expansion cards to be used. Digitizers, RF generators, DMMs, serial interface etc. Plus powerful quad core controller. OS is NI’s LabVIEW Real-Time, easily programmable in ‘almost’ standard LabVIEW language, with the stability and speed that real-time programming allows. Acquisition and interlock cards use FPGA interface for added reliability and speed. B. Woolley – CLICWS 2016 18/01/2016

Pulse and Power Control Algorithms Pulse length and LLRF frequency are set: Fast  pulse to pulse PID loop on the incident power to the structure Medium  seconds-minutes increase power by 10kW every few minutes if no BD reduce power by 10kW if successive BDs too close in time Slow  hours BDR measurement and stop power increase if it is too high BDR measurement performed across a moving window of approx. 1M pulses. Use PID loop using the system pressure as a process variable. Increase in pressure results in a reduction of power and vice versa. OR  B. Woolley – CLICWS 2016 18/01/2016

Xbox-1 Pulse Flattening PC Cavity Encoder read-out Stepper control Temperature changes lead to: Total volume offset  decrease in pulse flatness. Relative volume offset  Increased reflection to the klystron. Used to use stepper motors attached to pistons to tune the pulse compressor. B. Woolley – CLICWS 2016 18/01/2016

Xbox-1 Pulse Flattening PC Cavity Chiller temp control Chiller 1 Chiller 2 Temperature of each cavity is changed depending on the flat-top slope and the ‘klystron reflection ratio’ defined above. B. Woolley – CLICWS 2016 18/01/2016

Xbox-2 Pulse Flattening Better design of pulse compressor (Igor Syratchev), results in good thermal stability. No temperature control needed. Instead phase is controlled to flatten the top of the pulse: ɸn+1 = ɸn + g(ASP – A) ASP amplitude set point A current amplitude g feedback gain B. Woolley – CLICWS 2016 18/01/2016

Xbox-1 Up-time (TD26CC) 59% uptime for the 2015 dogleg run (TD26CC) Long periods of downtime due to modulator issues; solenoid PSUs and IGBT faults. General inconsistency of running due to pulse compressor detuning caused by excessive BDs in the waveguide network.

Xbox-2 Up-time 65% uptime for the 2015, T24 OPEN structure. Long periods of downtime in October/November linked to interventions to the area in preparation for Xbox-3 (water, electricity etc). Commissioning of Xbox-3 modulators required shutdown of Xbox-2 because of low cooling water flow rate. Some inconsistency of running caused by radiation interlocks which cannot be automatically reset.

Xbox-3 Layout Klystron/modulator Directional coupler RF /vacuum gate valve Directional coupler RF/vacuum pumping port 3 dB hybrid RF pulse compressor RF load WR90 waveguide network 7 MW x 4µs x 400 Hz 14MW x 4µs x 200 Hz 56 MW x 250 ns x 100 Hz B. Woolley – CLICWS 2016 18/01/2016

High Power RF Network Can be run as two separate units with a pair of klystrons each: Klystron/modulator Directional coupler RF pulse compressor RF load 14 MW x 4µs x 200 Hz 6 7 MW x 4µs x 400 Hz RF /vacuum gate valve? 3 dB hybrid 56MW x 250 ns x 200 Hz TS = TEST SLOT - Phase & amplitude 400MHz. @1.6GSPS  Structure RF Signals INC, REF, TRA. (3 /TS) - Phase & amplitude @400MHz @ 250MSPS  Phase but not speed is key KLYin, KLYout, PCin (3/TS) - Slow Amplitude only. Log det. @250MSPS  Reflected signals/machine protection (3/TS) -Faraday Cup Signals  (2/TS) B. Woolley – CLICWS 2016 18/01/2016

Xbox-3 LLRF Racks Each test stand will get it’s own temperature stabilized rack with some shared resources (PLL crate and power meters). The channels are split, one of the channels is MUX’d to a power meter for calibration and the other is sent to the mixing crates or log detectors. The mixing crates are based on the Xbox-2 designs but contain fast multiplexers which switch in time with the power sent to the DUTs. Saving on ADC channels. B. Woolley – CLICWS 2016 18/01/2016

Progress of LLRF crates Log detector crate Up/down mixing plate (1 of 2 per crate) Manufacturing of the crates is progressing well. All components have arrived at CERN and are ready to be integrated. Commissioning and testing of the crates will start within the next few weeks. All crates to be completed + tested by end of February. Interlock/trigger crate B. Woolley – CLICWS 2016 18/01/2016

Xbox-3 Schedule Klystron and modulators are tested and ready to go. Unit A has had a long RF test and reached above nominal power at short pulses (800 ns) and longer pulse width (3.5us) at lower power. (Limited by waveguide network). Cooling system flow-rate upgrade complete; can now cool Xbox2+3. New solid state driver prototype successfully tested, with 4 production units on order. Should arrive before end of February. All parts for the LLRF and control systems have arrived at CERN. High quality RF cables are yet to arrive, were due before end 2015. LLRF sub-systems are being assembled. Expected completion before the end of February. Waveguide components have been manufactured with visual inspection of the components on going. Should be installed by end of February. First pair of cavities have been manufactured but one was not leak tight. Repairs are ongoing. However, cold RF test was successful.  Manufacture of 5 more pulse compressors launched. Expected delivery of all 6 pulse compressors will not be for another few months.  Xbox-3 will be commissioned without pulse compressors. Racks have been installed in the experimental area and the waveguide supports are almost complete. B. Woolley – CLICWS 2016 18/01/2016

Summary Over the past ~3 years we have greatly increased our understanding of the operation of high power X-band test stands. Control system upgrades and increased automation have allowed us to develop tools to more safely and quantitatively condition structures. Apart from some major interventions the up-time of the Xboxes has been very good. Work on Xbox-3 is progressing steadily and most/all of the hardware should be in place by the end of February. B. Woolley – CLICWS 2016 18/01/2016

Thank you! B. Woolley – CLICWS 2016 18/01/2016

Extra slides B. Woolley – CLICWS 2016 18/01/2016

2-Way Combination Demonstration 10 mW amplifier RF pulse compressor Co-ax Hybrid RF loads KREF1 KREF2 KLYOUT1 KLYOUT2 PCIN1 TRA1 TRA2 PCREF1 WG network 12 GHz FAST Signals (x5) LLRF CRATE 400 MHz IF (x5) Down mixing Stage (Aq.) 12 GHz LO PLL 2.9 GHz LO PLL 2.4 GHz Up mixing Stage1 (Gen.) Up mixing Stage2 (Gen.) 12 GHz 2.4 GHz 2.4 GHz PXI CRATE RFSG 1 (IQ gen. & VM) 12 GHz SLOW Signals (x3) RFSG 2 (IQ gen. & VM) 1.6 GSPS ADC x5 Diode/Log detector CRATE Diode/log detectors x4/x8 DC coupled 50 MHz (x3) 250 MSPS ADC x1 (4ch.) PXI and LLRF crates are locked by 10 MHz reference B. Woolley – CLICWS 2016 18/01/2016

Results Concept of phase switching proved in 2013 with modified version of the Xbox-2 LLRF system. Low power hybrid and the Xbox-2 pulse compressor were used. Switching at 400 Hz was demonstrated (lower left). Ch1 Ch2 0.5ms /div B. Woolley – CLICWS 2016 18/01/2016