Status of the MICE RF System K Ronald, University of Strathclyde For the MICE RF team MICE Project Board & RLSR, 24th November 2014 1

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Status of the MICE RF System

K Ronald, University of StrathclydeFor the MICE RF team

MICE Project Board & RLSR, 24th November 2014

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Content


• Impact of the transition to the ionisation cooling experiment• Timescales and revised RF apparatus• Implications for components required• Projected acceleration performance• Implications for integrated RF system tests: MPB/RLSR Recommendation

• Status of RF drive system• Plans & progress for tests of amplifiers• Plans for delivery, installation of amplifiers• Status of the LLRF systems• Development of RF controls• RF Cavity Test Progress

• Muon-RF phase determination• Initial tests with real hardware and waveforms• Procurement of hardware for further tests

• Plans for installation and commissioning of RF modules at RAL

MICE and ISIS synergies: RF subsystems and controls: MPB/RLSR Recommendation

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MICE HPRF systems


• MICE HPRF system requirements have changed• Fewer cavities, no coupling coil• Required operational date is Autumn 2017• Enables demonstration in data campaign from 2017-2018 of ionisation

cooling with energy restoration

• The MICE Demonstration of Ionisation Cooling requires

• Two individual cavities bracketed by two thin LiH absorbers, sandwiching main absorber

• Cavities themselves are unchanged• Each cavity is 430mm long with a Q of 44,000 and is resonant at

201.25MHz• The cavities must still operate in a strong magnetic field environment• Cavities are estimated (by simulation) to deliver 8MV/m at 1MW

dissipation- shunt impedance 5.9 MW

• Alan has described the cavity test progress

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MICE HPRF systems


• The MICE Demonstration of Ionisation Cooling requires

• Two individual cavities bracketed by two thin LiH absorbers, sandwiching main absorber

• Cavities themselves are unchanged• Each cavity is 430mm long with a Q of 44,000 and is resonant at

201.25MHz• The cavities must still operate in a strong magnetic field environment• Cavities are estimated (by simulation) to deliver 8MV/m at 1MW

dissipation- shunt impedance 5.9 MW

• Alan has described the cavity test progress

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Expected performance


• 2MW peak output from RF drive amplifiers, also unchanged• LLRF requires ~10 % overhead to achieve regulation• Estimated ~10 % loss in transmission line• Power delivered to each cavity 1.62 MW,• Anticipated gradient in each cavity 10.2 MV/m

• Slight uplift in gradient from 7.2 MV/m in each ‘STEP V’ cavity

RF system tests

• During summer 2014 an early integrated system test plan was developed• Based on MPB/RLSR Recommendation• Eminently feasible, cost and schedule implications fully developed

• Installation next to Daresbury amplifier test stand

• Schedule implications incompatible with new imperative- operation in 2017• New configuration magnetically similar to MTA tests- enhanced derisking• Maximal exploitation of tests at Daresbury and MTA for risk mitigation• Integrated system tests- 2 months available in installation plan

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HPRF System Status


• MICE RF systems demonstrated• Nominal power levels 2MW, Frequency (201.25MHz) for

1ms @ 1Hz• First amplifier tested in MICE hall• Triode amplifier (output stage) remains installed

• Tetrode and all modulator racks shipped to Daresbury

• New higher voltage solid state crowbar tested• Electrical completion of triode No. 2 will commence• Triode 2 will be tested using No. 1 tetrode and modulators

• Will use upgraded Triode No.1 modulator• Each major No. 1 subsystem will be swapped for No. 2

sequentially• Make fault finding more rapid• Remote control philosophy being developed• Will be tested during commissioning of No. 2 system

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PSUs #1 – Progress at Daresbury • The racks are re-installed at DL and connected to power • The 40 kV modulator is being upgrade with a solid-state crowbar switch. • Testing of the two new 40 kV crowbar switches sucessfull

– Switches integrated with trigger system– Switches hold off over 40 kV with no false trips – Run at 42kV for long periods. – Discharge capability of two switches tested at up to 38 kV with the full 140 uF. – Thyristors barely get warm.

• Switch 1 has had over 120 shots at various voltage/charge levels.


Test apparatus showing crowbar switch, resistor bank and CT

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Crowbar Tests• Tests carried out:

– Circuit tests using second switch as a load to trigger the crowbar and measure “arc” energy


Test voltage: 24 kV Capacitor: 140 uF Dump resistor: 5 ohms

CH 1 Overcurrent detector (trigger) CH 2 Firing pulse to crowbarCH 3 Capacitor current (10 dB) CH 4 Current in LoadTimebase 2.5 us / div

Peak current in crowbar: 4.6 kAPeak current in load: 1.2 kAEstimated energy into load: <10J

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LLRF systems


• MICE LLRF: provide 1% amplitude, 0.5o phase regulation• Will control tuner system

• LLRF system being developed by Daresbury LLRF group• Using digital LLRF4 boards already procured• First board operating at 201MHz in tests during August 2014

• Synergy with ISIS requirements for LLRF system• For new ISIS LINAC amplifier test and commissioning stand• Similar installation to the MICE amplifier test stand

• System is closely related to the implementation for existing Daresbury accelerators• 0.1 % amplitude and 0.3o demonstrated in 1.3 GHz accelerating cavities• Power ramp programming already demonstrated

• Boards will be tested during the amplifier commissioning programme

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Implications for Power Distribution Network


• The change to a two cavity system has some implications for the RF delivery network

• Transmission lines planned to travel under floor level- no requirement to change

• Most components available from stock procured by Mississippi MRI grant

• Fewer hybrid splitters used- one amplifier driving each cavity• Simpler tuning control and feedback system

• New experiment will demand higher power in 4” lines under floor• This suggests it may be worth implementing SF6 insulation

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RF Control System


• RF systems will require remote, automated control system • ‘State Machine’ description being evolved by MICE Team

• ‘Operator perceived’ states mapped for Amplifiers

• OFF- Fully hardware inhibited state

• ENABLED• RF system verified closed: Hardware inhibits cleared

• STANDBY• Heaters On: Highest state without PPS permit• Hardware interlocked to coolant, monitoring of heater drive systems

• READY• HT PSU’s Online, HT Grounds lifted, LLRF Online• Hardware interlocked to PPS Permit, coolant, enclosure integrity

• ON• RF system running• Hardware interlocked to PPS Permit, coolant, enclosure integrity• Software monitoring of forward and reverse power, coupler signals

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RF Control System


• Detailed logic states within this overall philosophy are being informed by the ISIS linac control system- excerpt below

4616 Filament + Water

4616 Filament - Water

4616 Grid Water 4616 Filament I/L

4616 Screen Water

4616 Anode Water

4616 Dummy Load Water

Dummy Load I/L

4616 Dummy Load @ Load

Injector Personnel 1

Personnel I/L

Injector Personnel 2

LC1202 Charging Unit Water

20kV Water I/L

20kV Ignitron Water Personnel I/L Dummy Load I/L

4616 Filament I/L 20kV To Dummy Load I/L

4616 Filament Regulator I/L 20kV Water I/L 20kV I/L 20kV I/L

4616 Filament Voltage 4616 Filament ON 4616 Filament ON

4616 Filament Current

4616 Grid Bias PSU Status

Earth Sticks Stowed

Cubicle Door Closed Capacitor Cubicle I/L

Emergency Stop

• Will be built by Daresbury using established standard architecture

• Fast local hardware switches for critical system/safety protection• PLC’s for more complex, less time critical functions

• Interface to EPICS MICE control system for monitoring

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RF drive systems- plans to complete


• Two RF drive systems are to be delivered to the MICE hall

• Amplifier No. 2 will be progressively commissioned through 2014 into 2015• Remote control and monitoring systems will be implemented during these

tests• LLRF system will be tested with the amplifiers

• Delivery and installation of RF system No. 1 can be incremental

• As primary subsystems are replaced by the No. 2 units at Daresbury • Taking account of STEP IV operations• Installation resource requirements well understood from TIARA tests

• RF system No. 2 planned to be available for installation in 2016

• Four month commissioning window ending Nov. 2016• This will be undertaken as an intensive delivery and installation operation

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Timing System Specification


• We wish to know the difference between

• Transit time of any of our muons (in essence through ToF1)• A zero crossing of the RF system in any cavity- choose the first cavity• Use tracker measurement of trajectories to project forward to each cavity in turn

• LLRF phase (0.5o) stability specification is ~3x stricter than the resolution desired for the RF timing system <20ps or <0.4% of the RF cycle

• In turn specification for RF timing is ~3x stricter than ToF resolution 50ps ~1%

• Should mean the timing accuracy is ~1% of RF cycle, defined by ToFs resolution

• Stability, and/or accurate knowledge, of all parameters in the system will be important

• Long cable runs, with dielectric insulated coaxial lines?• Phase relationship between the cavity fields and the signals on the test ports• Relationship between ToF signals and actual Muon transit

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Overview of Timing Critical Elements


• Sketch illustrates relationships of key components in the Demonstration experiment• Work in progress: Mathematical tests of digitiser interpolation

• Test sensitivity to vertical resolution, temporal sample rate, noise• Work in progress: Understand cable stability• Work to be undertaken: Test TDC/Discriminators in 201.25 MHz environment

ToF 1Cavity 1

RF Amp 1

LLRF

Beamline

HPRF

RF DriveLLRF Feedback

TDC’

s (T

oF)

TDC’

s (R

F)D

igiti

sers

Datarecorders

RF

Clock

Trigger

Dis

crim

inat

ors

(RF)

Dis

crim

inat

ors

(ToF

)

ToF Signals RG213

201.25 MHz LLRF MO

MO Signal (RG213)

Com

pute

rs

RF Amp 2

HPRF

Cavity 2

RF Drive

Cavity 2 (RG213)Cavity 1 (RG213)

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‘Sub’ Nyquist digitisation

• To acquire at Nyquist on 200MHz would demand a sampling rate of ~1-2G.Sa/sec, for 1ms– Demands ~1 to 2MB per acquired channel, > 7.2GB/hr (assuming an 8 bit digitiser)

• Subsampling – The Fourier Transform of the undersampled data maps the signal into its ‘unaliased’, relatively low

frequency range

• We may then retransform to the time domain to determine the time evolution of the signal at some arbitrary point in time

• Must satisfy Nyquist on the linewidth- for our cavity natural linewidth is ~5kHz, effective linewidth is ~10kHz, so sampling rate ~few hundred k.Sa/sec should be sufficient

• We assume 20M.Sa/sec, with 1ms we now have about 20kB per 8 bit recorded channel, data rate of ~72MB/hr per channel


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Comparison of rebuilt 20M.Sa/sec subsampled oscilloscope signal with 2G.Sa/sec recording: Agilent DSO-X G2004A


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Timing hardware and Tests


• Use TDC and discriminators used in ToF system

• TDC’s CAEN V1290 25 ps multi-hit• 25ps bin size maps to 7ps uncertainty (assuming Uniform PDF)

• LeCroy 4415A discriminators• Needs to be tested in RF environment

• Use of same electronics as ToF mitigates systematic uncertainty & drift• Both TDC’s and discriminators will travel to Strathclyde tomorrow

• To make efficient integration into DAQ ideally use VME digitisers for the sub-sample reconstruction

• At present continue to use fast, 8 bit, DSO’s to capture signal• Plan to use CAEN V1761 digitisers • 1GHz, 4G.Sa/sec, 10 bit, 2 Channel instrument• Capable of 57.6MS/Ch

• RF cavity tests at MTA have provided real cavity probe signals for analysis

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RF Installation and Commissioning


• RF amplifiers already discussed • One amplifier previously installed• Services and support systems well understood• 1st Amplifier reinstalled- working around STEP IV operations• 2nd Amplifier- 4 month installation plan- completion projected late 2016• Pre testing to 1MW possible into hybrid and three 500kW loads

• RF main power lines installed from August ‘16 to February ’17• Lines from final hybrid measured by VNA• Matched for electrical length (allowing for hybrid), trimmed with phase

tuners

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• Cavities

• SCTS Cavity tests proceeding very successfully at MTA

• Two cavities and 4 Be windows + spare set will be preselected, electropolished by LBNL• Based on measurement of resonant frequency• Four RF couplers will be built to upgraded design• Delivery to RAL planned for Spring 2016

• Cavity assembly: RF team working with Mechanical assembly team

• Benefits from experience with similar SCTS

• Assembly planned at RAL, can be conducted in separate hall, 6-8 weeks• Cavity will be installed into the vacuum chamber with Be windows• Couplers installed and tuned for critical coupling (revised coupler clamp)• Pick up probe calibration will be adjusted and measured• Cavity tuning tested and measured, Q, f0 checked• 2 weeks allowed for RF tuning of cavity

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• Cavity vessels will be integrated with absorber vessels and focus coils

• Moved into beamline and pumped down, estimate 2 weeks effort

• MTA tests indicate X-ray shield requirements to be modest

• Require pressure < 10-7mB inside cavity• Experience from MTA SCTS informs evacuation process • Retest RF performance of cavities

• Complex cavity chamber environment limits bake options• MTA test shows light bake is adequate on EP cavities• Use hot water in cooling tubes to bake to ~80oC directly

• Estimate 2 weeks to evacuate and 2 weeks for bakeout

• Review RF performance after ultimate vacuum reached

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• HPRF tests can commence once Amplifiers, Cavity and transmission lines installed • Prerequisites planned to be complete Feb. ‘17• One month of RF testing planned• Initially without B-field• Full tests of LLRF with tuner control

• Magnet commissioning derives from STEP IV plan• Commence April ‘17 after RF pre-commissioning• Requires addition of one further focus coil • All magnets exist and have been tested at currents > requirements

• Once magnets commissioned RF commissioning with B-field• This will build on tests at MTA• Essentially repeat of tests without B-field• Estimated 1 month of tests (May ’17)

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Risk management and Resilience


• Certain risk and procurement items have been eliminated or mitigated• Distribution network simplified• 9 cavities available (2 needed)• All major RF modulator components in hand• 4 off Thales 116 Triode valves available (2 required)• 2 spare sets of valve amplifier assemblies readily available

MICE & ISIS RF Subsystem: Synergies and Interaction

• MPB/RLSR Recommendation

• Strong correlations between MICE and ISIS Linac RF systems• MICE RF Engineer has requested to participate in ISIS Linac commissioning• ISIS Linac RF amplifier test station similar to MICE amplifier installations • MICE RF Team working with ISIS Linac RF Team on LLRF systems• ISIS Linac control philosophy used as model for MICE RF• MICE RF system safety under MICE-ISIS Safety committee

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Summary


• Progress achieved enhancing the capabilities of the RF amplifier modulators• In environment where most EE effort focussed on STEP IV• Plans developed for commissioning two amplifiers chains by 2016• Progress on LLRF system for 201MHz implementation

• Synergies with ISIS project

• Progress in Muon-RF phase determination• Sub-sampling and reconstruction shown to work with real 8 bit data

• Includes wideband noise and digitisation artifacts (8 bit vertical resolution, with timebase jitter)

• Equipment to test TDC based system available now

• Resilient plan in place to bring system together for commissioning tests• Completion of hardware, Spring 2017• Coherent experimental plan achievable if operational by Autumn 2017

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Crowbar Switch Design

• Fast crowbar switch needed to protect high power amplifier tube from potentially damaging internal arcs. ~ 100kJ in the capacitor banks.

• Switch characteristics:• fast turn-on to low impedance state • capability to discharge large amounts of

stored energy.

• Hybrid design combines a small fast switch in parallel with a slower large area slow switch

• The resistors R1-R2 ensure that current is shared between SW1-SW2 initially but then they also force the current into SW3 as SW3 turns on. C1 and R3 assure AC and DC voltage sharing between stages.


APP Crowbar Switch Model S62-2-12

48 kV

Conceptual Schematic C1: Snubber CapacitorR1-R2: Resistors for Current SharingR3: Balancing ResistorSW1-SW2: Fast ThyristorsSW3: Large Area Thyristor

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Crowbar Tests• Tests carried out:

– Leakage current measurement on each thyristor in the stack– Voltage withstand tests up to 42 kV dc for 30 minutes– Crowbar discharge tests up to 38 kV with 6 uF, 70 uF and 140 uF

capacitance


Crowbar discharge test – 38 kV 140 uF 1 us/divCh 1 – trigger signal (TGP 110) Ch 2 – trigger pulse (APP EB0046)Ch 3 – current (6dB attenuator) Ch 4 – Switch voltage (x10)Note rapid turn on of switch; Switch voltage down to 30% (11 Kv) at 1 us after trigger pulse

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Testing of Spectral Domain Remapping

• 201.25MHz signals computed (with ramp envelopes) and recorded at both 2G.Sa/sec and 20M.Sa/sec effective digitisation rates

• Signals compared after FFT and spectral region remapping, and again after iFFT, to compare the time domain of source signal

– Good agreement obtained• Computer used to simulate vertical digitisation error (i.e. 8 bit resolution of digitising typical

oscilloscope)– Again signals compared and reasonable agreement obtained

• Realistic data obtained by high speed oscilloscope– Gives realistic vertical (8bit) resolution error and horizontal jitter– Reconstruction process repeated


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Comparison of synthesised 8-Bit digitised 201.25MHz wave recorded at 2G.Sa/sec with IFT of padded 20M.Sa/sec data


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Real data taken from Agilent DSO-X G2004A


Ampl

itude

10.50Time/ms

-0.4

0

0.4

Documents

Status of the MICE RF System K Ronald, University of Strathclyde For the MICE RF team MICE Project Board & RLSR, 24th November 2014 1