Status of the MICE RF System K Ronald, University of Strathclyde For the MICE RF team 1MICE Project Board, 30 th April 2014

Requirement for MICE HPRF systems 2 MICE Project Board, 30 th April 2014 To demonstrate sustained cooling (MICE Step VI) requires 8 cavities at 8MV/m Two sets of four cavities bracketed by the absorber/focus coil modules Each cavity is 430mm long with a Q of 44,000 and is resonant at MHz The cavities must operate in a strong magnetic field environment Driver system must provide 1MW to each cavity (500kW on each coupler) Provide required energy with four 2MW amplifier chains Distribution network must not impede service access to cooling channel LLRF phase control of 0.5 o and 1% in amplitude regulation Key objective: Demonstrate interoperability of Liq H 2 /HPRF/Cyromagnet systems This will prove sustained ionisation cooling is technically possible Require a system to determine the RF phase in each cavity during the transit of each individual Muon Required to allow the experiment to compare the impact of the cooling channel on each particle Comparison of tracker measurements of phase space with predictions will test our understanding of the cooling process

Content 3 MICE Project Board, 30 th April 2014 Report on the HPRF drive system status Installation of 1 st Amplifier chain in MICE hall Recent TIARA tests at RAL Cavity developments Preparation for 1 st cavity tests Hardware and simulations, initial low power tests Mechanical assembly status and plan for MTA tests reported by Alan Bross Developments in Muon-RF phase determination diagnostic Plans to test the mathematical approach Plans for testing required hardware Potential for integrated system test at RAL Exploiting existing hardware

Status of the High Power Driver System The RF cavities are to be driven in adjacent, coupled pairs with a fixed phase angle between coupled pairs Each coupled pair to be driven by a 2MW, MHz amplifier chain Arbitrary phase control between separate coupled pairs of cavities SSPA (~4kW) driving Tetrode (~250kW max) driving Triode (2MW max) As reported last meeting, the prototype amplifier chain met these requirements Demonstration achieved summer 2013 External TIARA funding required demonstration of system operation in MICE hall Shown complex (and large) amplifier chain can be installed in tight space for RF power stations From Autumn, Amplifier no. 1 installed at RAL Deadline of year end 2013 to meet external deliverable 4 MICE Project Board, 30 th April 2014

Demonstration of Required 2MW Triode DC bias and drive brought up together Maintaining ~10dB gain Performance achieved: 2.06MW output RF 34kV bias voltage 129A forward average current  =46% (electronic) Gain 10.8dB Input port return loss -12.5dB VSWR 1.6 Drive from Tetrode 170kW output RF 18kV bias voltage 15.5A forward average current  =61% (electronic) Gain 19dB 5 Drive from SSPA 2.27kW Drive from synthesised oscillator 3.7dBm MICE Project Board, 30 th April 2014

Distribution network and components Through work of D. Summers, Univ. Mississipi and the US NSF MRI programme: Vast majority of distribution network procured Encompasses Loads, Hybrid Couplers, Reducers, Gas Barriers, Directional Couplers, elbows, line trimmers, etc In addition Mississippi have procured key components to build further amplifiers chains and components for the RF cavities, including Capacitors and Chargers Tetrode valves and tetrode valve amplifier enclosures LLRF boards Tuner components for cavities Some $1M (US) delivered to RAL under MoU between STFC and Univ. of Mississippi Total consignment > 6 tonnes 6 MICE Project Board, 30 th April 2014

Installation at the MICE Hall 7 – Entire amplifier chain and PSU’s transported to MICE hall – Installation completed to demonstrate practicality of operation in situ – Due to space constraints large 2MW loads not suitable in MICE hall at this time Test to maximum power rating of reject load 2.06MW operation therefore previously demonstrated at Daresbury Will be able to achieve full power MICE once cavities are available MICE Project Board, 30 th April 2014

MICE Hall RF Installation Services – Water cooling (high quality de-ionised water) and compressed air installation – Water cooling distribution panel Provides cooling to triode and tetrode systems Monitors flows rate Monitors coolant Temp 8 MICE Project Board, 30 th April 2014

MICE Installation Progress Images showing Tetrode amplifier and power supplies installed – Required quite accurate alignment due to rigid coaxial waveguides 3” (250kW) line installed to triode amplifier SSPA and synthesised oscillator installed 9 Tetrode Amp 3” O/P Line Tetrode HT PSU AUX and SSPA Top Cap Triode Amp AUX rack Triode HT rack MICE Project Board, 30 th April 2014

MICE Installation Progress Images showing triode amplifier and valve installed 3” input line (250kW) line installed from tetrode amplifier 6” output line (2MW) installed with reject load 10 Craning in of 2MW amplifier 3” Input 3” line from tetrode 8” to 6” adapter And 6” output line Input Tuning Box 2MW amplifier In situ Triode Top Cap with Valve MICE Project Board, 30 th April 2014

Installation and Tests in MICE Hall 11 TIARA requirement: Demonstrate the prototype amplifier operating in the MICE RF power station Amplifier No.1 dismantled at DL and Transported to RAL Includes SSPA, Preamplifier and Final Stage Amplifier subsystems with PSU’s Extensive water and air distribution systems installed Pre-amplifier operating since the 4 th December Final stage operating since the 12 th December Installation and operation achieved slightly ahead of a tight timetable Testing progressed very successfully: Power limited only by load capacity At present space constraints limit size and power capacity of the RF load Triode Performance -531kW output RF -22kV bias voltage -Gain 10.8dB -Input port return loss 11dB -Drive from Tetrode 44kW MICE Project Board, 30 th April 2014

Installation and Tests in MICE Hall 12 TIARA requirement: Demonstrate the prototype amplifier operating in the MICE RF power station Amplifier No.1 dismantled at DL and Transported to RAL Includes SSPA, Preamplifier and Final Stage Amplifier subsystems with PSU’s Extensive water and air distribution systems installed Pre-amplifier operating since the 4 th December Final stage operating since the 12 th December Installation and operation achieved slightly ahead of a tight timetable Testing progressed very successfully: Power limited only by load capacity At present space constraints limit size and power capacity of the RF load Triode Performance -531kW output RF -22kV bias voltage -Gain 10.8dB -Input port return loss 11dB -Drive from Tetrode 44kW MICE Project Board, 30 th April 2014

Cavities in magnetic fields: Simulations of RF fields 13 MICE Project Board, 30 th April 2014 E Field Magnitude B Field Magnitude MICE cavities (and any ionisation cooling cavity) needs to operate in strong magnetic fields This is known to impact on the attainable gradient Simulations of the E and B field have been performed using SLAC ACE3P Software Simulations have also been used to test the risk of multipactor breakdown

Cavities in magnetic fields: Multipactor Simulations Simulations show marked impact of the static guide magnetic field E-field range over which multipactor can arise no longer clearly ‘band’ constrained Larger (x10) no of secondary particles predicted when the magnetic field is applied Particular problems focussed in the vicinity of the couplers and waveguides Consistent with the measurements of the prototype cavity Informs the TiN plating of the production couplers soon to be tested 14 MICE Project Board, 30 th April 2014

Cavities: Tuner tests Tuner system performance simulated and measured Excellent agreement in ‘stretch’ Good agreement in ‘pinch’ Note CF is offset by 500kHz Due to components not mounted during tuning tests See later for final CF Shows 700kHz tuning range achieved Slight hysteresis introduced by pneumatic system 15 MICE Project Board, 30 th April 2014

Cavity Tuner tests: Resilience and Redundancy 16 MICE Project Board, 30 th April 2014 Tuning range reduced to 600kHz Reduction of 100kHz Still adequate to tune cavity Resilience to failure of a single tuner tested Still obtain good tuning performance Reduces risk of needing to interrupt operation- e.g. for maintenance

Cavities: Cold tests Cold test with copper end plates, vacuum and RF ports Centre Freq. now MHz Well within reach of tuners Measurement of through signal to test ports (balanced drive to both input ports) Thru’ attenuation > 50dB, to beyond noise floor of VNA Ports adjusted to 0.26dB balance 17 MICE Project Board, 30 th April 2014 Cavity Q measured to be 47,000 All pre-installation tests completed Cavity now ready for installation in MTA for HPRF tests

Muon-RF Phase determination, Desired 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 Will require Step IV data / simulation of momentum retardation and straggle in absorbers and diffuser Will require simulations of acceleration in each cavity LLRF phase stability is x3 stricter than the resolution desired for the RF timing system ~0.34% In turn specification for RF timing is ~3x stricter than ToF resolution 50ps ~1% Should mean the timing accuracy is ~1%, defined by ToF’s 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 18 MICE Project Board, 30 th April 2014

Timing System, absolute or relative We can either try to know the muon transit phase as an accurate, precise measurement OR As an inaccurate, precise measurement i.e. a high resolution measurement with an unknown but stable systematic This does not immediately have implications for the design of the RF phase detection system It is a question of how tightly we wish to couple it with the ToF system This coupling in any case needs to be very close In any event the precision, the internal and mutual stability are over-riding considerations If we have a reliable, accurate and precise measurement for the muon RF phase This can be used to select particles in suitable phase relationships for analysis It allows direct testing of the analysis of the experiment by selecting different experimental conditions in an independent way If we have a stable, precise but inaccurate measurement We can sort particles to know what their relative phase relationships would be Use analysis of large numbers of particles: identify those that were well aligned in phase Hence resolve systematics retrospectively 19 MICE Project Board, 30 th April 2014

Obvious sources of instability RF system and ToF system can share certain instrumentation This reduces some of the source of instability, since similar components should give similar performance The clocks of the RF and ToF digitising recorders need to be synchronised Ideally instruments should be of same type, co-located, else need to be checked for environmental impacts on performance At present it seems likely that the TDC’s from the ToF system are suitable Discriminators are less clearly suitable: require testing Digitisers (alternative/complementary method) can also be used, these will require to be clock synchronised Assessed for tolerable sensitivity to environmental factors Can use at least some of the same cable type Long cables may drift in electrical length with stress and temperature Again try to benefit from ‘co-drifting’ 20 MICE Project Board, 30 th April 2014

Overview of Timing Critical Elements Sketch illustrates relationships of key components in STEP V configuration STEP VI similar 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 MHz environment If necessary test alternative hardware 21 ToF 1 Cavities 1&2 RF Amp 1 LLRF Beamline HPRF RF Drive LLRF Feedback TDC’s (ToF) TDC’s (RF) Digitisers Datarecorders RF Clock Trigger Discriminators (RF) Discriminators (ToF) ToF Signals RG MHz LLRF MO MO Signal (RG213) Computers RF Amp 2 HPRF Cavities 3&4 RF Drive Cavities 1&2 (RG213) Cavities 3&4 (RG213) MICE Project Board, 30 th April 2014

Test of Digitiser sub sampling To mitigate the total amount of data required it is desirable to sub sample the wave form We know the frequency is within ~5kHz of MHz, (cavity Q) We can satisfy Nyquist on lower bandwidth (instead of 200MHz), reduce data stored Compared to 2GSa/sec at 1ms: 2MB for 8bit digitiser, on each cavity, at 1Hz 20MSa/sec would give 20kB for 8 bits on each cavity at 1Hz Mathematical tests show potential of realising this scheme 22 MICE Project Board, 30 th April MHz, 1ms duration signal sampled at 2GSa/sec & 20MSa/sec Fourier Transform subsampled signal Rebuild real spectrum Inv. FT rebuilt spectrum, compare original data

Development plan for RF phase diagnostic Work presently in progress Test cable thermal stability and repeatability Underway for RG213- these are the longest cables from the ToF to the datarecorders. Prove that the RF signal can be rebuilt by DSP on subsampled data With realistic digitiser resolution error, jitter and noise Underway as a mathematically exercise Test the digitiser DSP routine with real data from existing oscilloscopes Test the digitiser DSP routine with data from FNAL cavity tests Future activity Define and procure suitable digitisers Test LeCroy (or alternative Philips) discriminators and CAEN TDC’s on the bench Evaluate synchronisation stability between the TDC & digitisers with adequate stability (on bench) Implement a precision clock and a precision trigger for the datarecorders. Test diagnostic hardware on cavity return signal (FNAL) 23 MICE Project Board, 30 th April 2014

Integrated System Test Options It would be desirable to perform a full system test prior to the arrival of the fits RFCC system Currently scheduled for 6 th March 2018, Step V to be fully commissioned 28 th August 2018 At this point it will be possible to perform a full system test However problems would impact on Step V schedule Two approaches: Second single cavity test stand or prototype cavity Second approach minimises resource requirement Cavity could be delivered to RAL this FY in principle Requires relatively limited resources to repair coupler Requires vacuum system to be commissioned Would allow partial test of LLRF, full test of HPRF system No tuning system available on this cavity LLRF system can be reprogrammed to tune driver amplifier to cavity To perform high power test, cavity would need to be installed in MICE hall No radiation shielding at Daresbury amplifier test facility Would use amplifier no.1 as driver Amplifier PSU’s will need to be upgraded for remote control- planned for 2014 Cavity and amplifier could be installed at RAL once second amplifier system commissioned at DL- planned for 2015 (may delay amplifier no. 2 installation at RAL) Subject to Step IV operational requirements Would allow debugging of RF system ahead of the Step V requirements If funding available this plan could be executed in timeframe Only the tests themselves and the items in red significantly add to current project plan 24 MICE Project Board, 30 th April 2014

HPRF Summary High Power Drivers Have achieved specification on system No.1, 2MW for 1ms at 1Hz and MHz Installation of system No.1 at RAL complete Tested to 500kW (limit of reject loads) in December Meets TIARA deliverable requirement TIARA reports submitted: Newsletter article 1st cavity fully assembled and cold tested, ready for HPRF tests at MTA Mechanical assembly procedure fine tuned for single cavity test stand Couplers complete, Q measured Tuning hardware built and bench tested Multipactor simulations being undertaken Immediate Future Commissioning of systems No st tetrode and all PSU’s returned to Daresbury Upgrade PSU’s for remote control Will be used to test the second amplifier system Reduces the number of ‘new’ elements in the system Makes fault finding faster and hence commissioning more efficient Cavity No. 1 ready to be installed into MTA shielded enclosure Will require final assembly in situ (cannot negotiate Maze assembled) First HPRF tests (zero magnetic field) in early June, later tests in B-field RF workshop at FNAL 2 nd June, with UK and US participation in cavity tests 25 MICE Project Board, 30 th April 2014

Distribution network 26 Amplifiers installed behind shield wall Triodes on main floor, Tetrodes on Mezzanine Impact of B-fields negated by yoke Line installation planed before yoke support risers High power dynamic phase shifters removed 4 off 6 inch coax lines over wall Pressurised to increase power handling Hybrid splitters moved - more accessible Minimises clutter and increases service access to the amplifier stations Line lengths matched using 3D CAD Manually adjustable line trimmers installed at cavity to take up assembly errors in coax length Easier to assemble – introduced flexible coax Allows for small misalignments 2 Hybrids split output from the Berkeley Amplifiers (one on amplifier side of wall) CERN amplifiers have two outputs 9 hybrids on MICE side of shield wall Split power for the opposed couplers of each cavity Lines will be pressurised with 2Bar Nitrogen Amplifiers behind Shield Wall Distribution Network to MICE MICE Project Board, 30 th April 2014

27 MICE Project Board, 30 th April 2014 Progress on Cavities First MICE cavity will soon be tested at the MTA Tests will be done in a specially commissioned single cavity test stand Be windows in hand Actuators and tuner forks built New coupler fabrication complete at LBNL Couplers now plated Assembly tested At last report Couplers were being plated at LBNL This is now completed Assembly had been tested at FNAL Issues identified now successfully resolved