Status of the MICE RF System K Ronald, University of Strathclyde For the MICE RF team 1MICE Project Board, 6th April 2016

Status update: Highlights 2 Distribution network Adapted from components procured under NSF-MRI for earlier configuration Contractor identified, trial section modified Modified component returned- quality of work high Workshop viewed as qualified Less expensive and faster than further procurement Status of RF drive system Upgraded triode modulator No.1 operational at Daresbury Triode No. 2 under test, started mid March Exploiting 1 st tetrode, and upgraded No. 1 modulator racks Triode achieved 1MW using ex-ISIS valve (close to limit of valve) Interface channels for RF controls defined MICE Project Board, 6th April 2016

Status update: Highlights 3 Cavity module status Modified couplers under test at MTA- offer enhanced tuning and installation ease Proving very robust in operation Cavities selected for natural frequency Cavity body EP complete at LBNL Couplers: component fabrication complete Upgraded tuner actuators, components available Cavity vacuum vessels being fabricated at contractor Muon-RF phase determination Subsample method with Fourier domain signal reconstruction Accurately rebuilding signals from MTA experiments Digitisation hardware is on order RF discriminator delivered, currently under test at Strathclyde MICE Project Board, 6th April 2016

MICE High Power RF system: Requirements 4 MICE High Power RF system Two cavities, driven by two RF power amplifiers- 2MW output each Estimated gradient 10.3 MV/m- partial restoration of axial momentum Allowing for realistic LLRF overhead and losses Bracketed by two thin LiH absorbers, sandwiching main absorber 1st Amplifier proven and RAL(triode stage remains installed) 2 nd Amplifier build Daresbury Cavity proving well MTA Cavity construction in LBNL LLRF system to hold phase and amplitude; Cavity control to regulate freq. Determine RF phase on transit of each muon MICE Project Board, 6th April 2016

RF Distribution Network 5 Must Support 2MW in 6” line and 1MW in 4” line with full reflect 4” lines rated to 1.12MW at 1 atmosphere in dry air Therefore will be pressurised by SF bar gives safety factor of 2 in power handling (c.f. 1MW and full reflect) Will be treated as pressure vessels Some of the 6” and 4” line from the NSF MRI procurement will be modified All components/devices will be drawn from the NSF procured stock Quotes obtained for calibration equipment Procurement in next FY for component test MICE Project Board, 6th April 2016

RF Drive System 6MICE Project Board, 6th April st triode modulator upgraded with solid state crowbar Crowbar bench test previously reported Now tested up to 35kV (maximum intended operating voltage) in triode modulator Coupled to the triode amplifier

RF Drive System 7MICE Project Board, 6th April 2016 Glitches observed in modulator current traces when Tetrode operates above 50 kW output Completely independent of RF tuning of tetrode, triode, bias voltages on triode Does not happen when tetrode drives resistive load at much higher power Structure is very regular- possibly indicative of switched mode supply waveforms? Investigation underway this week, RF and Electrical engineering expertise

RF Drive Systems 8MICE Project Board, 6th April st Modulator set and Tetrode recommissioned at Darebury 2 nd Triode now under proving tests 1MW achieved using ex ISIS triode valve at 25kV  : 57%, Gain: 8.6 dB, Tetrode: 136kW,  : 52%, Gain: 19 dB Triode input return loss 11.5 dB At MICE duty and pulse duration US team participating in amplifier tests (Milorad Popovic)

RF Drive System 9MICE Project Board, 6th April 2016 First Amplifier Chain Has delivered required 2MW at Daresbury test stand Installed and commissioned at RAL autumn delivered 500kW Output (triode) stage remains installed at RAL Modulators and preamplifiers returned to Daresbury Crowbar upgraded Preamplifier recommissioned at Daresbury Includes modification to the input circuit- improves reliability Delivered 220kW Returns to RAL late Summer ‘16 Second amplifier chain Output stage complete and under test Second tetrode amplifier mechanically complete Solid state power amplifier tested Components for second modulator under construction ISIS Injector team working on upgrade to tetrode screen grid modulator

LLRF Control System 10MICE Project Board, 6th April 2016 LLRF hardware development with effort from ISIS Injector RF team Selection of clock and operation frequency refined Hardware under test- prototype batch of filters delivered Next batch of filters will be slightly refined, leading to order for production filters Required for both MICE and ISIS LLRF future requirements Block diagram of system shown

RF Cavities: Proving Tests 11MICE Project Board, 6th April st MICE production cavity: Tests underway at MTA Using production couplers, installed 27 th Jan- 6 th Feb 2016 Installation verifies much easier tuning expected for revised design Tuned to 2% of critical coupling, arms balanced to 1% UK staff (Colin Whyte) participated in coupler swap and tune- useful experience Opportunity taken to inspect cavity No evidence of sparks Couplers and cavity continue to behave as expected under high power MTA tests continue to provide critical data to Strathclyde for Muon timing diagnostics Cavity room frequency centre frequency adjusted by Al spacing rings Brings f MHz (from 200.8MHz). Tuning range +300/-400kHz

RF Cavities: Proving Tests 12MICE Project Board, 6th April 2016 Ionising radiation monitoring systems upgraded at MTA Allows operation in static magnetic field (e.g. shielded scintillator detectors) Increased speed of scintillation detectors and photomultiplier- approaching Removal of obstacles in line of sight from cavities –provide realistic representation of tracker exposure Apertures opened on both sides of cavity on vessel axis (strongest AC E-field) i.e. thin windows in heavy steel vessel endplates Scintillators may be placed upstream or downstream (or one either side) Scintillators supplanted by NaI detector for spectral measurments Additionally several slow scintillation counters and 5 IC’s (two different designs) Fast scintillating detectors provide diagnostic of multipacting bands Impact of MICE LiH absorbers simulated by filtering radiation through representative low Z materials

RF Cavities: Proving Tests 13MICE Project Board, 6th April 2016 Data currently being analysed (data in course of last week), initial impressions are that exposure is significant, but within expected range and manageable

RF Cavities: Module Progress 14MICE Project Board, 6th April Production couplers completed- 2 sent to MTA, 4 retained for MICE modules TiN plated on loops and inner of coaxial line Incorporates locating bracelet/clamp design to facilitate installation Improved gas isolation between jacket and cavity inner, protection system for Be windows New vessels nearing completion at contractor Incorporates additional aperture to enable better coupler tuning Window for inspection of Be caps will be added (delivered from MTA) Manufacturer will leak test pre-delivery- LBNL will verify and test for contaminants LBNL has assembly fixtures from MTA, cleanrooms ready for assembly

RF Cavities: Module Progress 15MICE Project Board, 6th April 2016

RF Cavities: Module Progress 16MICE Project Board, 6th April cavities selected for freq and surface finish and electropolish Be windows empirically selected for their impact on frequency Pair windows and cavities to give closest natural frequency Welding of cooling feedthroughs complete and ready for installation Cavities closed by Al plates & kept in clean rooms pending final assembly Expected delivery at RAL Aug – Sept ‘16

RF Controls and Monitoring Systems 17MICE Project Board, 6th April 2016 A channel list and state machine has been defined for the RF amplifier controls Enable the build of the controls hardware at Daresbury Also defines the logical interaction with the system states Software development now underway: associating channels with variables for EPICS control

RF Controls and Monitoring Systems 18MICE Project Board, 6th April 2016 Considering RF feedback model to keep cavities on tune: Estimate correct gain for feedback loop to tuners to hold cavity on frequency Plan to use measurement of reflection amplitude after several hundred microseconds Arrange feedback loop to minimise this indicator Dynamics: Cavity is 227 kg, Dissipated energy is < 2kJ/pulse Tuner control is about +3/-4 kHz/psi Tuning rate vs cavity body temperature = about -6 kHz/C Water must be supplied at precisely regulated temperature, Note: At the MTA it has been shown the cavity can be held on resonance with feedback- even in the face of a substantial thermal walk in the coolant system- see graph opposite

RF Controls and Monitoring Systems 19MICE Project Board, 6th April 2016 Overview of RF monitoring parameters NI hardware being developed at Daresbury to implement monitoring For reasons of speed and cost will use relatively simple but well characterised rectifiers rather than power meters for most measurements Envelope detectors and wide dynamic range log detectors on each measurement port

RF Controls and Monitoring Systems 20MICE Project Board, 6th April 2016 Relative RF phase should be set by LLRF feedback- however helpful to have independent analogue validation Special quadrature phase detector being developed Ensure accurate measurement over entire RF relative phase range NI subsystem will communicate to EPICS via well known routines

Muon Transit Phase Detection 21MICE Project Board, 6th April 2016 Time domain: signal (blue) from FNAL cavity tests  s window sampled at 5G.Sa/sec Subsample (red) at 12.5M.Sa/sec, reduce data by x400, and 48x < 200MHz Note time domain signal ‘windowed’: New data from MTA will remove this process Freq. domain: Red fft of entire recorded data, Blue enhanced dft of subsampled data f/100MHz Rel Magnitude Real Part f/100MHz Rel Magnitude Imaginary Part

Muon Transit Phase Detection 22MICE Project Board, 6th April 2016 Time/s Signal/V Freq. domain reconstructions: high fidelity to raw signal over entire pulse duration (no spark) Blue is original data through 1MHz Butterworth filter, Red is reconstructed subsample data Note dft is effectively a (hard edged) 100kHz filter 10ps precision achieved on arbitrary pulses from MTA test- various dft widths analysed Time/s Time Offset/s Digitiser is on order at this time: CAEN V1760 VME unit Will need to determine how to synchronise trigger clock with TDC’s TRST signal- discussion with CAEN suggests several routes

Muon Transit Phase Detection 23MICE Project Board, 6th April 2016 Hardware for TDC method now available 4 Ch. 300 MHz leading edge discriminator (Philips 704D) on test at Strathclyde Some jitter- probably due to wideband detection (20GHz for the CRO) systems admitting noise- filters being developed for LLRF will help. Non-updating, gate on a single period on RF wave then self veto- manage event rate

Summary 24MICE Project Board, 6th April 2016 Distribution Network Capacity for modification of line lengths validated Ready to modify other lengths of co-axial line as required Quotations obtained for calibration components Power Amplifier tests Ongoing Input structure of first tetrode improved, tetrode proven at 220kW 2 nd Triode completed trials underway at this time Second SSPA proven at MICE duty LLRF Frequencies for the clock and RF refined Filters designed- refinement in progress for production batch RF cavities and modules Most fabrication complete- awaiting vacuum vessels for final assembly Delivery expected late Aug and Sept. Couplers and radiation levels proven by MTA tests Diagnostics, controls, monitoring and feedback Channel list defined- allows hardware fabrication and software development Hardware for monitoring system outlines, procurement underway, will interface to EPICS Subsample diagnostic has required performance and minimises mathematics, hardware for TDC diagnostic under test