MICE RF DAQ Possible Solutions?

1. MICE RF DAQPossible Solutions? Paul J Smith University of Sheffield

2. MICE RF • I’m making a lot of assumptions in this presentation, of which many may be challenged. • After much discussion with both Yordan and Kevin over the last few months we feel that we had come up with a good starting point wrt how we build a DAQ for the MICE RF. • However a couple of weeks ago I was contacted by Peter Corlett and Trina Ng from Daresbury who had independently presented 2 techniques that could be used: • The first technique involves an optical system; this is novel and I really like it – although as presented it may not work with the MICE DAQ. Hopefully we can discuss this further. I’ve included some slides that they sent to me. • The second system involves using various sampling techniques requiring FPGA’s to measure the phase and amplitude very accurately. • Not really time to discuss these in detail in our talk so I’ve not included. • Unsure how these techniques would fit into our existing infrastructure that the RF DAQ will need to interface to – requires discussion, but could be useful! P. J. Smith - Physics & Astronomy, University of Sheffield

3. Problem • Muons travelling through the MICE channel will arrive at the cooling channel randomly within the MICE spill gate period. • Because it is not possible to synchronise the operation of the RF cavities to individual muons the first RF cavity could be at any phase as the muon traverses through it. • The relative phase angles between all eight cavities should be well known [i.e. Control] but we will still want to measure these phase angles directly [i.e. DAQ]. • The amplitude of the Electric Field in the cavity should also be well known [i.e. Control] but it may decay during the spill. We will want to measure the Amplitudes within the cavities. [DAQ] • The purpose of the RF DAQ is to establish both what the E phase angle and the E amplitude was within a given cavity when a muon traversed through it. P. J. Smith - Physics & Astronomy, University of Sheffield

4. Problem • The purpose of the RF DAQ is to establish both the E phase angle and the E amplitude within a given cavity as a muon traverses through it. • In order to achieve this the cavity phase must be time correlated to hits in other MICE detectors to the appropriate resolution. From this it should be possible to compute what the correct RF phase angle was when a muon entered a cavity. • I’m not an RF expert and so I will happily take on board any constructive criticism and/or advice on the best way forward with this problem. • My Goal: I would like to leave the RF meeting with a firm consensus about what direction(s) we are taking this problem, as we would like to start work on this asap. P. J. Smith - Physics & Astronomy, University of Sheffield

5. Constraints • I’m working with the following assumptions: • The amplitude must be known to 1% – This is the same figure that our colleagues from Daresburyused. • The phase of the cavity must be known to within 5 degrees as the muon traverses through it. I’m not sure of the source of this figure? • I’m assuming that this means +/- 5 degrees error. Is this correct? • At 201.25 MHz period = 4.97ns => 5 deg = 69 ps. • Is 69 ps an absolute or a RMS value? For now I’m assuming the first case.... • I will be expressing the phase difference as a delay, as this lends itself to much better analysis with the electronics; • i.e. We have a RF Timing error budget of +/- 69 ps with the DAQ P. J. Smith - Physics & Astronomy, University of Sheffield

6. Method 1 P. J. Smith - Physics & Astronomy, University of Sheffield

7. Event Builder (PC) TOF Particle Trigger? β α γ (α – γ) Phase Monitors TDC Discriminator Cavity Probe TOF Particle Trigger Slow Digitiser (or same digitiser as below?) Reference Oscillator for Cavity 1 Digitiser Fast n Bit Amplifiers P. J. Smith - Physics & Astronomy, University of Sheffield

8. Digitisers • I think that we will need to digitise at least one return signal from each set of RF cavities or from a master signal. • Advantages • This will permit an absolute measurement of both phase and amplitude (if from the Cavity) on the first RF cavity over a short period of time. (Possibly Decay over a longer period) . • The phase measurement would provide an absolute phase value by which to compare the other cavities with and will provide a cross check on any discriminator. • It could make it easier to correct for any systematics ‘found post data taking’. • Could help improve the resolution of the fits over amplitude and phase measurements alone. • Disadvantages • Will generate a lot of data – so we may not want to keep every digitisation record. This implies data reduction on the fly. • Digitiser would presumably have to work on an event by event basis rather than a spill by spill - this may complicate the DAQ. Depends on data rate etc. • OTHERS ?? P. J. Smith - Physics & Astronomy, University of Sheffield

9. Discriminator • A fast discriminator (level/zero crossing/fraction?) could provide a series of timing pulses that would lock a given phase value of the RF to the other MICE DAQ triggers. • For example if the timing pulses were logged by the TOF TDC then we could in principle correlate the phase of the RF (tagged by the timing pulses) to timing events within theTOFs. With this information it would be possible to reconstruct what the phase of the RF was when the muon traversed a cavity. • ... This makes some aggressive assumptions about timing stability which clearly needs some analysis. Note: This is a composite Image of LF Sine Wave (Few MHZ) with a discriminator to demonstrate the principle

10. Digitiser Simulations • I have been running some simulations/reconstructions to give me a feel for the kind of sample rate/resolution required to get reasonable timing resolution on the reconstruction of a digitised signal. • Of course it is not realistic....and I prefer to build hardware anyway. But it is useful to determine a starting point to give some indication of what performance we need from a digitiser. • The simulation doesn’t take account of • Timing delays, Cross talk, Varying DC Bias – and other things I’ve not yet thought of which will all degrade the performance/introduce errors and need to be quantified... • Simulation/Reconstruction has added a white noise source. • I’ve started looking at discriminator signals but I’m not happy with the systematics in the the model yet. Early indications are that the sigma is good. P. J. Smith - Physics & Astronomy, University of Sheffield

11. Simulation Details • Create a clean ‘master’ RF sine signal of a known phase, frequency, amplitude (and decay). For this I create a sample at 25ps intervals where the sine value is stored to double precision (i.e. not digitised) • Create a second sine wave at a sample rate of n Gs/sec. • Values are digitised to an accuracy of x bits. • Add white noise with Gaussian at a fraction of the signal amplitude. • Create a sample length of 30ns. • Fit the digitised wave. • Compare fit parameters with the master RF signal and see how well the fit compares to the true amplitude, phase, DC bias (And Decay). This gives some idea of how noise, sample rate and bit resolution affects the reconstruction. • I’m assuming that I’m capturing the data on an event by event basis with a 30ns capture time (roughly time of flight of a muon through the experiment) P. J. Smith - Physics & Astronomy, University of Sheffield

12. Power Decay • If the RF amplifiers are operated without feedback (i.e. open loop full power) then it is expected that there will be a droop in the output power during the 1ms of operation. • Assuming a 10% droop during 1ms: • = 0.9 ~Time of Flight ~Current Sampling period per Event (TOFs) Basically it’s flat over any reasonable ‘event based’ sample period. P. J. Smith - Physics & Astronomy, University of Sheffield

13. RF Signal (MTB) Example of RF signal from MTB at Fermilab…. Unable to obtain a screenshot! P. J. Smith - Physics & Astronomy, University of Sheffield

14. Plots 1) High Res Master – Note Exponential Decay is Exaggerated. 2) Same Plot with noise added where 1σ = 0.05 3) Master Plot digitised, 8 bit 5Gs/sec – noise added as 2) 4) Fit plotted to digitised sample. Fit parameters are then compared with 1)

15. Plots 5)Phase Error fitted to previous plots (5000 iterations with random starting phases) 6)Same Sequence with Amplitude Error % (Note only 8 bit digitiser) 7) And DC Bias % Error. P. J. Smith - Physics & Astronomy, University of Sheffield

16. Tables 5 degrees = 70ps Amplitude ~1% Increasing the amount of White Noise on a simulated signaland the subsequent fit parameters Increasing the number of bits does not make a significant difference to the error on the fit. P. J. Smith - Physics & Astronomy, University of Sheffield

17. Tables 5 degrees = 70ps Amplitude ~1% The phase accuracy is very sensitive to sample rate over a 30ns period. Discriminator model... I’ve yet to understand a systematic in the model so I’m not including the data but (ignoring systematic) the fit to multiple discriminator hits is good but is more sensitive to noise (not surprising as there are less points) System resolution = error on digitiser fit + error on discriminator fit ~tens of ps P. J. Smith - Physics & Astronomy, University of Sheffield

18. Tables - Added Crosstalk Crosstalk at the same frequency (201.25Mhz) and phase shifted by 119 degrees was added to the signal to see what effect it had… Clean cross talk at a single frequency just shifts the mean (as expected) but doesn’t appear to adversely affect the sigma of the fit. P. J. Smith - Physics & Astronomy, University of Sheffield

19. Instrumentation - Components From the earlier diagram this is what I think we need for Method 1 Several Phase monitors. Discriminator. TDC, same as already used on MICE, for Development. A slow(er) Digitiser for recording phase monitor signals (Fast Digitiser) Some way of monitoring the amplitude of the RF signal (Second Channel on a fast digitiser?) Fast Scope – 1GHz+ - four channel. 2 Channel Signal Generator with accurate phase control. P. J. Smith - Physics & Astronomy, University of Sheffield

20. Method 2 • I’ve copied these slides directly from the • presentation that Peter sent to me. P. J. Smith - Physics & Astronomy, University of Sheffield

21. OPTICAL TIMING – Phase information Detector Detector Trigger from Muon event Laser Diode Pulse carving 10GHz Optical modulator Photodiode TRIG Photodiode ADC RF oscillator (201.25 MHz) • Optical pulses are carved by the event triggers. • Pulse pair is split to generate an ADC trigger and probe pulse • Probe pulse is amplitude modulated by the RF oscillator to determine timing with respect to RF phase. • Pulse amplitude is sampled with ADC • expected jitter < 10 ps (assuming no trigger-RF oscillator jitter) Slides on Optics provided by Peter Corlett, STFC

22. OPTICAL TIMING – Amplitude information Detector Detector Cavity probe Trigger from Muon event 10GHz Optical modulator Photodiode Laser Diode Pulse carving 10GHz Optical modulator Photodiode TRIG Photodiode ADC Amplitude Phase Reference RF oscillator (201.25 MHz) • Compare amplitude samples from ‘clean’ oscillator and cavity probe to measure decay Because of the jitter on the Particle trigger (100ps + ns) the pulse carving/TDC interface may require some thought – However the core optical system could be a useful technique! Slides on Optics provided by Peter Corlett, STFC

23. OPTICAL TIMING – Multiply for many cavities Detector Detector Trigger from Muon event Cavity probes 10GHz Optical modulator Photodiode Laser Diode Pulse carving 10GHz Optical modulator Photodiode 10GHz Optical modulator Photodiode 10GHz Optical modulator Photodiode 10GHz Optical modulator Photodiode Photodiode TRIG RF oscillator (201.25 MHz) ADC

24. Implementation P. J. Smith - Physics & Astronomy, University of Sheffield

25. RF Monitoring – Test Setup Practical Work • Phase 1 (LAB) • Decide on the design with consideration of sources of noise and jitter etc. • Purchase of enough suitable equipment to generate a test bench. • Prove that reconstruction to the desired accuracy is possible, including consideration of signal delays, jitter etc. • Add appropriate noise to 200MHz sine-wave to understand its effects on the accuracy of reconstruction. • Phase 2 (RF Test Stand at RAL?) • To use the above system on real RF cavity(ies) to show that reconstruction is possible using real signals. • Phase 3 (Integration into MICE) • Purchase electronics for additional channels and install into MICE with RF Calibration and Data Taking. P. J. Smith - Physics & Astronomy, University of Sheffield

26. Questions • Further Questions from Audience? • Is there a general consensus that this problem is being tackled in the correct way? • Is there a preferred method that we pursue? • Is there funding available to purchase the necessary test equipment and the instrumentation to build a test bench? P. J. Smith - Physics & Astronomy, University of Sheffield