RTML feed-forward correction
Embed Size (px)
Transcript of RTML feed-forward correction
RTML feed-forward correction
RTML feed-forward correctionR. Apsimon, A. LatinaMotivationPre-linac betatron collimationLimit emittance growth through collimatorBeam jitter < ~ 0.25 @ end of RTML in both planesBeam jitter < 0.1 @ start of RTML in both planesDamping ring extraction systemStringent jitter requirementsUnlikely kicker and septa can meet these requirementsUse RTML feed forward systemsCorrect beam jitter in RTMLLimit emittance growthProposed locations
e-FF1e- FF2e+FF2The e+ RTML has a chicane rather than a loop for the central arc; pFF1 will be different to the other FF systems.
BColl: betatron collimation systemEC1 + EC2: energy collimator systems
FF1:Correct DR extraction jitterLimits emittance growth along RTML
FF2:Correct jitter at entrance of betatron collimator system (BC)Prevents significant emittance growth in BC systemBCollBCollEC2EC2EC1BPMskickersFeed forward electronicse-To main linace+FF1Fix names3Feed forward correctionsP1P2K1K2Transfer matricesKicker correctionsSystem latency
LCoaxial cables are fast, but for low attenuation, very thick cables (~20 mm diameter) would be needed; this would be difficult to install and repair.
Optical cables are low loss, compact, but very slow; the latency budget might not be enough.System latencyExperience from the FONT feedback system at ATF2 suggests that the minimum latency requirement would be ~150 ns.
Additional latency allows for improvements:Digitise BPM signals: less susceptible to noiseUse of high resolution ADCs and DACsUse of 32- or 64- bit processing for the digital feed-forward electronicsE.g. Xilinx Virtex-7 FPGASystematic correction of the bunch-to-bunch profile within the train
In summary, the large latency budget provided by coaxial cables would allow for a very high resolution digital feed forward system. The limiting factor would be the resolution of the BPMs.BPM resolution
To achieve good jitter correction, the BPM resolution must be much smaller than the expected beam jitter.
The expected beam jitter in the FF regions is ~10m horizontally, but the required BPM resolution is ~140nm; this requires cavity BPMs.
Factor of ~100 between dynamic range and resolution; is the achievable?Look at the resolution and dynamic range7FF kicker specificationsParameterValueLength1 mKicker typeElectrostaticReproducibility> 1 %Field homogeneity> 1 %Rise / fall time> 10 nsFlat top duration~160 nsDeflection angle~ 0.8 radFor a kicker stability of 2%, the resulting jitter at the entrance of the BC system will be ~20nm; smaller than the resolution of any existing BPM system.
Therefore we can assume the kickers are perfect for simulation purposes.Tracking simulationsTracking in PLACETNo FF correctionOnly FF1Only FF2FF1 + FF2Jitter amplification + emittance growthVs. initial jitterVs. BPM resolution
Following slides only show horizontal beam as this is the more critical.RTML emittance growth budgetThe aim is to allocate 25% of the dynamic budget to emittance growth due to beam jitter.
Tracking simulations show that only 50 nm of the horizontal budget is used, therefore the remaining 10 nm will be allocated to the beam jitter budget.x vs. initial jitter
Final jitter vs. initial jitter
x vs. initial jitter + collimation
Final jitter vs. initial jitter+ collimation
BPM resolution vs. initial jitter
BPM resolutionThis plot shows how the BPM resolution varies with initial jitter to produce 15 nm of emittance growth due to beam jitterPut in emittance budgets and explain and say its horizontal15Extraction system
Thick septumThin septumKickerTolerances for damping ring extractionThe kicker good field region has been reduced from a radius of 1mm to 0.5mm.
This combined with the proposed FF systems relaxes the stability requirements for the extraction system by a factor of ~16.
The stability requirements for the extraction elements have been optimised to maximise the combined extraction stability.Add extraction system plot17Possible machine protectionDue to the large available latency, the feed forward electronics could double as a fast emergency dump system.
The FF kickers will only be able to deliver ~ 0.8 rad kicks. If the beam trajectory is too far from the nominal orbit, the kickers will not be able to fully correct the orbit. If the trajectory is dangerously far from the design orbit, the feed forward electronics could be used to trigger a dump kicker downstream of the FF kickers.
This would reduce the risk of damage to the collimation system in the event of total beam loss.Determination of an unsafe beamBPM: P2BPM: P1e- / e+xx'BPMskickersFeed forward electronicse-To main linacDump kickerCalculate FF kicksSafe beam?ToFF kickersNoFire dump kickerBPMsignalsFeed forward firmwaree+ FF1 ConsiderationsWithout FF1, extremely low BPM resolution is required for the e+ RTML to relax requirement for the DR extraction system: probably not achievable.
150 ns latency can be achieved if the signal velocity > 0.945c:Use free-space optical links ( > 0.999c)The signals are transmitted by a laser through a narrow tunnel~300 ns of latency
Due to the smaller latency budget for the e+ FF1 system, many of the high-latency features would have to be disabled. This would be a stripped down version of the normal FF systemLower resolution digitisation and processingThe emergency dump feature should remain without any problem.E+ FF121e+ FF1 latency curves
Minimum latencySay it can work!22SummaryRTML FF systems are essential to:Minimise beam jitter at the entrance of the main linacsRespect the emittance growth budget of the RTMLJitter through betatron collimator is criticalRelax stability requirements of damping ring extraction system
The main requirements of the FF system has been outlinedLatency requirementCable typeBPM resolutionKicker requirementse+ FF1 system is possible, but will have a small latency budgetVertical beam is less critical since the vertical motion damps along the RTML
Tracking simulations investigated:Emittance growth and jitter amplificationBPM resolutionLimits on initial jitter
FF system requirements seem achievable given FONT and cavity BPM studies at ATF2Talk about vertical case23