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Studies for a Low EMittance Muon Accelerator CERN, July 2 nd 2019

This proposal explores the feasibility of a low emittance muon accelerator for extending the high energy frontier. It covers areas such as accelerator physics, high energy theory, and engineering material science. Collaboration with international experts and informal contacts have begun.

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Studies for a Low EMittance Muon Accelerator CERN, July 2 nd 2019

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  1. Studies for aLow EMittanceMuon AcceleratorCERN, July 2nd 2019 P. Raimondi (ESFR) Special thanks to M. Boscolo, M. Antonelli, O. Blanco, A. Ciarma

  2. Low EMittanceMuon Accelerator team: INFN institutions involved: LNF, Roma1, Pd, Pi, Ts, Fe Universities: Sapienza, Padova, Insubria Contributions from: CERN, ESRF, LAL, SLAC This new proposal covers different areas of research: accelerator physics, high energy, theory, engineering material science, … Many colleagues are interested to collaborate, informal contacts with international experts has started We believe in the potential of this idea, but key challenges need to be demonstrated to prove its feasibility. I will show the work done up to now that may lead to a Conceptual Design Report

  3. Low EMittanceMuon Accelerator team

  4. Outline • Low emittance muon beam production concept • Preliminary scheme • Target options • First design of the e+ ring • Multi-pass and Single-pass scheme • First considerations about target thermo-mechanical stresses • Positron source requirements • Conclusion and Plans

  5. Muon based Colliders • A m+m- collider offers an ideal technology to extend lepton high energy frontier in the multi-TeV range: • No synchrotron radiation (limit of e+e- circular colliders) • No beamstrahlung (limit of e+e- linear colliders) • but muon lifetime is 2.2 ms (at rest) • Best performances in terms of luminosity and power consumption • Great potentiality if the technology proves its feasibility: • cooled muon source • fast acceleration • m Collider • radiation Safety (muon decay in accelerator and detector)

  6. Muon Colliders potential of extending leptons high energy frontier with high performance luminosity per wall-plug power vs c.m. energy J.P. Delahaye, M. Palmer, et al., arXiv:1502.01647 (updated by A. Blondel, P. Janot, F. Zimmerman)

  7. Muon Source Goals • Neutrino Factories: Rate > 1014m/sec within the acceptance of a m ring • Muon Collider: luminosities >1034/cm-2s-1 at TeV-scale (≈Nm21/em) Options • Tertiary production through proton on target: cooling needed, baseline for Fermilab design study production Rate > 1013m/sec Nm= 2×1012/bunch(5 108m/sec today @PSI) • e+e- annihilation: positron beam ontarget: very low emittance and no cooling needed, baseline for our proposal here production Rate ≈1011 m/secNm≈ 5×109/bunch • by Gammas (gNm+m-N): GeV-scale Compton gs productionRate ≈ 5×1010 m/sec Nm≈ 106 (Pulsed Linac) production Rate >1013 m/sec Nm≈ few×104 (High Current ERL) 10-20Hz cycle not discussed here see also: W. Barletta and A. M. Sessler NIM A 350 (1994) 36-44 (e-Nm+m- e- N)

  8. M. Boscolo, MAC, LNGS, 10 Oct. 2017 Proton based source

  9. M. Boscolo, MAC, LNGS, 10 Oct. 2017 Proton based source

  10. Exploring the potential for aLow Emittance MuonCollider • D. Alesini et al., “Positrondrivenmuon source for a muon collider”ARXIV (2019) • M. Boscolo et al., “Lowemittancemuonacceleratorstudies with production from positrons on target”, PR-AB 21 061005 (2018) • M. Boscolo et al.,“Studies of a scheme for low emittance muon beam production from positrons on target”, IPAC17 (2017) • M.Antonelli, “Very Low EmittanceMuon Beam using Positron Beam on Target”, ICHEP (2016) • M.Antonelliet al. , “Very Low Emittance Muon Beam using Positron Beam on Target”, IPAC (2016) • M. Antonelli, “Performance estimate of a FCC-ee-based muon collider”, FCC-WEEK 2016 • M. Antonelli, “Low-emittancemuon collider from positrons on target”, FCC-WEEK 2016 • M. Antonelli, M. Boscolo, R. Di Nardo, P. Raimondi, “Novel proposal for a low emittancemuon beam using positron beam on target”, NIM A 807 101-107 (2016) • P. Raimondi, “Exploring the potential for a Low Emittance Muon Collider”, in Discussion of the scientific potential of muon beamsworkshop, CERN, Nov. 18th2015 • M. Antonelli, Presentation Snowmass 2013, Minneapolis (USA) July 2013,[M. Antonelli and P. Raimondi, Snowmass Report (2013) also INFN-13-22/LNF Note Also investigated by SLAC team: L. Keller, J. P. Delahaye, T. Markiewicz, U. Wienands: • “Luminosity Estimate in a Multi-TeV Muon Collider using e+e- m+m- as the Muon Source”, MAP 2014 Spring workshop, Fermilab (USA) May ’14 • Advanced Accelerator Concepts Workshop, San Jose (USA), July ‘14

  11. Muon beams emittance from proton on target: p+targetp/Km typically Pm≈100 MeV/c (p, K rest frame) whatever is the boost PT will stay in Lab frame  very high emittance at production point  cooling needed! from direct m pair production: Muons produced from e+e-m+m- at √s around the m+m- threshold (√s ≈ 0.212GeV) in asymmetric collisions (to collect m+ andm-) NIM A Reviewer: “A major advantage of this proposal is the lack of cooling of the muons…. the idea presented in this paper may truly revolutionise the design of muon colliders … “

  12. Advantages: • Low emittance possible:qmis tunable with in e+em+m-qmcan be very small close to the m+m- threshold • Low background: Luminosity at low emittance will allow low background and low n radiation (easier experimental conditions, can go up in energy) • Reduced losses from decay:muons can be produced with a relatively high boost in asymmetric collisions • Energy spread: muon energy spread also small at threshold,itgets larger as increases Disadvantages: • Rate: much smaller cross section wrt protons (mb) s(e+em+m-) 1 mb at most

  13. Possible Schemes • Low energy collider with e+/e- beam (e+ in the GeV range): • Conventional asymmetric collisions (but required luminosity 1040 is beyond present capability) • Positron beam interacting with continuous beam from electron cooling (too low electron density, 1020 electrons/cm3 needed to obtain a reasonable conversion efficiency to muons) • Electrons at rest (seems more feasible): • e+ on Plasma target • e+ on standard target (eventually crystals in channeling) • Need Positrons of 45 GeV • g(m)200 and m laboratory lifetime of about 500 ms Beam with e+andm+m- e+ beam target • Ideally muons will copy the positron beam

  14. Muons beam divergence and energy spread as a function of the e+ beam energy • s(e+e-m+m-) mb 1 0.8 0.6 0.4 0.2 0 Ebeam(e+) GeV mrad qmmax 2 1.6 1.2 0.8 0.4 0 r.m.s.(Em)/Em 0.3 0.25 0.2 0.15 0.1 0.05 0 The value of sqrt(s) (i.e. E(e+) for atomic e- in target) has to maximize the muons production and minimize the beam angular divergence and energy spread 44 44 44 46 46 46 48 48 48 50 50 50 52 52 52 54 54 54 56 56 56 58 58 58 60 60 60 GeV Ebeam(e+) Ebeam(e+) GeV

  15. Contribution to m beam size due to finite target lenght [Babayaga3.5] m+/- e+ beam on target e+ L e+ x’ x1’= x0’ 1 mrad If L was a drift e+ x x1 = Lx0’ x0 x0’ E(e+) 43.1 45.2 51.8 x’ Muon beam at the exit of a 3 mm Be target em=0.19 nm (45 GeV e+ beam) Muons produced uniformly along target, rifts [0,L] x’max=qmmax m+/- xmax=L x’max thin light materials targets have negligible multiple scattering contribution [Geant4] The emittance contributions due to muon production angle: em = x x’max/12= L (qmmax)2/12 emcompletely determined by L and s -by target thickness and c.o.m. energy

  16. Criteria for target design Number of m+m- pairs produced per e+e- interaction is given by • N(m+m-)= s(e+e⟶m+m-)N(e+) r(e-)L • N(e+)number of e+ • r(e-)target electron density • L target length • To maximiseN(m+m-): • N(e+) max rate limit set by e+ source • r(e-)Lmax occurs for L or r values giving total e+ beam loss • e- dominated target: radiative Bhabha is the dominant e+ loss effect, giving a maximal m+m-conversion efficiency N(m+m-)/N(e+) s(e+e⟶m+m-)/srb 10-5 • standard target: Bremsstrahlung on nuclei and multiple scattering are the dominant effects, Xo and electron density will matter N(m+m-)/N(e+)  s(e+e⟶m+m-)/sbrem

  17. Criteria for target design Luminosity is proportional to Nm21/em optimal target: minimizes m emittance with highest m rate • Heavy materials, thin target • minimize em: thin target (em∝L with high densityr Copper: MS and m+m- production give about same contribution to em BUT high e+ loss (Bremsstrahlung is dominant) so s(e+loss)  s(Brem+bhabha)  (Z+1)s(Bhabha)  N(m+m-)/N(e+)  sm/[(Z+1)s(Bhabha)]  10-7 • Very light materials, thick target • maximize m+m- conversionefficiency  10-5(enters quad) H2 Even for liquid targets O(1m) needed em∝L increase • Not too heavy materials (Be, C) • Allow low em with small e+ loss N(m+m-)/N(e+)  10-6

  18. Possible schemes for muon production e- gun e- gun m- m- • Multi-pass scheme • Single-pass scheme e+ e+ T T e+ Linac e+ Linac m+ m+ e+ e+ Muons acceleration Recovery system or secondary e+ source Muons acceleration Ramping e+ storage ring Ramping e+ storage ring or recirculatinglinac

  19. Multi-pass scheme Goal: @T 1011 m/s Efficiency 10-7 (with Be 3mm)1018 e+/s needed @T e+ stored beam with T need the largest possible lifetime to minimize positron source rate LHeC like e+ source required rate with lifetime(e+) 250 turns [i.e. 25% momentum aperture (+/-12%)] n(m)/n(e+ source) 10-5 • Low emittance and high momentum acceptance 45 GeV e+ ring • O(100 kW) class target in the e+ ring for m+ m- production • High rate positron source • High momentum acceptance muon accumulator rings

  20. Low emittance 45 GeV positron ring cell circumference 6.3 km: 197 m x 32 cells (no injection section yet) Table e+ ring parameters P. Raimondi momentum acceptance Physical aperture=5 cm constant no errors Good agreement between MADX PTC / Accelerator Toolbox, both used for particle tracking in our studies

  21. Multi-turn simulations • Initial 6D distribution from the equilibrium emittances • 6D e+ distribution tracking up to the target (AT and MAD-X PTC) • tracking through the target (with Geant4beamline and FLUKA and GEANT4) • back to tracking code • At each pass through the muon target the e+ beam • gets an angular kick due to the multiple Coulomb scattering, so at each pass changes e+ beam divergence and size, resulting in an emittance increase. • undergoes bremsstrahlung energy loss: to minimize the beam degradation due to this effect, Dx=0 at target • in addition there is natural radiation damping • (it prevents an indefinite beam growth) no damping with damping sx(mm)

  22. e+ lifetime with Be target 3mm Be Target (0.8% Xo) Lifetime ∝ 1/thickness as expected determined by bremsstrahlung and momentum acceptance Lifetime with ~ 40 turns 2-3% e+ losses happen in the first turn

  23. Beam dynamics e+ beam in ring-with-target M. Boscolo, NuFact18, 16 August 2018 More details in: PR-AB 21, 061005 (2018) e+ emittance growth controlled with proper b and D values @ target Bremstrahlung Multiple scattering @Target : linear and non-linear terms of horizontal dispersion hx =0 After 40 turns

  24. M. Boscolo, NuFact18, 16 August 2018 Muonemittancecontributions e(m)= e(e+) ⊕ e(MS) ⊕ e(rad) ⊕ e(prod) ⊕ e(AR) Turns in accumulator ring e(e+)   = e+ emittance e(MS) = multiple scattering contributione(rad) = energy loss (brem.) contributione(prod) = muon production contributione(AR)    = accumulator ring contribution ] 3 mm Be Target Allthesevaluesneed to be matched to minimizeemittancegrowth due to beamfilamentation. by L. Keller muon production angle + MS contribution muon production angle sx and sx’  and correlations of e+ and mbeamshave to be similar Proc. of IPAC18, Vancouver, MOPMF087

  25. Comments on multi-pass scheme CONS • High poweron target • Lownumber of muons per bunch: do nothave a scheme for recombinationat high energy • Muonbeamalmost in CW, notcompatible with acceleration by synchrotron • The sameistrue for positronbeamreplacement (source + acceleration + injection) PROS • muonemittanceis small

  26. Single-pass scheme Single-pass schemewhere the positronbeampassesonly once through a ~X0 long targetfor muon production • More muonsproduced per bunch • Power can be distributed over a longer target • Positronbeamisdegraded by interaction with target • Muonemittancegrowsalong the target • Still high Peak Energy Density Distribution (PEDD)

  27. 1st extraction of 27 trains of 10 bunches, 1km spaced 2nd 3rd 4th 5th to fast acceleration Straight section with targets at 360 phase advance for muons, 180 phase advance for positrons. Magnets strengths scaled to cope for positrons energy loss Accumulator e+ rf Gamma bursts of 450ms at 100Hz Bunches synchronized to muon accumulator m- Possible n targets linac 4 delay loops e+ 27km 27 x 5 x 10 (135 x10) bunches of 1011 -12 e+ I = 260mA 10 Hz repetition rate ACC = 2x SS (10-50m) FODO + 2x ARC (100m) arcs rf m+ g to fast acceleration e+ 1.35 1016 e+/s 1 bunch of m every 135 accumulator turns (450ms) or 135*n target interactions or 1 positron ring cycle. 1011-12e+ x 135 bunches x 100 targets x 7.4 10-8 (production rate) = 109 m (neglecting muon lifetime) Ramp down Ramp@45GeV Extract on targets (450ms) inject Not to scale

  28. Timeline of the production cycle single-pass scheme Big effortisbeing put into the development of high energyacceptanceoptics for the accumulator ring

  29. Thickness of the target 3e11 e+ @45GeV 10 x 0.1X0 of Be The e+ beamlosesenergy due to Bremsstrahlung, and most of the particles are below the production threshold(E<43.7GeV) About 90% of the muons are produced in the first 3 targets -> 0.3X0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0 (Be X0)

  30. Thickness of the target Samestudyhasbeenperformedalso for other candidate materials, samebehaviourobserved

  31. Emittancegrowth in thick target 0.03 0.06 0.09 0.12 0.15 0.18 0.21 0.24 0.27 0.3 X0 6nm positron emittance, @45GeV

  32. Considerations on m accumulation Accumulation must be performed in Ring must be as short aspossible • Number of muons can be increased by using a thick target (single pass scheme) • driftcontribution on beamsize • MScontribution on emittance • Possible solutions: • Spaghetti-like targets • Multiple targets to help powerdissipation

  33. Muon accumulator, asynchronous and achromatic Tracking 1000 turns dE/E +-10%

  34. Multiple IP, multiple targets Targets separated by a transport line wheremagnetsare common to the threebeams(e+, μ+ and μ−), focusingthe beamsateach IP to achieve the production of new muons with minimalgrowth to the finalbeamemittance. • Best lattice design: • Lenght < 5 m • magnetgradientat 200 T/m • aperture radius 1 cm • Twotripletsare used to focus the beamson bothtransverseplanes, and theyare put in asymmetry in order to partiallycancelchromaticityat 45 GeVas in the apochromatic design

  35. Conventional options for m target • Aim at bunch (3x1011 e+) transverse size on the 10 mm scale: rescaled from test at HiRadMat (5x1013p on 100mm) with Be-based targets and C-based (HL-LHC) • No bunch pileup Fast rotating wheel (20000 rpm) • Power removal by radiation cooling (see for instance PSI muon beam upgrade project HiMB) • Need detailed simulation of thermo-mechanical stresses dynamics • Start using FLUKA + AnsysAutodyn(collaboration with CERN EN-STI) • Experimental tests: • FACET-IIavailable from 2019 • 1011 e-/bunch, 10 mm spot size, 100 Hz • DAFNEavailable from 2020, see later [F. Maciarielloet al., IPAC2016] [A. Knecht, NuFact17]]

  36. Option for liquid H2 target Liquid H2 or He jets of diameter in order to reduce multiple scatteringcontribution on muonemittanceduringaccumulationprocess Possibleissues: • Longtargets (driftbecomesrelevant) • Vacuum must be replacedat a very high rate due to vaporization of the target

  37. Positron source requirements for LEMMA Positron source rate isindependent on the scheme(multi- or single-pass) Maindependences on target material and recoverysystemenergyacceptance Single-pass scheme To evaluate the number of positrons per second required from the source we assume to have 1500bunches with 51011 e+/ bunch on target at 10Hz (total of 7.5E+15 positrons/sec) We conclude that the added value of the positron recovery would be only of a factor 2 at best, and it would require a system to reset the 6D phase space of the positrons to the originals.

  38. Positron sources studies on the market • Summary of e+ sources projects (all very aggressive): In [F. Zimmermann, et al., ‘POSITRON OPTIONS FOR THE LINAC-RING LHEC’, WEPPR076 Proceedings of IPAC2012, New Orleans, Louisiana, USA] • This is a key issue to be studied

  39. Embedded positron source Straightforward (in principle) to produce low energy damped accumulated e+ with a yield>1 (SLC yield=1.1 @22GeV primary beam) Positron source extending the target complex? Possibility to use the g’s from the m production target to produce e+ e+ 45 GeV e+ e- pairs g’s Focusing based on AMD under study promising preliminary results on collection efficiency Thin light target (eventually crystal in channeling) Dipole magnet Thick heavy target Produce a fraction of e+ of the incoming positron beam high rate energy gthanks to very thin target and cw structure of the stored beam 3 mm Be [Geant4] N(e+e-)/N(e+)[%] NX0 g’s angular distribution at the target exit

  40. Conclusion • Preliminary studies for a low emittance muon source are promising • We will continue to optimize all the parameters, lattices, targets, etc. in order to assess the ultimate performances of a muon collider based on this concept Some of the key challenges: • Low emittance and high momentum acceptance 45 GeV e+ ring • O(100 kW) class target in the e+ ring for m+ m- production • High rate positron source • High momentum acceptance muon accumulator rings • First design of low emittance e+ ring with preliminary studies of beam dynamics • Optimization requires other issues to be preliminary addressed: • target material & characteristics • e+ accelerator complex • muon accumulator rings design • luminosity parameters optimization

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