prospects for an energy-frontier muon collider
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Prospects for an Energy-Frontier Muon Collider. Tom Roberts Muons, Inc. Illinois Institute of Technology. Outline. Background Why muons? The major challenges Surmounting the challenges Recent innovations that have improved the prospects for success - PowerPoint PPT PresentationTRANSCRIPT
Feb 12, 2008 TJR Prospects for a Muon Collider 1
Prospects for an Energy-Frontier Muon Collider
Tom Roberts
Muons, Inc.Illinois Institute of Technology
Feb 12, 2008 TJR Prospects for a Muon Collider 2
Outline
• Background
• Why muons?
• The major challenges
• Surmounting the challenges
• Recent innovations that have improved the prospects for success
• Viewgraph-level design of a Muon Collider
• Current R&D Efforts
• Summary
Feb 12, 2008 TJR Prospects for a Muon Collider 3
Background Reminders
Historically, every significant increase in energyhas taught us something completely new.
Every new type of particle beam has alsotaught us something completely new.
The LHC is turning on later this year, so the “energy frontier” is above 14 TeV for protons,
or above ~1.5 TeV for leptons.
Feb 12, 2008 TJR Prospects for a Muon Collider 4
The Livingston Plot
X ILC
X 5 TeV MC
2025
Con
stitu
ent
Cen
ter-
of-M
ass
Ene
rgy
Panofsky and Breidenbach,Rev. Mod. Phys. 71, s121-s132
(1999)
Feb 12, 2008 TJR Prospects for a Muon Collider 5
Why Muons?
• Electrons have problems at the energy frontier– At the TeV scale, radiative processes limit both energy and
luminosity for electrons• Synchrotron radiation losses linear, large, and very expensive
• Beamstrahlung ~ E2, approaches the beam energy in one crossing low luminosity at peak energy, huge beam energy spread
– Remember those beautiful, narrow peaks for the J/Ψ? They won’t happen again because:
• The beam energy spread is very large
• Resonances above 2MW will have large weak-decay widths
• Protons have problems at the energy frontier– Without some tremendous breakthrough in high-field magnets,
the machine must be truly enormous (expensive)– As composite particles, beam energy must be considerably
higher than for leptons
Feb 12, 2008 TJR Prospects for a Muon Collider 6
Muons
• Clearly a whole new window into electroweak processes
• A path to the energy frontier– Radiative processes are far from limiting (as for
electrons)– Circular machine is possible, as are recirculating
linacs– Lepton, so beam energy and machine size are
significantly lower than for protons
• For S-channel Higgs production, cross-section~ m2 – 40,000 times larger than for e+e-.
Feb 12, 2008 TJR Prospects for a Muon Collider 7
Muons
[Ankenbrandt et al., PRST-AB 2, 081001 (1999)]
A 5 TeV muon collidercould fit on the existing
Fermilab site.
Feb 12, 2008 TJR Prospects for a Muon Collider 8
The Major Challenges
• Muons decay in 2.2 microseconds• Muons are created with a very large emittance, too
large for conventional accelerators, too large to give reasonable luminosity
• Muon production from 8-40 GeV protons scales roughly as proton beam power, independent of energy – A 1 to 4 Megawatt proton beam is required– The production target is also a challenge
• Muons decay into an electron plus neutrinos– Electron backgrounds in detector– Neutrino radiation problem (!)
Feb 12, 2008 TJR Prospects for a Muon Collider 9
Reducing the Phase Space – “Cooling”
• Loosely: the muons produced occupy the size of a beach ball (60 cm), the ILC accelerating cavities can accept a BB (4 mm) – take advantage of ILC R&D and optimization.
– overall reduction in phase space ~106.
• Luminosity ~ N2·ε┴-2 so lower transverse emittance
permits a reduction in N (which reduces other problems).
• Must select a process that avoids Liouville’s theorem.
• Must select a method consistent with the muon lifetime (2.2 μsec).
• Desirable to select a method consistent with the peak momentum of the produced muons (~300 MeV/c).
Feb 12, 2008 TJR Prospects for a Muon Collider 10
Muon Ionization Cooling
• Alternate absorbers and RF cavities• RF cavities restore the energy lost in the absorbers• A factor of 1/e reduction in transverse phase space occurs when the
total energy lost in absorbers equals the beam energy (both planes)• Optimal energy corresponds to a momentum of 100-250 MeV/c• Works only for muons (electrons shower, hadrons interact)• Transverse cooling only (small longitudinal heating due to straggling)
Absorberdp/dz || -p
RF Cavitydp/dz || +z
p┴ reduced,
p|| unchanged
(Skrinsky & Parkhomchuk, 1981)
Feb 12, 2008 TJR Prospects for a Muon Collider 11
Muon Ionization Cooling
Transverse Emittance change per unit length in the absorber:
Cooling term(energy loss)
Heating term(multiple scattering)
• Want:– Lower β┴ (stronger focusing at the absorber)– Minimize multiple scattering– Maximize energy loss
Here Here is the normalized emittance, Eis the normalized emittance, Eµµ is theis the muon energy, dEmuon energy, dEµµ/ds and X/ds and X00 are the are the
energy loss and radiation length of the absorber material, energy loss and radiation length of the absorber material, is the transverse beta- is the transverse beta-
function of the magnetic channel, and function of the magnetic channel, and is the particle velocity. is the particle velocity.
Lattice design
Absorber Material
Feb 12, 2008 TJR Prospects for a Muon Collider 12
Absorber Materials
Fcool ~ (Energy Loss) / (Multiple Scattering)
Feb 12, 2008 TJR Prospects for a Muon Collider 13
Emittance Exchange
Ionization cooling is only transverse. To get longitudinal cooling,use emittance exchange.
Feb 12, 2008 TJR Prospects for a Muon Collider 14
Innovation: Helical Cooling Channel
• Cools in all 6 dimensions – higher-energy particles have longer path length in the absorber
• A remarkable thing occurs: for specific values of the geometry, the solenoid, helical dipole, and helical quadrupole fields are all correct.
• With absorber and RF, parameters remain constant; with absorber only, parameters decrease with momentum.
• Acceptance is quite large compared to most accelerator structures.
These coils just surround the beam region.
All coils are normal to the Z axis; their centers are offset in X and Y
to form the helix.
The helical solenoid is filled with a continuous absorber, and perhaps with RF cavities.
BeamFollows
Helix
Feb 12, 2008 TJR Prospects for a Muon Collider 15
HCC Simulation
• Four sequential HCCs with decreasing diameter and period, increasing field (8 T max)
• Emittance reduction is 50,000 over 160 m(~15% decay)
• In the analogy of starting with a beach ball and needing a BB, this is a small marble (~1 cm dia.)
Feb 12, 2008 TJR Prospects for a Muon Collider 16
Related Innovation: Guggenheim Cooling Channel
• Helix with radius >> period• Also capable of emittance exchange• More like a ring cooler that has been “stretched” vertically
Figure is mine; concept is Palmer et al, BNL
Feb 12, 2008 TJR Prospects for a Muon Collider 17
Innovation: High Pressure Gas RF Cavities
• High-pressure hydrogen reduces breakdown via the Paschen effect• No decrease in maximum gradient with magnetic field• Need beam tests to show HPRF actually works for this application.
Paschen region
Electrode breakdown region
805MHz
Feb 12, 2008 TJR Prospects for a Muon Collider 18
Innovation: High Pressure Gas RF Cavities
• Copper plated, stainless-steel, 805 MHz test cellCopper plated, stainless-steel, 805 MHz test cell
• HH22 gas to 1600 psi and 77 K gas to 1600 psi and 77 K
• Paschen curve verified (at Fermilab’s Lab G and MuCool Test Area)Paschen curve verified (at Fermilab’s Lab G and MuCool Test Area)
• Maximum gradient limited by breakdown of metalMaximum gradient limited by breakdown of metal
• Fast conditioning seenFast conditioning seen
• Unlike vacuum cavities, there’s no measurable limitation for magnetic field!Unlike vacuum cavities, there’s no measurable limitation for magnetic field!
Feb 12, 2008 TJR Prospects for a Muon Collider 19
Understanding RF Breakdown
Scanning electron microscope images; Be (top) and Mo (bottom).
Feb 12, 2008 TJR Prospects for a Muon Collider 20
Innovation: Parametric Resonance Ionization Cooling
Clever method to greatly reduce Clever method to greatly reduce without increased magnetic fields. without increased magnetic fields.
Excite ½ integer parametric resonance (in Linac or ring)Excite ½ integer parametric resonance (in Linac or ring)
• Like vertical rigid pendulum or ½-integer extractionLike vertical rigid pendulum or ½-integer extraction
• Elliptical phase space motion becomes hyperbolicElliptical phase space motion becomes hyperbolic
• Use xx’=const to reduce x, increase x’ Use xx’=const to reduce x, increase x’
• Use IC to reduce x’Use IC to reduce x’
Detuning issues are being addressed (chromatic and spherical aberrations, Detuning issues are being addressed (chromatic and spherical aberrations, space-charge tune spread). Simulations are underway. space-charge tune spread). Simulations are underway.
Smaller beams from 6D HCC cooling are essential for this to work!Smaller beams from 6D HCC cooling are essential for this to work!
xX
X’
X
X’
Feb 12, 2008 TJR Prospects for a Muon Collider 21
Innovation: Reverse Emittance Exchange
• p(cooling)~200MeV/c, p(colliding)~2.5 TeV/c room in Δp/p space• After cooling and acceleration, the beam has much smaller
longitudinal emittance than necessary.• Reduce transverse emittance to increase luminosity, trading it for
increased longitudinal emittance (limited by accelerator acceptance and interaction point **).
EvacuatedDipole
Wedge Abs
Incident Muon Beam
Feb 12, 2008 TJR Prospects for a Muon Collider 22
Innovation: Bunch Coalescing
• Start with ~100 MeV/c cooled bunch train.• Accelerate to ~20 GeV/c with high-frequency RF.• Apply low-frequency RF to rotate the bunches longitudinally.• Permit them to drift together in time.• Avoids space charge problems at low energy.
p
t
1.3 GHz Bunch Coalescing at 20 GeV
RF
Drift
Cooled at 100 MeV/c
RF at 20 GeV
Coalesced in 20 GeV ring
Feb 12, 2008 TJR Prospects for a Muon Collider 23
Innovation: Dual-Use Linac
• Fermilab is considering “Project X”, a high-intensity 8 GeV superconducting linac
• Use it also to accelerate muons (after cooling)
~ 700m Active Length
Possible 8 GeV Project X Linac
Target and Muon Cooling Channel Recirculating
Linac for Neutrino Factory
Bunching Ring
NeutrinoFactoryaimed atSoudan, MN
Feb 12, 2008 TJR Prospects for a Muon Collider 24
Innovation: Pulsed Recirculating Linac
• Accelerating from 20 GeV to 2,500 GeV requires a lot of RF!• Muon decay dictates high ratio of RF/length.• A “dogbone” recirculating linac is a reasonable trade-off between
cost, size, and muon decay.• By pulsing the quadrupoles of the linac, more passes can be made
without losing transverse focusing.• This linac is several km long, so pulsing is feasible.• With careful design this can handle both μ+ and μ (time offset in RF
cavities, FODO vs DOFO lattice, travel opposite directions in arcs).
Injection
ExtractionLinac
Feb 12, 2008 TJR Prospects for a Muon Collider 25
Innovation: High-Field HTS Superconducting Magnets
• The high-temperature superconductors have a remarkable property: at low temperature (2-4 K) they sustain a high current density at large magnetic fields.
• Measured up to ~40 T, expected to hold to even higher fields.
• It is likely that solenoids in the range of 30 T to 50 T can be constructed.
• Higher field lower , so lower emittance can be achieved via ionization cooling.
• These materials are a challenge to work with…
Feb 12, 2008 TJR Prospects for a Muon Collider 26
Many New Arrows in the Quiver
• New Ionization Cooling TechniquesNew Ionization Cooling Techniques– Helical Cooling Channel Helical Cooling Channel – Momentum-dependent Helical Cooling ChannelMomentum-dependent Helical Cooling Channel– Guggenheim cooling channelGuggenheim cooling channel– Ionization cooling using a parametric resonanceIonization cooling using a parametric resonance
• Methods to manipulate phase space partitionsMethods to manipulate phase space partitions– Reverse emittance exchange using absorbersReverse emittance exchange using absorbers– Bunch coalescing (neutrino factory and muon collider share Bunch coalescing (neutrino factory and muon collider share
injector)injector)• Technology for better coolingTechnology for better cooling
– Pressurized RF cavities Pressurized RF cavities – High Temperature Superconductor for up to 50 T magnetsHigh Temperature Superconductor for up to 50 T magnets
• Acceleration TechniquesAcceleration Techniques– Dual-use Linac– Pulsed Recirculating Linac
Feb 12, 2008 TJR Prospects for a Muon Collider 27
Conceptual Block Diagram of a Muon Collider
Proton Driver(8-40 GeV)
ProductionTarget
Pion Capture, Decay Channel,Phase Rotation, and Pre-Cooling
Muon Ionization Cooling
Acceleration(0.2 to 20 GeV)
Reverse EmittanceExchange
Bunch Coalescing
Acceleration (20 to 2,500 GeV)
Storage Ring andInteraction Regions
Experiments
Must of course deal with both μ+ and μ-.
Feb 12, 2008 TJR Prospects for a Muon Collider 28
Fernow-Neuffer Plot
HCC 400 MHz
HCC 800 MHz
HCC 1600 MHzPIC
REMEX &Coalescing
Start Cooling: After Capture, Decay, Phase Rotation,
Pre-Cooling
AccelerationTo 20 GeV
End Cooling:Start
Acceleration to2.5 TeV
Feb 12, 2008 TJR Prospects for a Muon Collider 29
Viewgraph-level Design
Target, pion capture,Phase rotation
Helical cooling channel
Proton driver
2.5 km ILC-likelinacs
2.5 + 2.5 TeV muonstorage ring with
two IRs1 km radius
(= Fermilab Main Ring,but it’s not deep enough)
Final cooling, preacceleration
μ+
μ–
10 recirculating arcsIn one tunnel
L ~ 1035 cm-2 s-1
Feb 12, 2008 TJR Prospects for a Muon Collider 30
Related Facility: Neutrino Factory
• Muons in a storage ring with a long straight section aimed at the far neutrino detector
• Concept is more fleshed out that a muon collider– Cheaper, of striking current interest, perhaps more feasible
• Thousands of times more neutrino intensity than alternatives
• Higher energy neutrinos, with narrower energy spectrum• Essentially perfect purity (no π decays) – great for
wrong-sign appearance measurements of oscillation• Near detector looks a lot like old fixed-target hadron
experiments:• 30 cm liquid hydrogen target• Event rate ~ 1-100 Hz• Must be careful about material (spontaneous muons!)
Feb 12, 2008 TJR Prospects for a Muon Collider 31
Neutrino Factory
Feb 12, 2008 TJR Prospects for a Muon Collider 32
Current R&D Efforts
• Six different (but greatly overlapping) collaborations, more than 200 physicists:– Neutrino Factory and Muon Collider Collab.
• Umbrella U.S. collaboration– MERIT Collab.
• Mercury jet target in 15 Tesla solenoid• 24 GeV protons at CERN• Analyzing data
– MuCool Collab.• Engineering studies for individual components• ~4 years of studies so far, at Fermilab• Test beam (400 MeV H-) ~ SUMMER
– MICE Collab.• Single-particle demonstration of emittance reduction• First muon Beam (140-300 MeV/c μ) “Real Soon Now”
– MANX Collab.• Just forming
– Fermilab’s Muon Collider task Force
• Plus other Neutrino Factory organizations
Feb 12, 2008 TJR Prospects for a Muon Collider 33
Merit – Target Test
• High-power target test using a mercury jet in a 15 T solenoid, at CERN
• Data taking completed last fall, data analysis in progress• Preliminary conclusion: concept validated up to 4 MW at 50 Hz
1234
Syringe PumpSecondaryContainment
Jet Chamber
ProtonBeam
Solenoid
Feb 12, 2008 TJR Prospects for a Muon Collider 34
MuCool
Tests in progress at Fermilab MuCool Test Area (MTA)near Linac, with full-scale (201 MHz) and 1/4-scale (805 MHz) closed-cell (pillbox) cavities with novel Be windows for higher on-axis field
Feb 12, 2008 TJR Prospects for a Muon Collider 35
MICE(~10% 4d Cooling in 5.5 m)
• Installation in ISIS R5.2 is progressing• Beamline commissioning “Real soon now” (2-3 weeks)• A month or two until beamline is complete• Summer or fall until trackers are complete
Feb 12, 2008 TJR Prospects for a Muon Collider 36
The MANX Experiment(~500% 6d Cooling in 4 m)
• Purpose is to demonstrate the Helical Cooling Channel.• Could well become a “Phase III” of MICE (total is 2.5 m longer than MICE Stage VI – fits in hall).
Feb 12, 2008 TJR Prospects for a Muon Collider 37
Summary
• A number of clever innovations have made a Muon Collider much more feasible than previously thought.
• To make it possible to actually construct such a new facility, an ongoing program of research and development is essential.
• We are hosting a Low Emittance Muon Collider Workshop, at Fermilab in April.
• There is lots to do – come join us!
http://www.muonsinc.com