Transcript MICE Tapered B1 Study - Science and Technology Facilities

Prospects for an EnergyFrontier Muon Collider
Tom Roberts
Muons, Inc.
Illinois Institute of Technology
Feb 12, 2008 TJR
Prospects for a Muon Collider
1
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
2
Background Reminders
Historically, every significant increase in energy
has taught us something completely new.
Every new type of particle beam has also
taught 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
3
The Livingston Plot
Constituent Center-of-Mass Energy
X 5 TeV MC
X ILC
2025
Panofsky and Breidenbach,
Rev. Mod. Phys. 71, s121-s132
(1999)
Feb 12, 2008 TJR
Prospects for a Muon Collider
4
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
5
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
6
Muons
A 5 TeV muon collider
could fit on the existing
Fermilab site.
[Ankenbrandt et al., PRST-AB 2, 081001
(1999)]
Feb 12, 2008 TJR
Prospects for a Muon Collider
7
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
8
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
9
Muon Ionization Cooling
Absorber
dp/dz || -p
RF Cavity
dp/dz || +z
p┴ reduced,
p|| unchanged
• 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)
(Skrinsky & Parkhomchuk, 1981)
Feb 12, 2008 TJR
Prospects for a Muon Collider
10
Muon Ionization Cooling
Transverse Emittance change per unit length in the absorber:
Cooling term
(energy loss)
Heating term
(multiple scattering)
• Want:
Lattice design
– Lower β┴ (stronger focusing at the absorber)
– Minimize multiple scattering
– Maximize energy loss
Absorber Material
Here  is the normalized emittance, Eµ is the muon energy, dEµ/ds and X0 are the
energy loss and radiation length of the absorber material,  is the transverse betafunction of the magnetic channel, and  is the particle velocity.
Feb 12, 2008 TJR
Prospects for a Muon Collider
11
Absorber Materials
Fcool ~ (Energy Loss) / (Multiple Scattering)
Feb 12, 2008 TJR
Prospects for a Muon Collider
12
Emittance Exchange
Ionization cooling is only transverse.
To get longitudinal cooling,
use emittance exchange.
Feb 12, 2008 TJR
Prospects for a Muon Collider
13
Innovation: Helical
Cooling Channel
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.
Beam
Follows
Helix
The helical solenoid is filled with a
continuous absorber, and
perhaps with RF cavities.
• 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.
Feb 12, 2008 TJR
Prospects for a Muon Collider
14
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
15
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
16
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.
805
MHz
Electrode breakdown region
Paschen region
Feb 12, 2008 TJR
Prospects for a Muon Collider
17
Innovation: High Pressure
Gas RF Cavities
•
•
•
•
•
•
Copper plated, stainless-steel, 805 MHz test cell
H2 gas to 1600 psi and 77 K
Paschen curve verified (at Fermilab’s Lab G and MuCool Test Area)
Maximum gradient limited by breakdown of metal
Fast conditioning seen
Unlike vacuum cavities, there’s no measurable limitation for magnetic field!
Feb 12, 2008 TJR
Prospects for a Muon Collider
18
Understanding RF
Breakdown
Scanning electron microscope images; Be (top) and Mo (bottom).
Feb 12, 2008 TJR
Prospects for a Muon Collider
19
Innovation: Parametric Resonance
Ionization Cooling
Clever method to greatly reduce  without increased magnetic fields.
Excite ½ integer parametric resonance (in Linac or ring)
• Like vertical rigid pendulum or ½-integer extraction
• Elliptical phase space motion becomes hyperbolic
• Use xx’=const to reduce x, increase x’
• Use IC to reduce x’
Detuning issues are being addressed (chromatic and spherical
aberrations, space-charge tune spread). Simulations are underway.
Smaller beams from 6D HCC cooling are essential for this to work!
X’
X’
X
x
Feb 12, 2008 TJR
X
Prospects for a Muon Collider
20
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 *).
Incident Muon
Beam
Wedge Abs
Evacuated
Dipole
Feb 12, 2008 TJR
Prospects for a Muon Collider
21
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
Drift
RF
t
Cooled at 100 MeV/c
RF at 20 GeV
Coalesced in 20
GeV ring
1.3 GHz Bunch Coalescing at 20 GeV
Feb 12, 2008 TJR
Prospects for a Muon Collider
22
Innovation: Dual-Use Linac
• Fermilab is considering “Project X”, a high-intensity 8 GeV
superconducting linac
• Use it also to accelerate muons (after cooling)
Possible 8 GeV
Project
X
Linac
~ 700m Active Length
Neutrino
Factory
aimed at
Soudan, MN
Feb 12, 2008 TJR
Bunching
Ring
Target and Muon Cooling
Channel
Prospects for a Muon Collider
Recirculating
Linac for Neutrino
Factory
23
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
Linac
Feb 12, 2008 TJR
Prospects for a Muon Collider
Extraction
24
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
25
Many New Arrows in the
Quiver
• New Ionization Cooling Techniques
– Helical Cooling Channel
– Momentum-dependent Helical Cooling Channel
– Guggenheim cooling channel
– Ionization cooling using a parametric resonance
• Methods to manipulate phase space partitions
– Reverse emittance exchange using absorbers
– Bunch coalescing (neutrino factory and muon collider share
injector)
• Technology for better cooling
– Pressurized RF cavities
– High Temperature Superconductor for up to 50 T magnets
• Acceleration Techniques
– Dual-use Linac
– Pulsed Recirculating Linac
Feb 12, 2008 TJR
Prospects for a Muon Collider
26
Conceptual Block Diagram
of a Muon Collider
Proton Driver
(8-40 GeV)
Production
Target
Pion Capture, Decay Channel,
Phase Rotation, and Pre-Cooling
Muon Ionization Cooling
Acceleration
(0.2 to 20 GeV)
Reverse Emittance
Exchange
Bunch Coalescing
Acceleration (20 to 2,500 GeV)
Storage Ring and
Interaction Regions
Experiments
Must of course deal with both μ+ and μ-.
Feb 12, 2008 TJR
Prospects for a Muon Collider
27
Fernow-Neuffer Plot
End Cooling:
Start
Acceleration to
2.5 TeV
Start Cooling: After
Capture, Decay,
Phase Rotation,
Pre-Cooling
HCC 400 MHz
REMEX &
Coalescing
HCC 800 MHz
Acceleration
To 20 GeV
Feb 12, 2008 TJR
PIC
HCC 1600 MHz
Prospects for a Muon Collider
28
Viewgraph-level Design
2.5 + 2.5 TeV muon
storage ring with
two IRs
1 km radius
(= Fermilab Main Ring,
but it’s not deep enough)
L ~ 1035 cm-2 s-1
μ+
2.5 km ILC-like
linacs
10 recirculating arcs
In one tunnel
μ–
Final cooling, preacceleration
Helical cooling channel
Target, pion capture,
Phase rotation
Proton driver
Feb 12, 2008 TJR
Prospects for a Muon Collider
29
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
30
Neutrino Factory
Feb 12, 2008 TJR
Prospects for a Muon Collider
31
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
32
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
Solenoid
Secondary
Containment
Jet Chamber
Syringe Pump
Proton
Beam
4
Feb 12, 2008 TJR
Prospects for a Muon Collider
3
2
1
33
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
34
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
35
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
36
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
Feb 12, 2008 TJR
Prospects for a Muon Collider
37