NuFACT06 Summer School -Factory Front End and Cooling David Neuffer f Fermilab
NuFACT06 Summer School-Factory Front End
and Cooling
David Neuffer
fFermilab
2
0utline Lecture I –Front End
General introduction– Study 2A ν-Factory– variations
Capture and decay from target Bunching and φ-E rotation
Lecture II – Cooling Ionization cooling concepts Cooling for a ν-Factory
– MICE experiment µ+-µ- collider cooling
3
References “Cost-effective design for a neutrino factory”, J. Berg et
al., PRSTAB 9, 011001(2006) “Recent progress in neutrino factory …”, M. Alsharo’a et
al., PRSTAB 6, 081001 (2003) “Beams for European Neutrino Experiments (BENE)
CERN-2006-005 S. Ozaki et al., Feasibility Study 2, BNL-52623(2001). N. Holtkamp and D. Finley, eds., Study 1, Fermilab-Pub-
00/108-E (2000). The Study of a European neutrino factory complex,
CERN/PS/2002-080. R. Palmer- NuFACT05 Summer School lecture notes
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Neutrino Factory - Study 2A Proton driver
Produces proton bunches 8 or 24 GeV, ~1015p/s, ~50Hz
bunches
Target and drift (> 0.2 /p)
Buncher, bunch rotation, cool
Accelerate to 20 GeV or more Linac, RLA and FFAGs
Store at 20 GeV (0.4ms) e ++ e
*
Long baseline Detector >1020 /year
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Target for π production Typical beam: 10 GeV protons up to 4 MW
1m long bunches up to 4×1013/bunch, 60Hz
Options: Solid targets
– C (graphite targets) (NUMI) – Solid metal (p-source) – rotating Cu-Ni target
Liquid Metal targets– SNS – type (confined flow)– MERIT – Hg jet in free space
– Best for 4MW ??
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The Fundamental Problem with Solid Targets
What do we need in materials to get us
to multi-MW Power Levels? low elasticity modulus
(limit Stress = EαΔT/(1-2ν) low thermal expansion high heat capacity good diffusivity to move heat away
from hot spots high strength resilience to shock/fracture strength resilience to irradiation damage That’s All !
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Liquid Targets Contained liquid flow (~SNS)
Damage to containment vessel possible Shock of short pulse
Liquid Jet target Hg jet ~ Jet is disrupted by beam
– δT = 50 s ? Need target material capture and recirculation
system
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MERIT experiment at CERN
Target date: November 2006! i.e. ready to receive and install the solenoid and Hg-loop
Beam parameters:Beam parameters: Nominal momentum 24 GeV/c Intensity/bunch – baseline: harmonic 16 (i.e. 16 buckets in PS, t=125ns)
2-2.5 1012 protons / bunch total maximum ~30 1012 protons/pulse
Next steps:Next steps: MD time in 2006 assigned
To address the most critical configurations – priorities should be defined Set-up time at the beginning of 2007 may be required to achieve the
highest intensities
Magnet tested at 15THg jets
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π capture from target Protons on target produce large
number of π’s Broad energy range (0 to 10+GeV) More at lower energies Transverse momentum
(up to ~0.3GeV/c)
Capture beam from target Options:
Li lens
Magnetic horn
Magnetic Solenoid
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Li Lens properties Current-carrying conducting cylinder Focusing Field:
Fermilab values: R0=1cm, I=0.5MA, L=15cm, B(R0)=10T
Focuses 9GeV/c p with p < 0.45 GeV/c
Problems Pulsed at <1Hz, need liquid for 10+ Hz Absorbs particles (π,p-bar) Forward capture Captures only one sign
θ 0 total 20
rB (r) = μ I
2πR
Focusing angle:Θ=(0.3B(r) L)/P
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Magnetic Horn after target Baseline capture for superbeams/NUMI Magnetic field from I on wall
Lenses can be tuned to obtain narrow band or broad-band acceptance
Pulsed current, thin conductors Breakage over many pulses Beam lost on material
focuses + or - particles
inside conductorθB (r) = 0
total
θ o
IB (r) = μ
2 r /
θ pathfocus
B LΔθ =
3.33P
NUMI beam line
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NUMI target, beam
Target segmented graphite, water cooled 954mm long; 47 20mm segments Movable: can be positioned up to
2.5m upstream of horn to tune beam energy
Parabolic horns Pulsed at up to 200kA; 3T peak field Focus π‘s into decay tunnel
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Solenoid lens capture Target is immersed in high field solenoid Particles are trapped in Larmor orbits
Produced with p = p‖, p
Spiral with radius r = p/(0.3 Bsol)
Particles with p < 0.3 BsolRsol/2 are trapped
p,max < 0.225 GeV/c for B=20T, Rsol = 0.075m
Focuses both + and - particles
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Solenoid transport Magnetic field adiabatically
decreases along the transport Transverse momentum
decreases Busch’s theorem: B rorbit
2 is constant B=20T→2T (r=3.75cm →= 12cm) P = 0.225→0.07GeV/c
Emittance = ~σx σpx/105.66
~8cm×25 MeV/c/105.66≅0.02m
P remains constant (P‖ increases)
Transport designed to maximize π→ acceptance
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Homework problems: targetry How many 24 GeV protons per second are in a 4 MW
beam? With 60Hz bunches, how many protons/bunch? a beam of 24GeV protons produces, on average, one
pion pair per proton with mean momentum of 250 MeV/c (per pion). What percentage of the proton beam kinetic energy is converted to pions?
If the target is surrounded by a 20T solenoid with a 5cm radius, what maximum transverse momentum of pions is accepted?
If B is adiabatically reduced to 1T what is the resulting transverse momentum and beam size?
Estimated normalized emittance?
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π→μν decay in transport π-lifetime is 2.60×10-8 s
L = 7.8 β m For π μ+ν,
<PT,rms> is 23.4 MeV/c, E=0.6 to 1.0Eπ
Capture relatively low-energy π μ 100 – 300 MeV/c
Beam is initially short in length Bunch on target is 1 to 3 ns rms
length
As Beam drifts down beam transport, energy-position (time) correlation develops:
L=0m
L=36m
0
0.4 GeV
-20m 100m
arrival
Lc
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Phase-energy rotation To maximize number of
~monoenergetic μ’s, neutrino factory designs use phase-energy rotation
Requires: “short” initial p-bunch Drift space Acceleration (induction linac or rf)
– at least ±100 MV Goal:
Accelerate “low-energy tail” Decelerate “high-energy head: Obtain long bunch
– with smaller energy spread
L=1m
L=112m
rf
0
0.5GeV/c
-50m 50mLL
δL = δβ(p )
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Phase Energy rotation options Single bunch capture
Low-frequency rf (~30MHz) Best for collider (?) (but only + or -)
Induction Linac Nondistortion capture possible Very expensive technology, low gradient Captures only + or -
“High Frequency” buncher and phase rotation Captures into string of bunches (~200MHz) Captures both + and -
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Phase/energy rotation Low-frequency rf;
capture into single long bunch 25MHz – 3MV/m +25% 50MHz 10m from target to 50m
But: Low-frequency rf is very
expensive Continuation into cooling
and acceleration a problem (200MHz?)
12 m
Only captures one sign …
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Induction Linac for φ-E Rotation Induction Linac can provide
long pulse for φ-E rotation Arbitrary voltage waveform
possible
Limited to < ~1MV/m need > ~200MV, > 200m
Very expensive, large power requirements
Only captures one sign
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Nondistortion φ-E rotation Cancellation with single
induction linac gives distortion (Head has larger δE than tail)
Sequence of 2 (or more) linacs can spread beam out evenly
Goal is to spread beam out evenly mapping Kinetic Energy to length (Δcτ); all at same final energy (0.25 to 0.225MeV) to (0 to 80m)
2 11
0 1final
L LLz
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Study 2 system Drift to develop Energy- phase correlation
Accelerate tail; decelerate head of beam, non-distortion (280m induction linacs (!))
Bunch at 200 MHz ~0.2 /p
Inject into 200 MHz cooling system Cools transversely (to t= ~0.002m
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High-frequency Buncher + Rotation
Drift (110m) Allows beam to decay;
beam develops correlation
Buncher (~333230MHz) Bunching rf with E0 = 125 MeV,
1 = 0.01 { L 1 =~1.5m at Ltot
= 150m}
Vrf increases gradually from 0 to ~6 MV/m
Rotation (~233200MHz) Adiabatic rotation Vrf =~10 MV/m
Cooler(~100m long) (~200 MHz) fixed frequency transverse cooling system
Replaces Induction Linacs with medium-frequency rf (~200MHz) !
Captures both μ+ and μ- !!
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Adiabatic Buncher overview
Want rf phase to be zero for reference energies as beam travels down buncher
Spacing must be N rf
rf increases (rf frequency decreases)
Match to rf= ~1.5m at end:
Gradually increase rf gradient (linear or quadratic ramp): 2
D Drf 2
B B
z - z z - zE (z) = B + C
L L
Example: rf : 0.901.5m
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Adiabatic Buncher example Adiabatic buncher (z=90→150m)
Set T0, : 125 MeV/c, 0.01
In buncher:
Match to rf=1.5m at end:
zero-phase with 1/ at integer intervals of :
Adiabatically increase rf gradient:
m5.1L11
L rf1
tot01
tot
2
2( ) 2 6 /D Drf
tot D tot D
z z z zE z MV m
L z L z
1
0n
n11
rf : 0.901.5m
)(z)z( 1rf
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Rotation At end of buncher, change rf to
decelerate high-energy bunches, accelerate low energy bunches
Reference bunch at zero phase, set rf less than bunch spacing
(increase rf frequency)
Place low/high energy bunches at accelerating/decelerating phases
Can use fixed frequency (requires fast rotation) or
Change frequency along channel to maintain phasing “Vernier” rotation –A. Van Ginneken
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Fast “Vernier” Rotation At end of buncher, choose:
Fixed-energy particle T0
Second reference bunch TN
Vernier offset Example:
T0 = 125 MeV Choose N= 10, =0.1
– T10 starts at 77.28 MeV Along rotator, keep
reference particles at (N + ) rf spacing 10 = 36° at =0.1 Bunch centroids change:
Use Erf = 10MV/m; LRt=8.74m High gradient not needed … Bunches rotate to ~equal
energies.
R10rf10R10 z)sin(Ee)0(T)z(T rf : 1.4851.517m in rotation;rf = ct/10 at end
(rf 1.532m)
Nonlinearities cancel:T(1/) ; Sin()
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“ICOOL” Adiabatic Rotation
At end of buncher, choose: reference particle T0
Reference bunch TN (N bunches from 0)
V’ rf gradient, offset Example:
T0 = 125 MeV Choose N= 10, =0.1
– T10 starts at 77.28 MeV
In ICOOL T0 = T0
+ E0'z…
TN =TN + EN' z
Rotate until T0 ≅ TN
Along rotator, keep reference particles at (N + ) rf spacing EN' ≅eV' sin(2π)
λrf ~1.4 to 1.5 m over buncher
•~Adiabatic•Particles remain in bunches as bunch centroids align•Match into 201.25 MHz Cooling System
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Initial Study 2A(12/03) Drift (110.7m) Buncher (51m)
P1=280, P2=154 MeV/c, NB=18
Vrf= 3 L/51 + 9 (L/51)2 MV/m
Vernier Phase Rotator (54m) NV = 18.05, Vrf=12 MV/m
Cooler (up to 100m) Alternating solenoid 2.7T, 0.75m cells 2cm LiH/cell 16MV/m rf (30°)
5000 particle simulation
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ICOOL results-Study 2A (12/03)
0
500
1000
1500
2000
2500
3000
3500
0 50 100 150 200 250 300
accepted / 5000
Transverse emittance
0.00E+00
2.00E-03
4.00E-03
6.00E-03
8.00E-03
1.00E-02
1.20E-02
1.40E-02
1.60E-02
1.80E-02
2.00E-02
0 50 100 150 200 250 300 m
~0.23 μ/p within reference acceptance at end of 80m cooling channel (ε⊥<0.03m)
~0.11 μ/p within restricted acceptance (ε⊥<0.015m)
At end of φ-E Rotator:
A~0.10 μ/p and 0.05 μ/p
Rms emittance cooled from ε⊥= 0.0185 to ε⊥= ~0.008m
Longitudinal rms emittance ≅0.070m (per bunch)
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Study2A June 2004 scenario Drift –110.7m Bunch -51m
V(1/) =0.0079 12 rf freq., 110MV 330 MHz 230MHz
-E Rotate – 54m – (416MV total) 15 rf freq. 230 202 MHz P1=280 , P2=154 NV = 18.032
Match and cool (80m) 0.75 m cells, 0.02m LiH
“Realistic” fields, components Captures both μ+ and μ-
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Features/Flaws of Study 2A Front End
Fairly long section – ~300m long Study 2 was induction linac 1MV/m, 450m long
Produces long bunch trains of ~200 MHz bunches ~80m long (~50 bunches)
Transverse cooling is ~2½ in x and y No cooling or more cooling ?
Method works better than it should …
Requires rf within magnetic fields 12 MV/m at B = 1.75T
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Another example: ~88 MHz Drift – 90m Buncher-60m
Rf gradient 0 to 4 MV/m Rf frequency: 166→100 MHz Total rf voltage 120MV
Rotator-60m Rf gradient 7 MV/m – 100→87 MHz 420MV total
Acceptance ~ study 2A (but no cooling yet) Less adiabatic
0 GeV/c
0.5 GeV/c
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rf in Rotation/Cooling Channels: Can cavities hold rf gradient
in magnetic fields??
MUCOOL 800 MHz result : V' goes from 45MV/m to
12MV/m (as B -> 4T) Vacuum rf cavity
Worse at 200MHz ??
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Use gas-filled rf cavities? Muons, Inc. tests:
Higher gas density permits higher gradient
Magnetic field does not decrease maximum allowable gradient
Gas filled cavities may be needed for cooling with focusing magnetic fields
Density > ~60 atm H2 (7.5% liq.)
Energy loss for µ’s is >~ 2MV/m
Can use energy loss for cooling
Mo electrode, B=3T, E=66 MV/mMo B=0 E=64MV/mCu E=52MV/mBe E= 50MV/m 800 MHz rf tests
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Gas-filled rf cavites (Muons, Inc.)
Cool here
Add gas + higher gradient to obtain cooling within rotator
~300MeV energy loss in cooling region
Rotator is 54m; Need ~4.5MeV/m H2 Energy 133atm equivalent 295ºK gas ~250 MeV energy loss
Alternating Solenoid lattice in rotator
20MV/m rf cavities Gas-filled cavities may enable
higher gradient (Muons, Inc.)
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High-gradient rf with gas-filled cavities
0
0.005
0.01
0.015
0.02
0.025
100 120 140 160 180 200 220
c
Transverse emittance
Acceptance (per 24GeV p)
Pressure at 150Atm Rf voltage at 24 MV/m
Transverse rms emittance cools 0.019 to ~0.008m
Acceptance ~0.22/p at εT < 0.03m
~0.12/p at εT < 0.015m About equal to Study 2A
0
0.1
0.2
0.3
0.4
0.5
0.6
160 170 180 190 200 210 220
n0
e < 0.015
e < 0.030
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Simulation results
50m
-50m
0
0.5 GeV/c
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Cost impact of Gas cavities Removes 80m cooling section (-185 M$)
Increase Vrf' from 12.5 to 20 or 24 MV/m Power supply cost V'2 (?) 44 M$ 107M$ or 155M$
Magnets: 2T 2.5T Alternating Solenoids 23 M$ 26.2 M$
Costs due to vacuum gas-filled cavities (??)
Total change: Cost decreases by 110 M$ to 62 M$ (???)
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Cost estimates: Costs of a neutrino factory (MuCOOL-322, Palmer and Zisman):
Study 2 Study 2A
“Study 2A front end reduces cost by ~ 350MP$
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Summary Buncher and E Rotator (ν-Factory) Variations
Gas-filled rf cavities can be used in Buncher-Rotator Gas cavities can have high gradient in large B (3T or more?)
Variations that meet Study 2A performance can be found Shorter systems – possibly much cheaper??
Gas-filled rf cavities
To do: Optimizations, Best Scenario, cost/performance … More realistic systems
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Postdoc availability – Front end
SBIR with Muons, Inc. – capture, - rotation and cooling with gas-filled rf cavities