NuFACT06 Summer School Factory Front End and Cooling

1
NuFACT06 Summer School?-Factory Front Endand
Cooling

• David Neuffer
• f
• Fermilab

2
0utline

• Lecture I Front End
• General introduction
• Study 2A ?-Factory
• variations
• Capture and decay from target
• Bunching and f-E rotation
• Lecture II Cooling
• Ionization cooling concepts
• Cooling for a ?-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.
  Alsharoa 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

4
Neutrino Factory - Study 2A

• Proton driver
• Produces proton bunches
• 8 or 24 GeV, 1015p/s, 50Hz bunches
• Target and drift
• ??? (gt 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
• gt1020 ?/year

5
Target for p production

• Typical beam 10 GeV protons up to 4 MW
• 1m long bunches up to 41013/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 ??

6
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 Ea?T/(1-2?)
• 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
• Thats All !

7
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
• dT 50 ?s ?
• Need target material capture and recirculation
  system

8
MERIT experiment at CERN

• Target date November 2006!
• i.e. ready to receive and install the solenoid
  and Hg-loop
• Beam parameters
• Nominal momentum 24 GeV/c
• Intensity/bunch baseline harmonic 16 (i.e. 16
  buckets in PS, Dt125ns)
• 2-2.5 ? 1012 protons / bunch
• total maximum 30 ? 1012 protons/pulse
• 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

Hg jets
Magnet tested at 15T
9
p capture from target

• Protons on target produce large number of ps
• Broad energy range (0 to 10GeV)
• More at lower energies
• Transverse momentum (up to
  0.3GeV/c)
• Capture beam from target
• Options
• Li lens
• Magnetic horn
• Magnetic Solenoid

10
Li Lens properties

• Current-carrying conducting cylinder
• Focusing Field
• Fermilab values
• R01cm, I0.5MA, L15cm, B(R0)10T
• Focuses 9GeV/c p with p? lt 0.45 GeV/c
• Problems
• Pulsed at lt1Hz, need liquid for 10 Hz
• Absorbs particles (p,p-bar)
• Forward capture
• Captures only one sign

Focusing angle T(0.3B(r) L)/P
11
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

NUMI beam line
12
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 ps into decay tunnel

13
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? lt 0.3 BsolRsol/2 are trapped
• p?,max lt 0.225 GeV/c for B20T, Rsol 0.075m
• Focuses both and - particles

14
Solenoid transport

• Magnetic field adiabatically decreases along the
  transport
• Transverse momentum decreases
• Buschs theorem B rorbit2 is constant
• B20T?2T (r3.75cm ? 12cm)
• P? 0.225?0.07GeV/c
• Emittance sx spx/105.66
• 8cm25 MeV/c/105.66?0.02m
• P remains constant (P? increases)
• Transport designed to maximize p?? acceptance

15
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?

16
p?µ? decay in transport

• p-lifetime is 2.6010-8? s
• L 7.8 ß? m
• For p ? µ?,
• ltPT,rmsgt is 23.4 MeV/c, E?0.6 to 1.0Ep
• Capture relatively low-energy p ? 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

0.4 GeV
L0m
0
L36m
100m
-20m
17
Phase-energy rotation

• To maximize number of monoenergetic µs,
  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

0.5GeV/c
L1m
0
L112m
rf
-50m
50m
dL
18
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 ?-

19
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?)

Only captures one sign
12 m
20
Induction Linac for f-E Rotation

• Induction Linac can provide long pulse for f-E
  rotation
• Arbitrary voltage waveform possible
• Limited to lt 1MV/m
• need gt 200MV, gt 200m
• Very expensive, large power requirements
• Only captures one sign

21
Nondistortion f-E rotation

• Cancellation with single induction linac gives
  distortion
• (Head has larger dE 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 (?ct) all at same final energy
• (0.25 to 0.225MeV) to (0 to 80m)

22
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

23
High-frequency Buncher ???? Rotation

• Drift (110m)
• Allows ??? beam to decay
• beam develops ???? correlation
• Buncher (333?230MHz)
• 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 (233?200MHz)
• Adiabatic rotation
• Vrf 10 MV/m
• Cooler(100m long) (200 MHz)
• fixed frequency transverse cooling system

m
Replaces Induction Linacs with medium-frequency
rf (200MHz) !
Captures both µ and µ- !!
24
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)

Example ?rf 0.90?1.5m
25
Adiabatic Buncher example

• Adiabatic buncher (z90?150m)
• Set T0, ??????
• 125 MeV/c, 0.01
• In buncher
• Match to ?rf1.5m at end
• zero-phase with 1/? at integer intervals of
  ??????
• Adiabatically increase rf gradient

?rf 0.90?1.5m
26
???? 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

27
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 LRt8.74m
• High gradient not needed
• Bunches rotate to equal energies.

?rf 1.485?1.517m in rotation ?rf ?ct/10 at
end (?rf ? 1.532m) Nonlinearities
cancel T(1/?) Sin(?)
28
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(2p?)
• ?rf 1.4 to 1.5 m over buncher

• Adiabatic
• Particles remain in bunches as bunch centroids
  align
• Match into 201.25 MHz Cooling System

29
Initial Study 2A(12/03)
5000 particle simulation

• Drift (110.7m)
• Buncher (51m)
• P1280, P2154 MeV/c, NB18
• Vrf 3 L/51 9 (L/51)2 MV/m
• Vernier Phase Rotator (54m)
• NV 18.05, Vrf12 MV/m
• Cooler (up to 100m)
• Alternating solenoid 2.7T, 0.75m cells
• 2cm LiH/cell
• 16MV/m rf (30)

30
ICOOL results-Study 2A (12/03)

• 0.23 µ/p within reference acceptance at end of
  80m cooling channel (e?lt0.03m)
• 0.11 µ/p within restricted acceptance
  (e?lt0.015m)
• At end of f-E Rotator
• A0.10 µ/p and 0.05 µ/p
• Rms emittance cooled from e? 0.0185 to e?
  0.008m
• Longitudinal rms emittance ?0.070m (per bunch)

31
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
• P1280 , P2154 ?NV 18.032
• Match and cool (80m)
• 0.75 m cells, 0.02m LiH
• Realistic fields, components
• Captures both µ and µ-

32
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

33
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

0.5 GeV/c
0 GeV/c
34
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 -gt 4T)
• Vacuum rf cavity
• Worse at 200MHz ??

35
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 gt 60 atm H2 (7.5 liq.)
• Energy loss for µs is gt 2MV/m
• Can use energy loss for cooling

Mo electrode, B3T, E66 MV/m Mo B0 E64MV/m Cu
E52MV/m Be E 50MV/m 800 MHz rf tests
36
Gas-filled rf cavites (Muons, Inc.)

• 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.)

Cool here
37
High-gradient rf with gas-filled cavities

• Pressure at 150Atm
• Rf voltage at 24 MV/m
• Transverse rms emittance cools 0.019 to 0.008m
• Acceptance 0.22?/p at eT lt 0.03m
• 0.12?/p at eT lt 0.015m
• About equal to Study 2A

Transverse emittance
Acceptance (per 24GeV p)
38
Simulation results
0.5 GeV/c
0
50m
-50m
39
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 (???)

40
Cost estimates

• Costs of a neutrino factory (MuCOOL-322, Palmer
  and Zisman)

Study 2
Study 2A
Study 2A front end reduces cost by 350MP
41
Summary

• Buncher and ???E Rotator (?-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

42
Postdoc availability Front end
SBIR with Muons, Inc. capture, ?-? rotation and
cooling with gas-filled rf cavities