bunched-beam phase rotation for a neutrino factory
DESCRIPTION
Bunched-Beam Phase Rotation for a Neutrino Factory. David Neuffer Fermilab. Outline. Introduction Study 2 scenario Induction linac phase rotation + 200 MHz buncher “High-frequency” Buncher and Rotation Concept 1-D simulation 3-D simulations – Simucool, ICOOL - PowerPoint PPT PresentationTRANSCRIPT
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Outline Introduction Study 2 scenario
Induction linac phase rotation + 200 MHz buncher “High-frequency” Buncher and
Rotation Concept 1-D simulation 3-D simulations – Simucool, ICOOL Mismatch into cooling channel
Toward “realistic” implementation Elvira, Keuss Geant4 simulations Cost guesstimates …
Future Studies Variations Matching, Optimization Study 3
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Study 2 system Drift to develop Energy- phase
correlation
Accelerate tail; decelerate head of beam (280m induction linacs (!))
Bunch at 200 MHz
Inject into 200 MHz cooling system
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Study 2 Scenario – induction linacs
•Study II scenario uses ~ 280m of induction linacs to capture muons.
• Cost is very high
•Technology is difficult
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Adiabatic buncher + Vernier Rotation
Drift (90m) decay;
beam develops correlation
Buncher (60m) (~333200MHz) Forms beam into string of bunches
Rotation(~10m) (~200MHz) Lines bunches into equal energies
Cooler(~100m long) (~200 MHz) fixed frequency transverse cooling system
beam Drift Buncher
Rotator
Cooler
Overview of transport
Replaces Induction Linacs with medium-frequency rf (~200MHz) !
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Longitudinal Motion (1-D simulations)
Drift Bunch
E rotate Cool
System would capture both signs (+, -) !!
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Buncher overview
Adiabatic buncher 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
m/MVzL
zz8.4)z(E 2
Dtot
2D
rf
1
0n
n11
rf : 0.901.5m
)(z)z( 1rf
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“Vernier” Rotation At end of bunch, 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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1-D 3-D Simulations (A. van Ginneken) Initial examples are 1-D Add transverse focusing (1.25T solenoid); initial beam
from MARS simulations (Mokhov) of target production Use Large statistics tracking code (SIMUCOOL, A. Van
Ginneken) Reoptimize all parameters–
Drift to 76m, Buncher parameters:
– 384233 MHz– Linear ramp in voltage 0 to 6.5MV/m, 60m long
Rotator:– “vernier” frequency (20 + ) wavelengths between
reference bunches (234220 MHz), 10MV/m, 0.16– 30m long
– Obtains ~0.4 /p
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Bunching and Rotation
Beam after drift plusadiabatic buncher – Beam is formed intostring of ~ 200MHz bunches
Beam after ~200MHz rf rotation;Beam is formed into string of equal-energy bunches;matched to cooling rf acceptance
System would capture both signs (+, -) !!
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Next step: match into cooling channel !
Need to design a new cooling channel, matched to bunched/rotated beam
Do not (yet) have redesigned/matched cooling channel
Use (for initial tries): ICOOL beam from end of AVG simulations
Study 2 cooling channel
Direct transfer of beam (no matching section)
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Results (~ICOOL) In first ~10m, 40% of ’s from buncher are lost, 0.020m 0.012m Remaining ’s continue down channel and are cooled and
scraped, ~0.0022m, similar to Study 2 simulation.
Best energy, phase gives ~0.22 ’s /24 GeV p
Study 2 baseline ICOOL results is ~0.23 ’s/p
GeV
m
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Caveats: Not properly matched This is not the way to design a neutrino factory Not properly matched in phase space Cooling channel acceptance is too small
(add precooler ?) Correlation factors “wrong” “Cooling” channel collimates as much as it
cools …
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To do Move to more realistic models
Continuous changes in rf frequencies to stepped changes …
3-D fields (not solenoid + sinusoidal rf)
Match into realistic cooling channels …
Estimate/Optimize Cost /performance
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GEANT4 simulations (D. Elvira) Fully “realistic” transverse and longitudinal
fields Magnetic fields formed by current coils Rf fields from pillbox cavities (within solenoidal coils)
Studied varying number of different rf cavities in Buncher (60 (1/m) to 20 to 10) … 20 was “better”, 10
only a bit worse
Simulations of -δE rotation
Will (?) extend simulations + optimization through cooling channel
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10-frequency Buncher
Only 10 frequenciesand voltages.
(10 equidistantlinacs made of 6 cells)
62.2% of the particles survive at the end of the buncher.
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GEANT4 Phase Rotation (D. Elvira, N. Keuss)
Phase rotation successful Agrees with simplified models/simulationsNOT optimized; Need to continue with simulation into cooling channel
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Hardware/Cost For Buncher/Rotator
Rf requirements: Buncher: ~300~210 MHz; 0.14.8MV/m (60m)
(~10 frequencies; ~10MHz intervals) Rotator: ~210200 MHz; 10MV/m (~10m)
Transverse focussing B=1.25T solenoidal focusing;R=0.30m transport
System Replaces Study 2:
(Decay(20m, 5M$); Induction Linacs(350m, 320M$); Buncher(50m,70M$))
with: Drift (100m); Buncher (60m);Rf Rotator (10m)
(Rf =30M$ (Moretti); magnets =40M$(M. Green); conv. fac.,misc. 20M$)
(400M$ ?? 100M$ )
needs more R&D …
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Variations/ Optimizations … Many possible variations and optimizations
But possible variations will be reduced after design/construction
Shorter bunch trains ?? For ring Coolers ?? Can do this with shorter buncher/rotator ( with same total rf voltage …)
Other frequencies ?? 200 MHz(FNAL) 88 MHz ?? (CERN) ??? (JNF)
Cost/performance optima for neutrino factory (Study 3?)
Collider ?? both signs (+, -) !
Graduate students (MSU) (Alexiy Poklonskiy, Pavel Snopok) will study these variations; optimizations; First task would be putting buncher into MSU code COSY
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Summary High-frequency Buncher and E Rotator
simpler and cheaper than induction linac system Performance as good (or almost …) as study 2,
But System will capture both signs (+, -) !
(Twice as good ??)
Method should (?) be baseline capture and phase-energy rotation for any neutrino factory …
To do: Complete simulations with matched cooling
channel! Optimizations, Scenario reoptimization