Bunched-Beam Phase Rotationfor a Neutrino Factory

David Neuffer

Fermilab

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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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Neutrino Factory Baseline Design

Feasible, but expensive Find ways to reduce costs …

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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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ICOOL simulation –Buncher, , Cool

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Compare with Study II (Capture + Cooling)

x: –20 to 100m; y: 0 to 400 MeV

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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

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MuTAC results