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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

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Bunched beam phase rotation for a neutrino factory

Bunched-Beam Phase Rotationfor a Neutrino Factory

David Neuffer

Fermilab


Outline
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


Neutrino factory baseline design
Neutrino Factory Baseline Design

  • Feasible, but expensive

  • Find ways to reduce costs …


Study 2 system
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


Study 2 scenario induction linacs
Study 2 Scenario – induction linacs

  • Study II scenario uses

  • ~ 280m of induction

  • linacs to capture muons.

  • Cost is very high

  • Technology is difficult


Adiabatic buncher vernier rotation
Adiabatic buncher + Vernier  Rotation

  • Drift (90m)

    •  decay;

      beam develops  correlation

  • Buncher(60m)(~333200MHz)

    • Forms beam into string of bunches

  •  Rotation(~10m)(~200MHz)

    • Lines bunches into equal energies

  • Cooler(~100m long)(~200 MHz)

    • fixed frequency transverse cooling system

Replaces Induction Linacs with medium-frequency rf (~200MHz) !


Longitudinal motion 1 d simulations
Longitudinal Motion (1-D simulations)

Drift

Bunch

E rotate

Cool

System would capture both signs (+, -) !!


Buncher overview
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:

rf : 0.901.5m


Vernier rotation
“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.

rf : 1.4851.517m in rotation;

rf = ct/10 at end

(rf  1.532m)

Nonlinearities cancel:

T(1/) ; Sin()


1 d 3 d simulations a van ginneken
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:

      • 384233 MHz

      • Linear ramp in voltage 0 to 6.5MV/m, 60m long

    •  Rotator:

      • “vernier” frequency (20 + ) wavelengths between reference bunches (234220 MHz), 10MV/m,   0.16

      • 30m long

      • Obtains ~0.4 /p


Bunching and rotation
Bunching and  Rotation

Beam after ~200MHz rf rotation;

Beam is formed into

string of equal-energy bunches;

matched to cooling rf acceptance

Beam after drift plus

adiabatic buncher –

Beam is formed into

string of ~ 200MHz bunches

System would capture both signs (+, -) !!


Next step match into cooling channel
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)


Results icool
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



Compare with study ii capture cooling
Compare with Study II (Capture + Cooling)

x: –20 to 100m; y: 0 to 400 MeV


Caveats not properly matched
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 …


To do
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


Geant4 simulations d elvira
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


Bunched beam phase rotation for a neutrino factory

10-frequencyBuncher

Only 10 frequencies

and voltages.

(10 equidistant

linacs made of 6 cells)

62.2% of the particles survive at the end of the buncher.


Geant4 phase rotation d elvira n keuss
GEANT4 Phase Rotation (D. Elvira, N. Keuss)

Phase rotation successful

Agrees with simplified models/simulations

NOT optimized; Need to continue with simulation into cooling channel


Hardware cost for buncher rotator
Hardware/Cost For Buncher/Rotator

  • Rf requirements:

    • Buncher: ~300~210 MHz; 0.14.8MV/m (60m)

      (~10 frequencies; ~10MHz intervals)

    •  Rotator: ~210200 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 …


Variations optimizations
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


Summary
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 anyneutrino factory …

    To do:

    • Complete simulations with matched cooling channel!

    • Optimizations, Scenario reoptimization