Bunched-Beam Phase Rotation for a Neutrino Factory David Neuffer Fermilab

2 Outline  Introduction  Study 2 scenario  Induction linac phase rotation 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

3 Neutrino Factory Baseline Design  Feasible, but expensive  Find ways to reduce costs …

4 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

5 Study 2 Scenario – induction linacs Study II scenario uses ~ 280m of induction linacs to capture muons. Cost is very high Technology is difficult

6 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) !

7 Longitudinal Motion (1-D simulations) DriftBunch  E rotate Cool System would capture both signs (  +,  - ) !!

8 Buncher overview  Adiabatic buncher  Set T 0,  :  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

9 “Vernier”  Rotation  At end of bunch, choose:  Fixed-energy particle T 0  Second reference bunch T N  Vernier offset   Example:  T 0 = 125 MeV  Choose N= 10,  =0.1 –T 10 starts at MeV  Along rotator, keep reference particles at (N +  ) rf spacing  10 = 36° at  =0.1  Bunch centroids change:  Use E rf = 10MV/m; L Rt =8.74m  High gradient not needed …  Bunches rotate to ~equal energies. rf :  1.517m in rotation; rf =  ct/10 at end ( rf  1.532m) Nonlinearities cancel: T(1/  ) ; Sin(  )

10 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

11 Bunching and  Rotation Beam after drift plus adiabatic buncher – Beam is formed into string 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 (  +,  - ) !!

12 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)

13 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

14 ICOOL simulation –Buncher, , Cool

15 Compare with Study II (Capture + Cooling) x: –20 to 100m; y: 0 to 400 MeV

16 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 …

17 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

18 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

19 10-frequency Buncher Only 10 frequencies and voltages. (10 equidistant linacs made of 6 cells) 62.2% of the particles survive at the end of the buncher.

20 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

21 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 …

22 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

23 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

24 MuTAC results