a.poklonskiy (spbsu, msu), d.neuffer (fnal) c.johnstone (fnal), m.berz (msu), k.makino (msu)
DESCRIPTION
Exploring and optimizing A diabatic B uncher and P hase R otator for Neutrino Factory in COSY Infinity. A.Poklonskiy (SPbSU, MSU), D.Neuffer (FNAL) C.Johnstone (FNAL), M.Berz (MSU), K.Makino (MSU). Goal & Problems. Goal: - PowerPoint PPT PresentationTRANSCRIPT
20 December 2004 Taylor Models Workhop
Exploring and optimizing Adiabatic Buncher and Phase Rotator for Neutrino Factory in COSY Infinity
A.Poklonskiy (SPbSU, MSU), D.Neuffer (FNAL)C.Johnstone (FNAL), M.Berz (MSU), K.Makino
(MSU)
20 December 2004 Taylor Models Workshop
Goal & Problems
Goal:• Build neutrino factory to study different neutrino-
related things and/or muon collider… to collideProblems:
• Muons are short-living particles compact lattice, fast beam gymnastics
• Muons are produced with large initial momentum spread cooling
• Energy spread is large energy spread reduction before cooling
• Some desired beam manipulations requires new types of field configuration development of such new elements
• All these small muons production rate (<0.2) and…PRICE!
20 December 2004 Taylor Models Workshop
R&D goal: “affordable” e, -Factory
• Improve from baseline: – Collection
• Induction Linac “high-frequency” buncher
– Cooling• Linear Cooling Ring
Coolers
– Acceleration• RLA “non-scaling FFAG”+ e+ + +
e
– e– + e + and/or
The Neutrino Factory and Muon Collider Collaboration
http://www.cap.bnl.gov/mumu/mu_home_page.html
20 December 2004 Taylor Models Workshop
RF Cavity and Solenoid in Pictures
20 December 2004 Taylor Models Workshop
Adiabatic buncher + () Rotator (David Neuffer)
• Drift (90m) decay, beam develops correlation
• Buncher (60m) (~333Mhz200MHz, 04.8MV/m) – Forms beam into string of bunches
Rotator (~12m) (~200MHz, 10 MV/m)– Lines bunches into equal energies
• Cooler (~50m long) (~200 MHz)– Fixed frequency transverse cooling system
Replaces Induction Linacs with medium-frequency RF (~200MHz)
20 December 2004 Taylor Models Workshop
Longitudinal Motion (2D simulations)
Drift Buncher
(E) rotator Cooler
System would capture both signs (+, -)
20 December 2004 Taylor Models Workshop
Key Parameters
• Drift
– Length LD
• Buncher
– Length LB
– RF Gradients EB
– Final RF frequency RF (LD, LB, RF: (LD + LB) (1/) = RF)
• Phase Rotator
– Length LR
– Vernier offset, spacing NR, V
– RF gradients ER
20 December 2004 Taylor Models Workshop
Lattice Variations
– Shorter bunch trains (for ring cooler, more ’s lost)?
– Longer bunch trains (more ’s survived)?
– Different final frequencies? (200,88,44Mhz)
– Number of different RF frequencies and gradients in buncher and rotator (60…10)?
– Different central energies (200MeV, 280MeV, optimal)?
– Matching into cooling channel, accelerator
– Transverse focusing (150m B=1.25T solenoidal field or…)?
– Mixed buncher-rotator? – Cost/perfomance optimum?
OPTIMIZATION IS NEEDED
20 December 2004 Taylor Models Workshop
COSY Infinity Simulations
COSY Infinity code (M. Berz, K. Makino, et al.)
Where M – map of the equations of motion (flow), obtained as a set of DA – vectors (Taylor expansions of final coordinates in terms of initial coordinates) uses DA methods to compute maps to arbitrary order own programming language allows complicated optimization scenarios writing internal optimization routines and interface to add more provides DA framework which could significantly simplify use of gradient optimization methods model is simple now, but much more complicated in future and COSY has large library of standard lattice elements
0
0
0
000
00
,1
)(,,,,E
EEE
vttl
p
pby
p
paxZ yx
)),()(,()( 00 sZssMsZ ),(),(),( 021021 ssMssMssM
20 December 2004 Taylor Models Workshop
Big Problem
Use of Taylor series leads to tricky way of handling beams with large coordinate spread (and that is exactly the case) Relative coordinates should be < 0.5 (empirical fact)
20 December 2004 Taylor Models Workshop
Straightforward division
20 December 2004 Taylor Models Workshop
Equations of Longitudinal Motion
)sin()sin(
)sin(
))(sin()sin(
)sin(
2
2
2
2
ss
RF
ss
RF
s
s
RFss
RFz
sRFz
mv
qV
dt
d
v
zm
qV
dt
zd
zzz
zqVvztqV
dt
dp
qVdt
dp
nonlinear oscillator
synchronous particle
equations in deviations from synchronous particle
COSY Infinity uses similar coordinates
20 December 2004 Taylor Models Workshop
Consequences of Equations of Motion
• Existence of stable regions, where we have oscillatory motion and unstable regions, and, therefore existence of separatrix (depends on frequency, RF gradient, synch. phase, etc… ). Stable area is called the “bucket”.
20 December 2004 Taylor Models Workshop
Beam Evolution
20 December 2004 Taylor Models Workshop
Clever Division• Use central
energies as centres of boxes, use RF period as ranges for the box
• Add “jumping” between intervals after each step. We change buckets and particles could be lost in one bucket and re-captured in another
20 December 2004 Taylor Models Workshop
Still a Problem
• 50 central energies x 60 RF cavities in Buncher = 300 maps…
• We are using DA arithmetic, everything is a DA-vector, including elementary functions (sin), so we need relatively high expansion order. Use 2 times more intervals + 5th order leads to natural advantage in buncher… maybe.
• Use COSY’s ability to generate parameter-dependent maps with ease and special law of bunches central energies distribution (smaller energies tends to be closer to each other)
40-50 maps 12-15 maps Potential calculation time reduction. Implementing.• 6000 particles, 50 central energies, 70 RFs
– 1st order: 0 hrs 10 min– 7th order: 8 hrs some mins
OPTIMIZATION?
nT
1
20 December 2004 Taylor Models Workshop
Sin Taylor expansion
-2-1.5
-1-0.5
0 0.5
1 1.5
2
-3 -2 -1 0 1 2 3
3rd order
-2-1.5
-1-0.5
0 0.5
1 1.5
2
-3 -2 -1 0 1 2 3
5th order
-2-1.5
-1-0.5
0 0.5
1 1.5
2
-3 -2 -1 0 1 2 3
7th order
-2-1.5
-1-0.5
0 0.5
1 1.5
2
-3 -2 -1 0 1 2 3
9th order
-2-1.5
-1-0.5
0 0.5
1 1.5
2
-3 -2 -1 0 1 2 3
11th order
-2-1.5
-1-0.5
0 0.5
1 1.5
2
-3 -2 -1 0 1 2 3
13th order
20 December 2004 Taylor Models Workshop
Different Order Simualtions
20 December 2004 Taylor Models Workshop
Different Order Simualtions
20 December 2004 Taylor Models Workshop
Conclusions
• Model is implemented in COSY Infinity and checked for consistency with other codes
• Some removal of the obstacles is done
• Brute-force optimization still seems to be infeasible. Looking for some more sophisticated method.
20 December 2004 Taylor Models Workshop
Yet Unanswered Questions
• Should longitudinal motion be studied separately, or should it be included on the very early stages?
• Are there any map-dependent criterias which could be used for map-based optimization?
20 December 2004 Taylor Models Workshop
Second Optimization Approach
• From synchronism condition one could derive following relation for kinetic energies of synch particles:
nTn n
cn
,111
1
111
1)(
20
cc
c
n
WnT
20 December 2004 Taylor Models Workshop
Final Kinetic Energy Relation
– From the rotator concept one could derive amount of energy gained by n-th synchronous particle in RF
– So for final energy n-th particle has after the rotator consists of m RFs we have
)2sin()( nN
EnT RF
)()(),( nTmnTmnT
20 December 2004 Taylor Models Workshop
Evolution of central energies shape T(n,m)
20 December 2004 Taylor Models Workshop
Energies shape in buncher and amount of kick they get in rotator
20 December 2004 Taylor Models Workshop
Energy Shape Evolution in Rotator
20 December 2004 Taylor Models Workshop
Objective Functions
– The idea of the whole structure is to reduce overall beam energy spread and to put particles energies around some central energy. So we have general objective function:
– First, we can set and get
2)),(( cn TmnTcI
21 )),(( cTmnTI
nCn ,1
20 December 2004 Taylor Models Workshop
Different optimized paremters (n vs T_fin)
20 December 2004 Taylor Models Workshop
Different optimized paremters (T_0 vs T_fin)
20 December 2004 Taylor Models Workshop
Evolution of central energies shape (unoptimized)
20 December 2004 Taylor Models Workshop
Evolution of central energies shape (optimized)
20 December 2004 Taylor Models Workshop
Evolution of central energies shape (optimized)
20 December 2004 Taylor Models Workshop
Different optimized paremters (T_0 vs T_fin) + energies distribution
20 December 2004 Taylor Models Workshop
Objective Functions
– For calculating we can use particle’s energies distribution
22 )),(( cn TmnTcI
nc
n energy particles %---------------------------------------------- -12 963.96 1023 17.050000 -11 510.85 692 11.533333 -10 374.64 537 8.950000 -9 302.98 412 6.866667 …
20 December 2004 Taylor Models Workshop
Different optimized paremters (n vs T_fin)
20 December 2004 Taylor Models Workshop
Summary
Model of buncher and phase rotator was written in COSY Infinity
Simulations of particle dynamics in lattice with different orders and different initial distributions were performed
Comparisons with previous simulations (David Neuffer’s code, ICOOL, others) shows good agreement
Several variations of lattice parameters were studied
Model of lattice optimization using control theory is proposed
Model of central energies distribution is developed. Some results for parameters have been obtained
20 December 2004 Taylor Models Workshop
Future Plans
Finish central energies optimizations, try changing more parameters, check optimized parameters for whole distribution (COSY, ICOOL?)
Develop some criteria for simultaneous optimization of central energies and energies of all paritcles in a beam or use control theory approach for the whole longitudinal motion optimization
Study transverse motion and particles loss because of decay and aperture, final emittance cut
Different lattices for different cooling sections/targets/whatever proposed (project is on R&D status)