1 Front End Capture/Phase Rotation & Cooling Studies David Neuffer Cary Yoshikawa December 2008.
Transcript of 1 Front End Capture/Phase Rotation & Cooling Studies David Neuffer Cary Yoshikawa December 2008.
1
Front EndFront EndCapture/Phase RotationCapture/Phase Rotation
& Cooling Studies & Cooling Studies
David NeufferCary Yoshikawa
December 2008
2
0utline0utline
Introduction ν-Factory Front end
Capture and Φ-E rotation High Frequency
buncher/rotation •Study 2B ν-Factory
Shorter version ν-Factory→μ+-μ- Collider
Discussion
3
Variations tried …Variations tried …
Study 2A – ISS baseline Shorter bunch train example
nB= 10
Better for Collider; as good for ν-Factory ICOOL/G4Beamline simulations Study of “accepted” particles
Rf cavities in solenoids? Use “magnetic insulation” ASOL lattice Not too bad Variations Higher energy capture ??
4
Study2B June 2004 scenario (ISS)Study2B June 2004 scenario (ISS)
Drift –110.7m Bunch -51m
(1/) =0.008 12 rf freq., 110MV 330 MHz 230MHz
-E Rotate – 54m – (416MV total) 15 rf freq. 230 202 MHz P1=280 , P2=154 NV = 18.032
Match and cool (80m) 0.75 m cells, 0.02m LiH
Captures both μ+ and μ-
~0.2 μ/(24 GeV p)
5
Study 2B ICOOL simulation (NStudy 2B ICOOL simulation (NBB=18)=18)
s = 1m s=109m
s=166m s= 216m
-40 60
500MeV/c
0
Drift
Bunch
Rotate
500MeV/c
0
6
Features/Flaws of Study 2B Front EndFeatures/Flaws of Study 2B Front End
Fairly long system ~300m long (217 in B/R) Produces long trains of ~200 MHz bunches
~80m long (~50 bunches) Transverse cooling is ~2½ in x and y, no longitudinal
cooling Initial Cooling is relatively weak ? -
Requires rf within magnetic fields in current lattice, rf design; 12 MV/m at B = ~2T, 200MHz MTA/MICE experiments to determine if practical
For Collider (Palmer)
Select peak 21 bunches Recombine after cooling ~1/2 lost
-40 60m
500 MeV/c
7
Shorter Bunch train example Shorter Bunch train example
Reduce drift, buncher, rotator to get shorter bunch train: 217m ⇒ 125m 57m drift, 31m buncher, 36m rotator Rf voltages up to 15MV/m (×2/3)
Obtains ~0.26 μ/p24 in ref. acceptance Slightly better ?
• ~0.24 μ/p for Study 2B baseline
80+ m bunchtrain reduced to < 50m Δn: 18 -> 10
-30 40m
500MeV/c
8
Further iteration/optimizationFurther iteration/optimization
Match to 201.25 MHz cooling channel
Reoptimize phase, frequency f = 201.25 MHz, φ = 30º,
Obtain shorter bunch train
Choose ~best 12 bunches ~ 21 bunch train for Collider
at NB= 18 case
~12 bunches (~18m) ~0.2 μ/pref in best 12 bunches Densest bunches are ~twice
as dense as NB = 18 case0
20
40
60
80
100
120
1 6 11 16 21 26 31 36
Series1
9
Details of ICOOL model (NDetails of ICOOL model (NBB=10)=10)
Drift– 56.4m B=2T
Bunch- 31.5m Pref,1=280MeV/c, Pref,2 =154 MeV/c, nrf = 10
Vrf 0 to 15MV/m (0.5m rf, 0.25m drift) cells
360 MHz 240MHz
-E Rotate – 36m – Vrf = 15MV/m (0.5m rf, 0.25m drift) cells
NV = 10.07 (240 -> 201.5 MHz)
Match and cool (80m) Old ICOOL transverse match to ASOL (should redo)
Pref= 220MeV/c, frf = 201.25 MHz
• 0.75 m cells, 0.02m LiH, 0.5m rf, 16.00MV/m, φrf =30°
Better cooling possible (H2, stronger focussing)
10
Simulations (NSimulations (NBB=10)=10)
-30m 30m
500 MeV/c
0
Drift andBunch
s = 89ms = 1m
Rotate
s = 125m s = 219m
Cool
12
Comparisons of ICOOL and G4BLComparisons of ICOOL and G4BL
Simulations of front end and cooling agree ICOOL and G4Beamline results can be matched
Buncher – rotator – cooler sequence can be developed in both codes
Method Captures both μ+ and μ-
But some differences dE/dx is larger in ICOOL Phasing of rf cavities uses different model
13
12.9 m 43.5 m 31.5 m 36 m
drift buncher rotatorcapture
MC Front End Layout in G4beamline
“Cool and Match” 3 m (4x75 cm cells) “Cool” 90 m of 75 cm cells
Rotator 36 m long
75 cm cell 1 cm LiH
23 cm vacuum
50 cm 201.25 MHz
RF cavity
16
Reduce number of independent Reduce number of independent frequenciesfrequencies
Initial example had different
rf frequency for each cavity Buncher- 42 cavities -31.5m
• 360to 240 MHz Rotator- 48 cavities -36m
• 240 to 202 MHz
Reduce # by 1/3 14 in buncher; 16 in rotator Nearly as good capture
(<5%less) Similar to study 2B
discreteness Reduce by 1/6
7 in buncher, 8 in rotator Significantly worse (~20%)
Acceptance of Mu+'s Within Atrans<0.030 m-rad & Along<0.15 m (sigma6.0, To=475.5ns, phase=25.8deg)
0
1000
2000
3000
4000
5000
6000
0 20 40 60 80 100 120 140 160 180 200 220
z (m)
Nu
mb
er
of
Mu
+'s
pe
r 1
00
k P
OT
Benchmark
Grp3RF
Grp6RF
Grp3&6RF
Grp6&3RF
Longitudinal Emittance in Study 2A-like Front End (sigma6.0, phase=25.8deg, To=475.5ns)
0.05
0.07
0.09
0.11
0.13
0.15
0.17
0.19
0.21
0.23
0.25
0 20 40 60 80 100 120 140 160 180 200 220
z (m)
Em
itta
nc
e (
m-r
ad
)
a: Tapered Solenoid
b: Drift
c: Buncher
d: Rotator
e: Match & Cool (4m)
f: Cooler (opposing solenoids)
ba c d e f
(a)
(b)
17
Accepted particlesAccepted particles
Accepted particles fit final beam cuts: AX + Ay < 0.03m
AL < 0.2m
Initial beam has momenta from ~75 to ~600 MeV/c Final beam is ~200 to
300 MeV/c
Transverse emittance is cooled from ~0.014 to ~0.0036
600 MeV/c
600MeV/c
0 MeV/c
0 MeV/c
18
Accepted Longitudinal distrosAccepted Longitudinal distros
1m 135m
135m 196m
196m
-30m 40m
600 MeV/c
600 MeV/c
0 MeV/c
0 MeV/c
19
““Accepted” Beam propertiesAccepted” Beam properties
For study 2A acceptance means several cuts: AX + Ay < 0.03m
AL < 0.2m
For beam within acceptances, εt, N,rms = 0.0036m (from
~0.007) εL, N,rms = ~0.04m (from
~0.09)
Emittances are much smaller than the full-beam emittances … xrms = 6cm (all-beam)
xrms = 3.6cm (accepted-beam)-30cm +30cm
-30cm
+30cm
20
Variations - focusing Variations - focusing
Buncher and Rotator have rf within 2T fields Field too strong for rf field ?? Axial field within “pill-box”
cavities
Solutions ?? Open-cell cavities ?? “magnetically insulated”
cavities• Alternating Solenoid lattice is
approximately magnetically insulated
• Use ASOL throughout buncher/rotator/cooler
Use gas-filled rf cavitiesASOL lattice
21
Use ASOL lattice rather than 2TUse ASOL lattice rather than 2T
Study 2A ASOL Bmax= 2.8T, β*=0.7m,
Pmin= 81MeV/c 2T for initial drift Low energy beam is lost
• (P < 100MeV/c)
• Bunch train is truncated OK for collider
Also tried weaker focusing ASOL Bmax= 1.83T, β*=1.1m,
Pmax = 54 MeV/c 1.33 T for initial drift Match scaled from 2A match
+ -
B(z)
24
First ASOL results First ASOL results
Simulation results 2.8T ASOL 0.18 μ/24 GeV p 0.059 μ/8 GeV p Cools to 0.0075m
1.8T ASOL 0.198 μ/24 GeV p 0.064 μ/8 GeV p ~10% more than stronger
focussing Cools to 0.0085m
Baseline (2T -> ASOL) had ~0.25 μ/24 GeV p ~0.08 μ/8 GeV p
Weaker-focusing ASOL has ~10% better acceptance than 2.8T lattice Longer bunch train
25
Variant-capture at 0.28 GeV/cVariant-capture at 0.28 GeV/c
0.0
1.0GeV/c
1.0GeV/c
0.0
2T → 2.8T ASOL
-30m +40m -30m +40m
1.0GeV/c
s=59m s=66m
s=126ms=200m
26
Capture at 280 MeV/cCapture at 280 MeV/c
Captures more muons than 220 MeV/c For 2.T -> 2.8T lattice But in larger phase space area Less cooling for given dE/ds Δs
Better for collider Shorter, more dense bunch train If followed by longitudinal cooling
220 MeV/c 280 MeV/c
27
Higher-Energy Simulation resultsHigher-Energy Simulation results
Higher energy capture improves capture for high-field lattice Cooling is slower
Not as good for low-field lattice Weaker focusing reduces
cooling
For High field lattice: 2.8T ASOL
8GeV beam 0.065 μ/p in εt <0.03, εL <0.2
0.093 μ/p in εt <0.045, εL <0.3
24 GeV beam 0.19 μ/p in εt <0.03, εL <0.2
0.26 μ/p in εt <0.045, εL <0.3
For Low-field lattice• 1.8T ASOL
8GeV beam
• 0.053 μ/p in εt <0.03, εL <0.2
• 0.083 μ/p in εt <0.045, εL <0.3
• cools only to ~0.010m
28
DiscussionDiscussion
High frequency phase-energy rotation + cooling has been explored
Shorter system better for Collider Shorter bunch train; denser bunches
“magnetic insulated” lattice could be used rather than B = 2 or 1.75 T lattice Slightly worse performance (?)
•~10 to 20% worse for neutrino factory Ok for Collider
•Particles lost are at end of bunch train