March 2930 2016 Preservation of Magnetized Beam Quality in a NonIsochronous Bend Chris Tennant Jefferson Laboratory 1 Outline Longitudinal Match iterative process with front end injector merger ID: 682463
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Slide1
JLEIC Collaboration Meeting |
March 29-30, 2016
Preservation of Magnetized Beam Quality in a Non-Isochronous Bend
Chris Tennant
Jefferson Laboratory
1Slide2
OutlineLongitudinal Matchiterative process with front end (injector, merger)180° Recirculation Arc
“S2E” ResultsLinac Scan
Lattice FunctionsTracking ResultsEmittanceSummary2Slide3
Parameterspinj = 5 MeV/cpmax = 55 MeV/cf
RF = 952 MHzQbunch = 420 pCsz
= 2 cm (full) (at cooling channel)sdp
/p = 3×10-4 (rms
) (at cooling channel)sx=y = 1 mm (at cooling channel)Bsolenoid = 1 TBeam: magnetizedlinacsolenoid
Match from linac to arc
Match from
dechirper
to solenoid
180° arc
dechirper
3
b
x
=y
= 0.37 m
e
n,drift
= 289
mm-
mradSlide4
Longitudinal MatchRequired: electron beam parameters at coolerdefines linac phase set points
defines compaction requirements (R56, T
566)4
Linac
: -15 degreesArc: R56 = +0.55 m, T566 = -1.65 mDechirper: zero-crossing
linac
solenoid
Match from linac to arc
Match from
dechirper
to solenoid
180° arc
dechirperSlide5
Arc Architecture5Utilize indexed dipoles to provide azimuthally symmetric focusing
preserve magnetizationAvoid envelope modulation avoid space charge driven degradationWith uniform bending the dispersion is large and it is difficult to achieve desired R56
introduce reverse bendingThree bend achromats (TBA) with reversed center bend2 four-period achromatsTBA period, ¼-integer tunes
angles chosen to set compaction (q1= 20.4031
o, q2=18.1531o)(courtesy D. Douglas)Slide6
Arc Momentum Compactions
6Slide7
Arc Lattice Functions
7Slide8
Cooler ERL Layout
8
Magnetized Gun
Booster
50 MeV Linac Cryomodule
De-chirper
C
hirper
Ion Beam
1
Tesla Cooling Solenoid
Beam dump
start
endSlide9
Initial Beam: Linac Entrancest = 21 ps
(6.3 mm) fullsdp/p = 2.1% full
(sdp = 105 keV full)bx,y = 2.00 m
ax,y = -0.50Create flat beam (i.e. ex = 586 mm-mrad
, ey = 4.0 mm-mrad) and apply flat-to-round-beam transformTransverse: Gaussian distributionLongitudinal: Hard-edge distribution9Slide10
Round Beam
10Slide11
Beam Envelopes
11Slide12
Flat-to-Round-Beam Transform
Flat to round beam transform for arbitrary
b and a (JLAB-TN-15-026)
=
Flat Beam
Round Beam
12Slide13
Linac Entrance
Inject at 5 MeV/c
105
keV
21 ps13Slide14
Linac Exit: elegant
Six 5-cell 952 MHz cavitiesOperate at -15°
14Slide15
Arc Exit: elegant
R56 = +0.55 m, T566 = -
1.5 m2 cm bunch length (full)15Slide16
De-chirper Exit: elegant
Single 5-cell 952 MHz cavity with 3.65 MV gainOperate at zero crossing
25
keV
(4.5×10-4)16Slide17
Lattice Functions
17Slide18
Lattice Functions
18Slide19
Transverse Emittance: 0 pC
19Slide20
RMS Beam Sizes: TStep
(420 pC)20Slide21
(x,y
) Phase Space: TStep (420 pC)
linac entrancelinac exita
rc entrancearc exit
de-chirper exitsolenoid entrance21Slide22
22
s
x
= sy = 1 mmSolenoid Entrance: TransverseSlide23
(t,p
) Phase Space: TStep (420 pC)23
linac entrancelinac exit
arc entrancearc exit
de-chirper exitsolenoid entranceSlide24
24
Solenoid Entrance: Longitudinal
100
keV
(full)2 cm (full)can be further optimized to remove slope/curvatureno gross distortion from space charge wakeSlide25
An inverse flat-beam-transform (FBT) segregates the basis: magnetized modes go to one plane, Larmor modes go to the othermagnetized modes: defines beam size in cooling channel
drift emittance “x plane” emittance after inverse FBTLarmor modes: control the cooling rate
cyclotron emittance “y plane” emittance after inverse FBT25How are We Doing?!
(courtesy D. Douglas)Slide26
Round-to-Flat-Beam Transform: 420 pC26
581 mm-
mrad
25 mm-
mrad
307 mm-
mrad
313 mm-
mradSlide27
Cooler Design: An Iterative Process27
COOLING RATE
IBS RATE
Beam SizeBunch Length
Bunch ChargeB-FieldLongitudinal MatchArc Re-designCollective Effects
Aperture Constraints
Linac Re-design
Transverse MatchSlide28
Adding the “Start” to S2ENext iteration of S2E must include the beam formation processgun (400 keV
), booster (400 keV 5 MeV)
, merger (5 MeV)Space charge will induce unwanted correlationsneed to assess impact on transverse matching and cooling rate28Slide29
SummaryWe are converging on beam parameters for the coolerHave a complete longitudinal matchReducing the bunch length eases constraints on momentum compactions, de-chirper system and potential longitudinal phase space distortion
Results of particle tracking through the recirculation arc – with space charge – are encouragingNeed to take care in matching the beam from the linacStill to investigate:How does the system perform after we integrate front end?
Collective effects (mBI
gain, CSR, BBU)Cooling efficiency with degraded beam? Sensitivities?
29Slide30
30Slide31
Emittance Evolution31
Magnetized Gun
Booster
50 MeV Linac Cryomodule
De-chirper
C
hirper
Ion Beam
1
Tesla Cooling Solenoid
Beam dumpSlide32
Describing A Round BeamIdeally, a round beam can be described via the sigma matrix in the following way (TN-15-026):
We note that at the exit of the linac, the distribution from TStep contains many coupling terms that are not strictly zero
2.16E-039.73E-010.00E+00
2.33E-010.00E+00
0.00E+005.51E-04-2.33E-010.00E+000.00E+000.00E+002.16E-039.73E-010.00E+000.00E+00
5.51E-04
0.00E+00
0.00E+00
3.00E-03
0.00E+00
1.00E-03
2.16E-03
9.73E-01
-8.93E-05
2.30E-01
-1.07E-02
-1.11E-02
5.51E-04
-2.30E-01
-2.37E-04
-1.07E-02
-1.11E-02
2.16E-03
9.73E-01
4.87E-03
4.80E-03
5.51E-04
2.43E-03
2.29E-03
4.95E-12
9.98E-01
9.42E-03
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Description of an
ideal
beam at linac exit
Actual description of beam at linac exit
32