1. JLEIC 200 GeV Ion Injector Chain and Bunch Formation
Jiquan Guo
For the JLEIC team
JLEIC Collaboration Meeting
April 1-3, 2019

2. JLEIC with 100 GeV CM Energy
12 GeV electron and 200 GeV proton
Electron collider ring has 476.3MHz RF freq and maximum bunch rep-rate, uses CEBAF as injector
Ion collider ring uses MHz RF system, requires an injector chain capable to form the MHz bunch trains of various ion species that fits in MHz buckets
100m
12 GeV CEBAF
Electron source
Ion linac
Low energy
Booster
High energy
Ion collider
ring
Electron collider
Interaction
point
April 1-3, 2019
Spring 2019 JLEIC Collaboration Meeting

3. JLEIC ion injector chain for 200 GeV
ion sources
SRF Linac
Booster with DC cooler
collider ring with BB/DC cooler
285MeV H-
100MeV Pb67+
~8GeV H+
2-2.4GeV Pb67+
<=100GeV H+
<=40GeV Pb82+
Multi-turn injection
Bucket-to-bucket transfer
H- Strip
Pb Strip
Previous design for 100 GeV ion ring
April 1-3, 2019
Spring 2019 JLEIC Collaboration Meeting

4. JLEIC ion injector chain for 200 GeV
150 MeV H-
40 MeV/u Pb67+
~8 GeV H+
2 GeV/u Pb67+
~12.1 GeV H+
~4.3 GeV/u Pb82+
~200 GeV H+
~78 GeV/u Pb82+
Full size high energy booster/ stacker with DC cooler
Collider ring with bunched beam cooler
Low Energy Booster with DC cooler
H- Strip
Pb Strip
Multi-turn injection
Bucket-to-bucket transfer
ion sources
SRF Linac
Bucket-to-bucket transfer
Major changes:
Add a full size high energy booster (HEB), also functioning as a stacker
Ramping one ring from 8 GeV proton (and possibly 6.4 GeV p equivalent Pb82+) to 200 GeV equivalent is risky
Most of the bunch formation process can be done in the HEB, increasing the collider duty factor and time averaged luminosity
The low energy booster (LEB) changed to normal conducting magnets
Circumference almost doubled to 604m
Lower the linac energy to ~150 MeV for cost reduction
Double the LEB cycles to 54-56
April 1-3, 2019
Spring 2019 JLEIC Collaboration Meeting

5. Factors determining the energy of each injector chain components
Ramping ratio of each ring
Max/min dipole field ratio should be ≤20, desired to be <16,
Although RHIC demonstrated operations at low energy Bρ=19.3Tm (~1/5 of injection) and top energy Bρ=839.5Tm, the low energy operation is constrained by longitudinal and transverse acceptance.
Space charge limit
Laslett tune shift ∝𝑄 𝐿 𝑏𝑢𝑐𝑘𝑒𝑡 /(𝛽 𝛾 2 𝜀 𝑛 𝜎 𝑠 ), limits at ~0.15
Bottleneck at the injection energy of each ring, especially for H+ in LEB and Pb82+ in HEB; or when the bunch is cooled/compressed
DC cooling desired during/after stacking
DC cooler technology limits to ≤ 8 GeV/u ion energy to lower risk, demonstrated at Tevatron
~16 GeV technology under development for GSI-FAIR
Avoid ϒ transition for proton
Affordable RF voltage for all bunch splitting/compression steps
April 1-3, 2019
Spring 2019 JLEIC Collaboration Meeting

6. JLEIC ion beam formation steps for proton
150 MeV
8 GeV
DC cooler
4.3 MeV
Stacking, 54 LEB cycles,
ε preservation
Low-energy booster
Ek-trans 9 GeV
High-energy
Booster
Ek-trans ~14 GeV
Collider
Ek-trans ~11 GeV
Accumulation from linac
Charge strip injection
~20 GeV
Up to 200 GeV
Energy
Time
Bunch
splitting/capture
Bunched Beam
ERL cooler
Up to 109 MeV
Emittance
preservation
12.1 GeV
ε reduction
Pre-bunch
splitting
Ramp ratio 16.1
Ramp ratio 1.46
Ramp ratio 15.5
April 1-3, 2019
Spring 2019 JLEIC Collaboration Meeting

7. JLEIC ion beam formation steps for lead
41 MeV
2.08 GeV
DC cooler
1.1 MeV
Stacking, 28 LEB cycles,
ε preservation
Pb67+
Low-energy booster
Ek-trans 9 GeV
Pb82+
High-energy
Booster
Ek-trans ~14 GeV
Collider
Ek-trans ~11 GeV
Accumulation from linac
Phase painting
~20 GeV
Up to 78 GeV
Energy
Time
Bunch
splitting/capture
Bunched Beam
ERL cooler
Up to 43 MeV
Emittance
preservation
4.28 GeV
ε reduction
Pre-bunch
splitting
Ramp ratio 10.2
Ramp ratio 1.91
Ramp ratio 15.5
21 keV
April 1-3, 2019
Spring 2019 JLEIC Collaboration Meeting

8. JLEIC bunch formation steps
Accumulate in LEB at 150MeV (p) or 41 MeV (Pb67+) in coasting beam, with possible DC cooling to keep the emittance
Capture to RF bucket, accelerate to top energy 8 GeV (p) or 2.08 GeV (Pb67+),
Compress to bunch length ~6.7m rms for proton (13.4m bunch length for Pb, then split to two bunches of 6.7m length in two 40m buckets). 95% bunch length ~27m, with ~40ns gap between bunches for injection kicker rise time.
Extract from LEB, strip Pb67+ to Pb82+ in the beam transfer line, inject into HEB in ~40m buckets (h=58), ramp back LEB to injection
Repeats step 1-4 for 54 cycles with proton (28 cycles for Pb). HEB DC cooler turned on to maintain emittance
Ramp HEB to 8 GeV (p) or 4.28 GeV (Pb82+)
HEB DC cooler electron beam current turned up to reduce emittance, keep rms bunch length at ~6.7m.
Ramp HEB to 12.1 GeV for proton. Compress all bunch length to ~5m in ~7MHz bucket
Perform 4 binary bunch splits to h=928, rms bunch length ~0.3m in 119MHz buckets
Transfer the whole bunch train from HEB to collider ring
Ramp collider ring to collision energy. Perform two optional binary bunch splits to h=3712 in 476MHz buckets.
Manipulate the bunch train with 476MHz RF phase modulation to generate extra buckets for energies that requires “gear change” collision, h=
Compress the bunches ( MHz) into 952.6MHz bucket. Turn on 952.6MHz SRF.
April 1-3, 2019
Spring 2019 JLEIC Collaboration Meeting

9. Ramping parameters of the JLEIC injector chain
Proton Pb
Injection
Extraction (coll)
Inj
Ext (col)
Linac
Kinetic Energy (MeV)
150 41
Charge state -1
+67
Low Energy Booster (LEB)
Kinetic Energy (MeV)
8000
2080
Bρ (T-m)
1.84
29.7
2.90
Ramp ratio
16.1 +1
Circumference (m)
(15/58 of ion collider ring)
Booster cycles 54 28
Full size High Energy Booster
(HEB)
Kinetic Energy (GeV) 8
12.1
2.08
4.28
46.4
24.2
1.92
+82
(h=29*256=7424)
Collider ring
Kinetic Energy (GeV)
200
78.3
670.2
2336
15.5
April 1-3, 2019
Spring 2019 JLEIC Collaboration Meeting

10. Space charge parameters
Proton (54 cycles)
Deuteron (54 cycles)
Pb (28 cycles)
Collider ring (ICR)/HEB Ib (A)
0.75
0.63
0.25
Linac Energy (MeV/u)
150 85 41
LEB charge state 1+
67+
LEB total ion (1010), 95% transfer to HEB 71 60
0.54
LEB injection εx,y (µm)
1.87
1..38
0.95
LEB injection σ (x, y, mm) β=14m
6.7
LEB inj/capture νlas (σz≈100m)
0.163
0.133
0.116
LEB circumference (m)
604.13m
LEB extraction Ek (GeV)
8.0
3.60
2.08
LEB extraction σz (m)
26.7
HEB circumference (m) m
HEB ion per long bunch (40m bucket) (1010) 68 57
0.26
HEB inj νlass (assume same εn as LEB capture)
0.068
0.150
HEB DC cool energy (GeV) 8
5.63
4.28
HEB DC cooled νlass (σz=6.7m)
0.15
0.113
HEB DC cooled εn, x/y (μm)
0.85
0.88
0.42
HEB bunch splitting and extraction energy (GeV)
12.1
HEB bunch splitting/extraction νlass (σz=5m)
0.088
For protons, space charge bottleneck is at the capture stage in LEB, the collider ring beam current is limited by the linac energy, LEB aperture and the number of LEB cycles.
For deuteron and heavy ion, the bottleneck for the current design is at the injection stage of HEB, which is limited by the LEB extraction energy and the maximum transverse emittance.
HEB DC cooling energy limits the minimum transverse emittance can be reached
April 1-3, 2019
Spring 2019 JLEIC Collaboration Meeting

11. Bunch capture, compression and split
Adiabatic binary splitting is the baseline for JLEIC bunch splitting process
Maximize the split ratio with least RF frequencies compared to factor of ≥3 splitting
Minimum emittance growth
Mature and low risk
A total of 7 splits needed to reach 476MHz bunch rep-rate
2 splits in the collider ring, 4 splits in the HEB (7.4MHz to 476MHz)
LEB has 1 split for Pb. Proton does not need LEB split with 150 MeV ion linac, but can have 1 split if linac upgrades to ~300 MeV.
All split are done with normal conducting cavities
The 2 splits in collider ring can be skipped to increase luminosity when bunched beam cooling is not the bottleneck
For heavy ion with low beam current, particles per bunch is low
For high energy proton, BB cooling does not work well and IBS rate is slow.
Bunch compression/split energy needs to be as high as possible
LEB/HEB compression/split are at extraction energy
LEB needs a factor of 15 compression, requires an intermediate RF frequency of h=5
Need to compress the MHz bunch to 952MHz bucket in the collider ring, need to maximize the compression/split energy to keep voltage low.
Typical binary adiabatic bunch splitting
Relative RF voltage ramping for JLEIC binary bunch splitting
April 1-3, 2019
Spring 2019 JLEIC Collaboration Meeting

12. Adding extra buckets in JLEIC ion collider ring
JLEIC plans to apply “gear change” synchronization scheme
Limit the e-ring circumference continuous adjustment range to ~63cm (RF wavelength of 476MHz)
Harmonic number of ion collider ring needs to be changed to extend the ion energy further below ~40GeV
With the baseline binary splitting, ion harmonic number has to be multiple of 64 (in 476MHz)
RF gymnastics needed to add extra buckets to the ion ring
Use low Q 476MHz RF cavities, jump the phase in the abort gap to make harmonic number non-integer
Filled with 1-2 bunch trains,
3584 buckets
Abort gap, buckets, ~270ns
Inserting buckets in the ion ring by phase jump in the gap
stage Nh
fRF (MHz) for 39GeV/u
RF phase jump in the gap
before ramping
3712
Start freq ramping
3712+Δ (Δ=0~0.5)
×(1+Δ/3712)
-2πΔ/3712
ramp half finished
3712.5 -π
continue freq ramping
3713-Δ (Δ=0.5~0)
×(1-Δ/3712)
2πΔ/3712
ramping finished
3713
April 1-3, 2019
Spring 2019 JLEIC Collaboration Meeting

13. RF cavities for JLEIC bunch formation
Cavity function
Energy (GeV)
Frequency (MHz)
Cavity design
LEB acceleration/compress
0.04-8
MA loaded
LEB compress (h=5)
2.08-8
LEB split (h=15)
7.075
MA/ferrite loaded
HEB acceleration (h=58)
HEB bunch split
Button or ferrite loaded
button
button or QWR
Collider ring acc/bunch splitting
20-40
Button or HWR
Collider ring bunch splitting, bucket manipulation, acceleration
20-200
PEP-II-like with modified coupler and ferrite loaded
Compress into 952.6MHz
PEP-II with higher Qext coupler
PEP-II 476MHz elliptical cavity
CERN PS 40 MHz and 80 MHz button cavities for LHC bunching
JPARC RCS Magnetic Alloy (MA) loaded cavities, MHz
CERN PS MHz Ferrite loaded cavity
April 1-3, 2019
Spring 2019 JLEIC Collaboration Meeting

14. Forming the double intensity bunch train for RF transient compensation
Inominal Vc
2Inominal
Compensate ion ring RF transient with double intensity ion bunch train
Double charge e bunches
476.3 buckets
Normal e bunches
476.3 buckets
Kicker Gap ~20ns
Abort Gap ~247ns
Double charge bunches,
even buckets, 267ns
ion Bunches
Even buckets
ion Bunches
Horizontal axis: arrival
April 1-3, 2019
Spring 2019 JLEIC Collaboration Meeting

15. Spring 2019 JLEIC Collaboration Meeting
Forming the double intensity bunch section for RF transient compensation
For 0.25A Pb, the beam current is so low that we probably have enough klystron power to do OTFB/FF and don’t need double intensity compensation
For proton, our approach will be
forming the normal intensity 119MHz bunch train in HEB and transfer to the collider ring
Inject 4 long bunches (σz=6.7m in ~40m RF buckets) with regular intensity into HEB, cooled, then at 12.1GeV merge the 4 bunches and compress into one bunch of σz=12m in 80m bucket. Such a bunch will have Laslett tune shift of ~0.15
Split the double intensity bunch into 119 MHz ~267ns bunch train in HEB, and transfer the bunch train into collider ring with ~20ns gap between the normal intensity bunch train
Split the full bunch train to up to 476MHz in collider ring at higher energy
April 1-3, 2019
Spring 2019 JLEIC Collaboration Meeting

16. Spring 2019 JLEIC Collaboration Meeting
Ion Linac
RFQ1
MEBT
IH DTL
2-3 HWR CM
2 QWR CM
1 QWR CM
A/Q≤7
RFQ2
A/Q≤2
100MHz,
500keV/u
100MHz
5MeV/u
WARM
SRF
Carbon Stripper
Pb30+
Pb67+
(Pb) 13MeV/u
βg=0.15
200MHz
βg=0.30
(Pb) ~41MeV/u
(H) ~150MeV
Pb Energy (MeV)
Argonne design, B. Mustapha
150 MeV linac is sufficient for 0.75A proton beam current in the collider ring with 54 LEB cycles and
Pb charge stripping energy to be optimized
9MeV stripping yields Pb62+, maximizing linac Pb energy of the 150MeV proton linac (~44MeV/u Pb)
13MeV stripping yields Pb67+, maximizing linac Pb energy when linac upgrades to ~300MeV proton (~100 MeV/u Pb)
17MeV stripping yields Pb70+, linac Pb energy sufficient for LEB injection space charge bottleneck, improves LEB extraction energy and HEB injection space charge bottleneck
April 1-3, 2019
Spring 2019 JLEIC Collaboration Meeting

17. Spring 2019 JLEIC Collaboration Meeting
Summary
We modified JLEIC bunch formation scheme for the 200GeV ion energy.
The major change from the previous 100GeV ion energy design is the addition of the full size high energy booster
Optimization of the scheme is constrained by various factors for different ion species, such as space charge, magnet ramping, DC cooling, RF voltage for bunch splitting and compression, cost, etc. More optimization iterations needed.
Adiabatic binary bunch splitting remains the baseline, and barrier bucket bunch splitting scheme is still under investigation
April 1-3, 2019
Spring 2019 JLEIC Collaboration Meeting