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ILC Damping rings. G. Dugan PAC TDR review 12/13/12. Outline. Requirements Configuration, parameters, operating modes Lattice Beam dynamics issues Emittance tuning and nonlinear effects Electron cloud effect Fast ion instability Technical systems RF Magnets and power supplies - PowerPoint PPT Presentation
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ILC Damping rings
G. DuganPAC TDR review
12/13/12
Dec. 13, 2012 ILC Damping Rings
ILC Damping Rings 2
Outline• Requirements• Configuration, parameters, operating modes• Lattice• Beam dynamics issues
– Emittance tuning and nonlinear effects– Electron cloud effect– Fast ion instability
• Technical systems– RF– Magnets and power supplies– Vacuum, instrumentation and feedback– Injection/extraction
• Conclusion
Dec. 13, 2012
ILC Damping Rings 3
Damping rings functional requirements
Dec. 13, 2012
• accept e- and e+ beams with large transverse and longitudinal emittances from the sources and produce the low-emittance beams required for high-luminosity production;
• damp incoming beam jitter (transverse and longitudinal) and provide highly stable beams for downstream systems;
• delay bunches from the source to allow feed-forward systems to compensate for pulse-to-pulse variations in parameters such as the bunch charge.
Dec. 13, 2012 ILC Damping Rings 4
Ring ConfigurationCircumference: 3238 m, 2 x 710 m straights
5.6 μm-rad < γεx < 6.4μm-rad54 14-pole wigglers : length 2.1 m, Bpeak 2.2 T, period 30 cm
=>24 ms > τx > 12 ms
e+ (baseline)
e- (baseline)
Phase trombone ± 0.5 λβ
Chicane ± 4 mm pathlength12 – 650 MHz RF cavities => σl = 6 mmHarmonic number 7022
e+ (future option)
ILC Damping Rings 5Dec. 13, 2012
Operating modes and ring parameters• Three ILC operating
modes correspond to four DR configurations
• Two modes utilize a 5 Hz repetition rate: low power baseline (1312 bunches/ring); and high luminosity upgrade (2625 bunches).
• Third operating mode is at 10 Hz, with e- linac operated with alternating pulses: high energy for e+ production followed by low energy for collisions.
• Shorter damping times necessary to achieve the same extracted vertical emittance in half the nominal storage time.
ILC Damping Rings 6Dec. 13, 2012
Ring lattice
extraction
arc
phas
e tro
mbo
neRF
wig
gler
s
arc
circ
umfe
renc
e ch
ican
e injection
Arc cells
Dec. 13, 2012 ILC Damping Rings 7
Each cell contains :1 - 3m dipole, θ = π/753 – quadrupoles4 - sextupoles3 - corrector magnets 1-horizontal steering 1-vertical steering 1- skew quad2 beam position monitors
75-cells/arc
BPM BPM
• Wiggler straight– 2 wigglers/cell– 30 cells– 2.1 m wiggler– 1.5T< Bpeak< 2.2T– 54 @ 2.16T => τx =13ms (10Hz)– 54 @ 1.51T => τx = 25ms (5Hz)– 3 empty cells will accommodate
6 additional wigglers if required– H&V dipole corrector and BPM
adjacent to each quad
Damping Wigglers
Dec. 13, 2012 ILC Damping Rings 8
ILC Damping Rings 9
RF straight
Dec. 13, 2012
• RF– 2 cavities/cell– 22.4 MV => 6mm bunch
length @ τx =13ms => for 12 cavities 1.9MV/cavity 272kW/couplerLattice can accommodate 16 cavities if required
Cavities offset so that waveguides of upper and lower rings are interleaved
H&V corrector and BPM adjacent to each quadrupole
ILC Damping Rings 10
Emittance in 3rd GLS, DR and collidersR. Bartolini
Low Emittance Rings Workshop, Crete 3rd October 2011
Dec. 13, 2012
Emittance tuning-1
CesrTAATF Note that LS emittance results are for electron rings.
ILC Damping Rings 11
Emittance tuning-2
Dec. 13, 2012
• Measure and correct orbit using all steerings
• Measure betatron phase advance (by resonant excitation) – and correct using quadrupoles
• Measure coupling (by resonant excitation) and correct with skew quads
• Measure orbit, coupling, and vertical dispersion and simultaneously correct with vertical steerings and skew quads
Parameter RMS
BPM – Differential resolution 2 μm
BPM – Absolute resolution 100 μm
BPM – Tilt 10 mrad
BPM button – Gain variation 1%
Quads + Sexts – Offset (H+V) 50 μm
Quads – Tilt 100 μrad
Dipole – Roll 100 μrad
Wiggler – Offset (V only) 200 μm
Wiggler - Roll 200 μrad
Design: 2 pm
ILC Damping Rings 12
Nonlinear effects
Dec. 13, 2012
• Magnet misalignments as on previous slide.• Magnet multipole errors based on PEPII and SPEAR
magnet measurements.• Wiggler nonlinearities based on numerical wiggler field
model, checked against Cesr wiggler field measurements.
Dynamic aperturewith specified magnet misalignments and field
errors, and full Taylor map for wiggler nonlinearities
Tune footprint
Injected positron beam
Dec. 13, 2012 ILC Damping Rings 13
Electron Cloud Effect-outline
• Vacuum chamber design to minimize photon absorption in the chamber
• Vacuum chamber surface EC mitigation • EC buildup simulations to estimate ringwide average
cloud density• Comparison with analytic estimate of instability threshold• Comparison with numerical simulations of coherent and
incoherent emittance growth using CMAD
DR Vacuum System Design
Dec. 13, 2012 ILC Damping Rings 14
Antechamber with slanted interior end to reduce photon backscattering
Fully-absorbing photon stops
• DR vacuum chamber has been designed with the help of a new photon tracking code (Synrad3D) developed for CesrTA
• The code allows accurate determination of antechamber features to limit the number of photons absorbed within the vacuum chamber.
• It also provides an accurate estimate of the sources of the photoelectrons which seed development of the electron cloud.
Note that the vacuum chambers are shown rotated by 90o relative to their installed orientation.
EC Working Group Baseline Mitigation Recommendation
Drift* Dipole Wiggler Quadrupole*
Baseline Mitigation
TiN Coating+Solenoid Windings
Grooves with
TiN coating
Clearing Electrodes TiN Coating
Vacuum chamber surface treatment forSEY suppression
Mitigation Evaluation conducted at satellite meeting of ECLOUD`10 (October 13, 2010, Cornell University)
Dec. 13, 2012 ILC Damping Rings 15
SuperKEKB Dipole Chamber Extrusion DR Wiggler chamber concept with thermal spray clearing electrode – 1 VC for each wiggler pair.
Y. Suetsugu Conway/Li
SEY, TiN, from CesrTA
RFA current in wiggler, from CesrTA
16ILC Damping Rings
EC Suppression by Wiggler Electrode:
Crittenden
Wang
Wang
Electron cloud density from buildup simulations
Trapping in quadrupoles
Cloud density is average over 20 sigma around the beam, just before the pinch, in units of 1011/m3.Length is in meters. Dipoles have no grooves.
Based on photon rates from Synrad3D; Peak SEY = 0.94 (TiN)
Solenoids in drifts produce 100% suppression of cloud near the beam
Dec. 13, 2012
Drift Dipole Quad Sext Wiggler Total WeightedLength Density Length Density Length Density Length Density Length Density Length Density
Arc 1 406 0 229 0.4 146 1.5 90 1.4 0 871 0.135Arc 2 365 0 225 0.4 143 1.7 90 1.3 0 823 0.139
Wiggler cells 91 0 18 12 101 0.1 210 0.070Straights 1334 0 1334 0.000
Total 2196 454 307 180 101 3238 0.344(no dipoles): 0.288
Dec. 13, 2012 ILC Damping Rings17
Beam energy (GeV) 2 4 5CesrTA observed instability threshold (x1011/m3) 8 20
CesrTA threshold density, analytic estimate (x1011/m3) 13 27ILCDR threshold density, analytic estimate (x1011/m3) 2.3
ILCDR threshold density, analytic estimate, scaled down based on CesrTA observations (x1011/m3)
~1.5
ILCDR estimated ringwide average density, from simulation (x1011/m3) ~0.35
Comparison with instability thresholds
Analytic estimate (in coasting beam approximation)for the electron cloud density at threshold (Jin,Ohmi):
[Jin, Ohmi]: H. Jin et al., “ Electron Cloud Effects in Cornell Electron Storage Ring Test Accelerator and International Linear Collider Damping Ring,” Jpn. J. Appl. Phys. 50, 026401 (Feb. 2011).
ILCDR ringwide density/threshold density ~ 0.35/1.5 ~ 0.23
ILC Damping Rings 18
CMAD simulations of EC-induced emittance growth
Dec. 13, 2012
There is a clear threshold to exponentialgrowth between (3 – 5) x1011/m3 clouddensity
Real DR lattice, 0.35x1011/m3 cloud density
Incoherent emittance growth at 0.35x1011/m3 is about .001 in 300 turns
• Incoherent emittance growth at 0.35x1011/m3 is about .0016 in 300 turns
• The store time is about 18,000 turns• The emittance growth during the store
time should be about 10%.• Radiation damping is not included.
Damping time is about 2,000 turns.
Smooth focusing lattice
Smooth focusing lattice
ILC Damping Rings 19
Fast Ion Instability in Electron Damping Ring
Dec. 13, 2012
Simulation Codes confirmed by experimental results at ATF-DR, CesrTA, SPEAR3 and low emittance SR Rings
Control of this instability requires• Low base vacuum pressure ~ 10-7 Pa• Gaps (43 RF buckets) between mini-trains• Bunch-by-bunch feedback system with a 20 turn (~0.2 ms) damping time
No gap43 RF bucket gap
ILC Damping Rings 20
Technical systems: RF
Dec. 13, 2012
• 12 650 MHz SCRF cavities, operating CW at 4.5K• Gradient 6-8 MV/m• 6 klystrons, peak power 0.7 MW CW
• 3 Operating modes:• Baseline: 2 MW RF
power, 10 cavities, 14 MV RF
• 10 Hz: 3.8 MW RF power, 12 cavities, 22 MV RF
• Upgrade: 3.8 MW RF power, 12 cavities, 14 MV RF
ILC Damping Rings 21
Technical systems: Magnets and Power supplies
Dec. 13, 2012
Conventional magnets
Power supply system design based on “bus” powering of DC-to-DC converters for individual
magnet supplies.
• Superconducting magnets• 54 superferric wigglers, operating at 4.5K• Design based on Cesr-c experience• Shorter period, higher field than RDR spec.
ILC Damping Rings 22
Technical systems: vacuum and instrumentation
Dec. 13, 2012
• Antechambers and electron cloud mitigation as presented in slides 13, 14.• Base pressure 10-7 Pa from
• NEG strips in the dipole and wiggler antechambers.• Localized ion pumps (~5 m) and TiSP pumps.• Sufficient pumping speed to handle conditioning requirements.• Sliding joints cover bellows to control impedance
Vacuum system:
• BPMs with specifications given in slide 10.• Tune trackers• Visible and/or X-ray SR light monitors• Current monitors• Beam-loss monitors• Fast feedback systems to control coupled-bunch instabilities
• Bunch-by-bunch, all 3 planes• Bandwidth > 650 MHz• Damping time ~0.2 ms• 1 kW power
Instrumentation system:
ILC Damping Rings 23
Technical systems: Injection/Extraction
Dec. 13, 2012
• Tests at ATF with FID pulser have demonstrated required rise/fall times, jitter tolerance
• Kicker impedance issues still to be resolved
• Individual bunch injection/extraction (in the horizontal plane) requires very fast, very stable kickers
• Extraction kicker pulse rate 1.8 MHz (3 MHz for lumi upgrade)• For 6 ns bunch spacing, require rise/fall time ~ 6 ns (3 ns for lumi upgrade)• 42 strip-line 50 W kicker modules, 30 cm long, 30 mm gap• Total kick angle ~0.6 mrad (10 kV pulse on each electrode) for extracted beam• Kicker jitter tolerance (kick amplitude stability) < 5 x 10-4
Good field quality is required for the pulsed magnets (kicker, septum) in the extraction channel to preserve the ring emittance after extraction.Remainder of injection/extraction system is conventional and straightforward.
ILC Damping Rings 24
Conclusion
Dec. 13, 2012
• The TDR design for the ILC Damping rings has been reviewed.• The functional requirements, the ring configuration, and the principal
parameters and operating modes have been described.• The lattice design has been outlined.• The leading beam dynamics issues impacting ring performance have
been discussed: – Emittance tuning and nonlinear effects– Electron cloud effect– Fast ion instability
• The key elements of the principal technical systems have been described:– RF– Magnets and power supplies– Vacuum, instrumentation and feedback– Injection/extraction