ilc damping rings

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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

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Arc cells


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


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.


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


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


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


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)


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


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


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


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


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.


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:


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.


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

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