G Dugan PAC TDR review 121312 Dec 13 2012 ILC Damping Rings 1 Outline Requirements Configuration parameters operating modes Lattice Beam dynamics issues Emittance tuning and nonlinear effects ID: 443649
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Slide1
ILC Damping rings
G. DuganPAC TDR review 12/13/12
Dec. 13, 2012
ILC Damping Rings
1Slide2
Outline
RequirementsConfiguration, parameters, operating modesLatticeBeam dynamics issuesEmittance tuning and nonlinear effectsElectron cloud effectFast ion instabilityTechnical systemsRFMagnets and power suppliesVacuum, instrumentation and feedbackInjection/extractionConclusionILC Damping RingsDec. 13, 20122Slide3
Damping rings functional requirements
Dec. 13, 2012ILC Damping Rings3accept 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.Slide4
Dec. 13, 2012
ILC Damping Rings4Ring ConfigurationCircumference: 3238 m, 2 x 710 m straights5.6 μm-rad < γεx
< 6.4μm-rad14-pole wigglers : length 2.1 m,
Bpeak 2.2 T, period 30 cm
=>24
ms
>
τ
x
> 12
ms
e
+
(baseline
)
e
-
(baseline)
Phase trombone
± 0.5 λ
β
Chicane
± 4 mm pathlength12 – 650 MHz RF cavities => σl = 6 mmHarmonic number 7022
e
+
(future
option)Slide5
Dec. 13, 2012
ILC Damping Rings5Operating modes and ring parametersThree ILC operating modes correspond to four DR configurationsTwo 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.Slide6
Dec. 13, 2012
ILC Damping Rings6Ring latticeextractionarcphase tromboneRFwigglers
arc
circumference chicane
injectionSlide7
Arc cells
Dec. 13, 2012ILC Damping Rings7Each cell contains :1 - 3m dipole, θ = π/753 – quadrupoles4 - sextupoles3 - corrector magnets 1-horizontal steering 1-vertical steering 1- skew quad2 beam position monitors75-cells/arc
BPM
BPMSlide8
Wiggler straight
2 wigglers/cell30 cells2.1 m wiggler1.5T< Bpeak< 2.2T54 @ 2.16T => τx =13ms (10Hz)54 @ 1.51T => τx = 25ms (5Hz)3 empty cells will accommodate 6 additional wigglers if requiredH&V dipole corrector and BPM adjacent to each quadDamping Wigglers Dec. 13, 2012ILC Damping Rings8Slide9
RF straight
Dec. 13, 2012ILC Damping Rings9RF2 cavities/cell22.4 MV => 6mm bunch length @ τx =13ms => for 12 cavities 1.9MV/cavity 272kW/couplerLattice can accommodate 16 cavities if requiredCavities offset so that waveguides of upper and lower rings are interleavedH&V corrector and BPM adjacent to each quadrupole Slide10
Emittance in 3
rd GLS, DR and collidersR. BartoliniLow Emittance Rings Workshop, Crete 3rd October 2011Dec. 13, 2012ILC Damping Rings
10
Emittance
tuning-1
CesrTA
ATF
Note that LS emittance results are for electron rings.Slide11
Emittance tuning-2
Dec. 13, 2012ILC Damping Rings11Measure and correct orbit using all steeringsMeasure betatron phase advance (by resonant excitation) – and correct using quadrupolesMeasure coupling (by resonant excitation) and correct with skew quadsMeasure orbit, coupling, and vertical dispersion and simultaneously correct with vertical steerings and skew quads ParameterRMS
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 μmWiggler - Roll200 μrad
Design: 2 pmSlide12
Nonlinear effects
Dec. 13, 2012ILC Damping Rings12Magnet 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 aperture
with specified magnet misalignments and field errors,
and full Taylor map for wiggler nonlinearities
Tune footprint
Injected positron bea
mSlide13
Dec. 13, 2012
ILC Damping Rings13Electron Cloud Effect-outlineVacuum chamber design to minimize photon absorption in the chamberVacuum chamber surface EC mitigation EC buildup simulations to estimate ringwide average cloud densityComparison with analytic estimate of instability thresholdComparison with numerical simulations of coherent and incoherent emittance growth using CMAD Slide14
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 90
o
relative to their installed orientation.Slide15
EC Working Group Baseline Mitigation Recommendation
Drift*DipoleWigglerQuadrupole*Baseline Mitigation
TiN
Coating+
Solenoid Windings
Grooves with
TiN
coating
Clearing Electrodes
TiN
Coating
Vacuum chamber surface treatment for
SEY 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
CesrTASlide16
16
ILC 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 10
11
/m
3
.
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 bea
m
Dec. 13, 2012Slide17
Dec. 13, 2012
ILC Damping Rings17Beam energy (GeV) 245CesrTA observed instability threshold (x1011/m
3)
8
20
CesrTA
threshold density, a
nalytic estimate
(x10
11
/m
3
)
13
27
ILCDR
threshold density, a
nalytic estimate
(x10
11
/m
3
)
2.3
ILCDR
threshold density, a
nalytic estimate, scaled
down based on
CesrTA
observations
(x10
11
/m
3
)
~1.5
ILCDR estimated
ringwide
average density, from simulation (x10
11
/m3)
~0.35Comparison 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 ~ 0.23Slide18
CMAD simulations of EC-induced emittance growth
Dec. 13, 2012ILC Damping Rings18
There is a clear threshold to exponential
growth between
(3
–
5) x10
11
/m
3
cloud
density
Real DR lattice, 0.35x10
11
/m
3
cloud density
Incoherent
emittance
growth at 0.35x10
11
/m
3
is about .001 in 300 turnsIncoherent emittance growth at 0.35x1011/m
3
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 latticeSlide19
Fast Ion Instability in Electron Damping Ring
Dec. 13, 2012ILC Damping Rings19Simulation 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 gap
43 RF bucket gapSlide20
Technical systems: RF
Dec. 13, 2012ILC Damping Rings2012 650 MHz SCRF cavities, operating CW at 4.5KGradient 6-8 MV/m6 klystrons, peak power 0.7 MW CW
3 Operating modes:Baseline:
2 MW RF power, 10 cavities, 14 MV RF10 Hz:
3.8 MW RF power, 12
cavities,
22
MV
RF
Upgrade:
3.8 MW RF power
, 12
cavities, 14 MV
RFSlide21
Technical systems: Magnets and Power supplies
Dec. 13, 2012ILC Damping Rings21Conventional magnetsPower 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.Slide22
Technical systems: vacuum and instrumentation
Dec. 13, 2012ILC Damping Rings22Antechambers and electron cloud mitigation as presented in slides 13, 14.Base pressure 10-7 Pa fromNEG 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 impedanceVacuum 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:Slide23
Technical systems: Injection/Extraction
Dec. 13, 2012ILC Damping Rings23Tests at ATF with FID pulser have demonstrated required rise/fall times, jitter toleranceKicker impedance issues still to be resolvedIndividual bunch injection/extraction (in the horizontal plane) requires very fast, very stable kickersExtraction 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
.Slide24
Conclusion
Dec. 13, 2012ILC Damping Rings24The 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 effectsElectron cloud effectFast ion instabilityThe key elements of the principal technical systems have been described:RFMagnets and power suppliesVacuum, instrumentation and feedbackInjection/extraction