November 6, 2007-Beijing (Zisman) Global Design Effort 1 Perspective on LBNL-IHEP Damping Ring EDR...

November 6, 2007-Beijing (Zisman) Global Design Effort 1

Perspective on LBNL-IHEP Damping Ring EDR Activities

Michael S. ZismanCenter for Beam Physics

Accelerator & Fusion Research DivisionLawrence Berkeley National Laboratory


Introduction (1)• LBNL has a long history of participating in

storage ring designs for HEP– PEP, PEP-II, NLC-DR, ILC-DR

• Main LBNL activity in ILC is DR work– this is where we wish to focus

• LBNL participated in global DR planning effort via S3 task force– M. Zisman A. Jackson– M. Venturini

• LBNL is providing DR leadership for ART also– M. Zisman A. Jackson; also M. Palmer (Cornell)


Introduction (2)• Tasks of interest for DR EDR effort

– magnet design, vacuum system design, feedback system design, diagnostics design, mechanical integration, kicker design, injection/extraction, RF cavity design

• Also interested in beam dynamics R&D efforts– e.g., e-cloud, fast ions, impedance-related issues

• Some non-DR ILC tasks also of interest– overall timing/synchronization system

• of relevance to linac

– general magnet and vacuum system design• of relevance to RTLs and BDS


Introduction (3)• We have a history of successful

collaboration with IHEP– PEP-II quadrupoles fabricated and measured

here– PEP-II dipole fabrication supervised by IHEP

• and these magnets also measured here

• We have an MOU with IHEP in place to facilitate collaborative activities

• And...we like Chinese food!


People & Resources• ILC-ART resources

– $795k in FY07 • 2.2 scientist FTEs• 0.4 engineer FTEs

– $1751k in FY08• 2 scientist FTEs• 1 engineer FTE

• Additional manpower support from “core” program

• People contributing:– J. Byrd, D. Bates, C. Celata, S. DeSantis, M. Furman, A.

Jackson (program leader), S. Marks, D. Plate, G. Penn, I. Reichel, R. Schlueter, M. Venturini, J-L Vay, M. Zisman

• FY09 support will likely increase if overall ILC R&D budget does

– unfortunately, this is not a given


Responding to R&D Priorities• We continue to contribute to critical areas of DR EDR

needs by developing new capabilities and leveraging existing LBNL expertise and resources

• Already engaged in, or plan to start, activities in the following very high-priority R&D areas:– Electron cloud (ongoing)– Fast ion instability (measurements at ALS planned later this year)– Single-bunch instabilities (ongoing)– Low-emittance tuning – 650 MHz cavity design

• Additional activities include– Lattice optimization, single particle dynamics, wiggler modeling

(ongoing) – Characterization of space-charge effects (mostly completed)– Design of prototype kicker meeting DR specification (to be tested at

ATF/KEK); characterization of CSR at ATF/KEK (ongoing)– Multi-bunch instability, feedback systems, transients

• Vacuum design and mechanical integration (RDR EDR)


Suppression of e-cloud• Change of baseline has elevated rank of e-cloud R&D

– must demonstrate that e-cloud build-up can be suppressed to the level where it is harmless

• Suppression techniques being investigated include grooved chambers and clearing electrodes (+ more “conventional” surface coatings) – measurements conducted at PEP-II will test both proposed remedies.

Design of chamber w/ CE for experiment at PEP-II by D. Plate, LBNL

Proposed design of grooved chamber for PEP-II

experiment

Electrode, Copper 0.04” x 1.0” x 50.0”(49.606” between feedthrough centers)

Electrode, Copper 0.04” x 1.0” x 50.0”(49.606” between feedthrough centers)


e-cloud in Grooved Chambers • Simulations show that triangular groove geometry with a

sufficiently steep angle can suppress e-cloud effectively

To mitigate impedance, rounding the tips would be desirable …

… but it spoils the effectiveness of grooves

Max. longitudinal density of e– accumulated through a 111 e+ bunch train in DR dipoles drops by 100 for =75o

Simulations done w/ augmented version of POSINST (Venturini, Furman) max=1.75


Wiggler Modeling and Simulations

• Progress in e-cloud experiments/measurements and simulations must go hand in hand

• Making a substantial investment in characterizing e-cloud in wigglers, a significant issue for DRs – use/expand integrated code suite WARP/POSINST (already

successfully tested for HCX heavy ion experiment here at LBNL)

– study both e-cloud build-up and e-cloud induced instabilities

– ultimate-goal, a fully self-consistent simulation, very challenging but within reach

• LBNL to – model e-cloud measurements in

wigglers– design wiggler vacuum chamber

with clearing electrodes

Wigglers installed at CESR-c have inspired the technology choice for

current DR baseline

Proposed e-cloud experiment at CesrTA


3D e-Cloud Code Development

• Using WARP-POSINST code– beam and cloud evolve self-consistently (PIC)– refined mesh gives efficient calc. of beam

evolution– calculates in moving frame (~ 1000x speedup)

proton bunch radius vs. z

CPU time:• lab frame: >2 weeks• frame with 2=512: <30 min

CPU time:• lab frame: >2 weeks• frame with 2=512: <30 min

J.-L. Vay, PRL 98, 130405 (2007)

2D benchmark shows excellent agreement


Wiggler Vacuum Chamber Concept

• Wiggler vacuum chamber is a warm-bore insert – not integral to cryostat

• Design assumptions:– machined, welded aluminum

with antechamber– photon power absorbed within

chambers by copper absorber– pumping: NEG wafers mounted

on heater for regeneration– integral cooling to minimize

thermal load during regeneration

– NEG coating for reduction of secondary electrons

• LBNL provided mechanical integration for the DRsS. Marks, D. Plate, R. Schlueter

Tubular Heater Water Cooled

Absorber

NEG Coating

NEG

NEGNEG

NEG

10

120

60

R23

Cooling for NEG Activation

Vacuum chamber for quadsin wiggler section

Wiggler vacuum chamber


Fast Ion Instability

• Experimental validation of present fast ion instability models essential for DRs but largely unaccomplished

• New set of measurements planned for ALS promises to provide the required validation (Byrd, Steier)

• Use grow/damp techniques to measure growth rate under varying machine conditions and bunch train structure.

• First experimental evidence of Fast Ion Instability produced at ALS (ca. 1996, J. Byrd et al.)

100

80

60

40

Vert

ical

RM

S s

ize (

µm

)

403020100

Number bunches

He added nominal pressure

No. of bunches in bunch trainy-

rms

size

m

with He

nominal pressure


Single-bunch Longitudinal Instabilities • To avoid unacceptable emittance degradation down the

linac, collective instabilities can’t be tolerated– otherwise, DRs can be “source of all evil” (Anonymous from SLAC)

• Collaboration w/SLAC for characterization of single-bunch dynamics based on detailed modeling of impedance sources– goal: benchmark available tools and methods

Mode analysis of linearized Vlasov Eq. for longitudinal Motion may fail to give accurate Characterization of instability Venturini, ILC-DR06 Workshop

Mode analysis of linearized Vlasov Eq. for longitudinal motion may fail to give accurate characterization of instability Venturini, ILC-DR06 Workshop

Mode analysisMode analysis

Vlasov Eq. solutionin time domain

Vlasov Eq. solutionin time domain

Good agreement

No agreement

Mode analysis


Influence of Space-Charge• Equilibrium emittance in a non-ideal lattice

modified by space charge – radiation envelope formalism extended to account for

effective modification of linear lattice due to space charge (Venturini et al.)

• Formalism being extended to include IBS

Equilibrium vertical emittance for 200random realizations of sext. displacementw/o space charge …

Equilibrium vertical emittance for 200random realizations of sext. displacementw/o space charge …

… with space charge. Effect is small (current lattice)

… with space charge. Effect is small (current lattice)


Dynamic Aperture Studies

• Frequency maps indicate presence of harmful resonances and suggest ways for lattice optimization

• OCS6 lattice suffers from reduced degree of symmetry – different working point and harmonic sextupoles improve dynamic

aperture

Nominal DR lattice Improved lattice

regularmotion

chaoticmotion

x=52.40y=49.31

x=52.30y=49.275

I. Reichel, LBNLx (mm)

y (m

m)

y (m

m)

e+ at injectionx (mm)


Kicker Technology• ATF/KEK is test bench for DR kicker technologies (pulsers, striplines,

loads, feedthroughs,…) with specification close to or exceeding DR requirements

• Contributing to design of ATF striplines kicker structures:– demonstrate 5 mrad deflection, 2.8/5.6 ns bunch separation; stringent

requirements on field decay time (DR specs: 3.1/6.2 ns; 0.6 mrad)– transform voltage pulse into a deflecting field efficiently w/o introducing

undesired beam impedance– produced a kicker design; estimated impedance; transients analyzed

trailing bunch enters module

Time transient analysis

z (m)

Snapshot of field when trailing bunch Is in the middle

0.7% fluct..

S. De Santis

Energy stored vs. time

9 ns

Detail of the mesh (with coax for modeling bench measurement of impedance


Meeting Kicker Specifications

variation < 1% over 5 mm

250

200

150

100

50

0

70006000500040003000200010000

Frequency (MHz)

Longitudinal impedance (loss factor ~ 0.1 V/pc)

Analysis of deflecting field uniformity

Bunch at kicker’s

mid-length

Bunch at kicker’s

mid-length

x (mm)

• Specifications likely to be met for 5.6 ns– no pulser currently available with required

rise/fall time characteristics at 2.8 ns

• Residual uncertainty mainly connected with the development of high-voltage, high-repetition rate feedthroughs

Minimizing impedance and high-order modes

Minimizing impedance and high-order modes

Z (

)

High Order Modelocalized by the feedthrough


Universal Accelerator Parser:Undoing the Tower of Babel

• Different accelerator analysis programs use different input formats to describe a lattice

• The UAP library will provide a way to translate input files between various accelerator codes

Fred designs a complicated beamline using MADFormat: SIF

Eric wants to simulate this using PLACETFormat: SIF doesn’t workNeed to translate deck to PLACET’s native dialect!

Brian wants cross-check the result using ELEGANT

Algernon wants to do some BDSIM work

A Tower of Babel:

D. Bates in collaborationwith D. Sagan, A. Wolski

• Ease the way of using multiple platforms to study a complex accelerator system


Instrumentation and Feedback

• Transverse feedback [Barry, Byrd]– develop model to assess noise, gain, phase

margins– design prototype low-noise receiver

• Injection noise [Byrd, Penn]– characterize sources of jitter and develop tools

for transient analysis– assess implications for feedback system design


LLRF Activities (1)• Continued work on LLRF design for HINS

– suitable for ILC also

• Objectives– determine stability with multiple loads (HINS)– characterize state-of-the-art components

(HINS)– examine scalability + high-volume production

capability•In collaboration with SNS

•4 14-bit 80 MS/s digitizers

•2 14-bit DACs

•Xilinx Spartan-3 FPGA

•USB interface

•Bench tested and working


LLRF Activities (2)• Initial test results

– 2.5 bits rms wideband noise– clock jitter < 0.5 ps rms

• Modeling– goal: to improve understanding of single

klystron with multiple cavities• study microphonics noise at klystron and cavity• understand feedback configuration and system

stability


Areas of Mutual Interest• Recent completion of BEPC-II has greatly

enhanced IHEP’s technical strengths

• Areas where collaboration seems natural include– hardware

• vacuum, magnets, power supplies, feedback, diagnostics, LLRF

– simulations• lattice design, dynamic aperture, low-emittance tuning• instabilities

– impedance-driven, e-cloud, fast-ion

• Both areas could include a joint experimental program at BEPC-II and ALS


How To Work Together• Assign contact persons from each institution

– suggest Jie Gao (IHEP); Alan Jackson (LBNL)

• Next, we should together select a few key areas and technical problems on which to collaborate– e.g., vacuum, lattice/dynamic aperture, feedback

• choose topics already funded either by ART or core program

• Selected collaborators should meet initially in person– followed by phone conferences to continue the

technical interactions• propose overall deliverables

– define milestones and dates


Summary• LBNL has made significant contributions to the DR

design found in Baseline Configuration Document and RDR

• We wish to continue a strong role in ILC-DR design and focus on critical R&D areas needed to complete the EDR: – Beam dynamics

• Electron cloud (characterization of e-cloud in wigglers; assistance with design of experiments and data analysis)

• Fast Ions (measurements and validation of theory)• Collective effects (space-charge effects for RTML lines; estimate of

single-bunch threshold instabilities based on numerical impedance modeling)

• Low-emittance tuning • Study of transients at injection/extraction

– Engineering, design of technical systems• Kickers, feedback, LLRF, vacuum, mechanical integration

• An LBNL-IHEP collaboration will increase technical strength of DR EDR effort– and enhance contributions of both institutions

November 6, 2007-Beijing (Zisman) Global Design Effort 1 Perspective on LBNL-IHEP Damping Ring EDR...

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