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May 31, 2007-Hamburg (Zisman) Global Design Effort 1
LBNL Damping Ring R&D Activities
Michael S. ZismanILC Program Leader
Center for Beam PhysicsAccelerator & Fusion Research DivisionLawrence Berkeley National Laboratory
May 31, 2007-Hamburg (Zisman) Global Design Effort 2
Introduction• LBNL support of DR R&D effort remained
constant in FY07– received $0.8M (cf. $0.8M last year)
• essentially all is for DR work– this is where we wish to focus
• engineering effort is presently sub-critical
• Anticipate enhanced effort in FY08 and beyond– subject to success in obtaining the anticipated
budgets for the ART• which is not a given
• Participated in global planning effort via S3
May 31, 2007-Hamburg (Zisman) Global Design Effort 3
• Leadership/coordination within DR community• Involvement in ILC-related R&D at other facilities
(PEP-II/SLAC, ATF/KEK, CESR/Cornell)• Generic development of diagnostics, instrumentation
• Leadership/coordination within DR community• Involvement in ILC-related R&D at other facilities
(PEP-II/SLAC, ATF/KEK, CESR/Cornell)• Generic development of diagnostics, instrumentation
Vacuum engineeringVacuum engineering
Multi-bunch instabilities Feed-back systems
Multi-bunch instabilities Feed-back systems
Other ILC activitiesOther ILC activities
Overview of Activities
Low-emittance tuning Low-emittance tuning
Fast Ions I. Fast Ions I.
e-cloud e-cloud
Single-particle dynamics Lattice optimization
Single-particle dynamics Lattice optimization
Single-bunch classical instabilities Single-bunch classical instabilities
Space-charge, IBS Space-charge, IBS
Inj./Extr. lines Inj./Extr. lines
Inj./Extr. kickers Inj./Extr. kickers
Mechanical Integration Mechanical Integration
Transients Transients
May 31, 2007-Hamburg (Zisman) Global Design Effort 4
People & Resources• ILC-ART resources
– $681k in FY06• 2.0 scientist FTEs• 0.6 engineer FTEs• 1 student assistant
– $795k in FY07 • 2.2 scientist FTEs• 0.4 engineer FTEs
• Additional support from core program
• People contributing:– J. Byrd, D. Bates, C. Celata, D. Grote, S. de Santis, M.
Furman, S. Marks, D. Plates, G. Penn, I. Reichel, R. Schlueter, C. Steier, M. Venturini, J-L Vay, M. Zisman (program leader)
May 31, 2007-Hamburg (Zisman) Global Design Effort 5
Responding to R&D Priorities• We continue to contribute to critical areas of DR R&D
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 (to resume in 08, augmenting work carried out
in previous years)
• Additional activities include– Lattice optimization, single particle dynamics, wiggler modeling
(ongoing) – Characterization of space-charge effects (mostly completed)– Design of prototype of kicker meeting DR specification to be tested
at ATF/KEK (ongoing); characterization of CSR at ATF/KEK (ongoing)– Multi-bunch instability, feedback systems, transients (08)
• Vacuum design and mechanical integration (RDR, EDR)
May 31, 2007-Hamburg (Zisman) Global Design Effort 6
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)
May 31, 2007-Hamburg (Zisman) Global Design Effort 7
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
May 31, 2007-Hamburg (Zisman) Global Design Effort 8
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
May 31, 2007-Hamburg (Zisman) Global Design Effort 9
e-cloud Build-up in Wigglers
No photons reflected around the chamber
Projection of e-cloud in transverse plane
20% of photons hitting the edges of the antechamber are reflected
Snapshot of e-cloud in two wiggler periods seen from above
on-axis By
No photon reflection by the wall in the model for this calculation
Snap-shots taken after passage of 50 bunches (preliminary) C. Celata, J-L Vay, D. Grote
max=1.4max=2
x (m)
y (m) Antechamber
May 31, 2007-Hamburg (Zisman) Global Design Effort 10
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 providing 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
May 31, 2007-Hamburg (Zisman) Global Design Effort 11
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
May 31, 2007-Hamburg (Zisman) Global Design Effort 12
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
May 31, 2007-Hamburg (Zisman) Global Design Effort 13
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)
May 31, 2007-Hamburg (Zisman) Global Design Effort 14
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)
May 31, 2007-Hamburg (Zisman) Global Design Effort 15
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
May 31, 2007-Hamburg (Zisman) Global Design Effort 16
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
May 31, 2007-Hamburg (Zisman) Global Design Effort 17
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
May 31, 2007-Hamburg (Zisman) Global Design Effort 18
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
May 31, 2007-Hamburg (Zisman) Global Design Effort 19
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
May 31, 2007-Hamburg (Zisman) Global Design Effort 20
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
May 31, 2007-Hamburg (Zisman) Global Design Effort 21
Summary• LBNL has made significant contributions to the DR
design as documented in the Baseline Configuration Report and Reference Design Report
• We wish to play a leadership role for ILC-DR activities and stay focused on critical R&D areas needed for completion of Engineering Design Report (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
LBNL and IHEP have recently signed MOU to collaborate on DR R&D