Perspective on LBNL-IHEP Damping Ring EDR Activities

1. Perspective on LBNL-IHEP Damping Ring EDR Activities Michael S. Zisman Center for Beam Physics Accelerator & Fusion Research Division Lawrence Berkeley National Laboratory Global Design Effort

2. 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) Global Design Effort

3. 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 Global Design Effort

4. 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!  Global Design Effort

5. 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 Global Design Effort

6. 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) Global Design Effort

7. 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) Global Design Effort

8. e-cloud in Grooved Chambers • Simulations show that triangular groove geometry with a sufficiently steep angle can suppress e-cloud effectively Max. longitudinal density of e– accumulated through a 111 e+ bunch train in DR dipoles drops by 100 for a=75o Simulations done w/ augmented version of POSINST (Venturini, Furman) dmax=1.75 To mitigate impedance, rounding the tips would be desirable … … but it spoils the effectiveness of grooves Global Design Effort

9. 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-cloudbuild-up and e-cloud inducedinstabilities • ultimate-goal, a fully self-consistent simulation, very challenging but within reach Wigglers installed at CESR-c have inspired the technology choice for current DR baseline Proposed e-cloud experiment at CesrTA • LBNL to • model e-cloud measurements in wigglers • design wiggler vacuum chamber with clearing electrodes Global Design Effort

10. 3D e-Cloud Code Development proton bunch radius vs. z • 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) CPU time: • lab frame: >2 weeks • frame with2=512: <30 min 2D benchmark shows excellent agreement J.-L. Vay, PRL 98, 130405 (2007) Global Design Effort

11. 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 DRs Wiggler vacuum chamber Vacuum chamber for quads in wiggler section S. Marks, D. Plate, R. Schlueter Global Design Effort

12. Fast Ion Instability • First experimental evidence of Fast Ion Instability produced at ALS (ca. 1996, J. Byrd et al.) with He y-rms size mm nominal pressure No. of bunches in bunch train • Experimental validation of present fast ion instabilitymodels 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 growthrate under varying machine conditions and bunch train structure. Global Design Effort

13. 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 analysis Vlasov Eq. solution in time domain Mode analysis No agreement Good agreement Global Design Effort

14. 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.) Equilibrium vertical emittance for 200 random realizations of sext. displacement w/o space charge… …with space charge. Effect is small (current lattice) • Formalism being extended to include IBS Global Design Effort

15. Dynamic Aperture Studies Nominal DR lattice Improved lattice • 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 chaotic motion y (mm) y (mm) regular motion nx=52.30 ny=49.275 nx=52.40 ny=49.31 x (mm) x (mm) e+ at injection I. Reichel, LBNL Global Design Effort

16. 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 S. De Santis Detail of the mesh (with coax for modeling bench measurement of impedance Time transient analysis Snapshot of field when trailing bunch Is in the middle Energy stored vs. time 9 ns 0.7% fluct.. z (m) trailing bunch enters module Global Design Effort

17. Meeting Kicker Specifications variation < 1% over 5 mm Analysis of deflecting field uniformity • 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 Bunch at kicker’s mid-length x (mm) Minimizing impedance and high-order modes Longitudinal impedance (loss factor ~ 0.1 V/pc) Z (W) High Order Mode localized by the feedthrough Global Design Effort

18. Universal Accelerator Parser:Undoing the Tower of Babel A Tower of Babel: Fred designs a complicated beamline using MAD Format: SIF Eric wants to simulate this using PLACET Format: SIF doesn’t work Need to translate deck to PLACET’s native dialect! Algernon wants to do some BDSIM work Brian wants cross-check the result using ELEGANT • 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 • Ease the way of using multiple platforms to study a complex accelerator system D. Bates in collaboration with D. Sagan, A. Wolski Global Design Effort

19. 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 Global Design Effort

20. 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 Global Design Effort

21. 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 Global Design Effort

22. 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 Global Design Effort

23. 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 Global Design Effort

24. 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 Global Design Effort