Accelerator Research at SLAC

1. Accelerator Researchat SLAC Ronald Ruth Head Accelerator Research Department A (ARD-A) AARD HEPAP Subpanel December 21, 2005

2. Outline • Introduction to Accelerator Research at SLAC • Highlights of Beam Physics • Highlights of Advanced Computation • Conclusion • Special Note: • SLAC Accelerator Scientists and Management would like to thank the AARD HEPAP subpanel for their time and effort.

3. Accelerator Research • HEP Accelerator Research at SLAC • Deeply rooted in pushing the state of the art of accelerators • Driven by exploration at the frontier of HEP • Has significant spin-off impact on Photon Science. • Photon Science Accelerator Development • SPEAR3 now, LCLS coming soon • LCLS upgrades and enhancements--later • Foundation of these advanced facilities—HEP Accelerator Research • Success of these advanced facilities depends on the impact of the Accelerator Science at SLAC.

4. Fundamental Issues for HEP • High center-of-mass energy • Led to large storage ring development • Led to the invention of Linear Colliders • Drives acceleration gradient • Drives power source development • Stimulates exploration of advanced accelerator concepts • High luminosity • Drives the development of bright electron/positron beams • Generation and preservation of intense, low emittance e+e- beams • High-current storage rings • Special optics for beam demagnification • What about Photon Science? • Photon-electron interaction—FEL instability—collective effect • Ultra-bright electron beams  ultra-bright photon beams • Significant overlap of fundamental beam physics

5. SLAC Programmatic Prioritiesfor Accelerators for HEP • For the near term • Focus on B-factory performance and science • For the mid term • Focus on ILC—the highest priority new facility for the world community. • For the long term • Research and development in Accelerator Science • The future of the field • Make the next HEP accelerator after ILC technically feasible and affordable

6. The SLAC Approach to Accelerator Research • Push the envelope of operating accelerators • PEP-II + flavor factories world wide—all operating facilities • Study Beam Physics and develop Accelerator Technology and for next generation facilities. • ILC • Future Multi-TeV Linear Colliders—High Gradient Research • Exploit unique facilities for Accelerator Research • Final Focus Test Beam (FFTB) • NLC Test Accelerator (NLCTA) • Explore Advanced Accelerator Research • Laser Acceleration • Plasma Acceleration • Ultra-bright beam physics • Push the state of the art in computational tools • To bridge the gap between theory and technology

7. PEP-II Performance • Details of PEP-II development are not covered here. • Substantial laboratory effort and accelerator physics effort. • We include highlights of impact of accelerator research applied to PEP-II.

8. ILC at SLAC • High Energy LC is the highest priority for the world community. • SLAC has been a leader of LC development • Champion of warm RF technology • Impact of cold technology choice? • SLAC committed to ILC—independent of technology • Accelerator expertise and experience in all subsytems • R&D program restructured to address key issues for cold LC • SLAC staff are co-leading 4 of the technical subgroups.

9. SLAC ILC Research Activities (not part of this review) • Restructured Program to align with cold LC. • Accelerator Design and CDR • Electron/Positron sources • Damping Ring Design • Beam Delivery System • Instrumentation and control systems • Part of coordinated GDE effort. • Some Accelerator Research will be directed for technology support • For example, L-band power sources • Overall ILC program—Tor Raubenheimer this afternoon

10. Overview of Accelerator Researchand presentations today • Introduction and Overview (this talk) • Beam Physics (this talk) • Lattice Development and Beam Dynamics • Collective Effects and Bright Beam Physics • Advanced Computations (this talk) • New computational algorithms • RF modeling, frequency and time domain. • Beam device modeling • Calculation of beam-environment interaction.

11. Overview of Accelerator Research • Accelerator Technology Development (S. Tantawi, Next talk) • Advanced Concepts for near future programs-ILC • High Gradient Research toward Multi-TeV LC • Technology Research • Advanced Accelerator Research (Bob Byer, Stanford, Bob Siemann, SLAC) • Laser acceleration • Plasma acceleration • Facilities

12. Management and Budget • Accelerator R&D Annual Funding • Average ~$8.5M/yr for past 5 years (operating budget) • Split between • Beam Physics • Accelerator Technology • Advanced Computation • Advanced Accelerator Research --long term • SciDac ~$550k/yr • Advanced computation— near and mid term • Management • Organized around 3 departments • ARD-A—Ron Ruth • Beam Physics • Accelerator Technology • ARD-B—Bob Siemann • Advanced Accelerator Research • Advanced Computation—Kwok Ko Near and mid-term

13. Accelerator Research in the Context of other programs • SLAC—1500 staff, 3000 users (HEP + Photon Science) • Accelerator Physics-HEP— around 100 scientists (Including students)

14. Accelerator Research and Education • In the previous group of 100 Scientists • 8 Faculty • 19 Graduate Students • 5 Post Doctoral Research Associates • Several Openings for Post Docs • We seek to document our work in publications to achieve a long-lasting impact on our science. • Over the past 1-2 years SLAC Accelerator Physicists have authored • About 400 publications of all types • Over 70 publications in archival journals • Please see the SLAC Accelerator Research List of Recent Publications handout. • Please see the SLAC Accelerator Research Staff, Students, Post Docs handout

15. Accelerator Research--Major Facilities • The SLAC Linac —unique world facility • PEP-II—Pushes storage ring state of the art • Final Focus Test Beam (FFTB)—model final focus, now Adv. Acc. Research • NLC Test Accelerator (NLCTA)—beams for Adv. Acc. Research, power for high-gradient studies, ILC development. • Klystron Test Lab —RF technology development • Short Pulse Photon Source (SPPS)—ultra-short bunches of electrons/photons—Bunch compression for FFTB • Later, Linac Coherent Light Source (LCLS)—bright beam preservation, coherent effects • Possible future facility: South Arc Beam Experimental Region SABER which would replace the FFTB.

16. Beam Physics • Beam Physics research is driven primarily by the requirements for high luminosity • Complex beam manipulation with compensation of nonlinear effects • High intensity storage rings • Low emittance, high intensity => bright e beams • Development of low emittance sources and damping rings • Intensity limitations due to interaction with surroundings • High demagnification optics and bunch compressors => small spots and short bunches. • It is useful to divide the subject into: • Lattice Development and Dynamics of Beams • Collective Effects and Bright Beam Physics

17. Highlights of recent activities: Maintained and upgraded SPEAR3 and PEP-II lattices Developed a precision method: Model Independent Analysis (MIA) to improve the machine optics for PEP-II Developed a self-consistent simulation code for beam-beam effects at PEP-II Designed a new dogbone damping ring with improved acceptance and extraction lines for ILC Studied and proposed a phase-2 collimation system to reduce the impedance for LHC Near-term goals: Lead the lattice design efforts for selecting a baseline configuration of damping rings for ILC Continue the beam-beam simulation to optimize the luminosity of PEP-II Extend MIA to include dispersion and Improve the machine optics for PEP-II Continue the design the ILC extraction lines Improve the efficiency of collimation system for LHC Long-term vision: To continue to develop and apply the most sophisticated Lattice Dynamics tools To on site facilities, such as LCLS To future facilities for HEP--ILC Lattice Development and Dynamicsof Beams

18. Model-Independent Analysis (MIA)(Storage Ring Optics Modeling—PEP-II and future Damping Rings) • Excite the beam resonantly at the betatron or synchrotron frequency • Taking turn-by-turn beam position data at beam position monitors (BPM) in entire ring. • Accurately extract optical information with very high precision at the excited resonance • Reconstruct a complete six-dimensional model of accelerator using linear optical variations and BPM gains and crossing coupling • Use the model to improve accelerator and its performance Measured phase advance (red dots) vs. a fitted model (blue line) Measured beam tilt angles (blue), and expected improvement (red) using a MIA solution

19. Dispersion measurement from MIA The 3rd resonance excitation from sinusoidal perturbation on the RF voltage to extract accurate linear dispersion. Without using additional fitting variables, we have fitted also the dispersions in both planes. The accelerator model can also be passed to tracking code: LEGO, for beam-beam studies using BBI code. Measured dispersions (green), the ideal design (blue), and a MIA fitting (red).

20. Beam-Beam Simulation using Particle-In-Cell Method 1) Both beams are represented macro particles (160,000) 3) The distribution of particles in slice is used to solve two-dimensional Poisson equation on a regular grid (128x128). strong-strong y 2) A bunch is divided into some slices which include many macro-particles. Collision is calculated with every pair of slices in the time sequence. x 4) The solved potential then used to compute the kick experienced by a particle from the opposing slice. z IP

21. Simulations and Measurements with Parasitic Collisions at PEP-II Bunch Luminosity Specific Luminosity Beam-beam limit Lifetime limit The number of bunch was 1230 and bunch spacing was every two buckets. The ratio of currents in the measurement was not fixed as a constant, but the agreements are surprisingly good.

22. Beam-Beam Spectra at PEP-II e-, x e+, x Horizontal spectrums for two beams matched both in simulation and measurement. In x plane, s and p modes are clearly seen the simulation. (f0 = 136.312 kHz)

23. Positron Beam Distributionswith Beam-Beam Interaction The distributions are averaged after 40,000 turns to improve the statistics. Contours started at value of peak/sqrt(e) and spaced in e. Labels are in s of the initial distribution. The core distribution is not disturbed much by the nonlinearity in the ring while the tail is strongly effected. With a linear matrix or 8th order Taylor map (nx+=0.5125). Nonlinear map is important because it defines the dynamic aperture.

24. A Model Guided Strategy to Improve PEP-II Luminosity or Damping Ring performance 1.0x1034cm-2s-1 PEP-II MIA(YY) MS,JT LEGO(YC) FJD,YC BBI(YC) Model based and adiabatic correction scheme for luminosity improvement. Tuning was done during the delivery and guided by the luminosity reading.

25. Design of ILC Damping Ring to Improve Dynamic Aperture • Dynamic aperture of the DESY dogbone damping ring is not adequate with nonlinear wigglers in the lattice. • We designed a new damping ring based on a detuned p cell and non-interlaced sextupoles. • The new design significantly improves the dynamic aperture of on-momentum particles as shown in the figure. • We are planning to improve further the dynamic aperture of the off-momentum particles, analyze tolerance of the lattice, and make a specification of wigglers. 0.5 km 8 km 17 km dogbone damping ring dynamic aperture of damping rings with nonlinear single-mode wigglers.

26. Optics Design for SABER (the South Arc Beam Experimental Region project) • To replace FFTB as a user facility • Testing beam • Advanced accelerator research • Experiments for astrophysics • .Independent operation respect to LCLS • Use many existing accelerator infrastructure • 2/3 linac shared with PEP-II • South arc of SLC • Desired IP parameters • e+ or e- up to 30 GeV • 2 1010 (3 nC) per pulse • bunch length < 30 mm • rms x, y size < 10 mm • dispersion h = h’ = 0 • Design IP parameters • bx = 1 cm, by = 10 cm • h = h’ = 0 • gex = 50 mm, gey = 5 mm • sx = sy = 2.9 mm at 30 GeV (without aberrations) SABER lattice functions

27. SABER particle tracking • Shorten the bunch to 26 mm but with ±2% energy spread. • Sextupoles are introduced to reduce the second-order dispersion. • Achieved required beam parameters at the interaction point: • sx = 5.2 mm, sy = 5.4 mm, sz = 26 mm Bunch length and energy spread X and Y spread at the IP

28. Suppression of the secondary emission yield to mitigate electron cloud effects Dust particle dynamics in storage rings CSR in light sources and linear collider damping rings Resistive wall wakefields in the LCLS undulator FEL theory with slowly varying beam and undulator parameters Proposal of a low-charge bunch regime for the LCLS Collective Effects and Bright Beam Physics Recent achievements Future plans • Theory of wakefields for short bunches with application for ILC collimators. • Further investigations into micro-bunching instabilities • CSR effects in beam dynamics Physics of energy spread and emittance limitations of the RF guns • Methods of producing higher power and shorter saturation length in SASE FELs

29. Dark currents in High Frequency RF structures “Dark current” electrons emitted from irises of a high frequency accelerating structure may have various deleterious effects, one of which is an interaction with the primary electron (or positron) bunch. Kicks to the beam centroid caused by the field of the dark current dilute the beam emittance. Our simulations showed that contribution of dark currents is small compared to other sources of emittance growth. This may impact Multi-TeV High Gradient Designs. Breakdown currents will almost certainly cause missing pulses V. Dolgashev, K. Bane, J. Wu, G. Stupakov, T. Raubenheimer, PRST-AB, 2005

30. Suppression of SEY for grooved surfaces (Significant Possible Impact on ILC DR cost) Suppression of the secondary electron emission is an important technique of mitigating deleterious effect of the electron cloud in modern accelerators. We proposed to suppress effective SEY by using grooves on the surface of the metal. The suppression factor depends on the angle of the grooves, and can reach ~2 for 40 degrees angle. G. Stupakov, M. Pivi, SLAC-TN-04-045

31. Dust particle dynamics in storage rings A model of the dust particle dynamics explaining the long time of the dust events observed in the PEP-II B-factory and BEPC-II machines has been developed. Previous models predicted that dust particles should burn down in ~50 s. The new model includes into consideration large-amplitude 2D oscillations of a dust particle in the electric field of the beam. S. Heifets, Qing Qin, M. Zolotorev, PRST-AB, 2005

32. Nonlinear regime of the CSR instability time-domain simulations using a Vlasov equation solver (M. Venturini and R. Warnock, PRL). • Onset of instability developing from initial noise after a fraction of synchrotron period. • Saturation of instability causes smoothing of microbunching and enlargement of rms bunch-length. • Nonlinear analysis demonstrates bursting of the instability, in qualitative agreement with experiment. Distribution after 1.5 synchrotron oscillation periods.

33. Nonlinear regime of ion instability in electron rings S. Heifets and D. Teytelman, PRSTAB, 2005 An observed transverse instability in BESSY-II is explained as an ion instability in the ring. A simplified model of the instability shows a pattern qualitatively similar to the experimental results. The developed approach allows analyze the nonlinear regime of the instability, and could provide a new method of diagnostic of the beam parameters.

34. Surface roughness impedance of the LCLS undulator vacuum chamber Surface roughness in the LCLS undulator vacuum chamber generates geometrical wakefield which induces energy spread in the beam. The theory of roughness wake predicts that the wake decreases with rms height of the bumps and the average slope. Developed a computer program for processing roughness measurements of the undulator surface and will use it for monitoring the requirements in the production cycle. An examples of the measured roughness profile. The rms roughness ~20 nm, rms slope ~2.10-3

35. Advanced Computations Department (ACD) Formed in 2000 to focus on high performance computingto: • Develop a parallel simulation capability in electromagnetics & beam dynamics under SciDACto run on Office of Science’s (SC) flagship supercomputers (IBM SP3@NERSC, Cray X1E@NLCF), • Advance computational scienceto enable ultra-scale computing in solving challenging accelerator problems by working with SciDAC teams in computer science and applied math, • Apply to SC’s existing/planned accelerators including PEP-II, NLC/ILC, MIT (HEP), CEBAF, RIA (NP), and LCLS (BES), • Disseminate/train/educate – SBIR supports GUI development (codes in use @ KEK, FNAL,..), USPAS course in “Computational Methods in Electromagnetics”, graduated 3 PhDs/3 in progress.

36. Parallel EM codes: Finite Element Discretization up to 6th order S3P Omega2/3P T2/3P Track2/3P PIC2/3P Frequency Domain Time Domain Beam Tracking PIC S-Matrix Eigenmodes Wakefields Dark Current RF Gun Multipacting Klystron V3D– Visualization/Animation of Meshes, Particles & Fields ACD Parallel EM & BD Codes Parallel BD codes: • Weak strong beam-beam PLIBB (hadron machines) – speed- optimized tracking code resolving ~100 hours of Tevatron beam lifetime • Strong-strong beam-beam NIMZOVICH (lepton machines) – using parallelized fast elliptic solver that scales to 100’s of CPUs • Coherent Synchrotron Radiation TraFiC4 (FELs, ERLs) – high resolution scheme applied to LCLS parameter study.

37. Shape Optimization • UT Austin, Columbia, Sandia, U Wisconsin, LBNL, LLNL • Nonlinear Eigensolvers • LBNL, UCD, Stanford Electromagnetic Modeling @ SLAC Visualization - UC Davis Adaptive Mesh Refinement - RPI Performance Analysis - LBNL, LLNL Parallel Meshing - Sandia, U Wisconsin Advances in Computational Science (Details in Ryne’s talk on SciDAC) Under SciDAC, ACD is collaborating with 3 national labs and 6 universities on computational science research essential to the success of Large-scale EM simulations.

38. +1MHz -1MHz Red – Primary particles, Green – Secondary particles EM Modeling for PEP-II and NLC • PEP-II IR Heating – • NLC DDS Cell Design – • NLC DDS Wakefields – • NLC Dark Current –

39. EM Modeling for the ILC • ILC Cavity HOM Damping – TESLA & Low-Loss • ILC Input Coupler Multipacting - • ILC BPM & L-Band Structures – KEK design TTF3 design

40. Quad (βr)/mm EM Modeling for LCLS, CEBAF, RIA, MIT • LCLS RF Gun Cavity – Minimizing dipole, quadruple fields and pulse heating • CEBAF 12 GeV Upgrade – HOM & heating • RIA RFQ Cavity - Qo reduction MIT PBG Structure - Wakefields

41. ACD Summary • New parallel EM & BD simulation capability established and validated under SciDAC 1, • Significant advances achieved in computational science • Successful applications to many accelerator projects, existing and planned, • Focus on ILC R&D (Cavity, Couplers, Klystron…) • Competing for SciDAC 2 under HEP • Develop the NEXT level of simulation tools • Seek to include NP projects – CEBAF, RIA • Seek to include BES projects – LCLS, SNS

42. Conclusion • Accelerator Research at SLAC • Extends fully across the Laboratory’s programs • Pushes the reach of operating facilities • Gives birth to emerging new capabilities • Explores the advanced accelerator frontier • Pushes the state of the art in computation • Has a broad impact world-wide • We develop accelerator capability for the HEP community • which begins with today's accelerator science and facilities, • which encompasses the ILC, • but also extends far beyond the ILC to multi-TeV capability. • Next Presentation: Accelerator Technology Development and High Gradient Collaboration

43. Accelerator Departmentsand Their Human Resources *Computer Scientists

44. Brief Overview of Departments • Accelerator Research Department-A (Ron Ruth) • Pushes the capabilities of operating facilities • Develops the Beam Physics and Accelerator Technology for the next generation. • Selected topics of Advanced Accelerator Research • Advanced Computing Department (Kwok Ko) • Develops the next generation of computational tools • Uses these tools for accelerator development. • Accelerator Research Department-B (Bob Siemann) • Performs experimental research on new ideas for high gradient acceleration of particle beams • Potential of long-range but far reaching impact.