Advanced Accelerator Research Department

1. Advanced Accelerator Research Department Eric Colby November 9, 2010

2. Outline • Who we are, what we do • Overview of current research • Thoughts for the future

4. AARD Mission Develop new methods for extending the energy and intensity reach of accelerators Foster an academic environment with world-class training opportunities for students

5. AARD Mission Develop new methods for extending the energy and intensity reach of accelerators • Energy Reach: • HGRF work of Advanced Microwave Technology dept. 100 MV/m • Laser Acceleration work of Direct Laser Acceleration dept.  1 GV/m • Plasma Acceleration work of Plasma Wakefield Acceleration dept.  10 GV/m • Intensity Capabilities: • High rep rate low gradient RF work of AMT • Feedback and Instabilities work of Feedback & Dynamics group Foster an academic environment with world-class training opportunities for students • Home to 80% of ARD’s students • Members teach on campus, at the USPAS, and elsewhere • Strong experimental focus

6. AARD Mission (Early Draft) Mission Statement Advanced Accelerator Research Department What is Accelerator Science? Accelerator Science encompasses the physics and technology of particle accelerators and the physics and interaction of particle beams with other beams, their environment and beams of electromagnetic radiation. It is founded on the physics and technology of the acceleration process, the dynamics of particle beams under the influence of external electromagnetic fields, and collective effects caused by the self interaction of the beam with induced fields or other electromagnetic beams. While the technology and physics were initially motivated by pushing particle beams to ever higher energy for high energy and nuclear physics, the impact of accelerator science extends across the science landscape from the Synchrotron Light Sources and FELs producing photons to explore the atomic structure of matter to industrial accelerators which are used worldwide for the treatment of cancer. The SLAC AARD was formed to bring together accelerator physicists, graduate students and post docs to advance the state of the art in Accelerator Science. AARD research is aimed at probing the fundamental underpinnings of acceleration methods and particle beam physics using the unique experimental facilities at SLAC National Accelerator Laboratory. Founding Statement The SLAC Advanced Accelerator Research Department is dedicated to basic and applied research in accelerator science with the goals of advancing the state-of-the-art and educating accelerator scientists. Dedicated to a rigorous approach to accelerator physics, AARD pursues experiments with the goal of revealing the physical mechanisms and limitations of particle accelerators. --- Our primary emphasis is exploring the fundamental physics and technology of accelerators in rigorous academic manner. Recognizing that groundbreaking innovation most often occurs when deep physical insight, broad technical expertise, and compelling scientific questions are brought together in a collaborative environment, AARD brings these elements together to perform [far-reaching] experiments.  [too long—factor][plain spoken, but aim for the top][focal point for collaboration] [interdisciplinary aspects of accelerator science] As accelerator science draws on many scientific disciplines, AARD must [pull together] ideas from many disciplines to produce[develop] new ideas. AARD serves as the focal point for collaborative efforts, bringing together [[unique facilities and technical expertise] elements] to [solve problems] in accelerator physics. The academic pursuit of accelerator physics through theory, modeling, and experiment forms a rich learning environment. AARD educates students from Stanford and other universities, guiding their research efforts. Through strong academic ties to Stanford University and the US particle accelerator schools, AARD [contributes to the] teaching of accelerator science [and introduces new methods to other scientists in the field]. AARD carries out an integral part of the SLAC mission: providing strategic vision to the laboratory on future accelerator technologies that can transform the Lab’s science agenda, by applying expertise developed in the pursuit of basic R&D to address near-term lab objectives, and by educating future generations of accelerator scientists. [and develop the fundamental knowledge needed to [support/improve] present [machines/programs]]. Present Program Research Our present research emphasis is innovative particle acceleration methods and techniques utilizing novel ultra high power microwave, laser, and RF technologies, plasma physics, formal control theory for accelerator systems, and ultrafast feedback and control technology.  The energy frontier in High Energy Physics places very challenging demands on accelerating gradient, power efficiency, and luminosity. Addressing these challenges comes first on AARD’s research agenda, by pushing microwave acceleration techniques to the very limits of material strength, and by pursuing novel concepts using lasers and plasmas with the promise to provide breakthroughs in accelerating gradient. [emphasis on HEP seems weak compared to bulleted list for non-HEP] Additional requirements from the photon science branch of Basic Energy Sciences also drive AARD’s research. Photon science experiments will demand ever shorter pulses of highly coherent polarization-switchable x-rays. Developing femtosecond- and attosecond-beam manipulation techniques, novel radiation sources, and methods for fast polarization control will enable the next generation of photon science experiments. As a [strongly] experiment-oriented department, AARD’s research depends on the accessibility and capabilities of SLAC’s test facilities (ASTA, NLCTA, FACET, and others). As such, we work closely with the Test Facilities department to expand the capabilities as needed, and ensure the success of our research. [beam instrumentation and diagnostics as a core capability] We apply expertise developed in pursuit of the long-term R&D objectives to near-term objectives of our sister departments. Current research examples include the application of: X-band technology to produce ultrafast deflectors for LCLS X-band technology to high-gradient acceleration of protons for medicine High-speed electronic and mm-wave techniques to observational astrophysics Pulsed heating experimental techniques to test superconducting materials Laser-acceleration beam manipulation techniques to test concepts for FEL seeding Plasma-focusing techniques to produce novel sources of x-ray radiation High-speed Digital Signal Processing techniques to control e-cloud and other instabilities Others? Education AARD members are engaged with teaching applied physics and physics courses at Stanford, and in offering USPAS courses. We mentor graduate students in HGRF (Tantawi), plasma acceleration (Hogan), and laser acceleration (Colby), as well as nonlinear dynamics and FEL seeding (Ruth), and advanced electronics (Fox). Faculty mentorship for plasma and laser acceleration is presently by arrangement with faculty members in other departments (Chao, and Byer).

7. Test Facilities Disciplines Concepts Departments Applications Relevant Outcomes ASTA Material Science 0.1 GV/m Structures Advanced Microwave Technology Plasma Science ILC FELs Compact Linacs RF Sources RF Breakdown NLCTA Large-Scale Computation 1 GV/m Higher Energy Direct Laser Acceleration Lasers Laser Science Ultrashort Beams 10-13-10-14s 10-14-10-16s 10-16-10-17s Structures Photonic Xtals FACET 10 GV/m Shorter Beams Solid-State Physics Plasma Wakefield Acceleration Wakefield Generation Beam Physics Beam Propagation Higher Intensity & stability Anywhere & Everywhere Rings HI Linacs H. Stability Reduced Models Formal Control Theory Robust Filters Feedback & Dynamics System ID Advanced Electonics

8. Advanced Microwave Technology Research and development of normal conducting accelerators and power sources, with a focus on understanding the limitations in high-gradient and high-frequency microwave structures. Sami Tantawi Gordon Bowden Valery Dolgashev David FarkasJiquanGuo Jim Lewandowski Roger Miller Jeff Neilson Muhammad ShumailJuwen Wang Perry Wilson Dian Yeremian

9. High Gradient Research and Development Plan

10. Single Cell Accelerator Structures • Goals • Study rfbreakdown in practical accelerating structures: dependence on circuit parameters, materials, cell shapes and surface processing techniques • Difficulties • Full scale structures are long, complex, and expensive • Solution • Single cell standing wave (SW) structures with properties close to that of full scale structures • Reusable couplers We want to predict breakdown behavior for practical structures

11. Geometrical StudiesThree Single-Cell-SW Structures of Different Geometries 1)1C-SW-A2.75-T2.0-Cu 2) 1C-SW-A3.75-T2.0-Cu 3) 1C-SW-A5.65-T4.6-Cu 3 2

12. Geometrical Studies Different single cell structures: Standing-wave structures with different iris diameters and shapes; a/λ =0.215, a/λ =0.143, and a/λ =0.105

13. SEM Images Inside Copper Pulse Heating Region Metallography: Intergranular fractures 500X Material Testing ( Pulsed heating experiments) TE013-like mode |E| |H| Special cavity has been designed to focus the magnetic field into a flat plate that can be replaced. axis Q0 = ~44,000 (Cu, room temp.) • Economical material testing method • Essential in terms of cavity structures for wakefield damping • Recent theoretical work also indicate that fatigue and pulsed heating might be also the root cause of the breakdown phenomenon material sample r = 0.98” TE01 Mode Pulse Heating Ring Max Temp rise during pulse = 110oC HG workshop, Mar. 09 Slide credit: Sami Tantawi, SLAC

14. New Accelerator Architecture for Standing wave accelerator structures withy a combined damping and feeding. 2d u v • With a “new” type of planner cross-guide coupler the structure could be made simpler Jeff Neilson

15. Feedback & Dynamics Development of novel ultrafast and wide-bandwidth electronic circuits, signal processing systems, and laboratory measurement techniques for particle accelerators. John FoxThemisMastoridis Claudio RivettaOzhanTurgut Max Swiatlowski Toohig Fellow

22. Direct Laser Acceleration R&D on techniques for accelerating electrons and positrons using lasers and dielectric microstructures, with acceleration gradients orders of magnitude larger than traditional accelerators. Eric Colby Joel England RachikLaouar Chris McGuinness Johnny Ng Panofsky Fellow Siemann Fellow Bob Noble Edgar Peralta Ken Soong Jim Spencer Dieter Walz Ziran Wu Stanford Graduate Fellow

23. 2D Photonic Xtal: Fiber Structures er=2.13 (Silica) DIA=1.4l Zc=19.5W bg=0.58 1.305l X. Lin, Phys. Rev. ST-AB, 4, 051301, (2001). • Can be designed to support a single, confined, synchronous mode • All other modes at all other frequencies radiate strongly

24. Zc=22W Zc=5W Zc=1.5W Azimuthal Mode Amplitude [dB] Azimuthal Mode Amplitude [dB] Azimuthal Mode Amplitude [dB] Log10(r/R) Log10(r/R) Log10(r/R) Scaling of Coupling Impedance with ApertureExample: photonic band gap fiber

25. Planar Photonic Accelerator Structures Synchronous (b=1) Accelerating Field • Accelerating mode in planar photonic bandgap structure has been located and optimized • Developed method of optical focusing for particle guiding over ~1m; examined longer-range beam dynamics • Simulated several coupling techniques • Numerical Tolerance Studies: Non-resonant nature of structure relaxes tolerances of critical dimensions (CDs) to ~λ/100 or larger Y (mm) S. Y. Lin et. al., Nature 394, 251 (1998) X (mm) This “woodpile” structure is made by stacking gratings etched in silicon wafers, then etching away the substrate. Vacuum defect beam path is into the page silicon Structure contour shown for z = 0; field normalized to Eacc = 1

26. 3D Photonic Xtal: Woodpile Structures in Silicon Detailed Tolerance Studies of CDs Silicon woodpile structure produced at the Stanford Nanofabrication Facility (SNF) Best achieved: Width Variation: <40 nm RMS (~l/125) Layer Thickness: <65 nm RMS (~l/75) Layer Alignment: <65 nm RMS (~l/75) Measurement Technique Granularity: 7nm

27. Simple Variant: Fast Deflector T. Plettner et al, Phys. Rev. ST Accel. Beams 4, 051301 (2006) T. Plettner, submitted to Phys. Rev. ST Accel. Beams The Transmission Grating Accelerator Silica, l=800nm, Ez=830 MV/m

28. input Leff=2mm beam beam Distribution, delay, and mode shaping lines Silicon Chip ~80 mm Fiber coupled input l=2 mm 20 mJ/pulse 1 ps laser pulse Input waveguide 5mm 4-layer Structure Fabrication (completed at SNF) Simulation work in collaboration with Tech-X (SBIR, Phase-I submitted this year) Cutaway sketch of coupler region Image courtesy of B. Cowan, Tech-X Single-Pulse 32 MeV-Gain Woodpile Accelerator Chip (1 chip ≈ 1 ILC cavity)

29. Plasma Wakefield Acceleration R&D to explore the physics of electron- and positron-driven plasma wakefields, with acceleration gradients 2-3 orders of magnitude larger than traditional accelerators. Mark Hogan Joel England Joel Frederico Selina Li Mike Litos Dieter Walz Ziran Wu Panofsky Fellow M.J. Hogan, AARD - Plasma Page

30. Energy Reach of Plasma Accelerators:Plasma Livingston Plot Laser Driven Plasma Accelerators: Large Gradients: • Accelerating Gradients > 100GeV/m (measured) • Narrow Energy Spread Bunches • Interaction Length limited to cm’s Specialized Facilities: • Multi-TW-PW lasers • Plasma Channels/Capillaries Beam Driven Plasma Accelerators: Large Gradients: • Accelerating Gradients > 50 GeV/m (measured!) • Focusing Gradients > MT/m • Interaction Length ~ meters Unique SLAC Facilities: • FFTB < 2006, FACET > 2011 • High Beam Energy • Short Bunch Length • High Peak Current • Power Density • e- & e+ LWFA: T. Tajima an J. M. Dawson Phys. Rev. Lett. 43, 267 - 270 (1979) PWFA: P. Chen et al Phys. Rev. Lett. 54, 693 - 696 (1985)

31. E-167: Energy Doubling with aPlasma Wakefield Accelerator in the FFTB • Acceleration Gradients of ~50GeV/m (3,000 x SLAC) • Doubled energy of 45 GeV electrons in 1 meter plasma • Single Bunch Nature 445 741 15-Feb-2007 Next Step: Particle acceleration to beam acceleration @ FACET M.J. Hogan, AARD - Plasma Page

32. PWFA: Particle to Beam Acceleration Adjust final compression Disperse the beam in energy Witness Bunch x∝ΔE/E ∝t dp/p [%] 80cm Plasma z [mm] dp/p [%] Drive Bunch x [mm] ...selectively collimate • Collimation system to craft drive/witness bunch from single bunch (similar to BNL ATF wire system) • Vary charge ratio, bunch lengths, spacing by changing collimators and linac phase, R56 • Study wake loading in the non-linear regime for the first time M.J. Hogan, AARD - Plasma Page

33. Beam Parameters • New Installation in S20 with three functions: • Chicane for bunch compression • Final Focus for small spots at the IP • Experimental Area (25m) M.J. Hogan, AARD - Plasma Page

34. FACET Will Allow PWFA with Compressed Positron Bunches for the First Time • Accelerating gradient ~ 15GeV/m • Large energy spread • Emittance growth (transverse, longitudinal field variations) • Opportunity for new ideas, original solutions... • Acceleration of e+ on e- driven wake? M.J. Hogan, AARD - Plasma Page

35. Shaped Profile for Transformer Ratio ~ 5 ΔE/E < 1% Beam current profile • Application to colliders & X-FELs • Reduced energy spread • Higher efficiency (beam power) • Fewer stages Trailing Beam Drive Beam Initial wakefield see W. Lu et al “High Transformer Ratio PWFA for Application on XFELs”, PAC2009 Proceedings M.J. Hogan, AARD - Plasma Page

36. Closing thoughts • We must continually and aggressively look outside canonical accelerator science for innovations that will provide new capabilities • E.g. Engineered materials (multi-layer surfaces, photonic crystals, etc.) • Opportunities which overlap with SLAC’s strengths and unique, accessible expertise (e.g. Stanford, Silicon Valley) should be exploited • Connection to campus can and should be further strengthened • Outreach to local innovation centers in adjacent fields (e.g. SRI, KLA-Tencor, IBM, Intel, etc.) should be pursued as our applications mature • The applications case and support base must be broadened considerably beyond what has been traditionally pursued (HEPlinear collider) • There is strong support from the private sector for DOE labs to develop concepts to a point that is within reach of industry

37. Open Forums for Discussion In addition to the widely advertised: • Tuesday ARD Status Meetings 4pm • Thursday ARD Seminars 4pm • Friday ARD Coffee Break 10am There are also: • AARD Brown Bag Seminars—informal discussions centered on a short, open-ended presentation of a topic in AARD. Alternate Thursdays 12-1pm, Beige Room -- Contact: Bob Noble • AARD Applications Meetings—discussions of future applications for advanced accelerator concepts. Mondays 11:30-12:30, Beige Room -- Contact: Joel England