AARD

Advanced Accelerator Research Department

Eric ColbyNovember 9, 2010

AARD

Outline

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

AARD

AARD

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

AARD

AARD MissionDevelop 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

AARDAARD Mission (Early Draft)Mission StatementAdvanced 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 ResearchOur 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 LCLSX-band technology to high-gradient acceleration of protons for medicineHigh-speed electronic and mm-wave techniques to observational astrophysicsPulsed heating experimental techniques to test superconducting materialsLaser-acceleration beam manipulation techniques to test concepts for FEL seedingPlasma-focusing techniques to produce novel sources of x-ray radiation High-speed Digital Signal Processing techniques to control e-cloud and other instabilitiesOthers? EducationAARD 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).

AARD

MaterialScience

Plasma Science

Large-ScaleComputation

Laser Science

Solid-StatePhysics

Beam Physics

Formal Control Theory

Advanced Electonics

Structures

RF Sources

RF Breakdown

Advanced Microwave Technology

Direct Laser Acceleration

Plasma Wakefield

Acceleration

Feedback & Dynamics

ASTA

Anywhere & Everywhere

ILCFELsCompact Linacs Higher

Energy

Shorter Beams

Higher Intensity& stabilityRings

HI LinacsH. Stability

Ultrashort Beams10-13-10-14s10-14-10-16s10-16-10-17s

Structures Photonic Xtals

Lasers

0.1 GV/m

1 GV/m

10 GV/m

Relevant Outcomes

ApplicationsTest Facilities

DepartmentsConceptsDisciplines

Robust FiltersSystem ID

Reduced Models

Wakefield Generation

Beam Propagation

FACET

NLCTA

AARDAdvanced Microwave Technology

Sami Tantawi Gordon Bowden Valery Dolgashev David Farkas Jiquan Guo Jim Lewandowski

Roger Miller Jeff Neilson Muhammad Shumail Juwen Wang Perry Wilson Dian Yeremian

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.

AARDHigh Gradient Research and Development Plan

AARDSingle Cell Accelerator Structures

Goals • Study rf breakdown 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

AARDGeometrical Studies

Three 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

2

3

AARDGeometrical 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

8 0 1 0 0 1 2 0 1 4 0 1 6 0 1 8 0 2 0 0 2 2 01 0 7

1 0 6

1 0 5

1 0 4

1 0 3

1 0 2

1 0 1

1 0 0

G r ad ien t M V m Bre

akdo

wnPr

obab

ility1pulsemet

er

a 0.215, t 4.6m m, K EK 4a 0.143, t 2.6m m, SLA C 1a 0.105, t 2.0m m, SLA C 1

0 1 0 0 2 0 0 3 0 0 4 0 0 5 0 01 0 7

1 0 6

1 0 5

1 0 4

1 0 3

1 0 2

1 0 1

1 0 0

P eak Elec tr ic F ield M V m Bre

akdo

wnPr

obab

ility1pulsemete

r

a 0.215, t 4.6m m, K EK 4a 0.143, t 2.6m m, SLA C 1a 0.105, t 2.0m m, SLA C 1

0 1 0 0 2 0 0 3 0 0 4 00 5 00 6 0 01 0 7

1 0 6

1 0 5

1 0 4

1 0 3

1 0 2

1 0 1

10 0

P eak M agn etic F ield kA m Bre

akdo

wnPr

obab

ility1pulsemet

er

a 0.215, t 4.6mm, K EK 4a 0.143, t 2.6mm, SLA C 1a 0.105, t 2.0mm, SLA C 1

2 0 3 0 4 0 5 0 6 0 7 0 8 0 9 01 0 7

1 0 6

1 0 5

1 0 4

1 0 3

1 0 2

1 0 1

1 0 0

P eak P u ls e Heatin g d eg . C Bre

akdo

wnPr

obab

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ter

a 0.215, t 4.6mm, K EK 4a 0.143, t 2.6mm, SLA C 1a 0.105, t 2.0mm, SLA C 1

AARD

3/3/2009 HG workshop, Mar. 09 Page 13

Material Testing ( Pulsed heating experiments)

r = 0.98”

|E|

TE013-like mode|H|

Q0 = ~44,000 (Cu, room temp.)

material sample

axis

Special cavity has been designed to focus the magnetic field into a flat plate that can be replaced.

• 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

Metallography: Intergranular fractures 500X

TE01 Mode Pulse Heating Ring

Max Temp rise during pulse = 110oC

SEM Images Inside Copper Pulse Heating Region

Slide credit: Sami Tantawi, SLAC

AARD

2dv

u

New Accelerator Architecture for Standing wave accelerator structures withy a combined damping and feeding.

Jeff Neilson•With a “new” type of planner cross-guide coupler the structure could be made simpler

AARDFeedback & Dynamics

John Fox Themis Mastoridis Claudio Rivetta Ozhan Turgut Max Swiatlowski

Development of novel ultrafast and wide-bandwidth electronic circuits, signal processing systems, and laboratory measurement techniques for particle accelerators.

Toohig Fellow

AARD

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AARD

Direct Laser Acceleration

Eric Colby Joel England Rachik Laouar Chris McGuinness Johnny Ng

Bob Noble Edgar Peralta Ken Soong Jim Spencer Dieter Walz Ziran Wu

R&D on techniques for accelerating electrons and positrons using lasers and dielectric microstructures, with acceleration gradients orders of magnitude larger than traditional accelerators.

Panofsky Fellow Siemann Fellow

Stanford Graduate Fellow

AARD2D Photonic Xtal: Fiber Structures

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

DIA=1.4l

Zc=19.5W bg=0.58

1.305l

er=2.13 (Silica)

PE

Zc 2

22acc l

=

AARDScaling of Coupling Impedance with Aperture

Example: photonic band gap fiber

-1 -0.8 -0.6 -0.4 -0.2 0-60

-50

-40

-30

-20

-10

0

log10(r/R)

Azi

mut

hal m

ode

ampl

itude

(dB

)

R = 0.52a

m = 0m = 1m = 2m = 3m = 4m = 6m = 12

-1 -0.8 -0.6 -0.4 -0.2 0-60

-50

-40

-30

-20

-10

0

log10(r/R)

R = 1.34a

m = 0m = 1m = 2m = 5m = 6m = 12

-1 -0.8 -0.6 -0.4 -0.2 0-60

-50

-40

-30

-20

-10

0

log10(r/R)

R = 2.1a

m = 0m = 2m = 4m = 6m = 11m = 12

Zc=1.5WZc=22W Zc=5W

Log10(r/R) Log10(r/R) Log10(r/R)

Azim

utha

l Mod

e Am

plitu

de [d

B]

Azim

utha

l Mod

e Am

plitu

de [d

B]

Azim

utha

l Mod

e Am

plitu

de [d

B]

AARD

• 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

Structure contour shown for z = 0; field normalized to Eacc = 1

Vacuum defectbeam path is into the page silicon

Synchronous (b=1) Accelerating Field

X (mm)

Y (m

m)

Planar Photonic Accelerator Structures

This “woodpile” structure is made by stacking gratings etched in silicon wafers, then etching away the substrate.

S. Y. Lin et. al., Nature 394, 251 (1998)

AARD3D Photonic Xtal: Woodpile Structures in Silicon

Silicon woodpile structure produced at the Stanford Nanofabrication Facility (SNF)

Detailed Tolerance Studies of CDs

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

Process Version Rod width base Rod width top Taper Angle Layer Thickness Alignment Offset Period3 389 486 9.89624641 556 142.5 18343 402 507 10.69429961 660 146 18273 486 583 10.01988665 549 161.5 18343 486 583 10.01988665 688 102.5 18083 311 441 9.575247964 516 20133 280 391 11.1759075 658 17213 379 509 11.04285784 5593 348 485 10.49147701 7022 438 556 13.12686302 506 412.5 18442 419 506 9.755861898 681 400 18382 469 525 5.75140209 556 522 18132 450 544 9.595956437 545 516 18572 384 455 7.092112957 643 18702 366 446 6.301068652 580 18322 446 527 5.850496153 5272 464 518 8.7379923241 434 529 10.43182293 542 18181 503 669 15.86761887 516 17891 483 649 15.86761887 5841 480 690 19.90374954 580

average 420.85 529.95 10.55991867 586.7368421 300.375 1835.571std 62.16808709 76.49594072 3.503712238 64.14206637 179.4061135 62.12112version 3 mean 390.4285714 500 10.34633323 598 138.125 1839.5version 3 std 74.27062003 65.09649431 0.57608771 73.11243787 25.14416765 95.24022version 2 mean 429.5 509.625 8.276469191 576.8571429 462.625 1842.333version 2 std 37.27887184 39.6157887 2.542079837 63.49128174 65.34188932 19.84607

AARD

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The Transmission Grating Accelerator

xyz

laserbeam

cylindrical lensvacuum

channel

electron beam

cylindrical lens

top view

l/2

l

xyz

laserbeam

cylindrical lensvacuum

channel

electron beam

cylindrical lens

top view

l/2

l

top view

l/2

l

T. Plettner et al, Phys. Rev. ST Accel. Beams 4, 051301 (2006)

0=F

laserEE 21

|| ~

T. Plettner, submitted to Phys. Rev. ST Accel. Beams

Simple Variant: Fast Deflector

Silica, l=800nm, Ez=830 MV/m

AARD

Fiber coupled input

l=2 mm 20 mJ/pulse 1 ps laser pulse

Distribution, delay, and mode shaping lines

Leff=2mm

Silicon Chip

5mm 4-layer Structure Fabrication (completed at SNF)

~80 mm

Cutaway sketch of coupler region

beambeam

Simulation work in collaboration with Tech-X (SBIR, Phase-I submitted this year)

input

Input waveguide

Image courtesy of B. Cowan, Tech-X

Single-Pulse 32 MeV-Gain Woodpile Accelerator Chip(1 chip ≈ 1 ILC cavity)

29

M.J. Hogan, AARD - Plasma Page

Selina LiMark Hogan Mike LitosJoel England Ziran WuJoel Frederico

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.

Plasma Wakefield Acceleration

Panofsky FellowDieter Walz

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+

Energy Reach of Plasma Accelerators:Plasma Livingston Plot

LWFA: T. Tajima an J. M. DawsonPhys. Rev. Lett. 43, 267 - 270 (1979)

PWFA: P. Chen et alPhys. Rev. Lett. 54, 693 - 696 (1985)

31

M.J. Hogan, AARD - Plasma Page

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 plasmaSingle Bunch

Nature 445 741 15-Feb-2007

Next Step: Particle acceleration to beam acceleration @ FACET

32

M.J. Hogan, AARD - Plasma Page

PWFA: Particle to Beam Acceleration

WitnessBunch

DriveBunch

x ∝ ΔE/E ∝ tDisperse the beam in energy

Adjust final compression

...selectively collimate

x [mm]

dp/p

[%]

dp/p

[%]

z [mm]

80cmPlasma

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

33

M.J. Hogan, AARD - Plasma Page

Beam Parameters

New Installation in S20 with three functions:1.Chicane for bunch compression2.Final Focus for small spots at the IP3.Experimental Area (25m)

Energy 23 GeV

Charge 3 nC

Sigma z 14 µm

Sigma r 10 µm

Peak Current 22 kAmps

Species e- & e+

34

M.J. Hogan, AARD - Plasma Page

FACET Will Allow PWFA with Compressed Positron Bunches for the First Time

Accelerating gradient ~ 15GeV/mLarge energy spreadEmittance growth (transverse, longitudinal field variations)Opportunity for new ideas, original solutions...Acceleration of e+ on e- driven wake?

35

M.J. Hogan, AARD - Plasma Page

Shaped Profile for Transformer Ratio ~ 5

Beam currentprofile

Initial wakefield

ΔE/E < 1%

Drive BeamTrailingBeam

Application to colliders & X-FELs Reduced energy spreadHigher efficiency (beam power)Fewer stages

see W. Lu et al “High Transformer Ratio PWFA for Application on XFELs”, PAC2009 Proceedings

AARDClosing 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 (HEPlinear collider)– There is strong support from the private sector for DOE labs to develop

concepts to a point that is within reach of industry

AARDOpen 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