Accelerator Research
at SLAC
Ronald Ruth
Head
Accelerator Research Department A (ARD-A)
AARD HEPAP Subpanel
December 21, 2005
12/21/05
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Outline
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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.
12/21/05
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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.
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Fundamental Issues for HEP
• High center-of-mass energy
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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
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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
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SLAC Programmatic Priorities
for 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
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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
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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 PEPII.
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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.
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SLAC ILC Research Activities
(not part of this review)
• Restructured Program to align with cold LC.
– Accelerator Design and CDR
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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
12/21/05
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Overview of Accelerator Research
and 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)
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12/21/05
New computational algorithms
RF modeling, frequency and time domain.
Beam device modeling
Calculation of beam-environment interaction.
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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
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Management and Budget
• Accelerator R&D Annual Funding
– Average ~$8.5M/yr for past 5 years (operating budget)
• Split between
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Beam Physics
Accelerator Technology
Near and mid-term
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
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Accelerator Research in the Context of
other programs
• SLAC—1500 staff, 3000 users (HEP + Photon Science)
– Accelerator Physics-HEP— around 100 scientists (Including students)
Accelerator
Technology
Advanced Accelerator
Beam Physics 7%
Research
7%
15%
Advanced Computation
7%
Photon Science 3%
Advanced Accelerator Research
Advanced Computation
Photon Science
Operations
International Linear Collider
International Linear Collider
36%
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Operations
25%
Beam Physics
Accelerator Technology
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Accelerator Research and Education
• In the previous group of 100 Scientists
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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
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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.
12/21/05
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Beam Physics
• Beam Physics research is driven primarily by the requirements
for high luminosity
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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
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Lattice Development and
Dynamics of Beams
Highlights of recent activities:
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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
12/21/05
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
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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 sixdimensional model of
accelerator using linear optical
variations and BPM gains and
crossing coupling
• Use the model to improve
accelerator and its performance
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Measured phase advance (red dots) vs. a fitted model
(blue line)
Measured beam tilt angles (blue), and expected
improvement (red) using a MIA solution
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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.
12/21/05
Measured dispersions (green), the ideal design 19
(blue), and a MIA fitting (red).
Beam-Beam Simulation using
Particle-In-Cell Method
1) Both beams are represented macro
particles (160,000)
strong-strong
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.
12/21/05z
IP
3) The distribution of particles in slice
is used to solve two-dimensional
Poisson equation on a regular grid
(128x128).
y
x
4) The solved potential then used to
compute the kick experienced by
a particle from the opposing slice.
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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.
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Beam-Beam Spectra at PEP-II
e -, x
e+, x
Horizontal spectrums for two beams matched both in simulation and measurement.
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In x plane, s and p modes are clearly seen the simulation. (f0 = 136.312 kHz)
Positron Beam Distributions
with Beam-Beam Interaction
 
  16 min
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
12/21/05
map is important because it defines the dynamic aperture.
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A Model Guided Strategy to Improve
PEP-II Luminosity or Damping Ring
performance
1.0x1034cm-2s-1
MS,JT
PEP-II
FJD,YC
MIA(YY)
LEGO(YC)
BBI(YC)
Model based and adiabatic correction scheme for luminosity improvement.
Tuning
12/21/05 was done during the delivery and guided by the luminosity reading.
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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.
12/21/05
0.5 km
8 km
17 km dogbone damping ring
dynamic aperture of damping rings with
nonlinear single-mode wigglers.
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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
Design 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
• 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
12/21/05
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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
12/21/05
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Collective Effects and Bright Beam
Physics
Recent achievements
• 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
12/21/05
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
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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
12/21/05
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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
12/21/05
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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 ms. 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
12/21/05
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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.
12/21/05
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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.
12/21/05
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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.
An examples of the measured
roughness profile. The rms roughness
~20 nm, rms slope ~2.10-3
12/21/05
Developed a computer program
for processing roughness
measurements of the undulator
surface and will use it for
monitoring the requirements in
the production cycle.
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Advanced Computations Department (ACD)
Formed in 2000 to focus on high performance computing to:
 Develop a parallel simulation capability in electromagnetics &
beam dynamics under SciDAC to run on Office of Science’s (SC)
flagship supercomputers (IBM SP3@NERSC, Cray X1E@NLCF),
 Advance computational science to 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.
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ACD Parallel EM & BD Codes
Parallel EM codes: Finite Element Discretization up to 6th order
Frequency Domain
S3P
Omega2/3P
S-Matrix
Eigenmodes
Time Domain
Beam
Tracking
PIC
T2/3P
Track2/3P
PIC2/3P
Wakefields Dark Current
Multipacting
RF Gun
Klystron
V3D – Visualization/Animation of Meshes, Particles & Fields
Parallel BD codes:
 Weak strong beam-beam PLIBB (hadron machines) – speedoptimized 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.
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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.
Shape Optimization
- UT Austin, Columbia,
Sandia, U Wisconsin,
LBNL, LLNL
Nonlinear
Eigensolvers
- LBNL, UCD,
Stanford
Visualization
- UC Davis
Electromagnetic
Modeling @ SLAC
Parallel Meshing
- Sandia, U Wisconsin
12/21/05
Adaptive Mesh
Refinement - RPI
Performance Analysis
- LBNL, LLNL
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EM Modeling for PEP-II and NLC
 PEP-II IR Heating –
del_sf00
del_sf0pi
del_sf1pi
del_sf20
 NLC DDS Cell Design –
Single-disk RF-QC
2
Frequency Deviation [MHz]
1.5
+1M
1
0.5
Hz
0
-0.5
-1
-1.5
-2
0
 NLC DDS Wakefields –
50
-1MHz
100
Disk number
150
200
 NLC Dark Current –
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Red – Primary particles, Green – Secondary particles
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EM Modeling for the ILC
 ILC Cavity HOM Damping – TESLA & Low-Loss
 ILC Input Coupler Multipacting KEK design
TTF3 design
 ILC BPM & L-Band Structures –
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EM Modeling for LCLS, CEBAF, RIA, MIT
0.003
cylindrical cavity
racetrack with offset=0.05 "
0.002
Quad
(gβr)/mm
 LCLS RF Gun Cavity –
0.001
0.000
Minimizing dipole, quadruple
fields and pulse heating
-0.001
-0.002
-0.003
-200
-100
0
100
200
rf phase (degree)
 CEBAF 12 GeV Upgrade – HOM & heating
 RIA RFQ Cavity - Qo reduction
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MIT PBG Structure - Wakefields
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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
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Conclusion
• Accelerator Research at SLAC
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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
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Accelerator Departments
and Their Human Resources
Faculty
Staff
Research
Associates
Graduate
Students
ARD-A
3 + 2 Emeritus
18
2
5
ARD-B
1
4
1
9
ACD
7 + 6*
3
*Computer Scientists
ACD
ARD-A
ARD-A Admin
Lattice Dynamics
Collective Effects
Advanced Electronics
High Power RF
RF Structures
ARD-B
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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.
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