High Gradient Program

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High Gradient Program

• Sami Tantawi
• Spokesman for the US High Gradient Collaboration

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Overview

• High Gradient Research
• Structure and collaborators
• Goals and Methodology
• Budget
• FTE
• Support from KEK and CERN
• Expected collaborative work from other labs
• Test Facilities, ASTA and the two pack
• Experimental Program
• Basic Physics studies using Single cell
  structures
• Testing program at NLCTA
• Pulsed heating experiments
• Material studies
• Structure integration and wake field damping
• Applications
• Future work/Open problems
• Summary

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Overview of Financial Data FY2008
Includes 1.2 Ph.D. Physicists
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Overview of Financial Data 2007-2010
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The US High Gradient Research Collaboration

• The US Collaboration on High Gradient Research
  for a Multi-TeV Linear Collider has formed after
  the warm-cold decision for a future linear
  collider.
• Motivations
• The ILC will reach ½ to 1 TeV cm energy.
• Advanced Accelerator research is looking far
  beyond this, exploring laser and plasma
  acceleration
• Multi-TeV energy may be reachable with extension
  of normal conducting high gradient technology.
• After extensive development, NLC/JLC achieved
  reliable 65 MV/m for collider-ready structures
  (achieved much higher gradients in selected
  tests!).
• This collaboration aspires to build the bridge to
  span this gap.

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US Collaboration on High Gradient Researchfor a
Multi-TeV Linear Collider

• Current Members
• Laboratories
• Argonne National Laboratory
• Lawrence Berkeley National Laboratory
• Naval Research Laboratory
• Stanford Linear Accelerator Center (Also the host
  of the collaboration)
• Universities
• University of Maryland
• Massachusetts Institute of Technology
• Business Associates
• Omega-P, Inc.
• Calabazas Creek Research, Inc.
• Haimson Research Corporation
• Tech-X Corporation
• Communications and Power Industries
• Foreign Colleagues
• CERN

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US Collaboration on High Gradient Researchfor a
Multi-TeV Linear Collider

• Governance Structure
• Spokesman
• Sami Tantawi, SLAC
• Advisory Council
• Prof. Ron Ruth of SLAC (11.4 GHz research/overall
  technical coordination)
• Dr. Richard Temkin of MIT (high frequency
  research and RF source development)
• Dr. Gregory Nusinovich of UMD (theory and code
  development)
• Dr. Wei Gai of ANL (other experimental programs).
• Dr. Erk Jensen , CERN
• Prof. Toshi Higo, KEK

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Methodology We must lay a technical and
theoretical foundation

• Our research should be systematic and thorough,
  but it must be targeted due to limited resources.
• Traditionally linear collider programs dictated
  the performance of the accelerator structures.
  Here we would like to find the limitations of
  structures due to these choices and see if we can
  design the collider around an optimized structure
  design
• We have to address fundamentals early these
  include, but are not limited to
• Frequency scaling
• Geometry dependence
• Energy, power and pulse length
• Materials
• Surface processing technique (etching, baking,
  etc.)
• Theory

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Experimental Facilities Around the US

• MIT is upgrading its test facility at 17 GHz for
  high repetition rate operation
• NRLs RF components have been manufactured by
  SLAC and fully delivered. The upgraded facility
  at NRL is up and running.
• Collaborative effort with ANL to create a
  structure suitable for their wakefield
  acceleration facility is underway.
• SLAC facilities
• ASTA is being reconfigured for operation with two
  X-band klystrons and a pulse compressor.
• The two-pack modulator in NLCTA is up and
  running and the system is expected to run fully
  in this summer
• The two NLCTA stations are up and running serving
  a host of users including SLAC, CERN and KEK
  experiments
• Two individual X-band test stations in Klystron
  lab are serving users from SLAC, KEK, ANL, MIT,
  Frascati, and CERN
• We are making an enormous number of RF components
  to make the experimental procedure simple

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SLAC The Collaboration Host

• We concentrated on being accessible to the rest
  of the collaboration
• Improved our test facilities at 11.424
  GHz2-pack, ASTA and individual stations.
• Cost effective testing
• New reusable couplers made available to all
  collaborators.
• New types of gate valves to minimize, time,
  effort and cost for installations.
• All collaborators have been invited to take
  advantage of the available resources at SLAC for
  building and manufacturing accelerator
  structures.
• Supported other facilities such as NRLs magnicon
  facility
• Built structures based on designs by MIT such as
  the photonic band gap structures.
• Supported testing of Dielectric Structures for
  ANL
• Sent structures and RF components for the ANL
  wakefield experiments

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Pulse compressors at ASTA and Two-Pack

• All new, second generation, overmoded components
  for high reliability (So that we are testing
  structure rather than RF system)
• Flexible pulse length and gain
• High efficiency
• Each is powered by two klystrons

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ASTA

• ASTA has been rebuilt and is being commissioned
  with two test stations, one with a pulse
  compressor and another with out. ( Waiting on
  Safety sign off to turn on)

Two feeds for the two experimental stations
inside the ASTA bunker
The ASTA pulse compressor with variable iris
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ASTA (Continued)
The uncompressed arm has a variable phase shifter
and a gate valve
The ASTA pulse compressor with variable delay
delay-lines( Miller cup)
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ASTA Pulse Compressor Cold Tests
Test with a dual-mode in the delay line ( the
Miller cup is tuned for two modes)
Test with a single mode in the delay line
With input pulse modulation one gets a gain of
about 3 at 266 ns and a gain of about 2 at 399 ns
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Experimental Studies

• Basic Physics Experimental Studies
• Single and Multiple Cell Accelerator Structures
  (with major KEK and CERN contributions)
• traveling- wave single cell accelerator
  structures (Needs ASTA)
• single-cell standing-wave accelerator structures
  (Performed at Klystron Test Lab)
• Waveguide structures (Needs ASTA)
• Pulsed heating experiments (Performed at the
  klystron Test Lab, also with major KEK and CERN
  contributions)
• Full Accelerator Structure Testing (Performed at
  NLCTA, with CERN contributions)

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Experimental studies using the single cell
accelerator structure approach

• Tested
• Low shunt impedance, a/l 0.215,
  1C-SW-A5.65-T4.6-Cu, 4 tested
• Low shunt impedance, TiN coated,
  1C-SW-A5.65-T4.6-Cu-TiN, 1 tested
• Three high gradient cells, low shunt impedance,
  3C-SW-A5.65-T4.6-Cu, 2 tested
• High shunt impedance, elliptical iris, a/l
  0.143, 1C-SW-A3.75-T2.6-Cu, 1 tested
• High shunt impedance, round iris, a/l 0.143,
  1C-SW-A3.75-T1.66-Cu, 1 tested
• Choke in high gradient cell, 1C-SW-A5.65-T4.6-Chok
  e-Cu, 1 tested, another under test
• Total of 10 tests have been completed
• In manufacturing
• Photonic-Band-Gap in high gradient cell,
  1C-SW-A5.65-T4.6-Cu-PBG
• Highest shunt impedance, a/l 0.105,
  1C-SW-A2.75-T2.0-Cu
• Three cells, WR90 coupling to power source,
  3C-SW-A5.65-T4.6-Cu-WR90
• High shunt impedance, made of CuZr,
  1C-SW-A3.75-T2.6-CuZr
• Low shunt impedance, made of CuZr,
  1C-SW-A5.65-T4.6-CuZr

• Geometry
• Stored energy
• Electric field for same magnetic field
• Choke
• Choke WR90 coupler
• Shunt impedance, iris size, etc.
• Materials
• CuZr
• Molybdenum
• Coatings
• TiN

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Geometrical Studies
3 different single cell structures Standing wave
structures with different iris diameters and
shapes a/l0.21, a/l0.14 and a/l0.14 and
elliptical iris. Global geometry plays a major
role in determining the accelerating gradient,
rather than the local electric field.
Maximum surface electric fields MV/m
Maximum surface magnetic fields kA/m
Accelerating fields MV/m
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Surface processingA special structure was built
and processed (with best cleaning and surface
processing we can master) at KEK and hermetically
sealed, then assembled at SLAC at the best
possible clean conditions
Dr. Yasuo Higashi and Richard Talley assembling
Three-C-SW-A5.65-T4.6-Cu-KEK-2
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Two structured 1 processed normally and 2
processed similar to superconducting accelerator
structures
The near perfect surface processing affected only
the processing time. The second structure
processed to maximum gradient in a few minutes vs
few hours for the normally processed structure.
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Material Testing ( Pulsed heating experiments)
Max Temp rise during pulse 110oC
TE01 Mode Pulse Heating Ring

• Economical material testing method
• Essential in terms of cavity structures for wake
  field damping
• Recent theoretical work also indicate that
  fatigue and pulsed heating might be also the root
  cause of the breakdown phenomenon

SEM Images Inside Copper Pulse Heating Region
Special cavity has been designed to focus the
magnetic field into a flat plate that can be
replaced.
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Results from Pulsed heating experimnts
Copper Zirconium Temp70oC
Copper Temp70oC
Copper Temp110oC
Copper Zirconium Temp100oC
L. Laurent
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Material Studies

• Clamping Structure for testing copper alloys
  accelerator structure ( Mechanical Design Done,
  submitted to shop)

Diffusion bonding and brazing of copper
zirconium are being researched at SLAC.
The clamped structure will provide a method for
testing materials without the need to develop all
the necessary technologies for bonding and
brazing them. Once a material is identified, we
can spend the effort in processing it.
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Structure modifications for wake field damping

• CERN is pursuing side slotted structures ( to be
  tested soon at NLCTA)
• MIT PBG Structure ( Mechanical Design Done,
  submitted to shop)
• Choked structures has been manufactured and is
  currently under test.
• Side fed structures will pave the way to parallel
  fed structures with gradients above 140 MV/m
  (currently being manufactured)
• Other methods of damping are being studied
  theoretically.

PBG Structure
Choke Structure
Choke structure with side feed
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Standing-Wave Accelerator Structure Recent
Results (a/l0.14)
Each point in this graph represents 10 hours or
running at 60 Hz
Typical gradient (loaded) as a function of time.
t
Pulsed Temp Rise
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Full Accelerator structure testing ( the T18
structure)
Frequency. 11.424GHz
Cells 18inputoutput
Filling Time 36ns
a_in/a_out 4.06/2.66 mm
vg_in/vg_out 2.61/1.02 (c)
S11 0.035
S21 0.8
Phase 120Deg
Average Unloaded Gradient over the full structure 55.5MW?100MV/m
Field Amplitude

• Structure designed by CERN based on all empirical
  laws developed experimentally through our
  previous work
• Cell Build at KEK
• Structure was bonded and processed at SLAC
• The structure is also tested at SLAC

120
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RF Processing of the T18 Structure
RF BKD Rate Pulse Width Dependence at Different
Conditioning Time
RF BKD Rate Gradient Dependence for 230ns Pulse
at Different Conditioning Time
After 250hrs RF Condition
G108MV/m
G108MV/m
After 500hrs RF Condition
After 900hrs RF Condition
G110MV/m
After 1200hrs RF Condition
This performance maybe good enough for 100MV/m
structure for a warm collider, however, it does
not yet contain all necessary features such as
wake field damping. Future traveling wave
structure designs will also have better
efficiencies
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Possible Applications for Ultra-High-Gradient
Structures
Recently LLNL is looking to apply our high
gradient technology to their T-REX projects
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Future work/Open Problems

• Full length accelerator structures based on
  standing wave cells
• These are being theoretically designed and
  modeled. The structure will feature parallel
  coupling and would look matched like any other
  traveling wave structure from the outside.
• we expect to build an 86 cm long structure and
  test it in 2009.
• We hope to prove a structure capable of exceeding
  140 MV/m gradient
• Wake field damping features are being studied
  theoretically and experimentally through out the
  collaboration. This work have just began
• Accelerator structure made of copper alloys are
  being studied and in 2009 we should start to see
  some fruits from this effort.
• The effect beam-loading on gradient need to be
  verified.
• The development of theoretical understanding and
  Modeling of the RF breakdown phenomena is
  starting to take shape however, this is still at
  its infancy and during 2009 we hope that this
  effort will take off with the help of our
  collaborator at university of Maryland.
• Ultra High Gradient accelerator structures will
  be useless without the developments of an
  efficient RF sources to drive them. The
  developments of these source has to be given
  attention in the near future

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Summary

• The work being done is characterized by a strong
  national and international collaboration. This is
  the only way to gather the necessary resources to
  do this work.
• SLAC has developed and opened its test facilities
  for all collaborators
• The experimental program to date has paved the
  ground work for the theoretical developments.
• With the understanding of geometrical effects, we
  have demonstrated standing and traveling wave
  accelerator structures that work above 100 MV/m
  loaded gradient.
• Standing wave structures have shown the potential
  for gradients of 150 MV/m or higher
• Further understanding of materials properties may
  allow even greater improvements
• We still have not demonstrated a full featured
  accelerator structure including wake field
  damping. This is expected in the near future

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Acknowledgment

• The work being presented is due to the efforts of
  
• V. Dolgashev, Lisa Laurent, F. Wang, J. Wang, C.
  Adolphsen, D. Yeremian, J. Lewandowsky, C.
  Nantista, J. Eichner, C. Yoneda, C. Pearson, A.
  Hayes, D. Martin, R. Ruth, SLAC
• T. Higo and Y. Higashi, et. al., KEK
• W. Wuensch et. al., CERN
• R. Temkin, et. al., MIT
• W. Gai, et. al, ANL
• Gregory Nusinovich et. al., University of
  Maryland
• S. Gold, NRL