Transcript High Gradient Program Sami Tantawi Spokesman for the US High Gradient Collaboration

High Gradient Program
Sami Tantawi
Spokesman for the US High Gradient Collaboration
July 8, 2008
SLAC Annual Program Review
Page 1
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
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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
July 8, 2008
SLAC Annual Program Review
Page 2
Overview of Financial Data – FY2008
FY 2008 FTE by Job Category
High Gradient
Administrative
/ Technician,
0.2
FY 2008 Total K$ by Activity
High Gradient
Other, 0.0
Permanent
PhD, 1.5
Allocation of
PPA DPS, 586
Temporary
PhD, 0.8
Graduate
Students, 1.0
Engineer /
Computing
Professional,
7.5
Includes 1.2 Ph.D. Physicists
High Gradient,
2,591
Total K$ of High Gradient: 2,591
Total FTE: 11
July 8, 2008
SLAC Annual Program Review
Page 3
Overview of Financial Data 2007-2010
FY 2007-2010 Total K$ by Activity
High Gradient
FY 2007-2010 Total K$ By Cost Type
High Gradient
3,500
3,500
3,000
3,000
2,500
2,500
(
(
K
$
2,000
2,000
K
$ 1,500
1,500
)
)
1,000
1,000
500
500
0
0
FY07
FY08
Labor
July 8, 2008
M &S
FY09
FY10
Allocation of PPA DPS
SLAC Annual Program Review
FY07
High Gradient
FY08
FY09
Allocation of PPA DPS
Page 4
FY10
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.
July 8, 2008
SLAC Annual Program Review
Page 5
US Collaboration on High Gradient Research
for a Multi-TeV Linear Collider
*
Current Members:
– Laboratories:
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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
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Omega-P, Inc.
Calabazas Creek Research, Inc.
Haimson Research Corporation
Tech-X Corporation
Communications and Power Industries
– Foreign Colleagues
• CERN
• KEK
July 8, 2008
SLAC Annual Program Review
Page 6
US Collaboration on High Gradient Research
for 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
July 8, 2008
SLAC Annual Program Review
Page 7
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
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Frequency scaling
Geometry dependence
Energy, power and pulse length
Materials
Surface processing technique (etching, baking, etc.)
Theory
…
July 8, 2008
SLAC Annual Program Review
Page 8
Experimental Facilities Around the US
* MIT is upgrading its test facility at 17 GHz for high repetition rate
operation
* NRL’s 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
July 8, 2008
SLAC Annual Program Review
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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 GHz:2-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 NRL’s 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
July 8, 2008
SLAC Annual Program Review
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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
July 8, 2008
SLAC Annual Program Review
Page 11
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
July 8, 2008
The ASTA pulse compressor with
variable iris
SLAC Annual Program Review
Page 12
ASTA (Continued)
The uncompressed arm has a variable
phase shifter and a gate valve
July 8, 2008
The ASTA pulse compressor with
variable delay delay-lines( Miller cup)
SLAC Annual Program Review
Page 13
ASTA Pulse Compressor Cold Tests
5
6
Asta SLED Line Cold Test
133nS
ASTA SLED Line Cold Test
64nS
5
4
Powe Gain
Power Gain
4
3
3
2
2
1
1
0
-1000
-500
0
500
1000
0
-800
Time (ns)
-400
0
400
Time (ns)
800
Test with a dual-mode in the
Test with a single mode in the delay line delay line ( the Miller cup is
tuned for two modes)
With input pulse modulation one gets a gain of about 3 at 266 ns and a gain of about 2
at 399 ns
July 8, 2008
SLAC Annual Program Review
Page 14
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)
July 8, 2008
SLAC Annual Program Review
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Experimental studies using the single cell
accelerator structure approach
Geometry
* Stored energy
* Electric field for same
magnetic field
* Choke
* Choke WR90 coupler
* Shunt impedance, iris size,
etc.
* …
Materials
* CuZr
* Molybdenum
…
Coatings
* TiN
* …
July 8, 2008
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-T4.6Cu, 2 tested
•High shunt impedance, elliptical iris, a/l = 0.143, 1C-SW-A3.75-T2.6Cu, 1 tested
•High shunt impedance, round iris, a/l = 0.143, 1C-SW-A3.75-T1.66Cu, 1 tested
•Choke in high gradient cell, 1C-SW-A5.65-T4.6-Choke-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-CuWR90
•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
…
SLAC Annual Program Review
Page 16
Geometrical Studies
3 different single cell structures: Standing wave structures with different iris
diameters and shapes; a/l=0.21, a/l=0.14 and a/l=0.14 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]
July 8, 2008
SLAC Annual Program Review
Accelerating fields [MV/m]
Page 17
Surface processing
A 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-A5.65T4.6-Cu-KEK-#2
July 8, 2008
SLAC Annual Program Review
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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.
July 8, 2008
SLAC Annual Program Review
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Material Testing ( Pulsed heating experiments)
Max Temp rise during pulse = 110oC
TE01 Mode Pulse Heating Ring
Metallography: Intergranular fractures 500X
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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.
July 8, 2008
*
SLAC Annual Program Review
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
Page 20
Results from Pulsed heating experimnts
Copper: Temp=70oC
Copper Zirconium: Temp=70oC
Copper: Temp=110oC
Copper Zirconium: Temp=100oC
July 8, 2008
SLAC Annual Program Review
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L. Laurent
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.
July 8, 2008
SLAC Annual Program Review
Page 22
Structure modifications for wake field damping
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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
July 8, 2008
Choke Structure
Choke structure with side feed
SLAC Annual Program Review
Page 23
Standing-Wave Accelerator Structure Recent Results (a/l~0.14)
Each point in this graph represents ~10 hours or running at 60 Hz
Breakdown Probability /Pulse/Meter
0.1
Typical gradient
(loaded) as a
function of time.

0.01
Pulsed Temp Rise
0.001
0.0001
ns
ns
ns
-5
10
-6
10
100
120
140
160
180
Gradient(MV/m)
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SLAC Annual Program Review
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200
Full Accelerator structure testing ( the T18
structure)
Frequency.
11.424GHz
Cells
18+input+output
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
Eacc _ out Eacc _ in ~ 1.5
•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
Cumulated
•The structure is also tested at SLAC
120°
Phase Change
July 8, 2008
SLAC Annual Program Review
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RF Processing of the T18 Structure
RF BKD Rate Gradient Dependence for 230ns Pulse at Different
Conditioning Time
RF BKD Rate Pulse Width Dependence at Different
-4 Conditioning Time
10
-4
10
After 500hrs RF
Condition
-5
10
After 900hrs RF
Condition
-6
10
After 1200hrs RF
Condition
95
-5
G=108MV/m
10
-6
10
G=110MV/m
-7
-7
10
G=108MV/m
BKD Rate: 1/pulse/m
BKD Rate: 1/pulse/m
After 250hrs RF
Condition
100
105
110
Unloaded Gradient: MV/m
115
10
100
150
200
RF Flat Top Pulse Width: ns
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
July 8, 2008
SLAC Annual Program Review
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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
July 8, 2008
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Future work/Open Problems
*
Full length accelerator structures based on standing wave cells:
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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
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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
July 8, 2008
SLAC Annual Program Review
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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
July 8, 2008
SLAC Annual Program Review
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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
July 8, 2008
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Page 30