Post on 15-Jan-2016
description
Microwave-Based High-Gradient Structures and Linacs
Sami TantawiSLAC
04/21/23 1
Acknowledgment• The work being presented is due to the efforts of
– V. Dolgashev, L. Laurent, F. Wang, J. Wang, C. Adolphsen, D. Yeremian, J. Lewandowski, C. Nantista, J. Eichner, C. Yoneda, C. Pearson, A. Hayes, D. Martin, R. Ruth, S. Pei, Z. Li SLAC
– T. Higo and Y. Higashi, et. al., KEK – W. Wuensch et. al., CERN – R. Temkin, et. al., MIT– W. Gai, et. al, ANL– J. Norem, ANL– G. Nusinovich et. al., University of Maryland– S. Gold, NRL– Bruno Spataro, INFN Frscati
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Overview
• Review of experimental data on high gradient structure
• Efficiency and standing wave accelerator structure designs
• A 1 TeV collider – Improved efficiency– Possible parameter set
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04/21/23
Research and Development Plan
Experimental Studies
• Basic Physics Experimental Studies – Single and Multiple Cell Accelerator Structures (with major KEK and CERN contributions)
• single cell traveling-wave 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)
Can only be done at NLCTA at SLAC
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6 0 8 0 1 0 0 1 2 0 1 4 0
1 0 7
1 0 5
0 .0 0 1
0 .1
A c c e l e r a ti ng G r a d i e nt M V m
Bre
akdo
wnP
roba
bili
ty1pulse
m
600ns
150ns
Flat Top Pulse width
Breakdown Probability for a Standing Wave Accelerator Structure with a/=0.22
Typical gradient (loaded) as a function of time.
PulsedTemp Rise
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1 0 0 1 1 0 1 2 0 1 3 0 1 4 0 1 5 0 1 6 0 1 7 0
1 0 7
1 0 6
1 0 5
1 0 4
0 .0 0 1
0 .0 1
A c c e le r a ting G r a d ie nt M Vm
Bre
akdo
wn
Prob
abili
ty1pulse
m
300ns
200ns
150ns
Flat Top Pulse width
Breakdown Probability for a Standing Wave Accelerator Structure with a/=0.14
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1 0 0 1 2 0 1 4 0 1 6 0 1 8 0 2 0 0
1 0 6
1 0 5
1 0 4
0 .0 0 1
0 .0 1
0 .1
A c c e le ra tin g G ra d ie n t M V m
Bre
akdo
wnP
roba
bilit
y1pulsem
600ns
400ns
200ns
Flat Top Pulse width
Breakdown Probability for a Standing Wave Accelerator Structure with
a/=0.1
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Breakdown Probability for a Standing Wave Accelerator Structure with different
a/=0.21
8 0 1 0 0 1 2 0 1 4 0 1 6 0 1 8 0 2 0 0
1 0 5
1 0 4
0 .0 0 1
0 .0 1
0 .1
A c c e le r a ting G r a d ie nt M Vm
Bre
akdo
wn
Prob
abili
ty1pulse
m
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Breakdown Probability for a Standing Wave Accelerator Structure with different a/
4 0 5 0 6 0 7 0 8 0 9 0
0 . 0 0 1
0 . 0 1
0 . 1
1
P e a k T e m p r a t u r e R i s e C
Bre
akdo
wn
Prob
abili
ty1pulse
m
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9 0 1 0 0 1 1 0 1 2 0 1 3 0 1 4 0 1 5 0
1 0 5
1 0 4
0 .0 0 1
0 .0 1
0 .1
1
G r a d ie nt M Vm
Bre
akdo
wn
Prob
abili
ty1pulse
m
600ns
400ns
200ns
Flat Top Pulse width
Breakdown Probability for a Standing Wave Accelerator Structure with a/=0.22
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9 0 1 0 0 1 1 0 1 2 0 1 3 0 1 4 0 1 5 0
1 0 5
1 0 4
0 .0 0 1
0 .0 1
0 .1
G r a d ie nt M Vm
Bre
akdo
wn
Prob
abili
ty1pulse
m
Cu
CuZr
Hard Cu
Breakdown Probability for a Standing Wave Accelerator Structure with a/=0.22, Pulse
length=200ns
CuCr
We have not tested yet structure with small apertures and different material“Stay Tuned” This is coming very soon
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0 . 0 0 . 2 0 . 4 0 . 6 0 . 8 1 . 0 1 . 2
0 . 0
0 . 5
1 . 0
1 . 5
2 . 0
D i s t a n c e c m
Es/Ea
(Zo Es Hs)1/2/Es
Hs/Es
Field Profile over the Iris
DistanceThose two peaks are correlated for structures with different t and a/
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Peak H and Peak ExH
1 .1 1 .2 1 .3 1 .4 1 .5 1 .6
1 .2
1 .3
1 .4
1 .5
1 .6
P e a k H sE a
Peak
Zo
HsE
sE
a
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Research and Development Plan
CumulatedPhase Change
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 structure55.5MW100MV/m
Full Accelerator structure testing ( the T18 structure)
5.1~__ inaccoutacc EE
120°
FieldAmplitude
•Structure designed by CERN based on all empirical laws developed experimentally through our previous work•Cells Built at KEK•Structure was bonded and processed at SLAC•Structure was also tested at SLAC
04/21/23 Page 18
100 150 20010
-7
10-6
10-5
10-4
RF Flat Top Pulse Width: ns
BK
D R
ate:
1/p
ulse
/m
95 100 105 110 11510
-7
10-6
10-5
10-4
Unloaded Gradient: MV/m
BK
D R
ate
: 1/p
uls
e/m
RF BKD Rate Gradient Dependence for 230ns Pulse at Different Conditioning Time
After 250hrs RF Condition
After 500hrs RF Condition
After 900hrs RF Condition
RF BKD Rate Pulse Width Dependence at Different Conditioning Time
G=108MV/m
G=108MV/m
G=110MV/m
RF Processing of the T18 Structure
After 1200hrs RF Condition
This performance may be good enough for 100MV/m structure for a warm collider, however, it does not yet contain all necessary features such as wakefield damping. Future traveling wave structure designs will also have better efficiency
04/21/23 Page 19
2007-09 CERN/CLIC Design Structures Tested at NLCTA
In Beamline Structure Note Performance
11/06 – 2/07 C11vg5Q16First X-band Quad
- Irises Slotted Poor: 57 MV/m, 150 ns, 2e-5 BDR – grew
whiskers on cell walls
2/08 - 4/08C11vg5Q16
Redux Refurbished
Initially good (105 MV/m, 50 ns,1e-5 BDR) but one cell degraded
4/07 – 10/07 C11vg5Q16-MoMolybdenum Version of
AbovePoor: 60 MV/m, 70 ns, 1e-6 BDR
10/08 – 12/08 TD18vg2.6_QuadNo Iris Slots but WG
DampingVery Poor: would not process above 50 MV/m,
90ns – gas spike after BD
4/08 – 7/08 T18vg2.6-DiskCells by KEK, Assembled
at SLACGood: 105 MV/m, 230 ns at LC BDR spec of
5e-7/pulse/m but hot cell developed
7/08 – 10/08 T18vg2.6-DiskPowered from
Downstream EndGood: 163 MV/m, 80 ns, 2e-5 BDR in last cell,
consistent with forward operation
12/08 – 2/09T18vg2.6-Disk
CERNCERN Built, Operate in
Vac CanVery Poor: very gassy with soft breakdowns at
60 MV/m, 70 ns
(Yellow = Quad Cell Geometry, Green = Disk Cell Geometry)
Emax/Ea
HmaxZ0/Ea
SQRT(EmaxHmaxZ0)/Ea
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SQRT(EmaxHmaxZ0)/EaHmaxZ0/Ea
Emax/Ea
SW a/=0.22
SW a/=0.14
SW a/=0.1
SW
T18 Surface Field Parameters in Comparison with SW Structures
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So, What does all this imply for a 1 TeV collider parameters?
• High gradient requires high power density/unit length, quadratic with
gradient. Hence the two beam choice for the CLIC design
• However, since one also accelerates in shorter length the total required RF
power increases linearly with gradient.
• High gradient also implies reduced efficiency;
• However, one can compensate by increasing the efficiency the accelerator
structure and RF sources.
– Increasing the efficiency of the accelerator structure would reduce the power/unit
length, and it might allow for the use of a conventional RF unit
– At the moment the best ( published ) design that respects high gradient constraints
imply an RF to beam efficiency of about 28%
– Higher efficiency RF source and accelerator efficiency imply lower RF system cost
0~ ;1
s
a
x R Ix Ex
04/21/23 22
Yet another Finite Element Code
Motivated by the desire•to design codes to perform Large Signal Analysis for microwave tubes (realistic analysis with short computational time for optimization)•study surface fields for accelerators•the need of a simple interface so that one could “play”
•A finite element code written completely in Mathematica was realized. •To my surprise, it is running much faster than SuperFish or Superlance•The code was used with a Genetic Global Optimization routine to optimize the cavity shape under surface field constraints
0 .2 0 .4 0 .6 0 .8 1 .0
0 .1
0 .2
0 .3
0 .4
0 .5
0 .6
1 2 3 4 5
0 .4
0 .6
0 .8
1 .0
Surface field penalty function
04/21/23 23
Iris shaping for a structure with a/=0.14
Shunt Impedance 83 M/mQuality Factor 8561Peak Es/Ea 2.33Peak Z0Hs/Ea 1.23
Shunt Impedance 104 M/mQuality Factor 9778Peak Es/Ea 2.41Peak Z0Hs/Ea 1.12 •With 1 nC/bunch and bunch separation of 6 rf cycles the RF to beam efficiency~70%•The power required/m~287 MW
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Iris shaping for a structure with a/=0.1
Shunt Impedance 102 M/mQuality Factor 8645Peak Es/Ea 2.3Peak Z0Hs/Ea 1.09
Shunt Impedance 128 M/mQuality Factor 9655Peak Es/Ea 2.5Peak Z0Hs/Ea 1.04•With 0.5 nC/bunch, bunch separation of 6 rf cycles, and loaded gradient of 100 MV/m the RF to beam efficiency~53%•The power required/m~173 MW
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Feeding and Wakefield damping of a set of -mode structures
•Each cell is fed through a directional coupler. •The feeding port serve as the damping port•The system has a four-fold symmetry, only one section is shown
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Parameter Options for a 1 TeV machine, 2 1034 cm-2 s-1
Option-1 Option-2 Option-3
Frequency (GHz) 11.424
Gradient (MV/m) 100 100 80
Power/meter (MW)
287 173 126
Charge/bunch (nC) 1 0.5 0.5
Bunch separation ( RF cycles)
6
Number of bunches 300 600 600
<a/> 0.14 0.1 0.1
RF source Two beam Two Beam/Conventional
Unit
Conventional Unit
RF/Beam Efficiency(%) 73 53 60
Beam duration Pulse length (ns)
158 315 315
Repetition Rate (Hz) 60 60 6004/21/23 27
Conclusion
• With recent advances on high gradient accelerator structures, it is possible to think of an “efficient” room temperature collider
• Reduced power levels/unit length may permit designs based on conventional RF unit.
04/21/23 28