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ASTACapabilities and Projects
Accelerator Structure Test AreaHigh power X-band accelerator structure test facility
Deliver high power pulsed RF to high gradient accelerator structures
Based on lessons learned at the NLCTA
Stephen Weathersby
Capabilities
High gradient X-band testing of accelerator structures regularly exceeding 100 MV/m gradient
Up to ~300 MW peak power delivered to the structure by combining the power of two XL4 klystrons into a delay line pulse compression system.
Consists of two modulators, two klystrons, delay lines for pulse compression, a radiation enclosure, PPS system, interlocked vacuum and cooling water systems, llrf system, diagnostics and data acquisition…
Past RF gun testing incorporated a UV cathode laser system and small beam line with a beam spectrometer.
S-Band capability
High power RF capabilities
From Two 50 MW Klystrons
Variable irisVariable Delay line length through variable mode converter
Gate Valves
Two experimental stations inside the enclosure, one with compressed pulse and the other without the benefit of the pulse compressor.
With two 50MW XL4 klystrons ASTA can produce: 100MW @ 1.5 μs --> 550MW @ 63 ns at X-band and feed twoexperimental outputs in the enclosure.
Courtesy of Valery Dolgashev
components to support the experimental facilities
Tee for variable iris
Bends for low loss transmission and reliable RF systems
Dual moded delay lines with variable delay for a flexible pulse width
Courtesy of Sami Tantawi
Gate valve
SRS60 Hz
AFG
AFGTWT K
TWT K
llrf configuration
I&QMIXER
I&QMIXER
SRSDG645
4 port combiner
no SLED
SLED
Power meters Dark current signals
DUT FE/REKlystron RE
Vacuum
Pulse compression and pulse shaping
Each bin of has independent I&Q modulation via two channel AFGs
Forward power RF signals are I&Q demodulated and can be used in pulse shape feedback
Delay line tuning is handled by feedback
Pulse compressor forward power
Breakdown rates vs gradient
forward powerreflected powerfaraday cup 1faraday cup 2
Faraday cup signals register breakdowns and inhibit further pulsesGradient is calculated. Several weeks for typical structure characterizationGS/s acquisition ratesBreakdown traces are savedAutomated processing
50 100 150 20010 -7
10 -5
0.001
0.1
Gradient [M V /m ]
Bre
akdw
nP
roba
bilit
y[1
/pul
se/m
]
Breakdown rate vs. pulse length for C10-VG07
260 ns
130 ns
Accelerating structures
RF power
PETS
Main beamDrive beam Courtesy of Alessandro Cappelletti
Peak powerAvg powerEnergyBD
CERN CLIC PETS3 Testing
133 ns 266 ns
Revised: April 7, 2010
Jake Haimson
Recirculation Implementation
Some ongoing and planned HG studies
Test of a Vacuum Brazed CuZr and CuCr Structures
High Gradient Structures--AAC 2010Page 11
8 0 9 0 1 0 0 11 0 1 2 0 1 3 0 1 4 0 1 5 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 rad ien t M V m Bre
akdo
wnP
roba
bilit
y1pulsemeter
a 0.215, t 4.6mm , C uC r SLA C 1a 0.215, t 4.6mm , C uZ r SLA C 1a 0.215, t 4.6mm , F rascat i 2
Normal copper
Diffusion bonding and brazing of copper zirconium are being researched at SLAC.
Clamping Structure for testing copper alloys accelerator structure
•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.•Furthermore, it will provide us the opportunity to test hard materials without annealing which typically accompany the brazing process
Clamped Structure
Test of Hard Copper
Hard Copper showed an observable improvements of annealed brazed structures
Clamped Structure with Hard Copper cells
High Gradient Structures--AAC 2010Page 13
8 0 9 0 1 0 0 11 0 1 2 0 1 3 0 1 4 0 1 5 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 rad ien t M V m
Bre
akdo
wnP
roba
bilit
y1pulsemeter
a 0.215, t 4.6mm , C lamp ed SLA C 1
a 0.215, t 4.6mm , F rascat i 2
Cryogenic RF material testing at SLAC
• Test bed for novel SRF materials– Finding materials with higher quenching RF magnetic field
• Leading to higher gradient in SRF accelerator structures• Samples in different forms, thin film or bulk, multilayer, etc
– Unique X-band system with compact size and short pulses, resulting lower pulsed heating
– Quick testing cycles with small samples – Surface resistance characterization
Cavity design
High-Q cavity under TE013 like mode
Q0,4K=~224,000Q0,290K=~50,000(measured from bulk Cu samples)
Fres, design=~11.399GHzFres, 290K=~11.424GHzFres, 4K=~11.46GHz
Q0,4K=~350,000(Estimated for zero resistivity samples, using measured Cu sample results)
Sample R=0.95”
Tc~3.6µs(using Q value for copper at 4K) Qe~310,000
• High-Q hemispheric cavity under a TE013 like mode
– Zero E-field on sample– Maximize H-field on the sample, peak
on bottom is 2.5 times of peak on dome– Maximize loss on the sample, 36% of
cavity total– No radial current on bottom
• Copper cavity body– Stable, no transition or quenching– Higher surface impedance– Coupling sensitive to iris radius
• Nb cavity body being designed– Lower loss for more accurate surface
impedance characterization– Qext is much higher with smaller iris
H E
Selected test results: MgB2 on Sapphire
0
5 104
1 105
1.5 105
2 105
2.5 105
3 105
3.5 105
4 105
0 5 10 15 20 25 30 35 40
300nm MgB2 thinfilm on SapphireQ vs T
H=10mT vs low power04082010
Q0 from scope w/ Qe_NWQ0(MgB2_LP_04062010_corr)
Q0
fro
m s
cop
e w
/ Q
e_
NW
TSample(K)
5 104
1 105
1.5 105
2 105
2.5 105
3 105
3.5 105
4 105
10 15 20 25 30
MgB2 thinfilm on SapphireQvsH
T=3K, 04082010
Q0 from scope w/ Qe_NW
Q0
fro
m s
cop
e w
/ Q
e_
NW
Hpeak from Pf/Ue(mT)
Experimental Evaluation of Magnetic Field role in Breakdown Rate
Experiments with short standing wave structures and specifically with structures where magnetic field is increased due input slots or field-confining rods (PBG) showed that magnetic field plays an important role in determining the gradient limit.
Before we studied effect of rf magnetic fields on rf breakdown high-magnetic-field and low-magnetic-field waveguide tests (V.A. Dolgashev, S.G. Tantawi, RF Breakdown in X-band Waveguides, EPAC02)
Here we suggest a test that separately controls electric and magnetic fields using the TE01 and the TM02 modes
A standing wave accelerator cell with iris dimensions similar to standing wave accelerator structure
Electric Field along the surface
TM02 Mode with resonance frequency 11.443GHz
Feed with TM01 mode converter
S. Tantawi
A standing wave accelerator cell with iris dimensions similar to standing wave accelerator structure
Feed with TE01 mode converter
Magnetic Field along the surface
TE01 Mode with resonance frequency 11.4244GHz
S. Tantawi
Rf Breakdown at Cryogenic Temperatures at ASTA
We plant to test hypotheses that connect statistical properties of rf breakdowns to dislocation dynamics in metals: this dynamics dramatically changes at cryogenic temperatures
Single-Cell-SW structure
TM01 input waveguide
S. Tantawi et al.
Cryostat
“Cold head” of refrigerator
• Crystal migration due to pulse heating― Interferometer― High resolution microscopy
• Pulse temperature measurement by High-Speed Radiation Thermometer
• Particles observation by Laser scattering
In-Situ Observation of Metal Surface (KEK, SLAC)
SW structure New pulse heating cavity
Future plans for ASTA
• EPICS for remote monitoring and control• Spectrometer to measure gradient• Phase measurements and breakdown
localization• 24 hour unattended operation• Move cryostat to ASTA
Thanks for your attention