Transcript Slide 1

High power RF capabilities
With two 50MW XL4 klystrons ASTA can produce:
100MW @ 1.5 μs --> 550MW @ 63 ns at X-band and feed two
experimental outputs in the enclosure.
Gate Valves
Variable iris
Variable Delay line length
through variable mode
converter
From Two 50 MW Klystrons
Two experimental stations inside the enclosure,
one with compressed pulse and the other without
the benefit of the pulse compressor.
Courtesy of Valery Dolgashev
components to support the
experimental facilities
Gate valve
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
llrf configuration
Power meters
Dark current signals
DUT FE/RE
Klystron RE
Vacuum
I&Q
MIXER
TWT
K
4 port combiner
SRS
60 Hz
AFG
SRS
DG645
AFG
I&Q
MIXER
TWT
K
no SLED
SLED
Pulse compression and pulse
shaping
Pulse compressor forward power
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
Breakdown rates vs gradient
Breakdwn Probability [1/pulse/m]
forward power
reflected power
faraday cup 1
faraday cup 2
Breakdown rate vs. pulse length for C10-VG07
0.1
260 ns
0.001
10
-5
10 -7
130 ns
50
100
Gradient [MV/m]
Faraday cup signals register breakdowns and inhibit further pulses
Gradient is calculated.
Several weeks for typical structure characterization
GS/s acquisition rates
Breakdown traces are saved
Automated processing
150
200
CERN CLIC PETS3 Testing
133 ns
266 ns
Peak power
Avg power
Energy
BD
Drive beam
Main beam
Courtesy of Alessandro Cappelletti
PETS
Accelerating
structures
RF power
Recirculation Implementation
Revised: April 7, 2010
Jake Haimson
Some ongoing and planned HG studies
BreakdownProbability 1 pulsemeter
Test of a Vacuum Brazed CuZr and CuCr Structures
100
10
1
10
2
10
3
10
4
10
5
10
6
10
7
80
Normal copper
a
a
a
90
100
110
120
Gradient MV m
High Gradient Structures--AAC
2010
Page 11
0.215, t 4.6mm, Frascati 2
0.215, t 4.6mm, CuZr SLAC
0.215, t 4.6mm, CuCr SLAC
130
140
150
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1
Clamped Structure
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
Test of Hard Copper
Clamped Structure with Hard
Copper cells
Hard Copper showed an observable
improvements of annealed brazed structures
BreakdownProbability 1 pulsemeter
100
10
1
10
2
10
3
10
4
10
5
10
6
10
7
80
90
100
110
a
0.215, t 4.6mm, Frascati
a
0.215, t 4.6mm, Clamped SLAC 1
120
Gradient MV m
High Gradient Structures--AAC
2010
Page 13
130
140
2
150
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
H
E
• 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
Sample
Fres, design=~11.399GHz
Fres, 290K=~11.424GHz
Fres, 4K=~11.46GHz
Tc~3.6µs(using Q value
for copper at 4K)
– Stable, no transition or quenching
– Higher surface impedance
– Coupling sensitive to iris radius
R=0.95”
Q0,4K=~224,000
Q0,290K=~50,000
(measured from
bulk Cu samples)
Qe~310,000
Q0,4K=~350,000
(Estimated for zero
resistivity samples,
using measured Cu
sample results)
• Nb cavity body being designed
– Lower loss for more accurate surface
impedance characterization
– Qext is much higher with smaller iris
300nm MgB2 thinfilm on Sapphire
Q vs T
H=10mT vs low power
04082010
4 10
5
5
3.5 10
5
5
3 10
5
3 10
2.5 10
5
2.5 10
5
2 10
5
2 10
5
1.5 10
5
1.5 10
5
1 10
5
1 10
5
5 10
4
5 10
4
4 10
5
3.5 10
Q0 from scope w/ Qe_NW
Q0 from scope w/ Qe_NW
Selected test results: MgB2 on Sapphire
Q0 from scope w/ Qe_NW
Q0(MgB2_LP_04062010_corr)
MgB2 thinfilm on Sapphire
QvsH
T=3K, 04082010
Q0 from scope w/ Qe_NW
10
15
20
0
0
5
10
15
20
TSample(K)
25
30
35
40
Hpeak from Pf/Ue(mT)
25
30
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
Feed with TM01 mode converter
Electric Field along the surface
TM02 Mode with resonance frequency 11.443GHz
S. Tantawi
A standing wave accelerator cell with iris dimensions
similar to standing wave accelerator structure
Magnetic Field along the surface
TE01 Mode with resonance frequency 11.4244GHz
Feed with TE01 mode converter
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
Cryostat
“Cold head” of refrigerator
Single-Cell-SW structure
TM01 input waveguide
S. Tantawi et al.
In-Situ Observation of Metal Surface (KEK, SLAC)
• Crystal migration due to pulse heating
― Interferometer
― High resolution microscopy
• Pulse temperature measurement by High-Speed Radiation
Thermometer
• Particles observation by Laser scattering
SW structure
New pulse heating cavity
Future plans for ASTA
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•
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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