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Report from KEK
High gradient study results from Nextef(+ other related activities)
LCWS2011, GranadaSep. 27, 2011
T. Higo
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Contents
• Recent high gradient study at Nextef
• Structure fabrication status
• Preparation of another test stand.
2011/9/27 LCWS2011, Granada (Higo) 2
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Recent high gradient study at Nextef
• T24_Disk_#3– HG study in a usual manner– Earthquake and following deterioration– Total phase advance
• TD24_Disk_#4– Initial processing status
2011/9/27 3LCWS2011, Granada (Higo)
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T24 versus TD24
0 4 8 12 16 20 24240
50
100
150
200
250
iris number
P [
MW
] (b
lack
), E
s (
gre
en),
Ea (
red
) [M
V/m
],
T
[K
] (b
lue)
, S
c*50
[MW
/mm
2 ] (m
agen
ta)
7.5 8.4
176
205
3.03.2
90
108
41.1
23.4
Pinload = 41.1 MW, P
outload = 23.4 MW
Eff = 0.0 % tr = 0.0 ns, t
f = 0.0 ns, t
p = 100.0 ns
0 5 10 15 20 250
50
100
150
200
250
iris number
P [
MW
] (b
lack
), E
s (
gre
en),
Ea (
red
) [M
V/m
],
T
[K
] (b
lue)
, S
c*50
[MW
/mm
2 ] (m
agen
ta)
24.6 21.7
183193
3.3
2.9
94102
44.4
20.6
Pinload = 44.4 MW, P
outload = 20.6 MW
Eff = 0.0 % tr = 0.0 ns, t
f = 0.0 ns, t
p = 100.0 ns
Average unloaded of 100 MV/m
Difference is in pulse heating
Design by A. Grudiev
2011/9/27 4LCWS2011, Granada (Higo)
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HG test result on T24#3
• High gradient performance– BDR evolution– BDR at 100MV/m– Damage
• Deterioration due to earthquake– Air exposure
2011/9/27 5LCWS2011, Granada (Higo)
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Processed for 1744 hours.
2011/9/27 6LCWS2011, Granada (Higo)
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T24#3BDR evolution at 252nsnormalized 100MV/m
2011/9/27 7LCWS2011, Granada (Higo)
Assuming the same exponential slope as that at 400hr
We understand the BDR has been kept decreasing.
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Comparison of BDR in T18, TD18 and T24
2011/9/27 LCWS2011, Granada (Higo) 8
TD18#21600hrs
T18 T242800hrs
400hrs
1677hrs
T24#3
T18#2
①
②
③
① ② ③
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Nextef: before / after earthquake
14:46 on March 11, 2011Unfixed load was fallen
Accelerator structure was found to be atmospheric pressure.
Running T24
2011/9/27 9LCWS2011, Granada (Higo)
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After earthquake
0
200
400
600
800
1000
1200
1400
1600
1800
2000
0
20
40
60
80
100
120
140
160
0 500 1000 1500 2000 2500
Pulse width, # A
CC-BD<E
acc>
MV
/m
RF-On time [hr]
T24#3 History run1-41From Dec. 6, 2010 To Jul. 11, 2011(2206hrs)
F50 width [ns]
<Eacc> MV/m
#ACC-BD
震災
Processed For 2206hours.
Before earthquakeAfter
91ns
2011/9/27 10LCWS2011, Granada (Higo)
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BD location before and after earthquake
Run 32-34 = before at 412nsec, 110-120MV/mRun 38-39 = after 91nsec, ~100 MV/m
Breakdowns are located uniformly over full accelerator structure span. This behavior has been kept.
0
1
2
3
4
5
6
7
8
9
Cell Location of ACC-BD
#ACC-BD by Cell Locations
Before Earthquake
After Earthquake
T24#3 run 32-34 (N=86)T24#3 run 38-39 (N=32)
Before After
2011/9/27 11LCWS2011, Granada (Higo)
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Deterioration due to earthquake• WR90 waveguide was ruptured and the
structure was purged to almost 1 atm pressure.
• Processing memory was gone. Frequent breakdowns made it necessary to reach 100 MV/m even pulse width shortened to 91nsec pulse.
• Breakdown location was kept uniform before and after the earthquake.
2011/9/27 12LCWS2011, Granada (Higo)
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Trial to estimate the frequency change due to HG operation
Total phase advance from input to output
Received from SLAC Measurement setup at cleanroom
Measurement in cleanroom before HG test2011/9/27 13LCWS2011, Granada (Higo)
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T24#3: Change of total phase shift before to after high-gradient test
Total 2 degrees roughly +0.16MHz2011/9/27 14LCWS2011, Granada (Higo)
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Estimated frequency change
120/cell before HG
Freq
up
by H
G
Freq
dn
by
0.3d
egC
Less phase advance after HG
cellNf
f
cvg
/
120
Phase reading
Actual phase
+2 deg
)(exp zktj
Less phase advance
0.3 degC - 0.06MHz2 degree +0.1MHz (<vg/c=1.2% assumed)
2011/9/27 15LCWS2011, Granada (Higo)
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Deterioration in 10 years?• Roughly speaking, +0.16MHz over 1000hours at
100MV/m• If the same frequency shift continues at the same rate,
10-year operation results in ~10MHz, too large.• Thanks to the BDR reduction as time, we hope this to be
much smaller! It should be confirmed in the long running evaluation.
• The evaluation should be confirmed with bead pull. It is being prepared now.
• It also should be established in an actual prototypes, damped structures.
2011/9/27 LCWS2011, Granada (Higo) 16
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TD18_Disk
Possible breakdown triggered from high magnetic field area
Milling + Turning + Light etching <
1mm
Hs maximum point
17
Near max Hs
SEM inspection by CERN on eq. acc str, TD18#3
Markus Aicheler 13. Oct. 2010
Hs max
Pulse heat
damage
Strange shape at highest Hs point2011/9/27 LCWS2011, Granada (Higo)
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TD24 #4 Initial start up
Power monitor
Waveguide VAC input and output
2011/9/27 18LCWS2011, Granada (Higo)
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Initial stage of TD24#4 processing at 51nsec
2011/9/27 19LCWS2011, Granada (Higo)
Tentative in EaccPreliminaly estimated to be a little low
Here and following pages for TD24
0 20 40 60 80 100 120 140 160 180 2000
10
20
30
40
50
60
70
80
0
100
200
300
400
500
600
700
800
900
1000
TD24#4 History run1-8From Aug. 10, 2011 To Sep. 21, 2011(176hrs)
<Eacc> MV/m
#ACC-BD
F50 width [ns]
RF-On time [hr]
<Eac
c> M
V/m
Pulse width, # ACC-BD
Processed For 176hours.
Eac
c [M
V/m
] (
pre
lim
inar
y)
RF-ON time [hrs]
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Comparison of initial ramp upT24 vs TD24
2011/9/27 20LCWS2011, Granada (Higo)
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Comparison of initial ramp upT18 vs TD18
2011/9/27 21LCWS2011, Granada (Higo)
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Comparison of initial rampingstarting at 51nsec run
2011/9/27 22LCWS2011, Granada (Higo)
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Initial startup characteristics
• Damped is slower than undamped.• 24-cell structures seem faster than 18-cell.
• TD24 #4 are being ramped up at initial shortest pulse width 51nsec.
• The recovery route and speed from BD is determined by the KEK protocol. (Keep Tp)
2011/9/27 23LCWS2011, Granada (Higo)
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2011/9/27 24LCWS2011, Granada (Higo)
Dark current of TD24#4 in its initial stage of processing with 51nsec
Sep.
16-
18
Sep.
27
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Comparison of dark currentT18_Disk TD18_Disk T24_Disk
25
Undamped 90~100 MV/m damped 70~80MV/m
TD24_Disk
2011/9/27 LCWS2011, Granada (Higo)
0.01
0.1
1
10
100
50 60 70 80 90100 200
T18_#2 Dark Current evolution081128-081224-090224-090414-090515
FC-Mid [microA] (081128)
FC-Mid [microA] (081224)
FC-Mid microA (253ns, 090225)
FC-Mid microA (253ns, 090414)
FC-Mid microA 090515
FC-Mid microA
Eacc [MV/m]
Eacc for peak dark current of 10 m 90MV/m 70MV/m 100MV/m (80MV/m)
(51ns processing)
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BD Pulse shapes
forward
reflected
transmitted
FC up and Mid
Reflection phase
Reflection I, Q
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BD cell distribution from RF pulse timing
Rather uniform BD location, but maybe two frequent locations?
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Rs phase
BD Rs phase mostly in two phases
Input spike as a reference of meas. system
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BD-cell location versus Rs phase
BD cells are uniformly located but Rs in two phases, as described in the previous slides.
Rs phase at its peak Rs phase at BD timing
BD c
ell
BD c
ell
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Summary of test result TD24#4
• Processing speed is faster than TD18 and slower than T24
• BD location distribution is roughly uniform• BD reflection phase shows two peaks• Initial-stage dark current is less than TD18 but
higher than T24• It is kept running for 24hr/day need to wait
a month to reach nominal CLIC operation
2011/9/27 30LCWS2011, Granada (Higo)
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Structure fabrication• TD24R05 #1--#4
– #1--#2 in assembly at SLAC– #3--#4 on the way to SLAC
• TD24R05 12GHz– Problem found: it prevents from proper stacking– Additional cut is being made
• DDSA 12GHz test cell– Five test cells will delivered to KEK on Sep. 26– Stack measurement is in preparation
• We are struggling to deduce the relation between machining and high-gradient performance.
2011/9/27 31LCWS2011, Granada (Higo)
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Recently happened problem
2011/9/27 LCWS2011, Granada (Higo) 32
Cell stacking schematic with self fitting feature
Measurement of TD24R05(12GHz)
Bad corner radius shape in male side
Same problem may happen in other KEK-made cells!?It may enhance BD, though without vacuum problem!?
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Toward basic study on high gradient
• Single-cell setups are being prepared• Large-grain material is included as material to
be used to simplify the study• Setup is being prepared at another test stand,
called “shield-B” being driven by a single klystron at KT-1.
2011/9/27 33LCWS2011, Granada (Higo)
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Transport line KT1 to B being constructed
2011/9/27 LCWS2011, Granada (Higo) 34
KT1
B
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Nextef expansion is being proceeded
2011/9/27 35LCWS2011, Granada (Higo)
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Reusable coupler: TM01 Mode Launcher
Surface electric fields in the mode launcher Emax= 49 MV/m for 100 MW
SLAC made a set of launchers for KEK basic tests.KEK will prepare single cell test setups.
2011/9/27 LCWS2011, Granada (Higo) 36
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Conclusion • The high gradient test of T24 was finished
with low-enough BDR value with its continuing evolution.
• Processing of TD24 was recently started. Initial processing speed is slower than T24 but a bit faster than TD18. Sounds reasonably well behaved at 51ns, >80MV/m level now.
• Another test system is being constructed for basic studies at KEK.
2011/9/27 37LCWS2011, Granada (Higo)