Report from KEK H igh gradient study results from Nextef ( + other related activities)

Report from KEK

High gradient study results from Nextef(+ other related activities)

LCWS2011, GranadaSep. 27, 2011

T. Higo

Contents

• Recent high gradient study at Nextef

• Structure fabrication status

• Preparation of another test stand.

2011/9/27 LCWS2011, Granada (Higo) 2

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)

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


HG test result on T24#3

• High gradient performance– BDR evolution– BDR at 100MV/m– Damage

• Deterioration due to earthquake– Air exposure


Processed for 1744 hours.


T24#3BDR evolution at 252nsnormalized 100MV/m


Assuming the same exponential slope as that at 400hr

We understand the BDR has been kept decreasing.

Comparison of BDR in T18, TD18 and T24


TD18#21600hrs

T18 T242800hrs

400hrs

1677hrs

T24#3

T18#2

①

②

③

① ② ③

Nextef: before / after earthquake

14:46 on March 11, 2011Unfixed load was fallen

Accelerator structure was found to be atmospheric pressure.

Running T24


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


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


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.


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)

T24#3: Change of total phase shift before to after high-gradient test

Total 2 degrees roughly +0.16MHz2011/9/27 14LCWS2011, Granada (Higo)

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)


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.


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)

TD24 #4 Initial start up

Power monitor

Waveguide VAC input and output


Initial stage of TD24#4 processing at 51nsec


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]

Comparison of initial ramp upT24 vs TD24


Comparison of initial ramp upT18 vs TD18


Comparison of initial rampingstarting at 51nsec run


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)



Dark current of TD24#4 in its initial stage of processing with 51nsec

Sep.

16-

18

Sep.

27

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)

BD Pulse shapes

forward

reflected

transmitted

FC up and Mid

Reflection phase

Reflection I, Q

BD cell distribution from RF pulse timing

Rather uniform BD location, but maybe two frequent locations?

Rs phase

BD Rs phase mostly in two phases

Input spike as a reference of meas. system

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

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


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.


Recently happened problem


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!?

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.


Transport line KT1 to B being constructed


KT1

B

Nextef expansion is being proceeded


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.


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.


Documents

Report from KEK H igh gradient study results from Nextef ( + other related activities)