Status of high gradient experiments at Nextef

Kazue Yokoyama, Toshiyasu Higo, Yasuo Higashi,Shuji Matsumoto, Shigeki FukudaAccelerator Laboratory, KEK

T18_VG2.4_Disk #2 at NextefTD18_VG2.4_Quad_#5 at KEKNarrow waveguide at KT-1

2/27

T18_VG2.4_Disk #2

Disk-damp cell

3/27

T18_VG2.4_Disk #2

T18_VG2.4_Disk #2 was installed and the processing has started in October last year.

4/27

Nextef: RF Monitors along waveguide

5/27

Nextef: Monitors along beam axis

Steady state dark currents were evaluated at the Faraday cups (FC) at upstream and downstream of the beam line.

Downstream dark current can be energy analyzed.

RF

T18 trend

0

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120

0

500

1000

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2000

2500

3000

0 500 1000 1500 2000 2500

T18_VG2.4_Disk #2 Processing Historypower history at breakdown

(power meas. from DPO Top value by Ushimoto)

<Eacc> 51nsec Ushi

<Eacc> 113ns Ushi

<Eacc> 173n ushi

<Eacc> 213n Ushi

<Eacc> 253ns Ushimoto

Eacc keep 253ns Ushi

Eacc 51ns Ushi

Eacc 113ns Ushi

Eacc 173ns Ushi

Eacc 213ns Ushi

Eacc 253ns Ushi

Total BD

<Eacc> MV/m

Total# BD

RF-ON integrated (hr)

090221

6/27

T18_VG2.4_Disk_#2 in 2008Power trend recorded by control program November

December80MV/m (35MW) steady run

7/27

Power at BD’s and BDR during 27 days at 80MV/m (35MW) level

BDR

~17 str. BD / 566 hr

~0.030 BD/hr/str

~0.75 x10-6 BD/Pulse/m0

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20

30

40

50

0 100 200 300 400 500 600

BD power vs RF-ON period from Nov. 28-Dec. 25

Power MW Excessive power relatedPower FC-UP

Pow

er

M

W

(cal

ib. n

eede

d)

RF ON Period (hours)

Total 20 BD's/585hrs (3 BD's are over pulse driven)

Power is calculated from DPO with a background subtraction

Finished at 9:00 on Dec. 25

Started at 10:00 on Nov. 28

566 hrs run / 643 hrs= 88% ON

8/27

~10-5 ~10-6

Dark current trend during 35MW run

75cm 75cm 195cm

FC-DN

FC-UP

FC-Mid AM

0.01

0.1

1

10

50 55 60 65 70 75 80 85 90

Dark Current UP at 252ns, 35MW

FC-UP (081128) [microA]FC-UP (081203) [microA]FC-UP (081213) [microA]FC-UP (081224) [microA]

FC [microA]

<Eacc> MV/m

0.1

1

10

100

50 55 60 65 70 75 80 85 90

Dark Current Mid at 252ns, 35MW

FC-Mid (081128) [microA]FC-Mid (081203) [microA]FC-Mid (081213) [microA]FC-Mid (081224) [microA]

FC-Mid [microA]

<Eacc> MV/m9/27

Dark Current F-N plot

10-6

10-5

10-4

10-3

0.01 0.012 0.014 0.016 0.018 0.02

Dark Current FN-UP trend during 252ns run081128 - 081203 - 081213 - 081224

I_UP/Eacc^2.5 (081128)I_UP/Eacc^2.5 (081203)I_UP/Eacc^2.5 (081213)I_UP/Eacc^2.5 (081224)

I_UP/Eacc^2.5

1/<Eacc>

= 56

10-6

10-5

10-4

10-3

0.01 0.012 0.014 0.016 0.018 0.02

Dark Current FN-Mid trend during 252ns run081128 - 081203 - 081213 - 081224

I_Mid/Eacc^2.5 (081128)I_Mid/Eacc^2.5 (081203)I_Mid/Eacc^2.5 (081213)I_Mid/Eacc^2.5 (081224)

I_Mid/Eacc^2.5

1/<Eacc>

= 61

10/27

Typical breakdown rate: on Feb. 17

Nor

mal

pul

se

AC

C

BD

Nor

mal

p

BD

?

Nor

mal

Nor

mal

pul

seN

orm

al p

ulse

Nor

mal

pul

seN

orm

al p

ulse

BD

?

Nor

mal

pul

se

BD

?

AC

C

BD

65MW = 109MV/m run

2~3

BD

?

Include ACC-BD + all BD? 8 BD / 14hr < 0.6BD/hr ~ 3x10-6/pulse ~ 1.5x10-5/pulse/m

Need to analyze whether BD or not.

Now on the way to evaluate the breakdown rate carefully. 11/27

12/27

Summary of T18_VG2.4_Disk #2

Breakdown rates at steady-stare operation of 80 MV/m is approximately 0.75 x10-6 BD/Pulse/m .

We are going to do the high gradient experiments until the end of March.

The total run time will reach up to about 3000 h.

We are trying to estimate the BDR from the dark currant measurements.

13/27

TD18_VG2.4_Quad_#5

Quadrant

Measurement of TD18_VG2.4_Quad_#5

11.1 11.2 11.3 11.4 11.5 11.6 11.7-60

-55

-50

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-40

-35

-30

-25

-20

-15

-10

-5

0

5

10

Frequency (GHz)s1

1 (d

B)

-120

-100

-80

-60

-40

-20

0

s21

(dB

)

-24dB@11.424GHz

-2.57dB@11.424GHz

Port 1

NA

Port 2load

1 2

3 4

Quad

Measurements at CERN for TD18_quad made in CERN give -2.23 dB.

Comparing to this, KEK quad gives 2.56dB measured in transmission mode. About 0.33dB more attenuation due to some reason.

-2.56dB = t=0.295 Q/Q~83% is all attributed to t~1/Q

14/27

The result of the first measurement by Bead pull

50 100 150 200 250 300

0.005

0.01

0.015

0.02

0.025

Amplitude versys ZpositionInputOutput

reflection amplitude

MeasurementN5230A F_IF=1kHz, 3ptsFreq=11424MHzTcavity=20.9CPulse motor step ~ 0.2mmRF Input from input coupler side

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Quad_BeadPull_20090210-1

imag

real

15/27

Meas. At 11416MHz, 20.3degC

0 5 10 15

-160

-140

-120

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-80

-60Phase advance per cell

Average phase advance = 118.1 deg/cell

dF ~ (1.9/120)*11424*0.0138~ (11416 + 2.6) ~ 11418.6MHz

Average phase advance per cell -118.086 degrees / cell

-0.02 -0.01 0.01

-0.01

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0.02

Dwell point BLUE regular cells, REDend cells, GRNcntr of rglr

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20

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3

4

1619

17 18

16/27

Summary of TD18_VG2.4_Quad_#5 The frequency of the present

quad #5 at operation becomes 11418.6 MHz.

Freq. = 11420.6MHz with120deg/cell at operation should be tuned up by 3.4MHz.

Test tuning has started last week.

We do tuning accurately at the operation frequency after EBW of cooling connection.

High-gradient experiments will start in April.

v=cDrive

frequency

Actual

17/27

18/27

Narrow waveguide

Parts before bonding

Rectangular Waveguide: WR90Wavelength converter: Width 22.86(g 32.15 mm) → 14mm (g 76.59 mm)Cosine taper ( 1 g) : Height 10.16 mm → 1 mmCalculated to get a low VSWR by an HFSS.

Narrow Waveguide Design

field gradient of 200 MV/m at an RF power of 100 MW

group velocity of around 0.3c

19/27

CU004 Setup for High-Power processing @ Nextef

We are on going high power testing of coupper(CU004) at Klystron Test Stand.

PPM Klystron@11.424 GHz50 MW, 50 pps, 400ns

Narrow waveguidein 5mm lead shield

High powerDummy Load(Load Tree)

Cu002 tested at XTF(06.11 ～ 07.01) Moving to Nextef( ～ 07.04) Using for system

checking ( ～ 07.05) SUS003 Tested at KT-1 ( ～ 08.10) Cu004 Testing at KT-1(09.01 ～ )

20/27

PMT 1, 2, 3, 4

Acoustic sensors

Processing history (Accumulated No. breakdown events vs. power

RF pulse ranged 50ns to 400ns with 50MW at repetition rate of 50pps. SUS003 had less breakdown events than CU002. SUS003 attained higher electric field than Cu002.

@XTF @Nextef

21/27

22/27

104 120 134 [MV/m]

Breakdown rate as a function of pulse width of #SUS003 waveguide

#CU002 and #SUS003 after high-gradient experiments

Many breakdown damages were seen on the E-plane surface.

The surface is intensively damaged, and it could also melt due to breakdown.

Observation area

23/27

#CU002 Surface observation by SEM

Laser microscopeRF

24/27

#SUS003 Surface observation by SEM

Laser microscope

RF

25/27

Summary of narrow waveguide We’re conducting the high-gradient experiments of

Cu004 to confirm the previous data of Cu002 and to measure BDR of copper type.

- Prototype Cu002 and SUS003 had been tested under different system conditions (at XTF and Nextef).

- Number of break down events for SUS003 is less than that for Cu002 which may be a result of different systems .

We’re planning to test other materials. We’re trying to make a new narrow waveguide; one

side is made of copper and the other side is made of stainless-steel. We might know the surface damage of different materials at the same RF power.

26/27

Thank you for your attention !

27/27