3 GHz SICA: Breakdown measurement in CTF

Alexey Dubrovskiy

CLIC Workshop

January 29, 2013

Alexey Dubrovskiy @ CLIC workshop 2013 2

CTF3 Layout8 Klystrons + RF compressors (LIPS and BOC) @ 3 GHz

16 SICA Accelerating structures @ 3 GHz

Linac is daily powered in order to accelerate an electron beam of 3.5-4 A upto 125 MeV for commissioning and studying the drive beam generation scheme and for performing beam based experiments in CLEX.

CLEX

Drive beam is operated 200 days per year, 10-24 hours per day @ a rep. rate of 1-5 Hz:16 ACS * 2Hz * 150 days ≈ 4×108 RF+beam pulses per year

Klystrons are powered 200 days per year, 24 hours per day @ a rep. rate of 5-50 Hz:16 ACS * 25 Hz * 200 days ≈ 7×109 RF pulses per year ≈ 6 X-Boxes

MKS07

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3 GHz SICACTF3 Drive Beam Acc. Structures (3 GHz) – SICA (Slotted Iris – Constant Aperture):• 32 cells;• 1.2 m long;• 2π/3 mode;• HOM damping slots;• 96% - theoretical maximum RF-to-beam efficiency.

0 5 10 15 20 25 300

10

20

30

40

50

60Operational unloaded

acc. gradient 12.5 MeV/m

Operational loadedacc. gradient 8 MeV/m

Pin = 38 MW, Plen = 1.4 µs, Ibeam = 4 A

0 5 10 15 20 25 300

5

10

15

20

25

30

35

40vg/c

acc [MV]

Pout [MW]

Ploss [kW/5]

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Cell #

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RF load

MKS07 setupKlystron

BOCRF compressor

ACS1 ACS2Drive beam

3 dB

RF load

Incident

Transmitted

Reflected

Directional coupler

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Histogram

5×10-7

1×10-7

TotalBD rate

Operational BD rate

38.4 MWOperational power (96% of all pulses)

BOC detuning &Upstream BD

(0.3% of all pulses)

BD in ACS

56 days, rep. rate = 25 Hz29.01.2013

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BD as a result of the beam deceleration

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Signal is saturated

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BD as a result of the BOC detuning

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Signal is saturated

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BDs in ACS as a result of upstream BDs

Full waveforms Zoomed waveforms

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Cluster of BDsPulse# 1. Cell# 8 Pulse# 2. Cell# 28 Pulse# 3. Cell# 24

Pulse# 4. Cell# 31 Pulse# 7. Cell# 32 Pulse# 13. Cell# 28

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BD locations

0 5 10 15 20 25 300

10

20

30

40

50

60

vg/cacc [MV]Pout [MW]Ploss [kW/5]

Cell #

# of

BD

s

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 310

0.5

1

1.5

2

2.5

3

3.5

Cell #29.01.2013

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Fall time of the transmitted power

Time [ns] Cell #

56 32

60 31

82 24

94 28

102 32

118 28

122 30

128 29

140 30

176 8

• Avg. fall time is 110 ns• No precursors observed

PP90%

P10%

Fall time

40 60 80 100 120 140 160 180 2000

5

10

15

20

25

30

35

Fall Time [ns]

BD c

ell #

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Summary of fall times

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Test Frequency Measurement Fall Time

Simulation DC 0.25ns

CERN/ New DC System DC Voltage 12-13ns

Swiss FEL (C-Band) 5.7 GHz Transmitted Power 110–140 ns

KEK T24 (X-Band) 12 GHz Transmitted Power 20-40 ns

CTF/TBTS TD24 (X-Band) 12 GHz Transmitted Power 20-40 ns

CTF SICA (S-Band) 3 GHz Transmitted Power 60-140 ns

* Nicholas Shipman, ‘’High-repetition rate dc spark experiments” on 30 Jan 2013

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Summary

• The possibility of measuring BDs in 3 GHz SICA has been demonstrated ;

• The “unloaded” BDR was measured in the order of 10-7;

• Most of BDs occur in the last cells;

• The avg. fall time of the transmitted power is about 110 ns;

• In the normal conditions 6 out of 7 BDs appeared as a single BD. 1 BD appeared as a cluster of 6 BDs during 15 RF pulses.

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RF calibration

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32 MW - Saturation level for the transmitted power