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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Alexey Dubrovskiy @ CLIC workshop 2013 3
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 #
Alexey Dubrovskiy @ CLIC workshop 2013 4
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
Alexey Dubrovskiy @ CLIC workshop 2013 13
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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Alexey Dubrovskiy @ CLIC workshop 2013 1429.01.2013
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RF calibration
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32 MW - Saturation level for the transmitted power