3 GHz SICA:
Breakdown measurement in CTF
Alexey Dubrovskiy
CLIC Workshop
January 29, 2013
CTF3 Layout
8 Klystrons + RF compressors (LIPS and BOC) @ 3 GHz
MKS07
CLEX
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.
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
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Alexey Dubrovskiy @ CLIC workshop 2013
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3 GHz SICA
CTF3 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.
Pin = 38 MW, Plen = 1.4 µs, Ibeam = 4 A
Operational unloaded
acc. gradient 12.5 MeV/m
60
Operational loaded
acc. gradient 8 MeV/m
40
35
vg/c
acc [MV]
50
30
Pout [MW]
40
25
Ploss [kW/5]
30
20
15
20
10
10
5
0
0
0
5
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10
15
20
25
30
0
10
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30
Cell #
3
MKS07 setup
Klystron
Directional coupler
RF compressor
BOC
Reflected
Incident
3 dB
ACS1
ACS2
Drive beam
Transmitted
RF load
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RF load
Alexey Dubrovskiy @ CLIC workshop 2013
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Histogram
BOC detuning &
Upstream BD
(0.3% of all pulses)
BD in ACS
5×10-7
Total
BD rate
38.4 MW
Operational power
(96% of all pulses)
1×10-7
Operational
BD rate
56 days, rep. rate = 25 Hz
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BD as a result of the beam
deceleration
Signal is saturated
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BD as a result of the BOC
detuning
Signal is saturated
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BDs in ACS as a result of
upstream BDs
Full waveforms
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Zoomed waveforms
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Cluster of BDs
Pulse# 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
3.5
3
# of BDs
2.5
2
1.5
1
0.5
0
1
3
5
7
9
11 13 15 17 19 21 23 25 27 29 31
Cell #
60
50
40
vg/c
acc [MV]
30
Pout [MW]
20
Ploss [kW/5]
10
0
0
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5
10
15
20
25
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Cell #
10
Fall time of the transmitted power
35
30
BD cell #
P
P90%
56
32
60
31
82
24
20
94
28
102
32
118
28
122
30
5
128
29
0
140
30
176
8
15
0
50
100
150
Fall Time [ns]
P10%
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Cell #
25
10
Fall time
Time [ns]
200
• Avg. fall time is 110 ns
• No precursors observed
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Summary of fall times
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
32 MW - Saturation level
for the transmitted power
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