X-band Single Cell and T18_SLAC_2
Test Results at NLCTA
Faya Wang
Chris Adolphsen
Jul-9-2009
1
• Single cell SW structure test result
Breakdown with constant gradient but different pulse heating
Breakdown with constant pulse heating but gradient
• 2nd SLAC made T18 test result
2
1C-SW-A3.75-T2.60-Cu6N-KEK structure parameters
Parameters
Unit
Value
Frequency
GHz
11.427 (Nitrogen, 20 oC)
Cells
1+matching cell + mode launcher
Q (loaded)
4661
Coupling
0.97
Iris Thickness T
mm
2.6
Iris Dia. a
mm
3.75
Phase Advance Per Cell
deg
180
Es/Ea
2.03
Maximum surface electric field for
10 MW
MV/m
398.9
Maximum surface magnetic field
for 10 MW
A/m
667978.1
Peak pulse heating for 1 μs pulse
with flat field of 100 MV/m
oC
24
3
from Valery Dolgashev and James Lewandowski
Two 3 dB hybrid
Small load
RF In
Big load
To big load
45 dB coupler
Ion pump
Structure
Half cooling jacket
X-band Current Monitor
Ran cooling water
through a
quadrupole magnet
adjust structure
temperature.
4
Input RF Pulse
Maximized initial pulse
to reduce fill time
35
Input power of structure (arb.u.)
30
25
20
15
Main Pulse
10
Pre Pulse
After Pulse
5
0
0
500
1000
Time (ns)
1500
2000
5
RF Processing History During First 100 Hours
200
Unloaded Gradient (MV/m)
Dark Current at Breakdown (arb.u.)
180
Breakdown Rate (hr-1)
160
Flat Top of 100 ns
140
120
100
80
60
40
20
0
0
10
20
30
40
50
60
Time with RF On (hrs)
70
80
90
100
Detect breakdown from the large (> 0.8 on above scale) current produced
6
35
30
Power (arb.u.)
25
Input Power
Reflected Power Data
Power Dissipated in Cavity Data
Reflected Power Simulation
Power Dissipated in Cavity Simulation
Maximum Surface Pulse Heating (arb.u.)
RF Power and Heating
Measurements and Simulations
80
70
Pulse Heating
60
50
40
30
20
10
0
0
500
1000
Time (ns)
1500
2000
20
15
Ig
10
L
R
C
Simulations based
only on measured
input power
5
0
0
Rg
500
1000
Time (ns)
1500
2000
7
Breakdown Study with Constant Gradient but Different
Pulse Heating from the Pre-Fill ‘Warm-up’
Peak Pulse Heating
Input Power
25
70
60
15
50
o
10
5
0
0
500
1000
Time (ns)
1500
2000
30
Cavity Reflected Power (arb.u.)
Low Pulse Heating
Middle Pulse Heating
High Pulse Heating
20
Pulse Heating ( C)
Cavity Input Power (arb.u.)
30
Reflected Power
25
40
30
20
10
20
15
0
10
0
500
1000
Time (ns)
1500
2000
5
0
0
500
1000
Time (ns)
1500
2000
8
Breakdown Rate for Fixed Gradient
10
2
Breakdown Rate (1/hr)
135 MV/m
151 MV/m
1st Test of 145 MV/m
10
10
10
1
2
nd
Test of 145 MV/m
0
-1
35
40
45
50
55
o
Peak Pulse Heating ( C)
60
65
9
Comparison of these results with those from a similar structure
(same a/l) tested at the Klystron Test Lab where the pulse
shape was fixed so the gradient varies with pulse heating
Breakdown Rate (1/hr)
10
10
10
10
10
2
1
0
85 ns
150 ns
300 ns
200 ns
135 MV/m @ 150 ns
151 MV/m @ 150 ns
-1
-2
40
145 MV/m @ 150 ns - 1
st
145 MV/m @ 150 ns - 2
nd
50
60
Peak Pulse Heating (oC)
70
10
Breakdown Study with Constant Pulse Heating
50
30
High gradient
Middle gradient
Low gradient
40
Pulse Heating (oC)
Input power (arb.u.)
25
20
15
10
20
10
5
0
30
0
500
1000
Time (ns)
1500
2000
0
0
500
1000
Time (ns)
1500
2000
500
1000
Time (ns)
1500
2000
14
150
10
8
Gradient (MV/m)
Reflected power (arb.u.)
12
6
4
2
0
0
500
1000
Time (ns)
1500
100
50
2000
0
11
0
Breakdown Rate for Fixed Peak Pulse Heating
4
3.5
First Test
Second Test
Third Test
Breakdown rate (1/hr)
3
2.5
2
1.5
1
0.5
0
115
120
125
130
Flat top gradient (MV/m)
Flat top gradient for 160 ns.
135
140
(139/129)^25 =6.5
(139/119)^25 = 48.6
12
Test Results from Second SLAC T18 Disk Structure
Freq.: GHz
11.424
Cells
18+input+output
Filling Time: ns
36
Length: cm
29
Iris Dia. a/λ(%)
15.5~10.1
Group Velocity: vg/c (%)
2.61-1.02
S11/ S21
0.035/0.8
Phase Advace Per Cell
2π/3
Power Needed <Ea>=100MV/m
55.5MW
Unloaded Ea(out)/Ea(in)
1.55
Es/Ea
2
Pulse Heating ΔT: K (75.4MW@200ns)
16.9-23.8
High Power Test Time: hrs
1400
Total Breakdwon Events
2148
Field
Amplitude
Cumulated
Phase Change
120°
13
This time, processed structure by progressively lengthening the
pulse at constant gradient (110 MV/m)
50 ns
120
150 ns
100 ns
200 ns
100
80
60
-1
BKD Rate (hr )
Average gradient (MV/m)
40
20
0
0
50
100
150
200
250
300
14
Comparison of current BDR rate (blue circle) with the rate curves from
the First SLAC T18 structure at different processing times
10
-4
BKD Rate for 230ns
T18_SLAC_2
BKD Rate: 1/pulse/m
500hrs
10
-5
900hrs
250hrs
10
10
-6
1200hrs
-7
95
100
105
110
Unloaded Gradient: MV/m
115
15
RF Breakdown Locations
Blue dot: T18_SLAC_2 after 250 hrs running
Red square: T18_SLAC_1 after 1200 hrs running
40
T18_SLAC_2
Filling time for different cell: ns
35
Reflected Power -vs- Reflected Phase
90 1.5
120
60
1
150
30
0.5
30
25
20
180
15
10
0
210
5
330
240
300
270
0
-5
-150
-100
-50
0
50
Reflected Phase: Deg
100
150
16
Summary
• Reduce fill time with SLED for SW cavity
test
• It is possible to separate pulse heating and
gradient with SLED for the same structure.
• T18 is a good structure, however it is not
clear why there is a hot cell.
17