Transcript Cassany_161129x

Development of a Marx-Generator
for the drive beam electron gun
B. Cassany
K. Pepitone
[email protected]
Outline
• Why a new HV modulator is needed ?
• Schematics & concept
• Results
• Conclusion
2
Existing power supply (CTF3)
We need to operate with 5 A x 140 µs = 700 µC
-80
Droop for 4.5A , 140 µs pulse
Vacc (kV)
With the actual 10 nF capacitor :
• The stored charge is 1.4 mC
• The decay on voltage (energy)
for 140 µs pulse is 40 %
-100
~ 35
-120
%
-140
0
40
80
120
160
t (us)
To achieve 1% droop a 1̴ µF capacitor should be used and charged at 140 kV.
• The energy stored is ̴ 10 kJ
• This option requires a 140 kV opening switch protection in case of diode short circuit.
3
Technical solutions
Direct switch modulators
Transformer based modulators
N
V

C
Load
V
C ≈ 1µF at 140kV
Switch 140kV

C
Load
Flat top and overshoot
It has been decided to propose a new modulator based on Marx topology.
V
C
C
C
Load
The schematic is derived from a prototype developed at SLAC few years ago .
M.A. Kemp & al., Design of the second-generation ILC Marx modulator, SLAC-PUB-14249.
4
How it works ?
Vout
Sn
Dch
Dbp
Srn
STAGE N
Dbp
STAGE 2
Sr2
Dch
STAGE N
Sr2
Dch
STAGE 2
STAGE 1
Sr1
C
Dch
Charge
Dbp
Sr1
STAGE 1
C
Dch
STAGE 2
Dbp
Sr1
STAGE 1
C
Optional Crowbar
Vout
t
Sr2
Vin
Discharge
Vout
Dbp
S1
Dch
Vin
Vin
STAGE N
C
Dch
S1
Dbp
Srn
S2
Dbp
Dch
Dbp
C
Dch
C
Dch
S1
Dch
Srn
S2
Dch
C
Dch
Dbp
Dch
C
Dch
S2
Dch
Sn
Sn
Dch
C
Dch
Vout
Vout
Vout
t
t
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Previous results
• Design & Choice of components :
• 1700 V IGBT, Capacitors, Diodes, Power supply
• Hybrid auxiliary power supply
Main power
supply : 1.5kV
Vout
1.5kV
• Tests with 30 stages (6 cards)
2
0
0
-10k
-2
-20k
-4
-30k
-6
-40k
-8
-50k
-100µ
-50µ
0
50µ
100µ
Time (s)
150µ
200µ
250µ
AC
Auxiliary power
supply : 48V
Output current (A)
Output voltage (V)
DC
10k
7.5kV
GND
DC
AC
One card
-10
300µ
DC
AC
-1.5kV
6
-48V
Evolutions 2016
10 stages
Ten stages per card / Global size reduction
SMD components
First industrial prototype
IGBT drivers with overcurrent protection
0
Short circuit current (A)
•
•
•
•
300 V
400 V
500 V
-2
-4
-6
Short circuit protection
-8
0.0
20.0µ
40.0µ
Time (s)
60.0µ
2015
2016
7
Evolutions 2016
• Now only 2 OF / card (ten stages).
• The trigger propagates on the card through
optocouplers with 0.4 µs delay per stage.
Current in 1.8 k resisive load (A)
• Previously: 2 Optical Fibers / stage
 200 OF for the whole modulator !
• Needs to limit the dV/dt for EMC
 each card was triggered with few µs delay
0.0
-0.5
-1.0
-1.5
-2.0
-2.5
-3.0
0.0
2.0µ
4.0µ
6.0µ
8.0µ
Time (s)
Slow down rising time
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Results: Pulse to pulse variation
Allan Standard Deviation
• One card test
• 300 pulses on 1.8 k resistive load
• 50 Hz Rep. Rate
White noise
from digitizer
Drift due to
load heating
Allan Standard Deviation = A metric for stability = Two-sample Standard Deviation taken over variable interval of time or variable interval of pulses
9
Results: Flatness
Allan Standard Deviation
RC decay
1%
White noise
Ideal low pass
filter period
10
RC corrector
• RC in parallel with the load in order to absorb 1̴ %
of the energy during the first half of the pulse.
50 
V
6 nF
6.6 k
1.8 k
Without corrector
With corrector
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Conclusion
Modulator
•
•
•
•
Electrostatic analysis
Concept tested in 2015.
New improvements in 2016 (drivers, SMD).
Tests and mechanical integration are ongoing.
The new modulator will be assembled by S1 2017.
Power electronics for cathode (to do)
• Implement a fast correction on pulser (RF mosfet).
• Implement a new heather power supply.
• Improve all electrical diagnostics (10-3 stability).
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Thank you for your attention
Design
Vout
Vout
Sn
Sn
Dch
STAGE N
C
S2
Dch
C
C
Dch
Sr2
Dch
C
Charging resistors
replaced by
diodes
Dch
Srn
STAGE N
Dbp
Sr2
STAGE 2
Dbp
Sr1
STAGE 1
S2
Dch
STAGE 2
C
Dch
S1
S1
STAGE 1
Dbp
C
Dch
C
Dch
Vin
Classic Marx
Generator
Dch
STAGE 2
Dch
STAGE N
S2
S1
STAGE 1
Srn
Dch
C
Dch
C
Dch
S1
Vin
Dch
STAGE N
S2
STAGE 2
Sn
Sn
C
Dch
Vout
Vout
Sr1
Dch
STAGE 1
C
Vin
Grounding
resistors replaced
by switches
Dch
C
Vin
Bypass diodes
added
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