1. Development of a Marx-Generator for the drive beam electron gun
B. Cassany
K. Pepitone

2. Outline Why a new HV modulator is needed ? Schematics & concept
Results
Conclusion

3. Existing power supply (CTF3)
We need to operate with 5 A x 140 µs = 700 µC
With the actual 10 nF capacitor :
The stored charge is 1.4 mC
The decay on voltage (energy) for 140 µs pulse is 40 %
Droop for 4.5A , 140 µs pulse
~ 35 %
To achieve 1% droop a ̴1 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.

4. Technical solutions
Direct switch modulators
Transformer based modulators
C ≈ 1µF at 140kV
Switch 140kV  
Flat top and overshoot
It has been decided to propose a new modulator based on Marx topology.
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

5. How it works ?
Charge
Discharge
Optional Crowbar
Vout
Vout
Vout t t t

6. Auxiliary power supply : 48V
Previous results
Design & Choice of components :
1700 V IGBT, Capacitors, Diodes, Power supply
Hybrid auxiliary power supply
Tests with 30 stages (6 cards)
Main power supply : 1.5kV
1.5kV
Auxiliary power supply : 48V
7.5kV
GND
One card

7. Evolutions 2016 Ten stages per card / Global size reduction
Ten stages per card / Global size reduction
SMD components
First industrial prototype
IGBT drivers with overcurrent protection
Short circuit protection

8. Evolutions 2016 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
Now only 2 OF / card (ten stages).
The trigger propagates on the card through optocouplers with 0.4 µs delay per stage.
Slow down rising time

9. Results: Pulse to pulse variation
Allan Standard Deviation
One card test
300 pulses on 1.8 kW 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

10. Ideal low pass filter period
Results: Flatness
Allan Standard Deviation
RC decay
1 %
White noise
Ideal low pass filter period
RAW DATA

11. RC corrector
RC in parallel with the load in order to absorb ̴1% of the energy during the first half of the pulse.
50 W
6 nF V
1.8 kW
6.6 kW
Without corrector
With corrector

12. Conclusion Modulator Power electronics for cathode (to do)
Concept tested in 2015.
New improvements in 2016 (drivers, SMD).
Tests and mechanical integration are ongoing.
The new modulator will be assembled by S
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).
Electrostatic analysis

13. Thank you for your attention

14. Design Classic Marx Generator Charging resistors replaced by diodes
Grounding resistors replaced by switches
Bypass diodes added