A repetitive PFN-MARX generator based on an innovative

7 DÉCEMBRE 2016 | PAGE 1 CEA | 20 SEPTEMBER 2016

A repetitive PFN-MARX generator

based on an innovative design

for compactness and rise time improvement

Session 7

Oral 104

F. Lassalle, A. Morell, A. Loyen, T. Chanconie, B. Roques, M. Toury

CEA, DAM, GRAMAT, F-46500 Gramat France

Presented by Martial Toury

Contact : [email protected]

This work is supported by the DGA (Direction Générale de l’Armement)

www.cea.fr

mailto:[email protected]

GLOBAL SCOPE OF THIS STUDY


Square pulse Voltage plateau 100 kV – 1 MV

Duration 30 ns – 300 ns

Rise time < 10 ns

Repetitive operation Repetition 10 pps – 200 pps

Driver compactness voltage / length > 0,5 MV / m

stored energy / volume > 1 kJ / m3

Development of HV drivers with :

Applications

Pulsed power source (modulators) for :

Microwave, EM wave, laser, electron beam, ion beam, X-ray, plasma, etc …

Application domains : Defense, Security, Research, Industry, Others …

overshoot

Juin 2014

Vo

lta

ge

(k

V)

time (ns)

plateau duration

plateau

voltage

rise time

SPECIFIC OBJECTIVE OF THIS STUDY


‘Development of a Compact Narrow-band High Power Microwave System’ (see Proceedings of 2016 IEEE International Power Modulator and High Voltage Conference)

300 MW HPM

system inside a

cubic volume

65cm side

Charger

45 kV

HV Driver

400 KV,100 pps

HPM Source

BWO 2-300 MW

Prime Power

Batteries

Antenna

300 MW

Need a very compact

square pulse driver

400 kV – 80 ns – 5 ns rise

repetition 100 pps

Length < 65 cm

Diameter < 40 cm

POSSIBLE TECHNICS FOR THE DRIVER


SQUARE PULSE DRIVER TECHNICS

Transformer + Pulse Forming Line

Marx + Pulse Forming Line

Stacked cable Marx

Stacked Blumlein Marx

Stacked stripline Marx

…

Stacked PFN Marx Chosen for its compactness, reliability,

quality shape of the pulse, …

FAST RISE TIME

Typical design :

driver with ‘slow’ rise time

+ peaking stage for sharpening

Is it possible to avoid peaking stage ?

Need for a very low inductance driver

Rise time

1,2 L / Rtotal

Driver Matched load Rload = (L/C)^0,5

K

1 2

C

L R

Rload

DESIGN APPROACH

FOR MARX COMPACTNESS OPTIMIZATION


A standard Marx design

A possible zigzag design

for compactness optimization

in vertical direction A cylindrical

ceramic capacitor

ground

Cap 1

HV output

Cap 2

Cap 3 Cap 4

A switch

ground

Cap 1

HV output

Switch 1

Switch 2

Switch 3

Cap 2

Cap 3

Cap 4

THE SWITCHES ARE ARRANGED

WITHIN A COLUMN


Column of switches for a reliable Marx erection

Pre-ionisation of gaps thanks to UV radiation from switch to switch Very reliable timing sequence in Marx erection process

Only first switch is triggered Its gap is divided in 2 by a disk trigger electrode

30 kV trigger pulse from a small pulsed transformer

Stray capacitances of stages 2 to 4 are increased, to favor the erection This stray capacitance is adjusted by reducing the gap between the

upstream stage electrode and the grounded vessel

Small gap increase from switch 2 to switch 16 Gaps from 1,3 mm to 2,2 mm for SF6 gas at 6 atm.

Switches Electrodes Tungsten-Copper alloy, to limit erosion for repetitive operation

Photo of the

4 first switches

of this column

THE INDUCTANCE OF A MARX


For any Marx, during the discharge, the volume occupied by the magnetic field B is between

the Marx circuit (caps and switches) and the return current electrode (vessel).

Column of switches must be closed to the return current electrode

Reduction of this magnetized volume, and so, reduction of the inductance LMARX .

A

View from A

Return current

electrode

(vessel)

Switch 3

Switch 2

Switch 1

magnetized

volume

54 mm

with SF6 @ 6atm

for this Marxground

HV output

Cap 1Switch 1

Cap 2

Cap 3

Cap 4

Switch 2

Switch 3

But the zigzag design also enables more inductance reduction …

Example : the proposed Zigzag Marx

THIS INNOVATIVE ZIGZAG DESIGN

ALLOWS EXTRA INDUCTANCE REDUCTION


From flux expression,

inductance LMARX is :

IdSBLMARX /.

Rise time L / R rise time optimization

Thanks to this zigzag design, 2 phenomena contribute to extra reduction of inductance LMARX :

- The reduction of the magnetized volume, due to the reduction of the Marx length along Y axis

- The coupling between the antagonistic B fields which are generated around 2 successive switches

For the specific Zigzag Marx presented here, inductance is only 25 nH / stage It would be > 40 nH / stage for a ‘straight’ Marx.

View from A

ground

HV output

IMARX

A

Y

axis

Return current

electrode

(vessel)

B

Ireturn current

Ireturn current

Ireturn current

IMARX

switch 3

B

B

IMARX

switch 2

IMARX

switch 1

VOLTAGE PLATEAU IS OBTAINED

WITH STACKED PFNs


Marx with N stages,

each Marx stage is a PFN,

a PFN is S cells (L,C) in serie.

PFN Marx

(N=4 and S=6 for scheme below)

Rload

L

C

Plateau duration

Marx impedance

Plateau voltage

Beyond this rise time optimization, many applications need to hold a constant voltage :

Voltage plateau with amplitude Vp and duration Tp

DETAILED DESIGN OF A PFN STAGE


C = 2,1 nF

is a ceramic capacitor AVX - HP60E40242K

Ceramic N4700 (with Strontium)

diam. 58 mm, height 30 mm No rigid clamp on capacitors

S = 6

6 (L,C) cells are connected in serie

L = 36 nH

is given by this strip line geometry

Hemispherical electrodes of switch are

screwed in strip line electrode ends

Curved shape of this PFN is for integration

in a cylindrical vessel

Rload

C

L switch

Top view Bottom view

C

Strip line

Connexions

to charging

circuit

Half

switch

THE 16 STAGES PFN MARX


scale

100 mm

Vessel inner diam. 360 mm

: increased stray capacitance

• Zigzag design for compactness and rise time optimization

• PFN stages for 85 ns plateau duration

• 16 stages, 204 J stored energy @ Vch=45 kV

• Charging circuit with inductances for repetitive operation without resistive losses

during charging

• Gas pressurized vessel Volume 63 liters for these 16 stages and switches

• Weight 44 kg (without vessel)

• Can work in any position Vertical, horizontal, tilted

• Self supporting structure

SELF SUPPORTING STRUCTURE

Self-supporting structure None additional insulating support

Minimize the risks of losses due to surface ramping

+ easy maintenance, reduction of weight

• Charging circuit is made with

4 columns of stacked inductances

• These 4 columns support the 16 PFN stages

• Striplines of the PFN stages support the switches

Zoom

on a 140 µH

single inductance

of the

charging circuit

• Same volume of gas for switches and for stages insulation

Big gas volume beneficial for better dilution of by-products

(switch electrodes erosion, gas breakdown by-products)

Improve the reliability of system for repetitive operation

Column of

stacked

inductance

Column

height

56cm

PFN MARX DESIGN AND OPERATION ARE

ANALYSED THROUGH DETAILED SIMULATIONS


Pspice : circuit simulations Including dynamic model for switches resistance (Braginsky), stray capacitances, transmission lines,

inductances of charging circuit, Child-Langmuir model for e-beam diode, etc.

Example :

Comparison

simulation versus

experiment

for a load 68 - 90 nH

0 50 100 150

0

100

200

300

400

80ns

Vo

lta

ge

(kV

)

time (ns)

simulation

experiment

CST : 3D EM simulations static and time domain simulations

Example :

Electrostatic simulation

of the gas-vacuum HV

insulator

EXAMPLE OF APPLICATION :

PFN MARX DRIVING A MICROWAVE TUBE


output of

PFN Marx U shaped line

conical

HV insulator

(Length = 130 mm)

e-beam diode

of BWO

(Zload = 100 )

Connexion between Marx and load is optimized :

U shaped to keep a length of global system < 65cm

Low inductance connexion

80 line impedance to minimize pulse reflections

Same pressurized gas insulation as the Marx

Very compact gas-vacuum HV insulator

Self-supporting structure

The load is a microwave tube :

an X-band relativistic BWO

Nota :

Marx impedance is slightly undermatched, for more compactness :

Rload = 100 and ZMARX = 66 , with N=16 stages only.

EXPERIMENTAL RESULTS


1000 pulses burst with 85 pps repetition * (only 100 pulses shown here)

* Repetition rate is limited to 85 pps because of the capacitor charger

A new capacitor charger is needed for higher repetition rate

-20 0 20 40 60 80 100 120 140

0

100

200

300

400

500

PFN MARX on a 100 load (BWO ebeam diode)

Juin 2014

Vo

lta

ge

(k

V)

time (ns)

pulses 1 to 20

pulses 21 to 40

pulses 41 to 60

pulses 61 to 80

pulses 81 to 100

85ns (plateau duration)

380 kV +/- 8%

5ns (rise time 10%-90%)

CONCLUSION


• A PFN Marx driver based on an innovative design has been developped :

Square pulse 400 kV – 85 ns, with repetition rate 100 pps

• This innovative zigzag design * allows to reach :

High compactness : 0,6 MV / m

Fast rise time : 5 ns without peaking stage

• This zigzag design and other design rules described here can be used to develop

compact and fast HV drivers (square pulse or other pulse shapes)

for a large range of applications :

Microwave, EM wave, laser, electron beam, ion beam, X-ray, plasma, etc …

covering several application domains :

Defense, Security, Research, Industry, Others …

* Patent Demande de brevet d’invention n° FR 1 552 131, déposée le 16/03/2015 à l’Institut National de la Propriété Industrielle.

Titre de l’invention : « Générateur d’Impulsions de Haute Tension ».

Titulaire : Commissariat à l’Energie Atomique et aux Energies Alternatives.

Inventeur : Lassalle Francis.

PERSPECTIVES


• On going work

Run 3D EM simulations of full driver, to analyse detailed behavior of this prototype and to refine

improvement capabilities

Continue testing to complete the characterisation of this prototype :

What is repetition rate limitation when working with SF6 gas ?

What are characteristics when working with other gases (Dry air, ..) ?

What are limitations for > 10s bursts of 1000 pulses (life time, service procedure, …)

…

Continue study of a 300 MW HPM system inside a cubic volume 65cm side, using this compact driver

• Other perspectives

Further compactness improvements (capacitors with improved compactness and performances,

dielectric strip lines instead of PFN lines, etc.)

Further rise time improvements : reduction of insulation gaps, optimization of zigzag effect

(switches closer to vessel, conical vessel for a progressive gap increase versus each stage voltage, …)

Extend the scope of applications of drivers and modulators based on the design rules presented here.

DAM

DEA

SERE

LDRX

Commissariat à l’énergie atomique et aux énergies alternatives

Centre de Gramat | BP 80200 46500 Gramat

T. +33 (0)5 65 10 54 32 | F. +33 (0)5 65 10 54 33

Etablissement public à caractère industriel et commercial |

RCS Paris B 775 685 019 7 DÉCEMBRE 2016

| PAGE 18

CEA | 10 AVRIL 2012

EXAMPLE OF APPLICATION :

PFN MARX DRIVING A MICROWAVE TUBE


-40n -20n 0 20n 40n 60n 80n 100n 120n

0

100k

200k

300k

400k

500k

PF

N M

arx

ou

tpu

t v

olt

ag

e (

V)

time

0

100M

200M

300M

400M

500M

14ns

single pulse

BW

O X

ba

nd

po

we

r (W

)

Measured radiated E-field

at 10 m from the antenna

(normalized instantaneous

and RMS values of the

horizontal component).

PFN Marx vessel Inner diam.= 360 mm

Height = 650 mm

Microwave tube : BWO Disk antenna

R. Vézinet, F. Lassalle, S. Tortel, J.C. Diot, A. Morell , A. Loyen, A. Catrain, Q. Saurin, A. Paupert,

‘Development of a Compact Narrow-band High Power Microwave System’

Proceedings of 2016 IEEE International Power Modulator and High Voltage Conference

STRAY CAPACITANCES


Stray capacitances Cs of stages 2 to 4 are increased,

to favor the erection.

This stray capacitance is adjusted by reducing the gap between

the upstream stage electrode and the grounded vessel.

scale

100 mmSwitch S1 is triggered

Voltage on switch S2 is :

High V needs low Cg / Cs

V0

Vessel inner diam. 360 mm

3D EM SIMULATION

OF ZIGZAG EFFECT

7 DÉCEMBRE 2016 CEA | 20 SEPTEMBER 2016

Configuration : Zigzag with electrode 10mm ;

Plane return current electrode

Z

Y

X

3D current density B field module

BY BZ

zigzag plane 54 mm 54 mm

Z

Y

X

20 mm 20 mm

BY BZ

Gap 54 mm

Zigzag

inductance

37 nH / step

Zigzag step :

length 60mm along X

+ length 33 mm along Y Comparison

with a

straight electrode

length 93mm

along Y

Gap 20 mm

Zigzag

inductance

28 nH / step

Gap 20 mm

Straight

inductance

45 nH / step

Gap 54 mm

Straight

inductance

77 nH / step

CST MWS - Simulations @50 MHz ( 5ns rise)

zigzag plane

X cut view X cut view

X cut view X cut view

ROUGH CIRCUIT SIMULATION


A rough simulation can evaluate rise time

but can’t give the right shape and amplitude of plateau

Need for the detailed simulation presented page 13

-20 0 20 40 60 80 100 120 140

0

100

200

300

400

500

PSpice

(rise time 10%-90%)

(plateau duration)

380 kV +/- 8%

85ns

PFN MARX on a 100 load ( BWO ebeam diode)

Vo

lta

ge

(k

V)

time (ns)

Juin 2014

5ns

Experiment

Simplified PSPICE simulation without Braginsky model for switches

without stray capacitances

without detailed transmission lines

Etc.

{C}

{L}

{C}

{L} {L} {L} {L} {Lmarx}

{C} {C} {C} {C}

{C}

{L}

{C}

{L} {L} {L} {L} {Lmarx}

{C} {C} {C} {C}

{C}

{L}

{C}

{L} {L} {L} {L} {Lmarx}

{C} {C} {C}{C}

{C}

{L}

{C}

{L} {L} {L} {L} {Lmarx}

{C} {C} {C} {C}

{C}

{L}

{C}

{L}{L}{L}{L}{Lmarx}

{C}{C}{C}{C}

{C}

0

{C}

{L}

{C}

{L}{L}{L}{L}{Lmarx}

{C} {C}{C}{C}

{C}

{L}

{C}

{L}{L}{L}{L}{Lmarx}

{C} {C}{C}{C}

{C}

{L}

{C}

{L}{L}{L}{L}{Lmarx}

{C} {C}{C}{C}

{C}

{L}

{C}

{L}{L}{L}{L}{Lmarx}

{C} {C}{C}{C}

PARAMETERS:

Lg = 140u

Lv = 140u

{C}

{L}

{C}

{L}{L}{L}{L}{Lmarx}

{C} {C}{C}{C}

{C}

{L}

{C}

{L}{L}{L}{L}{Lmarx}

{C} {C}{C}{C}

U1TCLOSE = 0

1 2

{C}

{L}

{C}

{L}{L}{L}{L}{Lmarx}

PARAMETERS:

ROPEN = 1k

TTRAN = 2n

RCLOSED = 10m

{C} {C}

U2TCLOSE = 4n

12

U3TCLOSE = 8.3n

1 2

{C}{C}

U4TCLOSE = 10n

12

U5TCLOSE = 12.9n

1 2

U6TCLOSE = 14n

12

U7TCLOSE = 15n

1 2

U8TCLOSE = 16n

12

U9TCLOSE = 16.5n

1 2

U10TCLOSE = 17n

12

U11TCLOSE = 17.25n

1 2

U12TCLOSE = 17.5n

12

U13TCLOSE = 17.75n

1 2

Lv 3

{Lv}

U14TCLOSE = 18n

12

U15TCLOSE = 18.25n

1 2

U16TCLOSE = 18.5n

12

Lv 5

{Lv}

Lv 7

{Lv}

Lv 9

{Lv}

Lv 11

{Lv}

Lv 13

{Lv}

Lv 15

{Lv}

Lg3

{Lg}

Lg5

{Lg}

Lg7

{Lg}

Lg9

{Lg}

Lg11

{Lg}

Lg13

{Lg}

Lg15

{Lg}

PARAMETERS:

C = 2.1n

L = 36n

Vch = 41k

Rload

100

0

Lline = 140 nHTline

Z0 = 80

TD = 1.75n

00

PARAMETERS:

Lmarx = 20nH

LMARX total = 320 nH

{L}

{C}

{L} {L} {L} {L} {Lmarx}

{C} {C} {C} {C}

I

V

Lg2

{Lg}

Lv 4

{Lv}

Lv 6

{Lv}

Lv 8

{Lv}

Lv 10

{Lv}

Lv 12

{Lv}

Lv 14

{Lv}

Lv 16

{Lv}

Lg4

{Lg}

Lg6

{Lg}

Lg8

{Lg}

Lg10

{Lg}

Lg12

{Lg}

Lg14

{Lg}

Lg16

{Lg}

Lv 2

{Lg}

{C}

{L}

{C}

{L} {L} {L} {L} {Lmarx}

{C} {C} {C} {C}

{C}

{L}

{C}

{L} {L} {L} {L} {Lmarx}

{C} {C} {C} {C}

{C}

{L}

{C}

{L} {L} {L} {L} {Lmarx}

{C} {C} {C} {C}

Documents

A repetitive PFN-MARX generator based on an innovative