Sub micro and sub nanosecond HV pulses with high repetition rate for

Pulsed Electric Field (PEF) application

R. Ruscassié*1, S. Paquet2, L. Pécastaing1, A. De Ferron1, M. Rivaletto1, T. Reess1, P. Pignolet1

1Laboratoire SIAME, Université de Pau et des Pays de l’Adour (UPPA), Technopole Hélioparc Pau-Pyrénées, 2 av P. Angot, 64053 Pau Cedex 9, France

2Effitech, Technopole Hélioparc Pau-Pyrénées, 2 av P. Angot, 64053 Pau Cedex 9, France

SIAME Equipe Génie Electrique Tel. : (+33) (0)5 59 84 53 24 Fax. : (+33) (0)5 59 14 90 14 e-mail : robert.ruscassie@univ-pau.fr

Since more than 30 years the Pulsed Power (PP) group (which was previously named LGE) of the newly born SIAME laboratory is focused on High Voltage (HV) power supplies and their various

applications. Effitech is a Pau university spin-off which is also dedicated to HV pulsed power supplies with a specific expertise on semiconductor based architectures.

For several years now, due to the increasing interest of the scientific community for various bioelectric applications, both SIAME’s PP group and Effitech have developed systems dedicated to Pulsed

Electric Field (PEF) treatment applications. In particular Dielectric Barrier Discharge (DBD) device delivering extremely short rise time high repetition rate pulses have been developed for Pulsed

Electric Field (PEF) treatment applications

PEF treatment can break cells membrane leading to several benefits such as: food preservation (e.g fruit juice) without flavour degradation, cellular contents extraction (e.g sugar or polyphenol), solid

sludge volume reduction and sludge treatment shortening and numerous other medical electroporation cell based applications.

A series of short, high-voltage pulses breaks the cell membranes of vegetative microorganisms in liquid media by expanding existing pores (electroporation) or creating new ones. The membranes of

PEF-treated cells become permeable to small molecules; permeation causes swelling and eventual rupture of the cell membrane. Pore formation is reversible or irreversible depending on factors such as

the electric field intensity, the pulse duration, and Pulse Repetition Frequency (PRF).

• Available commercial technology for micro and sub microseconds PEF treatment with very high PRF

• Available laboratory technology for sub nanoseconds PEF treatment with high PRF

• Preliminary experiments on food samples successfully completed

• Possible experiments coupling between PEF and PAED

• Biological analysis know how needed

• New partners for a possible future research network are welcome

CONCLUSIONS AND FUTURE PLANS

SUB NANO PULSE GENERATOR FOR PEF

PULSED ARC ELECTRO-HYDRAULIC DISCHARGES (PAED)

During the last years, Pau laboratory developed

several fast pulse power supplies for various

applications.

•These pulsers architecture often integrate a

pulse forming line allowing very short fall time

and high PRF

•Dedicated specific measurements techniques

were also developed in parallel to these pulsers.

PULSE GENERATOR FOR ELECTROPORATION

•Voltage up to 230 kV

•Pulse width from 460 to 900 ps with rise time down to 70 ps

•PRF up to 900 Hz

MOS based Effitech pulser:

4 kV, 30 ns rise and fall time on a 250 ns pulse (left)

6kV, 200 kHz PRF on a 25 pF load (right)

SUB MICRO PULSE GENERATOR FOR PEF

Pau laboratory fast pulse generator examples:

PEF for alternative food processing technology

PEF process is performed adequately when the cell membrane is stressed with a high electric field

(typically several tens of kV/cm) during a given time (from sub nanoseconds up to microseconds

range).

Specific requirements due to PEF organic material process:

•Medium variable resistivity (which depends from the treated product but which also changes

during the pulse processing sequence).

•High intensity, short duration electric field (in order to open cell membranes efficiently).

•Energy minimisation (since applying a longer pulse than needed will only warm the liquid

without any extraction benefice).

•Furthermore, the up-scaling capacity from laboratory experiment to pre industrial or full

scale industrial system implies increasing the pulsed voltage (which will allow a higher

throughput) and the PRF.

Consequences on our design of the pulsed power supply (pulser):

•Low impedance pulser permit efficient energy transfer, at minimal voltage and to

perform better than:

•Pulse Forming Network (PFN) that shall be operated with fixed impedance and at a

voltage twice higher than the voltage applied to a matched load.

•Capacitor discharge with a typical bi-exponential pulse. The lower pulse part which

is below the threshold voltage will only warm the medium with no electroporation

effect.

•Tunable pulse duration and Pulse Repetition Frequency to allow parametric study for

a given medium and pulse sequence optimisation during laboratory optimisation.

•Modular pulser to permit the scaling up in order to achieve industrial system

•Rugged design allow easy and safe operation (including in case of load shortening).

Typical high voltage pulse with

breakdown generated by an energetic

Marx generator

Effitech pulser based on solid state switches (IGBT or MOSFET) meets the above requirements

for the submicroseconds range:

•Can be seen as a charged capacitor connected to a high voltage switch which is fully controlled

both for closing and opening by an insulated optical fiber command. This configuration allows

optimal load matching even in case of load impedance variation and full control of the pulse

duration.

•Formed by a combination of stacked modules leading easily to higher voltage and power

implementation simply by adding modules.

•Very high solid state switches reliability and is protected against current surge.

•Furthermore since the storage capacitor remains fully charged during all the operating duration,

the associated DC power supply will request half the current needed for a pulse generator based

on a PFN or capacitor discharge.

Pulse forming set

Marx structure

Pulse forming set

Marx structure

0 1n 2n 3n 4n 5n 6n

-20k

0

20k

40k

60k

80k

100k

120k

140k

Te

nsio

n (

V)

Temps (sec)

Transformer based fast pulse generator (left) and output

voltage waveform example (right) on 50 Ω output load:

26 kV, 70 ps rise time (600 ps pulse width), 900 Hz PRF

Marx Generator

Maximum output voltage : 250kV

Maximum energy : 1kJ

Also developed in Pau laboratory, some other type of Marx generator

based structure was designed for high energy applications. These

generators are able to deliver energy levels as high as 1 kJ inducing arc

discharge in water which leads to high pressure waves. In these

configurations, the output voltage can be up to 250 kV.

Such generators have been already successfully used for cellular content

extraction induced by pulsed arc electro hydraulic discharges.

Current (pink) and voltage (blue) wave shapes for different command pulse durations (yellow) using

IGBT based Effitech pulser on potato samples load. 5 kV, adjustable pulse width from 150 ns up to

several µs, 10 kHz PRF.

Effitech pulser dimensions

If sub micro PEF process has already been partially explored, sub nano PEF process remains widely

unexplored due to the complexity to generate appropriate waveforms. Indeed sub nanoseconds rise time can

not be achieved with semiconductor technology.

Specific knowledge for the very fast pulse generator

•Very high output voltage (typically hundred of kV leading to either very high applied electric field or

large material quantity treatment).

•Low impedance generator output in order to improve load energy transfer efficiency.

•Very short rise an fall time for better cell treatment and even possible interaction with internal cell

material (DNA).

•Pulse Repetition Frequency reducing the overall treatment duration.

Pau laboratory generators based on spark gap Marx generator or pulse transformer technologies comply to

these specifications:

Marx based fast pulse generator (left) and output voltage

waveform example (right) on 50 Ω output load: 230 kV,

380 ps rise time (460 ps pulse width), 350 Hz PRF

-25

0

25

50

75

100

125

150

175

200

225

250

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

t (ns)

Vs

(kV

)

Marx based fast pulse generator (left) and output

voltage waveform example (right) on 50 Ω output

load: 138 kV, 200 ps fall time (900 ps pulse

width), 100 Hz PRF

Effitech pulsers:

•Average power up to several kW

•Pulse width from 100 ns with rise time down to 10 ns

•PRF up to 200 kHz