Megaimpulse NPG30P11 User manual

HIGH VOLTAGE
NANOSECOND PULSE GENERATORS
NPG30P11 and NPG30N11
USER MANUAL
v. 1.0
© 2023 Megaimpulse Ltd.

Copyright © 2023 MEGAIMPULSE Ltd. All Rights Reserved.
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Megaimpulse Ltd. contact information
Address: 28 Polytechnicheskaya str., St. Petersburg, 194021 Russia
www: http://www.megaimpulse.com
e-mail: [e-mail]
fax: [phone]

CONTENTS
What are in the package .................................................................................... 4
General view and typical output pulse waveform ............................................. 4
Safety manual ................................................................................................... 5
Technical specification ..................................................................................... 6
Front view ......................................................................................................... 7
Basic operation principles ................................................................................. 8
Front and rear panels in detail ........................................................................... 9
Putting into operation ....................................................................................... 11
Triggering the generator ................................................................................... 14
SYNC OUT pulse ............................................................................................. 16
Overheating protection ..................................................................................... 17
Electronic fuse .................................................................................................. 17
Warranty ........................................................................................................... 17
Appendix A.
The lists of preset values for the frequency and number of pulses per burst 18
User manual of NPG30P11 and NPG30N11 3

WHAT ARE IN THE PACKAGE
The package includes all you need to set up the equipment and start the
experiments with the discharge:
NPG30P11 (NPG30N11) HV pulse generator (hereinafter "generator");
Power supply cable;
5 meters in length HV output coaxial cable with NPG30-M connector;
2 ml of silicone grease for the HV connectors.
What you may need more:
Oscilloscope with 500 MHz bandwidth and 5 Gsa/s or more;
Tektronix©P6015A probe for pulse voltage measurement;
Megaimpulse©CS-10/500 current shunt for pulse current measurement;
Megaimpulse© RC30 resistive coupler for the incident and reflected pulse
energy measurement, as well as voltage and current waveforms on the load;
BNC-to-BNC cable for the connection to the external triggering source;
BNC-to-BNC cable for registering the SYNC OUT pulse.
Fig.1. General view of NPG30P11 HV nanosecond pulse generator.
Fig.2. Typical output pulse waveform on matched 75 Ohm load at max amplitude.
MEGAIMPULSE LTD. 4

SAFETY MANUAL
Electrical safety
NPG30P11 (NPG30N11) pulse generator is a high voltage equipment.
Please be careful, and operate qualified personnel only.
The electric shock, strong electromagnetic interference, and damage to the
generator or other equipment are possible in a case of improper operation.
The grounding of the equipment is obligatory using a three-terminal power
supply cable and wall outlet and/or grounding the shell of HV output
connector/output coaxial cable braid.
Turning on the generator without the HV output coaxial cable is strongly
prohibited. The electrical arcing on the open connector will damage it and
the output circuit of the generator. Please use our special HV coaxial
cable/connector only. The cable length should be 5 meters or more.
Please turn off the generator before connecting to or disconnecting from the
load. Connect or disconnect any external triggering or measurement
equipment while the HV system of the generator is switched OFF by the
HV ON/HV OFF button.
Operation safety
Please read this manual before using the generator.
Make sure that all the cables are applicable and not damaged. The HV
connectors on the rear panel and coaxial cable should be clean, and the
insulator parts of both connectors should be covered by thin silicone grease.
This grease eliminates the air gap between mated connectors and prevents
unwanted discharge inside.
To avoid shorts, please keep metal parts like clips, screws, and staples away
from the generator.
The generator is designed for operation in normal laboratory conditions.
Please avoid dust, humidity, and temperature extremes. Do not place the
generator in any place where it may become wet.
Place the generator on a stable surface.
If you encounter any technical problems with the generator, please contact
Megaimpulse Ltd. Do not try to repair the generator by yourself.
User manual of NPG30P11 and NPG30N11 5

TECHNICAL SPECIFICATION
Output pulse amplitude
(typical)
smooth adjustable from 15 kV to 30 kV
on matched 75 Ohm load;up to 60kV
on the open cable and discharge reactor
Output impedance
75 Ohm
Output connector NPG30, special HV coaxial type connector
Output cable 5m coaxial cable with 75 Ohm impedance,
outer diameter 9.6 mm
Pulse polarity positive for NPG30P11
negative for NPG30N11
Pulse rise time < 5 ns (fast part of the output pulse)
Pulse width (FWHM) 11 ns … 12 ns, fixed
Pulse energy smooth adjustable from 30 mJ to 120 mJ
Peak pulse power
up to 12 MW
Operation modes continuous, burst, single pulse modes;
internal and external triggering
Continuous mode repetition
rates
from 1 Hz to 1 kHz (internal triggering)
from single pulse to 1 kHz (external triggering)
Burst mode repetition rates;
number of pulses per burst
up to 50 kHz;
up to 1000 pulses per burst / per second
External triggering BNC-type connector, +2.4 V ... +5 V amplitude
Internal generator delay ~ 1.2 μs
Jitter RMS (typical)
1 ns
Output pulse monitoring BNC-type connector, +5V amplitude
Power supply AC 110-230V, 50-60 Hz
Size
250 х 362 х 144 mm
3
Weight (without cables) 8.5 kg
MEGAIMPULSE LTD. 6

FRONT VIEW
2 3 4 5 6
1 7 8 9 10 11
Fig.3. Front panel control elements.
1– Power supply ON/OFF toggle switch
2– Electronic fuse
3– High voltage ON/OFF push button with ON state LED indicator
4– Internal/external triggering push button with LED indicator
5– Frequency and number of pulses per burst/second 4-digit display
6– Frequency and number of pulses per burst regulation knob with push button
7– BNC-type SYNC OUT connector
8– BNC-type SYNC IN connector
9– Overheat LED indicator
10 – Output pulse energy 2-digit display
11 – Output pulse energy regulation knob with push button
The HV output connector, main power supply connector, and the fans inlets/outlets
are located on the rear panel.
User manual of NPG30P11 and NPG30N11 7

BASIC OPERATION PRINCIPLES
The generator is a powerful and smart device. In spite of its compact size and
small number of control elements, it implements a lot of operation regimes and
high output power according to user demands. Please read this manual carefully to
familiarize yourself with the basic operation principles.
The generator has open and short load protection as well as overheating
protection. However, it is strongly prohibited to switch on the generator
without an HV output cable or if it is shorter than 5 meters in length.
The generator can operate in a single pulse, continuous, and burst operation
modes, as well as internal or external triggering. The generator’s control system
provides quartz-stabilized pulse sequences for continuous and burst operation in
the internal triggering mode and prevents improper operation in case of external
triggering. The complete lists of the preset frequencies and preset number of pulses
per burst/second are shown in Appendix A.
In all operation modes, the minimum pulse-to-pulse interval is limited to
20 µs, which corresponds to 50 kHz repetition rate. The maximum number
of pulses per second is limited to 1000. Therefore, the maximum frequency
in continuous mode is 1 kHz, and higher repetition rates are available in a
burst mode only. It is recommended to set 100 pulses per burst or less
because the amplitude of the following pulses becomes lower at high rates.
The following operation parameters can be set by the front panel controls:
-FREQUENCY from 1 Hz to 50 kHz, the default value is 100 Hz;
-NUMBER OF PULSES per burst/second from 1 to 1000, the default
value is 1000;
-PULSE ENERGY from 30% to 99%, the default value is 50%.
The continuous mode is activated if the set frequency in Hz is lower than or equal
to the set number of pulses. Otherwise, the burst mode is chosen automatically.
The period of bursts is fixed to one second. So, the FREQUENCY parameter sets
the pulse-to-pulse interval, while the NUMBER OF PULSES sets the burst length
or number of pulses followed by a pause up to the next burst.
The FREQUENCY and NUMBER OF PULSES parameters work as limits
for the external triggering pulses. Therefore, FREQUENCY sets the
maximum external pulse frequency (minimum pulse-to-pulse interval), and
NUMBER OF PULSES sets the maximum number of pulses per second.
So, the generator’s control system prevents overloading and damage to the
generator in case of improper external triggering.
MEGAIMPULSE LTD. 8

FRONT AND REAR PANELS IN DETAIL
NPG30-type HV coaxial connector on the rear panel.
Firmly attach the HV output cable before turning on
the generator. The recommended torque for the cable
connector nut is 10 N×m The HV connectors should
be clean, and insulating parts covered by thin silicone
grease. This grease fills the gap, eliminates air, and
prevents unwanted arcing or glow discharge inside.
Main power supply ON/OFF toggle switch.
Electronic fuse.
The red button should be pressed
down.
Non-latched push button which enables the HV output
pulses. The red LED on the button lights on when the
HV system is activated and ready for triggering. HV
system is set to OFF state at the powering on,
overheating, or in the TRIGGERING TEST mode.
Latched push button toggles internal and external
triggering modes. The upper state indicates the internal
triggering mode, the red LED on the button lights on,
and immediate triggering occurs when the HV system
is activated by the HV ON/HV OFF button. Press the
button to activate the external triggering mode. The
LED is off when no external triggering pulses and
1
Hz blinks when they are applied and successful
triggering occurs.
The FREQUENCY and NUMBER OF PULSES
parameters are indicated on a four-digit LED display
and set by the control knob with a push button. The
FREQUENCY is indicated in kHz with a decimal dot.
For example, 1 Hz is indicated as 0.001; 5
0 kHz is
indicated as 050.0. Press down
the control knob to
click and hold for one second to switch to NUMBER
OF PULSES regime. The LED display blinks and
indicates the NUMBER OF PULSES without a digital
dot. For example, 1 pulse setting is indicated as 0001;
1000 pulses setting is indicated as
1000
. Press down
User manual of NPG30P11 and NPG30N11 9

the control knob and hold for one second again to
switch back to the FREQUENCY mode. The preset
frequencies and number of pulses are shown in
Appendix A.
The PULSE ENERGY parameter is indicated on a
two-digit LED display and set by the
control knob
with a push button. The energy can be set from 30% to
99% with a 1% step. This LED display is always on in
the idle or continuous operation modes. It blinks in a
burst mode, the durations
of on and off states
correspond to the duty cycle. Press down the control
knob to click and hold for one second to switch into
the TRIGGERING TEST mode. The HV ON/HV OFF
button is blocked in this mode; the LED display shows
00, which means zero output power; the triggering
sequence from an internal or external source goes to
the SYNC OUT connector. This mode allows us to
check the triggering sequence without applyi
ng HV
pulses to the load. Press down
the control knob and
hold for one second again to switch back into the
PULSE ENERGY mode.
If the temperature exceeds the safe level, then the
OVERHEAT LED lights on and the
generator stops
the operation. It may occur due to too
high ambient
temperature, obstacles to the airflow, or after a long-
time operation at a high amplitude and high repetition
rate. The HV system is blocked in case of overheating.
Please keep
the generator in idle mode and allow
cooling by the fans for several minutes. The generator
will return to normal operation automatically when the
temperature decreases. Press the HV ON/HV OFF
button again to continue the operation.
BNC-type input connector for the external triggering
pulses. The pulse amplitude should be +2.4V … +5V
and the pulse width should be 1 µs or more. The
external synchronization mode is activated by pressing
down the INT/EXT green push button.
BNC-type output connector for SYNC OUT pulses.
The front edge of the SYNC OUT pulse precedes the
HV output pulse by ~1.2µs. SYNC OUT pulse width
is 400 ns and the amplitude is 5V.
MEGAIMPULSE LTD. 10

PUTTING INTO OPERATION
Please follow strictly the described steps. It will help to prevent damage to
the generator, other equipment, and personnel injury.
Step 1.
Unpack the generator and check the presence in the package of the following
items:
-NPG30P11 (NPG30N11) generator;
-power supply cable;
-5 m HV output coaxial cable.
Step 2.
Set up the generator. Ground it obligatory by using a three-terminal power supply
cable and/or by grounding the HV output coaxial cable braid.
Step 3.
Check the HV connectors on the rear panel of the generator and on the HV coaxial
cable. Both connectors should be clean and insulating parts covered by thin
silicone grease. Clean the connectors with alcohol and/or cotton buds if necessary.
After cleaning, apply a drop of silicone grease before mating the connectors. The
grease fills the possible air gap between connectors and eliminates glow discharge
inside.
Attach the cable connector to the generator's rear panel connector. The tight and
firm contact of the connectors is very important for reliable operation. Even a
small air gap between the connectors may result in a glow discharge, arcing, and
damage to the equipment.
The following procedure is recommended for the firm and tight connection:
1. Align both connectors.
2. Hold the generator with one hand to prevent moving and press the cable
connector with another hand toward the generator's connector.
3. Screw the cable connector nut by hand, usually one or two turns. Do not
rotate the cable connector body.
4. Press the cable connector toward the generator's connector again.
5. Again, screw the cable connector nut one or two turns.
6. Repeat steps 4 and 5 up to tight contact. Finally, screw the cable
connector nut firmly by hands or gently with a wrench. Do not apply
excessive force to the wrench. The recommended torque is 10 N×m.
After the first testing of the generator, it is highly recommended to check whether
the tight contact was attained. Unscrew the cable connector. There should be no
ozone or burnt smell from the connectors or any burnt traces.
User manual of NPG30P11 and NPG30N11 11

Please do not connect/disconnect the HV output cable many times to prevent the
connectors from wearing and contamination. Silicone grease has been already
applied to both connectors at the factory. It remains inside the connector pair for a
long time and prevents the discharge inside.
Step 4.
Connect the HV output cable to the load by soldering the cable central wire to the
HV electrode of the load and solder/screw the load ground electrode to the screw
and nut on the cable ground clamp. The Teflon cone prevents the arcing between
the central wire and the ground (cable braid) across the cable solid PE insulator
(See Fig.4). If necessary, the additional wires can be used for the connection to the
load, but please keep the length of these wires as short as possible.
The wires more than 10 cm between the load and the coaxial cable have
excessive stray inductance, distort the pulse waveform significantly, and
result in reducing the pulse amplitude on the load.
Fig.4. The load side connection: the HV central wire of the coaxial cable (1) in
solid PE insulator (2), the Teflon cone insulator (3) which prevents
unwanted arcing, and the ground contact (4), i.e. screw and nut on the
clamp connected to the coaxial cable braid.
MEGAIMPULSE LTD. 12
1
2
3
4

The length of the HV output coaxial cable is 5 meters. Significantly shorter
output cable may result in damage to the generator.
Step 5.
Connect the power supply cable to the wall power outlet.
Power on the generator by the toggle switch on the front panel. The LED
indicators should light on and the cooling fans should start.
Step 6.
Check the internal triggering mode. The INT/EXT green latched button should be
in upper state, and the red LED on it should light on.
Set the required frequency, number of pulses per second/per burst, and percent of
the max pulse energy by the knobs. It is clever to start the experiments with low
operation parameters, which helps to prevent or minimize possible damage to the
equipment in case of any fault.
Press the HV ON/HV OFF push button. The red LED on the button should light
on, and the HV output pulses should be generated. Adjust the amplitude and the
frequency by the corresponding knobs as necessary.
Step 7.
Always stop the operation with the HV ON/HV OFF push button, and only after
that turn off the generator by the power switch. The temperature of the generator's
components becomes high after a long-time operation at a high pulse amplitude
and frequency. Allow the idle mode to cool down with the fans for several minutes
before turning it off.
User manual of NPG30P11 and NPG30N11 13

TRIGGERING THE GENERATOR
The generator can operate in continuous and burst modes in both internal and
external triggering as well as single pulse mode.
Internal triggering mode
The upper position of the INT/EXT green latched push button indicates the
internal triggering mode. The red LED on the button should light on continuously.
It is possible to set continuous or burst operations in this mode. The repetition rate
is adjusted from 1 Hz to 50 kHz by the FREQUENCY knob. The number of pulses
per burst is set from 1 to 1000 by the same knob after one second of pressing
down. The burst operation is chosen automatically if the set number of pulses is
less than the set frequency in Hz. The complete lists of preset frequencies and
number of pulses are presented in Appendix A.
External triggering mode
Press down the INT/EXT green latched button to set the external triggering mode.
The red LED on the button lights off and blinks with 1 Hz frequency when the
external triggering pulses are applied to the BNC-type SYNC IN connector. The
recommended triggering pulse amplitude is +2.4V … +5V @ 50 Ohm input
impedance. The delay between the triggering pulse front and the HV output pulse
(internal generator delay) is 1.2 µs or less. Typical jitter (RMS) is about 1 ns.
The maximum allowable pulse repetition rate and number of pulses per
second are limited by set FREQUENCY and NUMBER OF PULSES
parameters. Please set the required values of these parameters by the
FREQUENCY knob.
External triggering burst enable mode
Each short external triggering pulse, i.e. 20 µs or less, generates a single HV
output pulse, of course, if it is not blocked by the set parameters. In addition, a
long-duration triggering pulse generates a burst with the repetition rate set by the
FREQUENCY parameter and the burst length determined by the triggering pulse
width (see Fig.5). So, the external triggering pulse works as an enable signal. The
HV pulses are generated continuously while the triggering pulse level is high. This
is the simplest way to get externally triggered burst mode.
The single pulse mode is possible for the external triggering only.
MEGAIMPULSE LTD. 14

Triggering test mode
Click and hold for one second the PULSE ENERGY knob to activate the
TRIGGERING TEST mode. The HV ON/HV OFF button is blocked in this mode;
two-digits LED display shows 00, which means zero output power; triggering
sequence from internal or external source goes to SYNC OUT connector. This
mode allows to test the triggering and see the exact triggering sequence without
HV output pulses generation. Click and hold the PULSE ENERGY knob for one
second again to switch back from this mode to normal operation.
Fig.5. External triggering burst enable mode. The FREQUENCY parameter
(50 kHz) sets the repetition rate of the output pulses, SYNC OUT (CH2,
green line). The burst length, i.e. 25 pulses, is determined by SYNC IN
pulse width (CH3, blue line), which works as an enable signal.
User manual of NPG30P11 and NPG30N11 15

SYNC OUT PULSE
The generator has a front panel BNC-type connector for the SYNC OUT pulse
which is synchronized with the HV output pulse. The SYNC OUT pulse amplitude
is 3 V on 50 Ohm load and 5 V on high impedance load, the pulse width is 400 ns.
The delay between a rising edge of the SYNC OUT pulse and the HV output pulse
is 1.2 µs or less.
The oscillogram of the SYNC OUT pulse is shown in Fig.6. The HV output pulse
with a few nanoseconds rise time is a source of strong interference. Therefore, one
can see the noise on the oscillogram at the moment of the HV output pulse
generation.
Fig.6. The oscillogram of SYNC OUT pulse (Channel 2, cyan line). The pulse
amplitude is 3 V on 50 Ohm load and 5 V on high impedance load, the
pulse width is 400 ns. The delay between a rising edge of the SYNC OUT
pulse and the HV output pulse is 1.2 µs or less.
MEGAIMPULSE LTD. 16

OVERHEATING PROTECTION
The generator has overheating protection system. If the generator operates for a
long time with high amplitude and high repetition rate and/or at a high ambient
temperature, then it may be overheated. OVERHEAT LED lights on in this case,
and the generator stops the operation. The HV system is switched off
automatically and the HV ON/HV OFF push button is disabled. Please keep the
generator in idle mode for several minutes and allow the fans to cool it down.
OVERHEAT LED lights off when the temperature decreases down to the safe
limit. The generator is ready for the operation again.
ELECTRONIC FUSE
The 5-ampere electronic fuse on the front panel is used for protection. The red
button on the fuse should be in a pressed-down position which allows the power
supply of the generator.
WARRANTY
Please see your sales agreement to determine the warranty period and terms. The
generator has warranty seals.
Removing the warranty seals terminates the warranty.
User manual of NPG30P11 and NPG30N11 17

Appendix A.
A list of preset values for the frequency is presented in Table 1. One can set any of
them in the internal triggering mode. More than 1 kHz frequencies are available in
a burst mode only.
Table 1.
Frequency
4 digits display
Frequency
4 digits display
1 Hz
0.001
1 kHz
001.0
2 Hz
0.002
1.5 kHz
001.5
3 Hz
0.003
2 kHz
002.0
4 Hz
0.004
2.5 kHz
002.5
5 Hz
0.005
3 kHz
003.0
6 Hz
0.006
3.5 kHz
003.5
7 Hz
0.007
4 kHz
004.0
8 Hz
0.008
4.5 kHz
004.5
9 Hz
0.009
5 kHz
005.0
10 Hz
0.010
5.5 kHz
005.5
20 Hz
0.020
6 kHz
006.0
30 Hz
0.030
6.5 kHz
006.5
40 Hz
0.040
7 kHz
007.0
50 Hz
0.050
7.5 kHz
007.5
60 Hz
0.060
8 kHz
008.0
70 Hz
0.070
8.5 kHz
008.5
80 Hz
0.080
9 kHz
009.0
90 Hz
0.090
9.5 kHz
009.5
100 Hz *)
0.100
10 kHz
010.0
200 Hz
0.200
15 kHz
015.0
300 Hz
0.300
20 kHz
020.0
400 Hz
0.400
25 kHz
025.0
500 Hz
0.500
30 kHz
030.0
600 Hz
0.600
35 kHz
035.0
700 Hz
0.700
40 kHz
040.0
800 Hz
0.800
45 kHz
045.0
900 Hz
0.900
50 kHz
050.0
*) The default value of 100 Hz is set at power on the generator.
MEGAIMPULSE LTD. 18

A list of preset values for the number of pulses per burst or per second is presented
in Table 2. The 4-digit display flashes at 1 Hz frequency, while displaying the set
value of the number of pulses.
Table 2.
Number of pulses
4 digits display
Number of pulses
4 digits display
1
0001
60
0060
2
0002
70
0070
3
0003
80
0080
4
0004
90
0090
5
0005
100
0100
6
0006
200
0200
7
0007
300
0300
8
0008
400
0400
9
0009
500
0500
10
0010
600
0600
20
0020
700
0700
30
0030
800
0800
40
0040
900
0900
50
0050
1000 *)
1000
*) The default value of 1000 pulses is set at power on the generator.