Simulating an avalanche pulse generator in LTspice

Question

I need to create a very short (<1 ns) pulse and control the pulse frequency between 1 MHz and 10 MHz. One method to create short pulse I came across is Jim Williams avalanche pulse generator. Before I build it, I wanted to try it in LTspice. Here at APPENDIX D there is the Jim Williams avalanche pulse generator:

I simulated this in LTspice with the same circuit and transistor:

The voltage amplitude is not 10 V but very low in 250 uV level. The repetition rate in my case is 19 kHz and the pulse width is more than 650 ns and the pulses stop after some ms. Here are the plots:

This shows the voltage at both node A and Vout. Close to 20 ms the node A becomes 90 V but the pulses stop:

Does this mean the transistor is not going into avalanche in simulation? Besides the simulation, if it would work as in the paper, would it be possible to control the pulse frequency?

Edit:

To make simulation quick I used a voltage source instead of boost converter. I followed some SPICE commands from the answer and had to increase the voltage upto minimum 120 V:

I get short pulse now around 800 ps with 2 pF and 1.3 ns with 4.7 pF:

But my problem is I need repetition rate from 1 MHz to 10 MHz and when I tweak the 1 Meg resistor I cannot achieve that. Is that possible in any way?

Answer 1

Here is an example of an LTSpice file ...

• Bordodynov\npnAvalanche\AvalancheMMBT2369\ExampleMMBT2369_v2.asc. Seems ok.
  Note the symbol of the transistor X1.
  Green curve is X1 collector.

For repetitive pulse, use a pre-charge cicuit and a pulse on "base" would be probably enough.

Sorry, don't know enough LTSpice changing colors ... :-(

To "help" (some sort of "synchronizing") a little with the "breakdown", I used this circuit.
But pulse is wider than needed :-( . However, the idea could help ...

Another circuit (2 ns pulse, 250ns recovery time). R1 must be greater than 5k.

I have tried this. Don't know if it is an "artefact" ...
Pusle has 400-500 ns wide.