Marx Generator | May 2016

Over the Spring of 2016 at Dartmouth, I designed and built a twelve-stage Marx generator for my final project in Professor William Lotko's course on electromagnetism in engineering. The generator I built is capable of creating discharges three times more powerful any other Marx generator at Dartmouth, and the model is currently used in Dr. Caitano da Silva's research of electrostatic discharge in the atmosphere.

Marx generators charge capacitors in parallel and then connect them in series suddenly. When the capacitors are connected in series, the potential difference between the first and last leads of the circuit will be a scalar multiple of what it was initially, and this now much larger potential difference allows the capacitors to discharge through the air, at a location called a spark gap. Typically the capacitors in a Marx generator are switched from parallel to series when several smaller spark gaps fire. This causes a short circuit in the initial layout, reforming the circuit with the capacitors in series.

FiringGif

Animation of Marx Generator Firing

The main problem with Dr. da Silva's original Marx Generator was that the spark gap of the system was not much larger than the spark gap of the short circuit. This meant that the potential difference across the spark gap during firing was not much larger than the potential difference across an individual capacitor during charging. Dr. da Silva had asked that I redesign the circuit such that the generator could fire across a spark gap of one inch, with a period of one second.

Video of My Marx Generator Firing

By increasing the number of stages in the circuit, I was able to increase the amplified voltage of the generator. I also experimented by changing the resistance in between the capacitors, in order to adjust the period of firing to approximately one second. Finally, I redesigned the spark gap to include sharper metal leads. This concentrated the electric field as it propagated through the air, allowing the larger spark gap. Dr. da Silva was pleased with the new generator and currently uses it in his research.