Dense Plasma Focus

The Dense Plasma Focus device (DPF) or just Plasma Focus

What it is and How it Works

The dense plasma focus device consists of two cylindrical copper or beryllium electrodes nested inside each other. The outer electrode is generally no more than 6-7 inches in diameter and a foot long. The electrodes are enclosed in a vacuum chamber with a low pressure gas filling the space between them.

A pulse of electricity from a capacitor bank (an energy storage device) is discharged across the electrodes. For a few millionths of a second, an intense current flows from the outer to the inner electrode through the gas. This current starts to heat the gas and creates an intense magnetic field. Guided by its own magnetic field, the current forms itself into a thin sheath of tiny filaments; little whirlwinds of hot, electrically-conducting gas called plasma. A depiction of this sheath of plasma filaments is shown below, thanks to Torulf Greek (who also animated the above video):

This sheath travels to the end of the inner electrode where the magnetic fields produced by the currents pinch and twist the plasma into a tiny, dense ball only a few thousandths of an inch across called a plasmoid. All of this happens without being guided by external magnets.

The magnetic fields very quickly collapse, and these changing magnetic fields induce an electric field which causes a beam of electrons to flow in one direction and a beam of ions (atoms that have lost electrons) in the other. The electron beam heats the plasmoid to extremely high temperatures, the equivalent of billions of degrees C (particles energies of 100 keV or more).

Lassoed Lightning: The Focus Fusion-1 plasma caught on camera

The collisions of the electrons with the ions generate a short pulse of highly-intense X-rays. If the device is being used to generate X-rays for our X-ray source project, conditions such as electrode sizes and shapes and gas fill pressure can be used to maximize X-ray output.

If the device is being used to produce fusion energy, other conditions can minimize X-ray production, which cools the plasma. Instead, energy can be transferred from the electrons to the ions using the magnetic field effect. Collisions of the ions with each other cause fusion reactions, which add more energy to the plasmoid. So in the end, the ion beam contain more energy than was input by the original electric current. (The energy of the electron beam is dissipated inside the plasmoid to heat it.) This happens even though the plasmoid only lasts 10 ns (billionths of a second) or so, because of the very high density in the plasmoid, which is close to solid density, makes collisions very likely and they occur extremely rapidly.

The ion beam of charged particles is directed into a decelerator which acts like a particle accelerator in reverse. Instead of using electricity to accelerate charged particles, they decelerate charged particles and generate electricity. Some of this electricity is recycled to power the next fusion pulse while the excess (net) energy is the electricity produced by the fusion power plant. Some of the X-ray energy produced by the plasmoid can also be directly converted to electricity through the photoelectric effect (like solar panels).

The DPF has been in existence since 1964, and many experimental groups around the world have worked with it. LPP’s unique theoretical approach, however, is the only one that has been able to fully explain how the DPF works, and thus exploit its full capabilities.