Nuclear fusion the easy way

Por • 20 jul, 2020 • Sección: Ciencia y tecnología

Jonathan Tennenbaum

This is the second in a three-part series. Read part 1 here.

15/07/2020. In Part 1 of this series, I introduced the reader to a promising innovative approach to nuclear fusion, utilizing a small, inexpensive device called the dense plasma focus (DPF).

The firm LLP Fusion, founded by plasma physicist Eric Lerner, has succeeded in producing large numbers of fusion reactions and record temperatures of 2.8 billion degrees with the DPF. In many respects, the Lerner device can compete with fusion experiments costing a hundred times more. How is this possible?

It’s time to explain how Eric Lerner’s DPF device works. (The interested reader can find more information on the LLPFusion website. I also recommend Eric Lerner’s video presentation.)

The physical principles of the dense plasma focus are well understood theoretically and have been demonstrated in countless experiments since the 1970s. Experiments reveal an astonishing complexity of phenomena in DPF discharges, characterized by self-organization and the formation of highly energy-dense structures.  

The specific DPF design used by Eric Lerner consists of a pair of concentric berylium electrodes, 10 centimeters long, mounted in a chamber filled with gaseous fuel at low pressure. The outer electrode, the cathode, has an outside radius of 5 centimeters. The inner electrode, the anode, is a hollow cylinder of 2.8 cm radius. 

The electrodes are connected via a fast switch to a bank of capacitors charged up to a voltage of (typically) 40,000 Volts. When the switch is closed, the capacitors send a powerful electricity pulse to the electrodes, causing an electrical discharge – a ring-shaped spark – to form between the electrodes. At its peak, over a million amperes of current flow through the device.

What exactly is this “spark”?  Connecting the capacitor bank to the electrodes creates an intense electric field in the space between them. The small number of electrons that happen not to be bound together with nuclei in the gas is accelerated with enormous force toward the anode, colliding with atoms along the way and setting further electrons free.

Atoms that have lost electrons become positively charged ions and are accelerated toward the cathode, colliding with other atoms as they move. Some also collide with the electrodes, liberating more particles (mainly electrons from the cathode).

An avalanche ensues, with more and more electrons being knocked out of the atoms, creating more and more free electrons and ions and more collisions. The gas is rapidly transformed into a hot, high-energy medium consisting of freely moving electrons and ions.

This medium is what physicists term a “plasma” – sometimes called “the fourth state of matter.” Actually, most of the matter in the universe exists in the plasma state.

Now the fun starts. The flows – of electrons to the anode and ions to the cathode – constitute electric currents. Electric currents generate magnetic fields. The magnetic fields act on the electrons and ions, which in turn can change the pattern of currents. 

The pinch effect

At this point, a well-known physical mechanism known as the “pinch effect” comes into play. The pinch effect provides the key mechanism by which the DPF concentrates its energy.

Put simply, the pinch effect refers to the fact that parallel electric currents attract each other. This effect is a consequence of the magnetic fields generated by the currents. 

As a result, a plasma carrying a strong current will be “pinched” – compressed – perpendicular to the direction of the current. 

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