Beryllium Cathode Arrives





The long-awaited beryllium cathode arrived at LPPFusion’s Middlesex lab on August 18. Since the beryllium anodes have been in hand for some months, this completes the delivery of the electrodes that are needed for the next crucial step in the Focus Fusion experimental program. This will be the first time beryllium electrodes are used in a dense plasma focus device.

Beryllium, a very light metal, has long been planned for the next set of electrodes and has strong advantages over other materials. “We expect that beryllium electrodes will solve the impurity problem that has been limiting fusion energy yields for years,” says LPPF Chief Scientist Eric J. Lerner. The key reason is that the effect of impurity ions on the plasma is proportional to the square of the ion’s electric charge. Since beryllium has only 4 electric charges (four protons in the nucleus) each beryllium ion has an effect of 16. That is 300 times less than one tungsten ion (used in the current FF-1 electrodes) and 50 times less than one copper ion (used in the earlier electrodes).

This great reduction in impact on the plasma is expected to greatly lift fusion yield. In addition, the plasma will radiate far less energy, reducing x-ray damage to the anode tip. Finally, beryllium is nearly transparent to most x-rays, further reducing the damage to the anode. This will allow anodes in a future fusion generator to withstand hundreds of millions of fusion pulses before needing replacement.

Beryllium, however, does have two drawbacks that have prevented their use in plasma focus devices thus far. For one thing, beryllium is expensive. The electrode set cost LPPFusion over $120,000. This expenditure was only made possible by the money raised in LPPF’s 2014 Indiegogo crowdfunding campaign. Second, although beryllium in bulk metal form is harmless, beryllium dust that is fine enough to be breathed is toxic. In susceptible people, tiny amounts of dust set off auto-immune responses that generate serious disease.

Figure 1. The new beryllium cathode (25 cm or 10 inches in diameter) sits at LPPFusion’s lab in its sealed bag. The protection is needed because exposure to atmospheric humidity for too long can damage the part’s surface.

To ensure the safety of our researchers, LPPFusion will be buying the needed safety equipment, including a glove box that allows objects to be manipulated in a sealed environment. We’ve also designed modifications to the vacuum system of FF-1 so that any dust created during shots will be trapped in a safe manner and not exhausted to the environment.

Once the present series of experiments with the tungsten electrodes is completed, probably during September, FF-1’s vacuum chamber will be disassembled and shipped for a recoating with titanium nitride. This stable material will cover up any tungsten that has been plated onto the chamber. This and other upgrades to FF-1 will take a few months, leading to the start of new experiments with the beryllium electrodes around year-end.

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