LPP Fusion Will Scale to Higher Fusion Yield With New Beryllium Electrode

On June 4th, 2019 LPPFusion’s research team started a new series of experiments using for the first time beryllium electrodes in a plasma focus device.

If LPP Fusion development succeeds then they will be able to mass-produce 5 megawatt nuclear fusion reactors with aneutronic (aka low radiation) reactions and each device will be about the size of a small shed. They would fit in a regular ten foot by ten foot room and they would capture arcs of energy directly as electricity.

The price would be ten to twenty times less than coal or natural gas at half a cent per kilowatt-hour.

After 44 shots to date, they have achieved their first goal of firing with low impurities.

Fusion yield has risen 60-fold since the first shot and is now 1/10th of a joule. This is
comparable with the best results achieved with the similar 10-cm long tungsten anode, but not yet above our record of ¼ J, achieved in 2016 with a longer 14-cm anode. They have not yet seen the long-lived filaments that they hope to produce as a step to getting much higher fusion yield. That is their next goal.

The main reason for replacing their tungsten electrodes with beryllium ones was to reduce impurities in the plasma. The tungsten electrode formed a deep, fragile, tungsten oxide outer layer, that was easily vaporized, unlike pure tungsten metal. They expected beryllium would be far better in this respect, and they were right, as it formed a self-limiting oxide layer only 10 nm thick.

The initial goal of getting low impurity was reached but it looked different than expected. The electrode looked really dirty as it was totally covered in dark dust. They roughly measured the amount of dust on the vacuum chamber windows, using a spectrometer. They estimate the thickness at 25 nm. That does not sound like much, but it was 20 times more than they had expected.

Subsequent shots rapidly removed the dust or melted it into a smooth layer on the electrode and vacuum chamber. As more and more of the dust was removed, the impurities in the plasma decreased.

Yield rising

While the beryllium overall has a small impact on the plasma, remaining concentrations of beryllium dust still have a big impact on the symmetry of the current sheath, especially at the start of the shot. This lack of symmetry, they think, is limiting the compression in the pinch and thus the density needed to achieve high fusion yield.

They are seeing a steady rise in fusion yield as tests continue. The first measurable fusion yield was on shot 3, with only 1.6 mJ. By shot 7, they were at 20 mJ. They started altering the axial field coil current, which controls the amount of spin on the plasmoid, reaching 100 mJ on shot 43. By comparison, their record yield with FF-1 was 250 mJ, a quarter-J. Their first fusion yield goal with the beryllium is 1 J and they aim to reach 10 J by 200 shots.

They have achieved the first goal of the 2019 plan and might get to the 200 shot and 10 joule per shot level in another month.

The commercial goal is to generate 5 megawatts. 5 megawatt is 5 million joules per second. This would mean generate a net of 10 kilojoules per shot with 500 shots per second or generate a net of 50 kilojoules per shot with 100 shots per second.

The energy available in the pinch is proportional to the square of the current, so with a current of around 2.8 MA, instead of the present 1.1 MA, energy into the pinch could be increased to 80 kJ, which is almost 70% of the maximum energy that can be put into FF-1.

Written By Brian Wang, Nextbigfuture.com

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