Historical research guide · 0730 · 2024
Preparations for pB11 tests in the FF-2B dense plasma focus
Eric J. Lerner · Syed M. Hassan
In one minute
Eric Lerner and Syed Hassan of LPPFusion describe the last steps before their dense plasma focus, FF-2B, is fired on hydrogen-boron fuel — the aneutronic reaction that hands back charged particles instead of neutrons. A dense plasma focus is a compact machine that drives a megampere current through gas and pinches it into a tiny, extremely dense knot of plasma called a plasmoid. The authors note that their earlier FF-1 device reached a record mean ion energy above 200 keV in 2016, comfortably inside the range proton-boron-11 burning needs. This paper is about fuel and instruments. The fuel is decaborane, a boron-hydrogen powder that can be warmed into a vapour and fed in like any fill gas, bought isotopically pure so almost no radioactive beryllium-7 is made. The instruments read the two rare side reactions — the neutrons and the twenty-minute carbon-11 they produce — to count fusion reactions and measure ion energy, density and confinement time from outside the chamber.
Connection
Chapter 12 argues that proton–boron-11 is the fuel that matters, because it returns charged particles you can convert directly rather than neutrons you must shield. This is that argument as a work order: named hardware, a named fuel, installed detectors and a first measurement. It is also chapter 9’s plasmoid seen from the inside — the DPF makes its fusion in a self-organised magnetic knot, the same structure the site tracks in plasmoid and orb physics.
From the source
Proton–boron-11 fusion requires mean ion energies well above 100 keV, and only the dense plasma focus, the z-pinch and the laser have shown they can reach it; LPPFusion’s FF-1 device set a record mean ion energy above 200 keV in 2016, enough to initiate significant pB11 burn, with a ten-shot mean of 125 keV in the same series.Section 1, Introduction
The same three devices are the only ones to have reached ion densities above 10¹⁵ per cubic centimetre, and the dense plasma focus has demonstrated densities as high as 10²¹ per cubic centimetre — though not yet simultaneously with high ion energy — in machines that are compact and, at megampere scale, cost less than a million dollars to construct.Section 1, Introduction
Decaborane is chosen as the fuel because it is the borane with the largest boron-to-hydrogen ratio, 0.71, is a solid at room temperature that reaches a working vapour pressure with modest heating, and stays at negative pressure relative to the laboratory if the vacuum system fails; isotopically pure decaborane at 0.07 percent boron-10 cuts production of the 53-day beryllium-7 by a factor of 350.Section 2, Decaborane fuel
Because the main pB11 reaction emits no neutrons, the plasma is read through two secondary reactions instead: protons on boron-11 making carbon-11 plus a neutron above a 3 MeV threshold, and the product alpha particles on boron-11 making nitrogen-14 plus a neutron, with roughly one nitrogen-14 reaction for every 70 pB11 reactions.Section 3, Diagnostic techniques
Time-of-flight photomultipliers at 11.5 and 17.5 metres, a silver activation detector at 1.3 metres and a gamma-ray spectrometer give overlapping sensitivity — the activation detector registers as few as 3.5 × 10¹⁰ pB11 reactions and the spectrometer detects as few as 5 × 10⁵ carbon-11 nuclei at 10 cm — so fusion yield, mean ion energy and confinement time can all be measured from outside the chamber.Section 3, Diagnostic techniques; Figures 1 to 3
Before the boron shots the team intends to raise the density-confinement product above 2 × 10¹³ seconds per cubic centimetre — their best so far is 2.4 × 10¹² — by improving the symmetry of the breakdown and therefore of the current sheath and the plasmoid; the first decaborane runs are then expected to produce the first observable pB11 fusion in a dense plasma focus.Section 3, Diagnostic techniques; Sections 4 and 5
The way in
https://doi.org/10.3389/fphy.2024.1438880How to cite it
Eric J. Lerner, Syed M. Hassan (2024) Preparations for pB11 tests in the FF-2B dense plasma focus doi:10.3389/fphy.2024.1438880