Section 2Fusion engineeringPublished and peer-reviewed

The benchtop fusion machines

Bench to university. · 2 min read

What it proposes

Two architectures produce real fusion neutrons on a table. The inertial electrostatic confinement device is a wire cage in a vacuum chamber held tens of kilovolts negative, so ions fall inward and recirculate through a dense core. The small plasma focus is a capacitor bank fired into coaxial electrodes, whose current sheet folds over the anode and collapses onto the axis into a pinch. Both give a student a real neutron count and a real diagnostic problem, and both are where the plasmoid physics of section 5 is learned by hand.

Who it is forPlasma experimentalistsPulsed-power engineersDiagnostics builders

Why the library suggests it

A Tokyo Institute of Technology device running deuterium at 40 kilovolts and 2 milliamps produced ten thousand neutrons a second steadily from a table-top, and the authors then did the harder work of establishing where the fusions happen — finding a virtual anode standing in the centre, in a probe measurement and a simulation that agree (Neutron production rate and plasma characteristics of spherically convergent beam fusion, 2001). The star mode, the virtual anode and the nested virtual cathode of such a device are modelled particle by particle against probe data in Kinetic characteristics of ions in an inertial electrostatic confinement device (2020), and the Defense Intelligence Agency's own survey of the architecture closes with a concrete proposal — twelve radio-frequency ion guns aimed at one core to demonstrate breakeven on hydrogen-boron fuel (DIRD Inertial Electrostatic Confinement Fusion, 2010). On the plasma-focus side, a Chilean group showed that a machine storing 32 to 98 joules still pinches, because it is fast rather than large — a 160 nanofarad bank, 38 nanohenries, current rising in about 150 nanoseconds (Pinch evidence in a fast and small plasma focus of only tens of joules, 2004). A few hundred joules with a 300-nanosecond rise gave about 1.06 million neutrons a shot (Neutron emission from a fast plasma focus of 400 Joules, 2003), and interferometry inside a tens-of-joules machine confirmed that the dynamics, pinch conditions and electron densities of the hall-sized machines are all present (Dynamics and Density Measurements in a Small Plasma Focus of Tens-of-Joules-Emitting Neutrons, 2011).

The experiment or build

Build the inertial electrostatic device first: the parts list is a vacuum chamber, a high-voltage supply, a wire cage and a neutron counter, and the whole thing has been sold commercially for ore inspection. Then build the fast, small plasma focus, which is a pulsed-power exercise — low inductance is the entire design problem. The settling measurement in both cases is the deuterium-deuterium neutron yield per shot or per second, with the yield scaling correctly against current and vanishing when the deuterium is removed, and with the counter calibrated against a known source. That last clause is what separates a fusion machine from a machine that sprays ions at a wall.

Where it stands

Published and peer-reviewed — both architectures have measured neutron yields in the literature at bench scale, and neither is close to net energy.

Take it up

The measurement that settles it: The settling measurement in both cases is the deuterium-deuterium neutron yield per shot or per second, with the yield scaling correctly against current and vanishing when the deuterium is removed, and with the counter calibrated against a known source.
What it costs to start: Bench to university.
The engineer it grows: This is the apprenticeship every fusion engineer in this programme went through.

What it rests on

Where it sits in the curriculum

Fusion machines: pinches, focus devices and inertial drivers Plasmoids, charge clusters and the orbs The reference documents and the institutional record