The Mega-Ampere Generator for Plasma Implosion Experiments. Admittedly, the acronym is a bit contrived, but it’s a pretty fair description of the machine, a house-sized experimental facility two storeys underground at Imperial College’s campus in South Kensington, London.

MAGPIE is a pulsed power machine. It is designed to deliver a short, large electrical current to a ‘load’, which is whatever you want to blast a current through. MAGPIE can use a range of loads, but normally a load is usually some arrangement of metal wires or piece of foil. Just like the filament in an incandescent lightbulb, when an electric current goes through these wires, they heat up. In MAGPIE, the current is so intense the electrons in the solid wires are blasted off the atoms, and a hot dense plasma forms. 

These plasmas only last for a few billionths of a second before cooling down, but during that time they act like nothing else on Earth. MAGPIE allows us to create the extremes of temperature and density normally only seen at the core of a planet, or in an exploding star. As stars are not easy things to fit inside a laboratory, we have an incredible opportunity to study these plasmas from every angle, instead of staring at them through a telescope from a billion billion miles away.

MAGPIE can generate a 1.4 MA current in 100 ns. For comparison, an electric lamp uses a million times less current, and a light switch is thousands of times slower. Generating a huge current quickly is technically challenging – most of the physical bulk of MAGPIE is dedicated to solving this problem, with only a relatively small volume for the actual experiments.

We start by charging four large banks of capacitors, which store electric charge. When we are ready for the experiment, we discharge the capacitor banks  – at this point, it still take milliseconds for the charge to all drain out, which is too slow for what we need. So we direct the charge into four 3m long section of metal pipe. When we open the switches at the other end of the line, the charge all flows out very quickly, giving us a very large current, very quickly. This current is then directed into the load, which melts, boils, ionises and implodes very rapidly.

More information on MAGPIE, including all of our journal articles, can be found on our project webpage. The explanation I’ve given here is quite simplistic, but it gets the gist across – by storing electric charge up and then releasing it very rapidly, it is possible to recreate and study extreme conditions that normally only exist in unusual or far distant events, like exploding stars.

Leave a Reply

Your email address will not be published. Required fields are marked *