COMPASS points to ITER

Fusion followers: the COMPASS reactor in Prague with delegates to the Research Connection conference

By Matin Durrani

When they reach retirement age, physicists in many countries are simply told to pack their bags and go.

Not so for Jan Stoeckel, former head of tokamaks at the Insitutute for Plasma Physics (IPP) in Prague. When he turned 65, he simply stepped down from the hotseat, found a successor in Radomir Panek, and carried on working.

At least that’s what he told me yesterday on a fascinating guided tour of the institute’s COMPASS reactor, organized as part of the European Commission’s massive 2009 “Research Connection conference”:Research Connection conference here in Prague.

In a sort of parallel with Stoeckel’s career, the COMPASS reactor, which used to be based at the UK Atomic Energy Authority’s based in Culham, was all set to be mothballed until the IPP stepped in with an offer to rebuild it in Prague.

As Stoeckel explained to me as he took me round the brand new building in which COMPASS is housed, the reactor was originally built in the late 1980s, but was sold to the IPP for one pound in 2007, shipped to Prague and rebuilt over the last 18 months.

What makes COMPASS still useful is it that it is essentially a scaled down, one-tenth version of the ITER fusion reactor being built in Cadarache in southern France.

Although COMPASS initially won’t actually fuse nuclei together – deuterium-tritium reactions can be dangerous and expensive – the reactor will still be useful to study turbulence in hydrogen plasmas. And because it’s basically a tiny version of ITER, that work should give invaluable insights into how to keep ITER’s plasma stable.

The plasma in the D-shaped reactor is heated thanks to massive 100kA currents running in big coils around the outside of the vessel. The magnetic fields produced by the coils then induce a current to flow toroidally through the plasma, which acts like the secondary loop of a transformer.

The reason for the turbulence in the plasma is the huge amount of energy pumped in the reactor . Physicists want to minimize and understand the turbulence as it can cool the plasma and require more and more energy to maintain its temperature.

After I asked Stoeckel where exactly the 100kA currents come from – not the sort of thing you can get from a couple of AA batteries — he led me into a basement building where two massive 20 tonne solid steel flywheels are located.

Motors drive the cylindrical flywheels, which float on a thin oil film. When they reach a top speed of over 1700 revs per minute, the motor is uncoupled and the flywheel acts as a massive generator. The resulting pulses of current are sent to the coils of the vessel, discharging in about 3s, allowing plasma experiments to be carried out.

As we headed back up stairs, Stoeckel pointed out that his lab used to be the site for the world’s first tokamak reactor, which had originally been built at the world-famous Kurcahtov Institute in the Soviet Union. Known in Prague as CASTOR, it has now being rebuilt for a second time at the Czech Technical University as a teaching and educational tool.

Seems like plasma physicists – and plasma-physics experiments – are never too old for science.