View full image The COMPASS tokamak in Prague has established its credentials by achieving H-mode operation

The COMPASS tokamak in Prague has established its credentials by achieving H-mode operation (picture: Thinkstock, Montage)

COMPASS shows the way to H-mode

A five year quest has borne fruit with the COMPASS tokamak in Prague’s Institute of Plasma Physics (IPP) achieving H-mode performance. The milestone marks a new era for fusion research in the Czech Republic, which began in 2007 when the COMPASS tokamak was transferred from the CCFE in UK.

“We have historical links which made us a regional centre for scientists from Hungary, Bulgaria and Poland, but now scientists from West Europe have also been visiting COMPASS – it’s another meeting point for the fusion community.” says fusion scientist Dr Jan Mlynář from IPP.

“It is very important that we can now do H-mode operation as this is the standard ITER scenario. We have invested lots of money into making an “ITER-like” operation scenario, in particular we purchased new heating neutral beams to achieve relevant ion temperatures and thus hopefully create Type I ELMs.”

Now the ITER-like mode of operation has been established, COMPASS can be used as a small scale test bed for ITER performance: combining COMPASS’s results with similar tests in ASDEX Upgrade (three times larger) and JET (six times larger) gives excellent extrapolation to ITER (ten times larger).

However, for some studies the overall size does not matter, and in these areas COMPASS really comes into its own. H-mode’s high confinement stems from a sharp increase in the pressure at the edge of the plasma, known as the edge transport barrier or pedestal; COMPASS’s ability to reproduce H-mode makes it arguably as useful a device as the bigger machines in studying this plasma edge phenomenon, says Dr Mlynář.

“We can now measure and detail properties of this pedestal. All machines that have H-mode have this edge pedestal, however nobody really understands the details of physics behind this pedestal… Our advantage is that we are not so expensive and so “heavy” in operation. It is simpler to test different ideas or different new hardware.”

“Also, big machines are usually overbooked – scientists need a really good reference to get research time at ASDEX or JET, and promising results from smaller tokamaks is a very good reference.”

With the result in Prague coinciding with the recent release of EFDA’s road map to fusion, it’s clear that COMPASS will have a significant part to play in the navigation towards the goal of fusion energy!

The Institute of Plasma Physics is the Czech Republic’s signatory to the European Fusion Development Agreement.