Subscribe options

Select your newsletters:

Please enter your email address:

@

News & Media

Latest ITER Newsline

  • Port cells | All 46 doors in place

    In ITER, ordinary objects and features often take on an awesome dimension. Take the doors that seal off the port cells around the Tokamak for instance. Doors th [...]

    Read more

  • Toroidal field coils | Two make a pair

    One of the essential 'building blocks' of the ITER Tokamak is the pre-assembly of two toroidal field coils, one vacuum vessel sector and corresponding panels of [...]

    Read more

  • Industrial milestone | Cryostat manufacturing comes to an end in India

    With a flag-off ceremony on 30 June, India's L&T Heavy Engineering marked the end of an eight-year industrial adventure—the manufacturing of the ITER cryost [...]

    Read more

  • Local partners | A celebration for ITER's "vital artery"

    ITER is made possible through the work of thousands of scientists, engineers, workers of all trades and industries across the globe. It is also made possible by [...]

    Read more

  • Photo reportage | Travelling with a coil

    From the salt marshes of the inland sea Étang-de-Berre to the rolling hills around the ITER site (with a view of some of the highest alpine summits) an ITER con [...]

    Read more

Of Interest

See archived entries

Bouncing dust

DIFFER Press Office

Tracks of different types of dust particles in the plasma beam of Pilot-PSI: small velocity (a) loss to large velocity loss (b) and even sticking. Once a dust particle sticks to the surface, it cools down and is no longer visible. Credit: Andrey Shalpegin et.al.*, Nuclear Fusion (Click to view larger version...)
Tracks of different types of dust particles in the plasma beam of Pilot-PSI: small velocity (a) loss to large velocity loss (b) and even sticking. Once a dust particle sticks to the surface, it cools down and is no longer visible. Credit: Andrey Shalpegin et.al.*, Nuclear Fusion
When the hot, dense plasma in a fusion reactor hits the reactor's exhaust wall, dust particles will inevitably erode from the wall and be swept away by the plasma, or ionised gas. But how do these dust particles travel and where do they end up?

An international team has used sensitive cameras to produce the first ever fully resolved movies of dust motion in experiments with DIFFER's linear plasma generator Pilot-PSI (Nieuwegein, The Netherlands). The new data will feed into improved models for dust motion in the fusion reactor ITER.

"Dust particles are a few millionth of a metre (micrometre) in size. A challenge with detecting their minute motions is that you want to have the camera really close to the plasma," says Pilot-PSI operator Kirill Bystrov. In a complete fusion reactor, there is seldom the space to do that—instrumentation ports are too far away from this plasma-surface interaction region. "In Pilot-PSI, we can get the camera within half a metre of where the plasma hits the target."

The experiments reached a record spatial sensitivity of 9 micrometres per pixel. Previous experiments reached 200 micrometres to a few millimetres per pixel - ten to fifty times less sensitive than the record set in Pilot-PSI. This gives unparallelled information about how the dust particles roll, skip and bounce, and how they are influenced by the constant wind of plasma particles. This information will feed into predictive models for the dust motion, to clear up where it will collect and which reactor areas need special focus when cleaning.

The new measurements managed to clear up a mysterious form of motion where a dust speck kept its high temperature while sliding across a cooled surface. Intuitively, that just cannot happen: the particle should cool down to the surface temperature if it is in constant contact. It turns out the 200 micrometre per pixel resolution of the original measurements was to blame - where they saw a particle rolling or sliding in constant contact with the cooled surface, the more accurate 9 micrometre video clearly shows the dust speck bouncing across the surface and only cooling down a fraction when it strikes the surface between bounces.

Source: Highly resolved measurements of dust motion in the sheath boundary of magnetized plasmas; A. Shalpegin, F. Brochard, S. Ratynskaia, P. Tolias, M. De Angeli, L. Vignitchouk, I. Bykov, S. Bardin, K. Bystrov, T. Morgan

Read the full report on the DIFFER website.


return to the latest published articles