Dusty Plasmas

M. Coppins

M. Bacharis

C. Willis

T. Zimmermann

J. Allen

Z. Ehsan

Dusty plasma

= plasma containing small ( 1 m) solid particles.

Such plasmas occur in:

• industry,

• space,

• fusion devices,

• laboratory experiments.

Dusty plasma experiments often carried out in “low temperature” RF discharges.

Problem: dust falls to the bottom.

Dusty plasma experiments are carried out in micro-gravity on the International Space Station.

There has been a huge growth in work on dusty plasmas in the last decade or so.

Less work has been done on:• dust in fusion,• basic dust-plasma interactions.

e.g. dust crystals.

But most of it concerns “collective phenomena”

Dust in Fusion

[Click on image for a movie of dust in the MAST Tokamak at Culham.]

Dust will be a critical issue for ITER.

Imperial College’s DTOKS code* can simulate the motion and lifetime of dust in ITER.

* J.D. Martin, et al, EPL, 83, 65001 (2008).

Basic dust-plasma interactions

Dust grains:

• become charged

• temperature can change

• shape and size can change

• experience forces from plasma

Standard theory of dust grain charging by ion/electron collection is OML...

...as explained in text books*

* e.g., P.K. Shukla and A.A. Mamun, Introduction to dusty plasmas (IOP, 2002).

More accurate treatments include induced space charge in plasma around dust grain and symmetry breakdown associated with plasma flow, e.g., SCEPTIC code* developed by I. Hutchinson at MIT:

electrostatic potential around a dust grain, including the effect of plasma flow (from the left).

*I.H. Hutchinson, Plasma Physics and Controlled Fusion, vol 44, p 1953 (2002), vol 45, p 1477 (2003), L. Patacchini and I.H. Hutchinson, Plasma Physics and Controlled Fusion, vol 49, p1193 (2007), vol 49, p 1719 (2007), I.H. Hutchinson and L. Patacchini, Physics of Plasmas, vol 14, p013505 (2007).

Dust is routinely collected from inside Tokamaks

e.g., TEXTOR

There are two interesting things about this dust...

Firstly, most of it is not spherical.

Most theoretical studies of dust-plasma interactions assume the dust is spherical.

Possible PhD Project

Charging of non-spherical dust in plasma

The project would be theoretical/computational, and would form part of our programme on dust in Tokamaks.

The second interesting thing about Tokamak dust is...

some of it is spherical.