A laboratory argon plasma sits in a uniform field inside a vessel of radius

PHYSICS · Multi-part · Fermi University Physics · Plasma Physics · The plasma state and single-particle motion · The plasma state and single-particle motion

Plasma Physics, Ch What makes an ionised gas a plasma: shielding, the plasma parameter and the natural frequencies

Problem

A laboratory argon plasma sits in a uniform field

B = 0.10\,\mathrm{T}

inside a vessel of radius

5.0\,\mathrm{cm}

. Its electron density is

n_e = 1.0\times10^{16}\,\mathrm{m^{-3}}

. The electrons have

T_e = 3.0\,\mathrm{eV}

, and the singly charged ions (

\mathrm{Ar^+}

, mass

40\times1.67\times10^{-27}\,\mathrm{kg}

) have

T_i = 0.030\,\mathrm{eV}

. Electrons collide with neutral atoms at a rate of

1.0\times10^{8}\,\mathrm{s^{-1}}

and ions at a rate of

1.0\times10^{6}\,\mathrm{s^{-1}}

. ((a)) Find the size of the gyrofrequency

|\Omega_s|

and the thermal Larmor radius

r_{Ls} = v_{ts}/|\Omega_s|

, with

v_{ts} = (T_s/m_s)^{1/2}

, for each species. ((b)) Decide which species is magnetised, testing both conditions. ((c)) Before using any of this, place the plasma on the density-temperature map (weakly coupled? classical? non-relativistic?) and check the three conditions for calling it a plasma, taking

L

as the vessel radius and

\tau

as the electron-neutral collision time.

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