A spacecraft in the solar wind at about astronomical units from the Sun reports ,…

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 spacecraft in the solar wind at about

0.3

astronomical units from the Sun reports

n_e = n_p = 5.0\times10^{7}\,\mathrm{m^{-3}}

T_e = T_p = 20\,\mathrm{eV}

(taken equal for this estimate) and

B = 50\,\mathrm{nT}

. A magnetic structure about

L = 1.0\times10^{5}\,\mathrm{m}

across is carried past the spacecraft in

10\,\mathrm{s}

, and the question is how the plasma responds to it. Take

\ln\Lambda = 25

as the quoted Coulomb logarithm. ((a)) Find

\lambda_{De}

N_D

f_{pe}

|f_{ce}|

, the proton gyrofrequency

\Omega_p

and the thermal Larmor radii

r_{Le}

and

r_{Lp}

, with

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

. ((b)) Find

\nu_{ei}

and the electron mean free path

\lambda_{\rm mfp} = v_{te}/\nu_{ei}

. ((c)) Place the plasma on the density-temperature map: is it weakly coupled, classical and non-relativistic? ((d)) For this structure, decide whether the plasma may be treated as quasineutral, whether each species is magnetised, and whether the response is collisional or collisionless. State which two numbers you compare in each case.

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