A lower-hybrid current-drive scheme resonates with electrons at in both of two discharges

PHYSICS · Subjective · Fermi University Physics · Plasma Physics · Kinetic theory, collisions and transport · Fusion plasmas

Plasma Physics, Ch Coulomb collisions: the Coulomb logarithm, the Fokker-Planck equation and Spitzer resistivity

Problem

A lower-hybrid current-drive scheme resonates with electrons at

v = 3v_{te}

in both of two discharges. (a) Discharge A:

T_e = 2.0\,\mathrm{keV}

n_e = 3.0\times10^{19}\,\mathrm{m^{-3}}

. (b) Discharge B:

T_e = 5.0\,\mathrm{keV}

n_e = 2.0\times10^{19}\,\mathrm{m^{-3}}

. Using the result that, at fixed

v/v_{te}

, the current driven per unit absorbed power scales as

T_e/(n_e\ln\Lambda)

, and treating

\ln\Lambda

as unchanged between the two discharges (it varies only logarithmically), find the factor by which the current-drive efficiency in discharge B exceeds that in discharge A.

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