A beam of tritons (mass

PHYSICS · Multi-part · Fermi University Physics · Plasma Physics · Kinetic theory, collisions and transport · Kinetic theory, collisions and transport

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

Problem

m_t = 3m_p

m_p

the proton mass) is injected at

600\,\mathrm{keV}

into a 50:50 deuterium-tritium plasma with electron temperature

T_e = 12\,\mathrm{keV}

. ((a)) The critical speed

v_c

, at which electron drag equals ion drag, depends on the background plasma but not on the fast ion's own mass, so the critical energy

E_c = \tfrac12 m_fv_c^2

scales linearly with the fast-ion mass

m_f

for a fixed background. Using the quoted result that

3.5\,\mathrm{MeV}

alpha particles (mass

4m_p

) in a D-T plasma at

10\,\mathrm{keV}

have

E_c = 33T_e

, find

E_c

for the triton beam. ((b)) Decide whether the tritons initially heat electrons or ions.

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