Fig. 4.18.4. The scheme of the sheet in the frame of two-dimensional geometry. According to Pustil'nik (1977b).

This approach gives rise to difficulties of principle when explaining the spectrum and chemical composition of the accelerated particles. It is of importance that the neglecting of the particle-plasmon elastic collisions involved in this approach is barely incorrect, since the sheet is opaque for them (vf >> Vv).

(2) Stochastic acceleration in the turbulent pulsation field resulting in energy diffusion. In terms of this approach, the particles are accelerated in the particle-plasmon inelastic collisions (predominantly with the Longmire plasmons). Though this approach can more realistically include the conditions in the current sheet of a solar flare, it also faces difficulties due to a small thickness of the current sheet which makes the sheet "transparent" for inelastic scattering (v < a/v for particles with energies E > 10 keV). Even along an acceleration path equaling the current sheet length l = L = 1010 cm, the sheet is "transparent" for inelastic processes at E > 10 MeV, which is drastically at variance with observations (Pustil'nik, 1977c).

4.18.7. The spatial diffusion in the electric field of the sheet in the case of two-dimensional geometry with pure anti-parallel magnetic field

As it was noted above, the particles accelerated in the current sheet should suffer multiple elastic collisions with the ion-sound plasmons. The frequency of such collisions is (Kaplan and Tsytovich, M1972)

vSP vSE cs

v vT

Le y

Ws s

As a result, the particle motion will take the form of one-dimensional diffusion to the walls of the sheet (one-dimensionality due to magnetization, vf << a>H).

After reaching the walls, the particles will be ejected from the accelerated region along the force lines. The spatial diffusion coefficient is

When diffusing along the electric field, a particle should gain energy at a rate

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