All Figures

$\begin{figure} \par\includegraphics[width=7.2cm,clip]{1102fg01.eps}\end{figure}$ Figure 1: The energy and pitch-angle diffusion: a) - depth variations of the initially mono-energetic beams with energies 4, 16, 36, 64 and 96 keV losing energy in pure Coulomb collisions without pitch-angle diffusion; b) - the same as in a) but with pitch-angle diffusion; c) - depth variation of a beam injected with a power-law spectrum ( $E_{\rm low}=16~{\rm keV}$ , $E_{\rm upp}=384~{\rm keV}$ and $\gamma = 3$ ). The beam differential spectra ( $\frac {{\rm d}N} {{\rm d}E} (\xi, E)$ ) versus energy plotted for different column densities from the corona (dashed and dotted lines), to transition region (dash-dotted line) and chromosphere (dash-dot-dotted and short-dashed lines).
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In the text

$\begin{figure} \par\includegraphics[width=13.4cm,clip]{1102fg02.eps}\end{figure}$ Figure 2: Energy - pitch-angle ( $E - \mu$ ) distributions (the vertical axis) versus energy E and pitch-angle cosines $\mu$ calculated without a return current effect for beams injected with the energy range 16-384 keV, spectral index $\gamma = 3$ and initial energy flux 10¹⁰ erg cm^-2 s^-1. a) Corresponds to column density 1.8 $\times$ 10¹⁸; b) to 1.3 $\times$ 10¹⁹; c) to 5.1 $\times$ 10²⁰; and d) to 2.9 $\times$ 10²² cm^-2.
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In the text

$\begin{figure} \par\includegraphics[width=7.5cm,clip]{1102fg07.eps}\end{figure}$ Figure 7: The variations of a) the ionisation degree with depth from Zharkova & Kobylinskii 1993 and b) the beam density with depth for initial beam flux $F_{\rm0}$ = 10⁸ erg cm^-2 s^-1 for different initial spectral indices. The solid curves correspond to beam densities in a fully ionized atmosphere, the dashed curves correspond to beam densities in the plasma with ionization degree profile as in a).
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In the text

$\begin{figure} \par\includegraphics[width=13.9cm,clip]{1102fg08.eps}\end{figure}$ Figure 8: The beam particle density variations with depth calculated without electric field a) for an initial energy flux of 10¹⁰ erg cm^-2 s^-1 and with an induced electric field, for the initial energy fluxes 10⁸ erg cm^-2 s^-1 b), 10¹⁰ erg cm^-2 s^-1 c) and 10¹² erg cm^-2 s^-1 d) and for initial spectral indices 7 (solid curves), 5 (dashed curves) and 3 (dot-dashed curves).
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In the text

$\begin{figure} \par\includegraphics[width=13.9cm,clip]{1102fg09.eps}\end{figure}$ Figure 9: The beam energy flux variations. The plots a)- d) correspond to the same models as in Fig. 8.
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In the text

$\begin{figure} \par\includegraphics[width=7.5cm,clip]{1102fg10.eps}\end{figure}$ Figure 10: The effect of the converging magnetic field. a) - The beam particle density variations versus column density for initial spectral index $\gamma = 3$ and initial energy flux $F_{\rm0}$ = 10⁸ erg cm^-2 s^-1 precipitating in a magnetic field converging with a factor of 10 (dot-dashed line) and with a factor of 100 (dotted line). The beam particle densities for a beam precipitating in a non-converging field is plotted by a solid line. b) - The ratio of the total non-thermal bremsstrahlung intensity produced in the corona (2 $\times$ 10¹⁷ cm^-2-2 $\times$ 10²⁰ cm^-2) to that in the chromosphere (>2 $\times$ 10²⁰ cm^-2) versus magnetic field convergence rate $\alpha$ .
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In the text

$\begin{figure} \par\includegraphics[width=7.5cm,clip]{1102fg11.eps}\end{figure}$ Figure 11: The HXR bremsstrahlung spectra produced by precipitating electrons with different sets of initial energy flux and spectral indices. In panel a) we show spectra for initial flux 10⁸ erg cm^-2 s^-1, b) 10¹⁰ erg cm^-2 s^-1 and c) 10¹² erg cm^-2 s^-1. The solid lines correspond to the initial beam spectral index $\gamma = 7$ , dashed to $\gamma = 5$ and dot-dashed to $\gamma = 3$ . The photon spectral indices measured using these spectra are presented in Table 2.
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In the text

$\begin{figure} \par\includegraphics[width=7.5cm,clip]{1102fg12.eps}\end{figure}$ Figure 12: Variations of the bremsstrahlung photon spectral indices $\delta$ for beams with different initial energy flux (see Table 2). The indices $\delta _{\rm high}$ of the higher energy part of the spectra (which is not dependent on the energy flux) are shown by the dotted line. The indices $\delta _{\rm low}$ of the lower energy part of the spectra are shown for initial energy fluxes 10⁸ erg cm^-2 s^-1 (the solid lines with squares), 10¹⁰ erg cm^-2 s^-1 (the dashed line with circles) and 10¹² erg cm^-2 s^-1 (the dash-dotted line with triangles).
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In the text

$\begin{figure} \par\includegraphics[width=14cm,clip]{1102fg13.eps}\end{figure}$ Figure 13: Low-energy flattening in the non-thermal bremsstrahlung spectra observed with RHESSI in the flares of 23 ( a), b)) and 20 ( c), d)) of July, 2002. HXR spectra observed in the 23 July flare at 00:23:44 UT a) and 00:25:32 UT b) (the courtesy of Holman et al. 2003) were fitted by the HXR simulations produced by a beam with initial electron spectral index $\gamma =3.7$ and with initial energy flux $\sim$ 3 $\times$ 10⁹ erg cm^-2 s^-1at the first moment and $\sim$ 10¹⁰ erg cm^-2 s^-1 at the second one. The plots c) and d) present the HXR spectra for the flare of 20th of July, 2002 taken at 21:15:20 UT and 21:20:20 UT respectively, which were also fitted by a single beam simulation (see for details Sect. 3.3.3).
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In the text

$\begin{figure} \par\includegraphics[width=13.4cm,clip]{1102fg03.eps}\end{figure}$ Figure 3: Energy - pitch-angle ( $E - \mu$ ) distributions (vertical axis) versus energy E and pitch-angle cosines $\mu$ calculated with a return current effect for a beam injected with the energy range $16{-}384~{\rm keV}$ , spectral index $\gamma = 3$ and initial energy flux 10¹⁰ erg cm^-2 s^-1. a) Corresponds to the column density 4.2 $\times$ 10¹⁷ cm^-2; b) to 8.4 $\times$ 10¹⁷; c) to 1.8 $\times$ 10¹⁸; d) to 1.3 $\times$ 10¹⁹; e) to 5.1 $\times$ 10²⁰ and f) to 2.9 $\times$ 10²² cm^-2.
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In the text

$\begin{figure} \par\includegraphics[width=13.4cm,clip]{1102fg04.eps}\end{figure}$ Figure 4: The same as in Fig. 3 but for spectral index $\gamma = 7$ and initial energy flux 10¹⁰.
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In the text

$\begin{figure} \par\includegraphics[width=13.4cm,clip]{1102fg05.eps}\end{figure}$ Figure 5: The same as in Fig. 3 but for spectral index $\gamma = 3$ and initial energy flux 10¹².
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In the text

$\begin{figure} \par\includegraphics[width=13.4cm,clip]{1102fg06.eps}\end{figure}$ Figure 6: The same as in Fig. 3 but for spectral index $\gamma = 7$ and initial energy flux 10¹².
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In the text

$\begin{figure} \par\includegraphics[width=13.9cm,clip]{1102fg08.eps}\end{figure}$	Figure 8: The beam particle density variations with depth calculated without electric field a) for an initial energy flux of 10¹⁰ erg cm^-2 s^-1 and with an induced electric field, for the initial energy fluxes 10⁸ erg cm^-2 s^-1 b), 10¹⁰ erg cm^-2 s^-1 c) and 10¹² erg cm^-2 s^-1 d) and for initial spectral indices 7 (solid curves), 5 (dashed curves) and 3 (dot-dashed curves).
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$\begin{figure} \par\includegraphics[width=13.9cm,clip]{1102fg09.eps}\end{figure}$	Figure 9: The beam energy flux variations. The plots a)- d) correspond to the same models as in Fig. 8.
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$\begin{figure} \par\includegraphics[width=13.4cm,clip]{1102fg04.eps}\end{figure}$	Figure 4: The same as in Fig. 3 but for spectral index $\gamma = 7$ and initial energy flux 10¹⁰.
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$\begin{figure} \par\includegraphics[width=13.4cm,clip]{1102fg05.eps}\end{figure}$	Figure 5: The same as in Fig. 3 but for spectral index $\gamma = 3$ and initial energy flux 10¹².
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$\begin{figure} \par\includegraphics[width=13.4cm,clip]{1102fg06.eps}\end{figure}$	Figure 6: The same as in Fig. 3 but for spectral index $\gamma = 7$ and initial energy flux 10¹².
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