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Fig. 4.26.3. Downstream energy spectra for test-particle numerical simulations for case of steady-state spectra obtained from simulations using different values of the shock-normal angle. According to Giacalone (2005a).

The Fig. 4.26.4 is for the case of a time-dependent acceleration process. Here, weaker turbulence was used and two different shock-normal angles are considered (as indicated).

10° 101 102 103 10" 10s 106 107 Energy (m U j~ / 2)

Fig. 4.26.4. Downstream energy spectra for test-particle numerical simulations for case of time-dependent spectra for two different shock-normal angles and weaker turbulence. According to Giacalone (2005a).

The results shown in Fig. 4.26.3 and Fig. 4.26.4 indicate that the injection energy, and therefore, the acceleration efficiency, does not have a strong dependence on the shock-normal angle. However, as shown in the Fig. 4.26.4, for any given time interval to accelerate the particles, perpendicular shocks produce the highest-energy particles. This is because, as it was discussed above, the acceleration rate is strongly dependent on the shock normal angle, provided k±/k// << 1.

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