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We selected flares according to the following criteria

On the Upward Motion of the Coronal HXR Sources in Solar Flares: Observational and Interpretation Problems. We selected flares according to the following criteria. The peak count rate in the Yohkoh M2-band (33--53 keV) is greater than 1000 counts per second per subcollimator

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We selected flares according to the following criteria

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  1. On the Upward Motion of the Coronal HXR Sources in Solar Flares: Observational and Interpretation Problems

  2. We selected flares according tothe following criteria • The peak count rate in the Yohkoh M2-band (33--53 keV) is greater than 1000 counts per second per subcollimator • The heliocentric longitude of an active region is greater than 80 degree

  3. The Study of Coronal HXR Sources • Removing a background from the HXT images • Selection of the most important sources and determination of their coordinates • Identification of the positions of a source in the successive images • The least-square analysis to obtain the average velocity V and its dispersion sigma

  4. Upward motion of the coronal HXR sourcein the Masuda flare • HXT M2-band images of the flare. The arrows show the direction of the HXR source motions • Height of the source centroid as a function of time

  5. The M3.6 flare on 1991 December 2 • The flare was particularly occulted by the solar limb • The average upward velocity of the upper HXR source was 23 km/sec

  6. For 5 of 20 selected flares, the average velocity V > 3 sigma • The upward component of average velocity is of about 10 - 30 km/sec • The effect should be studied statistically better by using the RHESSI high-resolution HXR and gamma- imaging data

  7. Particle Acceleration in a Collapsing Trap • A magnetic trap between the Super-Hot Turbulent-Current Layer (SHTCL) and a Fast Oblique Collisionless Shock (FOCS) above magnetic obstacle (MO) Ref.: Somov, B.V. and Kosugi, T., ApJ, 485, 859, 1997

  8. The First-order Fermi-type Accelerationas the Second-step Mechanism • Decrease of the field line length (collapse of the trap) provides an increase of the longitudinal momentum of a particle Ref.: Somov, B.V. and Kosugi, T., ApJ, 485, 859, 1997

  9. Acceleration of Electrons

  10. Acceleration of Ions Acceleration of protons • Each reflection of an ion on a moving mirror leads to a jumpy increase of the parallel velocity • Protons are easily accelerated from thermal to MeV energies Ref.: Somov, B.V., Henoux, J.C., Bogachev, S.A., Adv. Space Res., 30, No. 1, 55, 2002

  11. Two Effects in Collapsing Trap • Decrease of the field line length provides the first-order Fermi acceleration • Compression of the magnetic field lines provides betatron acceleration

  12. The Betatron Effect in a Collapsing Trap • As the trap is compressed, the loss cone becomes larger • Particles escape from the trap earlier • An additional energy increase by betatron acceleration is exactly offset by the decrease in a confinement time Ref.: Somov, B.V. and Bogachev, S.A., Astronomy Letters, 29, 621, 2003

  13. Both Effects Together Ref.: Somov, B.V. and Bogachev, S.A., Astronomy Letters, 29, 621, 2003

  14. Conclusions • The betatron effect significantly increases the efficiency of the first-order Fermi-type acceleration • Collapsing traps with a residual length (without shock) accelerate protons and ions well Ref.: Somov, B.V. and Bogachev, S.A., Astronomy Letters, 29, 621, 2003

  15. Collapsing Trap Model: Predictions • Two components: the non-thermal (N) and quasi-thermal (T) coronal HXRs • The upward motion of the coronal HXR source Ref.: Somov, B.V. and Kosugi, T., ApJ, 485, 859, 1997

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