### Abstract

The physics of particle acceleration by collisionless shocks is addressed using analytic theory and numerical simulations. In this paper we focus on the importance of the angle between the shock normal and upstream mean magnetic field, θ_{Bn}, in determining the energy spectrum of the accelerated particles. We show that the acceleration rate is strongly dependent on θ_{Bn} and is a maximum at perpendicular shocks. Moreover, we demonstrate that for a wide range of reasonable parameters, the acceleration effciency is weakly dependent on the shock normal angle. When applied to acceleration at supernovae blast waves, we find, therefore, for any given time interval, the highest-energy cosmic rays originate from regions in which the shock moves normal to the mean magnetic field. We also find that maximum energy is larger than that obtained using the well-known Bohm-limit.

Original language | English (US) |
---|---|

Article number | 020 |

Pages (from-to) | 160-167 |

Number of pages | 8 |

Journal | Journal of Physics: Conference Series |

Volume | 47 |

Issue number | 1 |

DOIs | |

State | Published - Oct 1 2006 |

### Fingerprint

### ASJC Scopus subject areas

- Physics and Astronomy(all)

### Cite this

**Shock acceleration of high-energy cosmic rays : The importance of the magnetic-field angle.** / Giacalone, Joe; Jokipii, J. Randy.

Research output: Contribution to journal › Article

}

TY - JOUR

T1 - Shock acceleration of high-energy cosmic rays

T2 - The importance of the magnetic-field angle

AU - Giacalone, Joe

AU - Jokipii, J. Randy

PY - 2006/10/1

Y1 - 2006/10/1

N2 - The physics of particle acceleration by collisionless shocks is addressed using analytic theory and numerical simulations. In this paper we focus on the importance of the angle between the shock normal and upstream mean magnetic field, θBn, in determining the energy spectrum of the accelerated particles. We show that the acceleration rate is strongly dependent on θBn and is a maximum at perpendicular shocks. Moreover, we demonstrate that for a wide range of reasonable parameters, the acceleration effciency is weakly dependent on the shock normal angle. When applied to acceleration at supernovae blast waves, we find, therefore, for any given time interval, the highest-energy cosmic rays originate from regions in which the shock moves normal to the mean magnetic field. We also find that maximum energy is larger than that obtained using the well-known Bohm-limit.

AB - The physics of particle acceleration by collisionless shocks is addressed using analytic theory and numerical simulations. In this paper we focus on the importance of the angle between the shock normal and upstream mean magnetic field, θBn, in determining the energy spectrum of the accelerated particles. We show that the acceleration rate is strongly dependent on θBn and is a maximum at perpendicular shocks. Moreover, we demonstrate that for a wide range of reasonable parameters, the acceleration effciency is weakly dependent on the shock normal angle. When applied to acceleration at supernovae blast waves, we find, therefore, for any given time interval, the highest-energy cosmic rays originate from regions in which the shock moves normal to the mean magnetic field. We also find that maximum energy is larger than that obtained using the well-known Bohm-limit.

UR - http://www.scopus.com/inward/record.url?scp=33947659960&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=33947659960&partnerID=8YFLogxK

U2 - 10.1088/1742-6596/47/1/020

DO - 10.1088/1742-6596/47/1/020

M3 - Article

AN - SCOPUS:33947659960

VL - 47

SP - 160

EP - 167

JO - Journal of Physics: Conference Series

JF - Journal of Physics: Conference Series

SN - 1742-6588

IS - 1

M1 - 020

ER -