UHECR acceleration in dark matter filaments of cosmological structure formation
- CASS and Department of Physics, University of California, San Diego, La Jolla, CA 92093-0424 (United States)
A mechanism for proton acceleration to ∼ 10{sup 21} eV is suggested. It may operate in accretion flows onto thin dark matter filaments of cosmic structure formation. The flow compresses the ambient magnetic field to strongly increase and align it with the filament. Particles begin the acceleration by E × B drift with the accretion flow. The energy gain in the drift regime is limited by the conservation of the adiabatic invariant p{sub p}erpendicular{sup 2}/B(r). Upon approaching the filament, the drift turns into the gyro-motion around the filament so that the particle moves parallel to the azimuthal electric field. In this 'betatron' regime the acceleration speeds up to rapidly reach the electrodynamic limit cp{sub max} = eBR for an accelerator with magnetic field B and the orbit radius R (Larmor radius). The periodic orbit becomes unstable and the particle slings out of the filament to the region of a weak (uncompressed) magnetic field, which terminates the acceleration. To escape the filament, accelerated particles must have gyro-radii comparable with the filament radius. Therefore, the mechanism requires pre-acceleration that is likely to occur in large scale shocks upstream or nearby the filament accretion flow. Previous studies identify such shocks as efficient proton accelerators, with a firm upper limit ∼ 10{sup 19.5} eV placed by the catastrophic photo-pion losses. The present mechanism combines explosive energy gain in its final (betatron) phase with prompt particle release from the region of strong magnetic field. It is this combination that allows protons to overcome both the photo-pion and the synchrotron-Compton losses and therefore attain energy ∼ 10{sup 21} eV. A customary requirement on accelerator power to reach a given E{sub max}, which is placed by the accelerator energy dissipation ∝E{sub max}{sup 2}/Z{sub 0} due to the finite vacuum impedance Z{sub 0}, is circumvented by the cyclic operation of the accelerator.
- OSTI ID:
- 22277849
- Journal Information:
- Journal of Cosmology and Astroparticle Physics, Vol. 2011, Issue 04; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 1475-7516
- Country of Publication:
- United States
- Language:
- English
Similar Records
TeV Signatures of Compact UHECR Accelerators
Ion and electron dynamics generating the Hall current in the exhaust far downstream of the reconnection x-line