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Energy Sources for GCR
Where does the energy come from? Supernovae of course! Seriously, shock waves travelling out of the galactic disk transmit energy to the cusp & compress it, just as much as turbulence in the intergalactic medium (IGM). The cusp is a low-Q object, energy (waves) goes in, and doesn’t come out.
The advantage over Fermi-acceleration at SN? Continuous acceleration, multiple energy sources, identifiable rigidity properties. And the clincher…
A natural explanation of the “knee”. At low-E, protons have the smaller rigidity, at high E, (due to gamma) Fe has the smaller rigidity. So they cross.