The "knee" in the primary cosmic ray spectrum as consequence of the anomalous diffusion of the particles in the fractal interstellar medium

The galactic cosmic ray spectrum is calculated on the assumption that inter stellar medium is a fractal medium. Anomalous diffusion equation in terms o f fractional derivatives is used for describing cosmic ray propagation. The calculations show that the "knee" in the primary cosmic rays spectrum appe ars due to fractal structure of the galactic magnetic fields. The source sp ectral exponent, found from experimental data in this approach, turns out t o be equal to 2.9.