  We describe a new model for the "stripes" of synchrotron radiation seen in
the remnant of Tycho's supernova. In our picture, cosmic rays streaming ahead
of the forward shock generate parallel (with respect to the local magnetic
field direction) circularly polarized Alfven waves that are almost free of
dissipation, and due to being circularly polarized exhibit no spatial variation
of magnetic field strength. Following interaction with the SNR shock with
nonzero obliquity, these parallel waves become obliquely propagating, due the
the wave refraction (different in principle for the different plane wave
components), and dissipation sets in. The magnetosonic polarization decays
faster, due to transit time damping, leaving only the Alfven mode. This
surviving mode now exhibits a spatial variation of the magnetic field, leading
to local maxima and minima in the synchrotron emission, i.e. the stripes. We
attribute the initial wave generation to the Bell instability, which in
contrast to the resonant generation of upstream Alfven waves, gives rise to a
preferred wavelength, and hence the single wave period at which the stripes are
seen. Based on estimates for damping rates due to turbulent cascade and transit
time damping, we estimate the dependence of the visibility of the stripes on
the shock obliquity, and determine a maximum cosmic ray energy in Tycho's SNR
in the range $6\times 10^{14} - 1\times 10^{15}$ eV.
