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

Wave Propagation at Oblique Shocks: How Did Tycho Get Its Stripes?