Spectra of protons accelerated at the northeastern limb of the Tycho SNR for a shock velocity v_sh = 2500 km s^-1 and upstream total density n₀ = 1 cm^-3. The three lines refer to neutral fraction f_N = 0.6 (solid line), f_N = 0.7 (dashed line), and f_N = 0.8 (dash-dotted line). A cutoff in the spectra of accelerated protons at ~10 TeV is used and reflects the non-resonant magnetic field amplification of magnetic field, as studied by Bell (2004).