  Synchrotron radiation from relativistic electrons is usually invoked as the
responsible for the nonthermal emission observed in Supernova Remnants (SNRs).
Diffusive shock acceleration (DSA) is the most popular mechanism to explain the
process of particles acceleration and within its framework a crucial role is
played by the turbulent magnetic-field. However, the standard models commonly
used to fit X-ray synchrotron emission do not take into account the effects of
turbulence in the shape of the resulting photon spectra. An alternative
mechanism that properly includes such effects is the jitter radiation, that
provides for an additional power-law beyond the classical synchrotron cutoff.
We fitted a jitter spectral model to Chandra, NuSTAR, SWIFT/BAT and
INTEGRAL/ISGRI spectra of Cassiopeia A and found that it describes the X-ray
soft-to-hard range better than any of the standard cutoff models. The jitter
radiation allows us to measure the index of the magnetic turbulence spectrum
$\nu_B$ and the minimum scale of the turbulence $\lambda_{\rm{min}}$ across
several regions of Cas A, with best-fit values $\nu_B \sim 2-2.4$ and
$\lambda_{\rm{min}} \lesssim 100$ km.
