Set the properties of the background thermal plasma.

        **Call signature**

        *T_K*
          The temperature of the background plasma, in Kelvin.
        *nth_cc*
          The number density of thermal electrons, in cm^-3.
        Returns
          *self* for convenience in chaining.

        Note that the parameters set here are the same as the ones that
        describe the thermal electron distribution, if you choose one of the
        electron energy distributions that explicitly models a thermal
        component ("thm", "tnt", "tnp", "tng", "kappa" in the code's
        terminology). For the power-law-y electron distributions, these
        parameters are used to calculate dispersion parameters (e.g.
        refractive indices) and a free-free contribution, but their
        synchrotron contribution is ignored.

def set_thermal_background(self, T_K, nth_cc):
        """Set the properties of the background thermal plasma.

        **Call signature**

        *T_K*
          The temperature of the background plasma, in Kelvin.
        *nth_cc*
          The number density of thermal electrons, in cm^-3.
        Returns
          *self* for convenience in chaining.

        Note that the parameters set here are the same as the ones that
        describe the thermal electron distribution, if you choose one of the
        electron energy distributions that explicitly models a thermal
        component ("thm", "tnt", "tnp", "tng", "kappa" in the code's
        terminology). For the power-law-y electron distributions, these
        parameters are used to calculate dispersion parameters (e.g.
        refractive indices) and a free-free contribution, but their
        synchrotron contribution is ignored.

        """
        if not (T_K >= 0):
            raise ValueError('must have T_K >= 0; got %r' % (T_K,))
        if not (nth_cc >= 0):
            raise ValueError('must have nth_cc >= 0; got %r, %r' % (nth_cc,))

        self.in_vals[IN_VAL_T0] = T_K
        self.in_vals[IN_VAL_N0] = nth_cc
        return self