code: def set_thermal_background(self, T_K, nth_cc):
          
          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
docs: 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.