code: def set_Courant_Snyder(self, beta, alpha, emit=None, emit_n=None):
          
  
          self._store_emit(emit=emit, emit_n=emit_n)
          
          self._sx   = _np.sqrt(beta*self.emit)
          self._sxp  = _np.sqrt((1+alpha**2)/beta*self.emit)
          self._sxxp = -alpha*self.emit
docs: Sets the beam moments indirectly using Courant-Snyder parameters.
  
          Parameters
          ----------
          beta : float
              Courant-Snyder parameter :math:`\\beta`.
          alpha : float
              Courant-Snyder parameter :math:`\\alpha`.
          emit : float
              Beam emittance :math:`\\epsilon`.
          emit_n : float
              Normalized beam emittance :math:`\\gamma \\epsilon`.