Measurement of beam stability and coupling impedance by RF excitation

The transverse stability limit and coupling impedance of proton beams in the CERN intersecting storage rings have been measured by external excitation of the beam. The impedance values at low frequencies thus obtained are in good agreement with the sum of the skin-effect and the wall-inductance which has been measured previously. The method can be extended to higher frequencies if the beam can be stabilized against low-frequency oscillations, e.g. by feedback.