Why is the low-impedance cavity ?

In order to capture and accelerate higher beams without beam losses, compensation techniques for heavy beam loading are essential. The beam loading for the accelerating mode cavity has been overcome successfully by the beam-feed forward system combined with the beam-phase loop to damp the dipole oscillations. A 2nd harmonic system is used to control the beam density distributions. Although a 2nd harmonic system is operated in the non-accelerating mode, i.e. beam-cavity phase is nearly zero, a large 2nd harmonic component of the beam would distort the cavity voltage, resulting in unstable control of the density. The low-output-impedance amplifier can provide a method to control the beam distribution more effectively because the beam loading to the system is negligibly small.