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.