The microwave pick-up is shown in Figure 192.

Fig. 192: Drawing of the microwave pick-ups attached above and below the vacuum chamber.

These microwave pick-ups are resonant to a high frequency of 10 or 18 GHz with a bandwidth of 20 Mhz. They provide signals that probe the microwave oscillation modes of the electron beam both along the vertical and longitudinal axis. The plots in Figure 193 show the build up of a coherent longitudinal microwave oscillation above a threshold current of 5 mA per bunch.

Fig. 193: Signal delivered by the microwave pick-up: a) shows a single peak the frequency of which is a high harmonic number of the revolution frequency (recorded with a 5 mA current); b) a set of sideband lines typical of the microwave instability (recorded at 10 mA).