Figure 3
Measuring the waveforms and frequency spectra of a SPIRE. SPIRE waveforms obtained by (a) the LFH and (b) the V397-SU. Data from a single measurement (left-hand column) and the results of averaging over 1000 measurements (central column) are shown. Time zero represents the time of irradiation by the beam. The black and red lines denote the results obtained with and without the spherical gold marker, respectively. In the time domain, both detectors detected a characteristic resonance signal about 17 μs after irradiation, which did not exist when the gold marker was not present. The strong signal observed around time zero is the electromagnetic noise emitted from the beam extraction kicker of the FFA: this was observed regardless of the presence or absence of the gold marker. The frequency spectra (right-hand column) were obtained from the Fourier transform of the averaged waveforms shown in the central column. To eliminate the influence of the kicker noise, waveforms from 15 to 90 μs after beam irradiation were analysed. Although the waveforms shown in (a) and (b) appear different in the time-domain due to the structural differences between the detectors, pronounced peaks were observed at 1.53 MHz in the spectra using both detectors. This is close to the theoretical prediction of 1.62 MHz.
