Stabilization of the arrival time of a relativistic electron beam to the 50 fs level

We report the results of a low-latency beam phase feed-forward system built to stabilize the arrival time of a relativistic electron beam. The system was operated at the Compact Linear Collider (CLIC) Test Facility (CTF3) at CERN where the beam arrival time was stabilized to approximately 50 fs. The system latency was 350 ns and the correction bandwidth $>23\mathrm{MHz}$. The system meets the requirements for CLIC.

Figure 1

Schematic of the CLIC drive-beam concept showing the electron acceleration complex [1].

Figure 2

Schematic of the CTF3 PFF prototype, showing the phase monitors ($M_1$, $M_2$ and $M_3$) and kickers ($K_1$ and $K_2$). The black box PFF represents the calculation and output of the correction. Bunches arriving early at $M_1$ are deflected on to longer trajectories in the chicane (blue), and bunches arriving late on to shorter trajectories (red). Dashed lines indicate beam lines that are not used.

Figure 3

Measured downstream (red) and upstream (blue) phase jitter vs TL1 $R_{56}$ value. Error bars show the statistical standard error on the measured jitter values.

Figure 4

Measured corrected beam phase jitter at $M_3$ vs PFF gain (points). Error bars show the statistical standard error on the measured jitter values. The expected performance is shown by the red shaded region (see text).

Figure 5

Correction of the pulse shape with the PFF system. Shown are: the incoming phase (${\varphi }_1$) measured in $M_1$ (green), and the downstream phase (${\varphi }_3$) measured in $M_3$ with PFF off (blue) and PFF on (red). Each trace is the average over a 30 minute dataset. (a) The whole beam pulse. Vertical dashed lines mark the time interval corresponding to the PFF dynamic range. (b) The same data zoomed in to the central portion of the pulse. Shaded areas represent the phase jitter at each sample point.

Figure 6

Amplitude of phase errors vs frequency ($f$) in bins of 2.3 MHz with the PFF system off (blue) and on (red), across a 30 minute dataset.

Figure 7

Distribution of the mean downstream phase with the PFF system off (blue) and on (red).

Figure 8

Mean downstream phase vs time with the PFF system off (blue) and on (red) subject to large additional phase variations added to the incoming phase (see text).