Coulomb-Driven Relativistic Electron Beam Compression

Coulomb interaction between charged particles is a well-known phenomenon in many areas of research. In general, the Coulomb repulsion force broadens the pulse width of an electron bunch and limits the temporal resolution of many scientific facilities such as ultrafast electron diffraction and x-ray free-electron lasers. Here we demonstrate a scheme that actually makes use of the Coulomb force to compress a relativistic electron beam. Furthermore, we show that the Coulomb-driven bunch compression process does not introduce additional timing jitter, which is in sharp contrast to the conventional radio-frequency buncher technique. Our work not only leads to enhanced temporal resolution in electron-beam-based ultrafast instruments that may provide new opportunities in probing material systems far from equilibrium, but also opens a promising direction for advanced beam manipulation through self-field interactions.

Figure 1

Coulomb-driven relativistic electron beam compression experiment setup. The laser is first split into two pulses with a beam splitter (BS1) and then combined with a second beam splitter (BS2). The high-energy pulse after pulse shaping is used to produce the drive beam, and the other low-energy pulse is used to produce the target beam. A solenoid lens is used to control the transverse size of the electron beam during beam propagation, and the electron beam longitudinal phase space is measured with an rf deflector and an energy spectrometer.

Figure 2

Current distribution (shaded yellow area, bunch head to the right) and the corresponding longitudinal Coulomb field (solid line) for the back drive beam (a), for the front drive beam (b), and when both drive beams are present (c).

Figure 3

Beam longitudinal phase space (bunch head to the up) as the total charge of the drive beams is gradually increased from 0.2 (a) to 3.2 (b), 4.5 (c), and 6.7 pC (d). The top and bottom distributions show the front drive beam and back drive beam, and the target beam is in the middle. The corresponding electron beam temporal profiles are shown with solid white lines, and the rms bunch lengths are also given. Note, due to the limited field of view of the screen, only part of the drive beam distribution is measured.

Figure 4

Measured final energy and time of the target beam centroid with (red dot) and without (magenta dot) the drive beams. The simulation results are shown with black (with drive beams) and blue (without the drive beams) lines. The simulated longitudinal phase spaces for the drive beams is shown with blue dots.

Figure 5

Measured pulse width and energy distribution for the target beam with 50 fC charge. The 50 consecutive single-shot measurements of the target beam longitudinal profile without (a) and with (c) the drive beams, and the rms pulse width statistics collected over 200 consecutive shots without (b) and with (d) the drive beams. The 50 consecutive single-shot measurements of the target beam energy distribution without (e) and with (g) the drive beams. The centroid beam energy for each individual shot (white circles) is used to evaluate the energy jitter without (f) and with (h) the drive beams.