Generation Of Ultrashort Electron Bunches Research Articles

Optimization of the thickness of the transition layer for the generation of ultrashort electron bunches by a laser pulse acting on a semi-bounded plasma

An analytical estimate is obtained for the range of thicknesses of the near-boundary plasma layer, which ensures the generation of ultrashort electron bunches under the action of a laser pulse on a semi-bounded rarefied plasma. Keywords: laser pulse, electron bunch, generation, injection.

Оптимизация толщины переходного слоя для генерации сверхкоротких сгустков электронов лазерным импульсом, воздействующим на полуограниченную плазму

An analytical estimate is obtained for the range of thicknesses of the near-boundary plasma layer, which ensures the generation of ultrashort electron bunches under the action of a laser pulse on a semi-bounded rarefied plasma

High-charge ultrashort electron bunch generation by an energy chirping cell-attached rf electron gun and its measurement using a transverse deflecting cavity

Ultrashort electron bunches are becoming increasingly important for applications such as free-electron lasers, time-resolved electron diffraction/microscopy, and advanced accelerator concepts. We report femtosecond electron bunch generation with a unique rf gun and its precise measurement using a transverse deflecting cavity. A bunch length of $323\ifmmode\pm\else\textpm\fi{}13\text{ }\text{ }\mathrm{fs}$ with 120 pC ($\ensuremath{\sim}7.5\ifmmode\times\else\texttimes\fi{}{10}^{8}\text{ }\text{ }\mathrm{electrons}$) was achieved at a distance of just 3 m from the cathode. A longitudinal phase space distribution was also achieved, and we successfully experimentally confirmed the linearly energy chirped electron bunch generation and self-compression by the velocity difference.

Lattice design and start-to-end simulations for the ARES linac

The SINBAD (Short INnovative Bunches and Accelerators at DESY) project is a dedicated, long-term accelerator research and development facility currently under construction at the DESY Hamburg campus, aiming to provide an infrastructure for developing ultrafast science and several types of novel high-gradient accelerators. We present the design of the magnetic lattice as well as the start-to-end simulation results for ultrashort electron bunch generation at the ARES (Accelerator Research Experiment at SINBAD) linac, which is one of the two experiments at the SINBAD facility. In order to meet the requirements for external injection into high-gradient accelerators, the ARES linac was optimized to provide ∼100 MeV, low charge (0.5 to 30 picocoulombs) and ultrashort electron bunches (sub-femtosecond to dozens of femtoseconds) with ultrasmall spot sizes (less than a few micrometers) and excellent timing stability (rms bunch arrival-time jitter <10 femtoseconds).

Violation of the transit-time limit toward generation of ultrashort electron bunches with controlled velocity chirp.

Various methods to generate ultrashort electron bunches for the ultrafast science evolved from the simple configuration of two-plate vacuum diodes to advanced technologies such as nanotips or photocathodes excited by femtosecond lasers. In a diode either in vacuum or of solid-state, the transit-time limit originating from finite electron mobility has caused spatiotemporal bunch-collapse in ultrafast regime. Here, we show for the first time that abrupt exclusion of transit-phase is a more fundamental origin of the bunch-collapse than the transit-time limit. We found that by significantly extending the cathode-anode gap distance, thereby violating the transit-time limit, the conventional transit-time-related upper frequency barrier in diodes can be removed. Furthermore, we reveal how to control the velocity chirp of bunches leading to ballistic bunch-compression. Demonstration of 0.707 THz-, 46.4 femtosecond-bunches from a 50 μm-wide diode in three-dimensional particle-in-cell simulations shows a way toward simple and compact sources of ultrafast electron bunches for diverse ultrafast sciences.

Femtosecond timing-jitter between photo-cathode laser and ultra-short electron bunches by means of hybrid compression

The generation of ultra-short electron bunches with ultra-low timing-jitter relative to the photo-cathode (PC) laser has been experimentally proved for the first time at the SPARC_LAB test-facility (INFN-LNF, Frascati) exploiting a two-stage hybrid compression scheme. The first stage employs RF-based compression (velocity-bunching), which shortens the bunch and imprints an energy chirp on it. The second stage is performed in a non-isochronous dogleg line, where the compression is completed resulting in a final bunch duration below 90 fs (rms). At the same time, the beam arrival timing-jitter with respect to the PC laser has been measured to be lower than 20 fs (rms). The reported results have been validated with numerical simulations.

Sub-fs electron bunch generation with sub-10-fs bunch arrival-time jitter via bunch slicing in a magnetic chicane

The generation of ultrashort electron bunches with ultrasmall bunch arrival-time jitter is of vital importance for laser-plasma wakefield acceleration with external injection. We study the production of 100-MeV electron bunches with bunch durations of subfemtosecond (fs) and bunch arrival-time jitters of less than 10 fs, in an S-band photoinjector by using a weak magnetic chicane with a slit collimator. The beam dynamics inside the chicane is simulated by using two codes with different self-force models. The first code separates the self-force into a three-dimensional (3D) quasistatic space-charge model and a one-dimensional coherent synchrotron radiation (CSR) model, while the other one starts from the first principle with a so-called 3D sub-bunch method. The simulations indicate that the CSR effect dominates the horizontal emittance growth and the 1D CSR model underestimates the final bunch duration and emittance because of the very large transverse-to-longitudinal aspect ratio of the sub-fs bunch. Particularly, the CSR effect is also strongly affected by the vertical bunch size. Due to the coupling between the horizontal and longitudinal phase spaces, the bunch duration at the entrance of the last dipole magnet of the chicane is still significantly longer than that at the exit of the chicane, which considerably mitigates the impact of space charge and CSR effects on the beam quality. Exploiting this effect, a bunch charge of up to 4.8 pC in a sub-fs bunch could be simulated. In addition, we analytically and numerically investigate the impact of different jitter sources on the bunch arrival-time jitter downstream of the chicane, and define the tolerance budgets assuming realistic values of the stability of the linac for different bunch charges and compression schemes.

Ultrashort electron bunch generation by an energy chirping cell attached rf gun

We present a new design for a rf electron gun to be used in ultrashort ($\ensuremath{\sim}1\text{ }\text{ }\mathrm{ps}$) electron bunch generation. Using both simulation and measurement we evaluated the principle of this new type rf gun and were able to confirm an ultrashort bunch generation. During simulation, a bunch length of less than 100 fs(rms) with a $100\text{ }\mathrm{pC}/\text{bunch}$ charge was confirmed at the optimum operating condition. The principle is to produce a linearly distributed longitudinal phase space by using an attached output cell specially designed for energy chirping. Such phase space distribution can be rotated by the velocity difference in the bunch. We already fabricated an energy chirping cell attached rf gun and successfully observed 0.2 THz coherent synchrotron radiation, which corresponds to less than 500 fs bunch. Such an electron gun can be used as a compact THz light source and a new electron injector with an ultrashort bunch.

Relativistic self-induced transparency effect during ultraintense laser interaction with overdense plasmas: Why it occurs and its use for ultrashort electron bunch generation

A novel explanation of the relativistic self-induced transparency effect during superintense laser interaction with an overdense plasma is proposed. It was studied analytically and verified with direct modeling by particle-in-cell simulations. Based on this treatment, a method of ultrashort high-energy electron bunch generation with durations on a femtosecond time scale is also proposed and studied via numerical simulation.

Generation of ultrashort electron bunches by colliding laser pulses.

A proposed laser-plasma-based relativistic electron source [E. Esarey et al., Phys. Rev. Lett. 79, 2682 (1997)] using laser-triggered injection of electrons is investigated. The source generates ultrashort electron bunches by dephasing and trapping background plasma electrons undergoing fluid oscillations in an excited plasma wake. The plasma electrons are dephased by colliding two counterpropagating laser pulses which generate a slow phase velocity beat wave. Laser pulse intensity thresholds for trapping and the optimal wake phase for injection are calculated. Numerical simulations of test particles, with prescribed plasma and laser fields, are used to verify analytic predictions and to study the longitudinal and transverse dynamics of the trapped plasma electrons. Simulations indicate that the colliding laser pulse injection scheme has the capability to produce relativistic femtosecond electron bunches with fractional energy spread of order a few percent and normalized transverse emittance less than 1 mm mrad using 1 TW injection laser pulses.

Micro-bunch production with radio frequency photoinjectors

In this paper we discuss the generation of ultra-short electron bunches using laser-driven RF guns. The designs are tailored for future plasma accelerators. Second generation plasma accelerators are expected to be very demanding in terms of bunch length, since the accelerated beam is expected to be short with respect to the wavelength of the excited Langmuir space-charge plasma wave. Since the anticipated wavelength ranges from 100 to 300 /spl mu/m, 10-50 /spl mu/m-long bunches are required with a bunch population of the order of 10/sup 8/ particles. The laser-driven RF gun is a promising candidate to attain such beams. The rationale for this choice as well as the main limitations in terms of minimum bunch length will be analyzed and discussed in the following. Two possible configurations are evaluated: the direct production at the photocathode surface of ultra-short electron bunches by illumination of the cathode with 160-fs-long laser pulses and the acceleration of a 1-ps electron bunch with further magnetic compression in a wiggler.