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We present an ultracompact plasma-based method to measure spatial and temporal concurrence of intense electron and laser beams nonintrusively at their interaction point. The electron beam couples with a laser-generated seed plasma in dependence of spatiotemporal overlap, which triggers additional plasma production and manifests as enhanced plasma afterglow. This optical observable is exploited to measure beam concurrence with ~4 μm spatial and ~26.7 fs temporal accuracy, supported by auxiliary diagnostics. The afterglow interaction fingerprint is highly sensitive and enables ultraversatile femtosecond-micrometer beam metrology.

The National User Facility for Advanced Accelerator Experimental Tests II (FACET-II) at SLAC National Accelerator Laboratory expands upon the experiments conducted at FACET. Its purpose is to build upon the decades-long experience developed conducting accelerator R&D at SLAC in the areas of advanced acceleration and coherent radiation techniques with high-energy electron and positron beams. This paper summarizes the motivations for the design and resulting capabilities of the FACET-II facility.

Plasma waves generated in the wake of intense, relativistic laser or particle beams can accelerate electron bunches to gigaelectronvolt energies in centimetre-scale distances. This allows the realization of compact accelerators with emerging applications ranging from modern light sources such as the free-electron laser to energy frontier lepton colliders. In a plasma wakefield accelerator, such multi-gigavolt-per-metre wakefields can accelerate witness electron bunches that are either externally injected or captured from the background plasma. Here in this work, we demonstrate optically triggered injection and acceleration of electron bunches, generated in a multi-component hydrogen and helium plasma employing a spatially aligned and synchronizedmore » laser pulse. This ‘plasma photocathode’ decouples injection from wake excitation by liberating tunnel-ionized helium electrons directly inside the plasma cavity, where these cold electrons are then rapidly boosted to relativistic velocities. The injection regime can be accessed via optical density down-ramp injection and is an important step towards the generation of electron beams with unprecedented low transverse emittance, high current and 6D-brightness. This experimental path opens numerous prospects for transformative plasma wakefield accelerator applications based on ultrahigh-brightness beams.« less

Here, we report on the experimental observation of the attraction of a beam of ultrarelativistic electrons towards a column of neutral plasma. In experiments performed at the FACET test facility at SLAC we observe that an electron beam moving parallel to a neutral plasma column, at an initial distance of many plasma column radii, is attracted into the column. Once the beam enters the plasma it drives a plasma wake similar to that of an electron beam entering the plasma column head-on. A simple analytical model is developed in order to capture the essential physics of the attractive force. Themore » attraction is further studied by 3D particle-in-cell numerical simulations. The results are an important step towards better understanding of particle beam–plasma interactions in general and plasma wakefield accelerator technology in particular.« less

High gradients of energy gain and high energy efficiency are necessary parameters for compact, cost-efficient and high-energy particle colliders. Plasma Wakefield Accelerators (PWFA) offer both, making them attractive candidates for next-generation colliders. Here in these devices, a charge-density plasma wave is excited by an ultra-relativistic bunch of charged particles (the drive bunch). The energy in the wave can be extracted by a second bunch (the trailing bunch), as this bunch propagates in the wake of the drive bunch. While a trailing electron bunch was accelerated in a plasma with more than a gigaelectronvolt of energy gain, accelerating a trailing positronmore » bunch in a plasma is much more challenging as the plasma response can be asymmetric for positrons and electrons. We report the demonstration of the energy gain by a distinct trailing positron bunch in a plasma wakefield accelerator, spanning nonlinear to quasi-linear regimes, and unveil the beam loading process underlying the accelerator energy efficiency. A positron bunch is used to drive the plasma wake in the experiment, though the quasi-linear wake structure could as easily be formed by an electron bunch or a laser driver. Finally, the results thus mark the first acceleration of a distinct positron bunch in plasma-based particle accelerators.« less