26 research outputs found
High-charge 10 GeV electron acceleration in a 10 cm nanoparticle-assisted hybrid wakefield accelerator
In an electron wakefield accelerator, an intense laser pulse or charged
particle beam excites plasma waves. Under proper conditions, electrons from the
background plasma are trapped in the plasma wave and accelerated to
ultra-relativistic velocities. We present recent results from a
proof-of-principle wakefield acceleration experiment that reveal a unique
synergy between a laser-driven and particle-driven accelerator: a high-charge
laser-wakefield accelerated electron bunch can drive its own wakefield while
simultaneously drawing energy from the laser pulse via direct laser
acceleration. This process continues to accelerate electrons beyond the usual
decelerating phase of the wakefield, thus reaching much higher energies. We
find that the 10-centimeter-long nanoparticle-assisted wakefield accelerator
can generate 340 pC, 10.4+-0.6 GeV electron bunches with 3.4 GeV RMS convolved
energy spread and 0.9 mrad RMS divergence. It can also produce bunches with
lower energy, a few percent energy spread, and a higher charge. This
synergistic mechanism and the simplicity of the experimental setup represent a
step closer to compact tabletop particle accelerators suitable for applications
requiring high charge at high energies, such as free electron lasers or
radiation sources producing muon beams
Electron bunch generation from a plasma photocathode
Plasma waves generated in the wake of intense, relativistic laser or particle
beams can accelerate electron bunches to giga-electronvolt (GeV) energies in
centimetre-scale distances. This allows the realization of compact accelerators
having emerging applications, ranging from modern light sources such as the
free-electron laser (FEL) to energy frontier lepton colliders. In a plasma
wakefield accelerator, such multi-gigavolt-per-metre (GV m) wakefields
can accelerate witness electron bunches that are either externally injected or
captured from the background plasma. Here we demonstrate optically triggered
injection and acceleration of electron bunches, generated in a multi-component
hydrogen and helium plasma employing a spatially aligned and synchronized 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,
is highly tunable and paves the way to 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 ultra-high brightness beams
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Helium and hydrogen plasma waveguides for high-intensity laser channeling
textThe results of cross polarized pump-probe experiments in preformed He plasma waveguides are reported. Pump and probe have same wavelength and duration of 800nm and 80fs respectively. Peak pump intensity is I[subscript guided] = 0.2X10¹⁸W/cm² ~1000 I[subscript probe]. Single shot probe spectra and mode profiles at the channel exit are discriminated from the pump with a polarization analyzer and captured at various relative time delays [Delta]t. Frequency-domain interference (FDI) between the probe and a weak depolarized component of the pump is observed for [scientific equation]. Although the depolarized component is nearly undetectable through measurement of pump leakage alone, FDI sensitively reveals its substantially non-Gaussian structure. The possible depolarization mechanisms are analyzed. When probe is positioned at the leading edge of the pump, [scientific equation], its spectrum suffers a blue shift not measurable in the transmitted pump itself. The evidence suggests the channel interior is fully ionized and the partially formed channel ends are the origin of both depolarization and blue shift. A robust, pulsed, differentially-pumped plasma channel generation cell for high intensity guiding experiments has been developed. The design includes an axicon lens, windows for transverse interferometry, and permits injection of one or two different gases (main gas plus high Z seed gas) with several millisecond injection times and simultaneous 0.1ms pressure sensing resolution. Very well formed plasma waveguides have been formed in helium as well as hydrogen, at repeatable and well controlled pressures up to 1000Torr, with very uniform interior density, rapid density drop at boundaries, and very low exterior density. The possible danger associated with the use of large amounts of hydrogen was considered and a complex safety system was designed, constructed and used. Extensive analysis of channel profile reconstruction through transverse interferometry was performed. This includes an intuitive, efficient reformulation and extension of the Phase Locked Loop (PLL) carrier fringe demodulation method. It is also demonstrated and explained how and under which conditions artificial fringe frequency multiplication can reduce demodulation distortions in both PLL and Fast Fourier Transform (FFT) methods.Physic