Laser plasma accelerators are highly versatile and are sources of both radiation and particle beams, with unique properties. The Scottish Centre for Application based Plasma Accelerators (SCAPA) 40 TW and 350 TW laser at the University of Strathclyde has been used to produce both soft and hard x-rays using a laser wakefield accelerator (LWFA). The inherent characteristics of these femtosecond duration pulsed x-rays make them ideal for probing matter and ultrafast imaging applications. To support the development of applications of laser plasma accelerators at the SCAPA facility an adjustable Kirkpatrick-Baez x-ray microscope has been designed to focus 50 eV - 10 KeV x-rays. It is now possible to produce high quality at silicon wafers substrates that can be used for x-ray optics. Platinum-coated (40 nm) silicon wafers have been used in the KB instrument to image the LWFA x-ray source. We simulate the source distribution as part of an investigation to determine the x-ray source size and therefore its transverse coherence and ultimately the peak brilliance. The OASYS SHAODOW-OUI raytracing and wave propagation code has been used to simulate the imaging setup and determine instrument resolution.
The Scottish Centre for the Application of Plasma-based Accelerators (SCAPA) is a research centre dedicated to providing high energy particle beams and high peak brightness radiation pulses for users across all scientific and engineering disciplines. A pair of Ti:Sapphire femtosecond laser systems (40 TW peak power at 10 Hz pulse repetition rate and 350 TW at 5 Hz, respectively) are the drivers for a suite of laser-plasma accelerator beamlines housed across a series of radiation shielded areas. The petawatt-scale laser delivers 45 W of average power that establishes it as the world leader in its class. The University of Strathclyde has had an operational laser wakefield accelerator since 2007 as the centrepiece of the ongoing Advanced Laser Plasma High-energy Accelerators towards X-rays (ALPHA-X) project. SCAPA, which is a multipartner venture under the auspices of the Scottish Universities Physics Alliance, continues the dedicated beamline approach pioneered by ALPHA-X and represents a significant expansion in the UK’s experimental capability at the university level in laser-driven acceleration. The new centre supports seven radiation beamlines across three concrete shielded bunkers that each nominally specialise in a different aspect of fundamental laser-plasma interaction physics and radiation sources: GeVscale electron beams, MeV/c proton and ion beams, X-rays, gamma rays and so on. Development of application programmes based on these sources cover a wide range of fields including nuclear physics, radiotherapy, space radiation reproduction, warm dense matter, high field physics and radioisotope generation.
With the increase of laser power at facilities reaching petawatt-level, there is a need for accurate electron beam diagnostics of the laser wakefield accelerator (LWFA), which are becoming important tools for a wide range of applications including high field physics. Electrons in the range of several 100s of GeV are expected at these power levels. Precise diagnostic systems are required to enable applications such as advanced radiation sources. Accurate measurement of the energy spread of electron beams will help pave the way towards LWFA based free-electron lasers and plasma based coherent radiation sources. We propose an innovative double dipole spectrometer suitable for characterizing bunches produced using a petawatt class laser.
High energy attosecond electron bunches from the laser-plasma wakefield accelerator (LWFA) are potentially useful sources of ultra-short duration X-rays pulses, which can be used for ultrafast imaging of electron motion in biological and physical systems. Electron injection in the LWFA depends on the plasma density and gradient, and the laser intensity. Recent research has shown that injection of attosecond electron bunches is possible using a short plasma density ramp. For controlled injection it is necessary to keep both the laser intensity and background plasma density constant, but set to just below the threshold for injection. This ensures that injection is only triggered by an imposed density perturbation; the peak density should also not exceed the threshold for injection. A density gradient that only persists over a short range can lead to the injection of femtosecond duration bunches, which are then Lorentz contracted to attoseconds on injection. We consider an example of a sin2 shaped modulation where the gradient varies until the downward slope exceeds the threshold for injection and then reduces subsequently to prevent any further injection. The persistence above the threshold determines the injected bunch length, which can be varied. We consider several designs of plasma media including density perturbations formed by shaped Laval nozzles and present an experimental and theoretical study of the modulated media suitable for producing attosecond-duration electron bunches.
Here we explore ways of transforming laser radiation into incoherent and coherent electromagnetic radiation using laserdriven plasma waves. We present several examples based on the laser wakefield accelerator (LWFA) and show that the electron beam and radiation from the LWFA has several unique characteristics compared with conventional devices. We show that the energy spread can be much smaller than 1% at 130-150 MeV. This makes LWFAs useful tools for scientists undertaking time resolved probing of matter subject to stimuli. They also make excellent imaging tools. We present experimental evidence that ultra-short XUV pulses, as short as 30 fs, are produced directly from an undulator driven by a LWFA, due to the electron bunches having a duration of a few femtoseconds. By extending the electron energy to 1 GeV, and for 1-2 fs duration pulses of 2 nm radiation peak powers of several MW per pC can be produced. The increased charge at higher electron energies will increase the peak power to GW levels, making the LWFA driven synchrotron an extremely useful source with a spectral range extending into the water window. With the reduction in size afforded by using LWFA driven radiation sources, and with the predicted advances in laser stability and repletion rate, ultra-short pulse radiation sources should become more affordable and widely used, which could change the way science is done.