Laser-plasma accelerator group

Abstract:

Laser-driven plasma accelerators provide acceleration gradients that are three orders of magnitude greater than those generated by conventional accelerators, offering the potential to shrink the length of accelerators by the same factor. To date, laser acceleration of electron beams to produce particle energies comparable to those offered by synchrotron light sources has been demonstrated with plasma acceleration stages that are only a few centimetres long. This Review describes the operation principles of laser-driven plasma accelerators, and gives an overview of their development from their proposal in 1979 to recent demonstrations. Potential applications of plasma accelerators are described, and the challenges that must be overcome before they can become practical tools are discussed. © 2013 Macmillan Publishers Limited.

Abstract:

We present experiments and numerical simulations which demonstrate that fully-ionized, lowdensity plasma channels could be formed by hydrodynamic expansion of plasma columns produced by optical field ionization (OFI). Simulations of the hydrodynamic expansion of plasma columns formed in hydrogen by an axicon lens show the generation of 200 mm long plasma channels with axial densities of order ne(0) = 1 × 1017 cm−3 and lowest-order modes of spot size WM ≈ 40 µm. These simulations show that the laser energy required to generate the channels is modest: of order 1 mJ per centimetre of channel. The simulations are confirmed by experiments with a spherical lens which show the formation of short plasma channels with 1.5 × 1017 cm−3 . ne(0) . 1 × 1018 cm−3 and 61 µm & WM & 33 µm. Low-density plasma channels of this type would appear to be well-suited as multi-GeV laser-plasma accelerator stages capable of long-term operation at high pulse repetition rates.

Abstract:

We demonstrate through experiments and numerical simulations that low-density, low-loss, meter-scale plasma channels can be generated by employing a conditioning laser pulse to ionize the neutral gas collar surrounding a hydrodynamic optical-field-ionized (HOFI) plasma channel. We use particle-in-cell simulations to show that the leading edge of the conditioning pulse ionizes the neutral gas collar to generate a deep, low-loss plasma channel which guides the bulk of the conditioning pulse itself as well as any subsequently injected pulses. In proof-of-principle experiments we generate conditioned HOFI (CHOFI) waveguides with axial electron densities of $n_\mathrm{e0} \approx 1 \times 10^{17} \; \mathrm{cm^{-3}}$, and a matched spot size of $26 \; \mathrm{\mu m}$. The power attenuation length of these CHOFI channels is $L_\mathrm{att} = (21 \pm 3) \; \mathrm{m}$, more than two orders of magnitude longer than achieved by HOFI channels. Hydrodynamic and particle-in-cell simulations demonstrate that meter-scale CHOFI waveguides with attenuation lengths exceeding 1 m could be generated with a total laser pulse energy of only $1.2$ J per meter of channel. The properties of CHOFI channels are ideally suited to many applications in high-intensity light-matter interactions, including multi-GeV plasma accelerator stages operating at high pulse repetition rates.