The Orion laser facility at the atomic weapons establishment (AWE) in the UK has been operational since April 2013, fielding experiments that require both its long and short pulse capability. This paper provides a full description of the facility in terms of laser performance, target systems and diagnostics currently available. Inevitably, this is a snapshot of current capability—the available diagnostics and the laser capability are evolving continuously. The laser systems consist of ten beams, optimised around 1 ns pulse duration, which each provide a nominal 500 J at a wavelength of 351 nm. There are also two short pulse beams, which each provide 500 J in 0.5 ps at 1054 nm. There are options for frequency doubling one short pulse beam to enhance the pulse temporal contrast. More recently, further contrast enhancement, based on optical parametric amplification (OPA) in the front end with a pump pulse duration of a few ps, has been installed. An extensive suite of diagnostics are available for users, probing the optical emission, x-rays and particles produced in laser-target interactions. Optical probe diagnostics are also available. A description of the diagnostics is provided.

The ORION laser facility is one of the UK's premier laser facilities which became operational at AWE in 2010. Its primary mission is one of stockpile stewardship, ORION will extend the UK's experimental plasma physics capability to the high temperature, high density regime relevant to Atomic Weapons Establishment's (AWE) program. The ORION laser combines ten laser beams operating in the ns regime with two sub ps short pulse chirped pulse amplification beams. This gives the UK a unique combined long pulse/short pulse laser capability which is not only available to AWE personnel but also gives access to our international partners and visiting UK academia. The ORION laser facility is equipped with a comprehensive suite of some 45 diagnostics covering optical, particle, and x-ray diagnostics all able to image the laser target interaction point. This paper focuses on a small selection of these diagnostics.

Wide-ranging measurements of sub-picosecond laser interactions with large noble gas cluster targets have been conducted in order to help clarify the nature and extent of the underlying laser-plasma heating. Within the sub-relativistic vacuum irradiance range of 10(16)-10(17) W cm(-2), we find that electron temperatures measured with continuum x-ray spectroscopy exhibit a pronounced multi-keV enhancement. Analysis indicates this behaviour to be consistent with collisional or collisionless resonant heating mechanisms. We also present the first measurements of laser-to-cluster energy deposition at relativistic vacuum irradiances, our data demonstrating absorption fractions of 90% or more. Optical probing was used to resolve the onset of a supersonic ionization front resulting from this very high absorption, and shows that despite significant pre-focus heating, the greatest plasma energy densities can be generated about the vacuum focus position. Electron energy spectra measurements confirm that laser-plasma super-heating occurs, and together with ion data establish that relativistic laser-plasma coupling in atomic clusters can take place without significant MeV particle beam production. In conjunction with optical self-emission data, the optical probing also indicates laser pre-pulse effects at peak vacuum irradiance of 5 x 10(19) W cm(-2). Laser absorption, plasma heating and energy transport data are supported throughout with analytical and numerical modelling.

The capability of the HELEN laser at the Atomic Weapons Establishment Aldermaston has been enhanced by the addition of a short-pulse laser beam to augment the twin opposing nanosecond time scale beams. The short-pulse beam utilizes the chirped pulse amplification (CPA) technique and is capable of delivering up to 60 J on target in a 500 fs pulse, around 100 TW, at the fundamental laser wavelength of 1.054 mu m. During the commissioning phase a number of diagnostic systems have been fielded, these include: x-ray pinhole imaging of the laser heated spot, charged particle time of flight, thermoluminescent dosimeter array, calibrated radiochromic film, and CR39 nuclear track detector. These diagnostic systems have been used to verify the performance of the CPA beam to achieve a focused intensity of around 10(19) W cm(-2) and to underwrite the facility radiological safety system.

With the increasing number of multi-terawatt (10(12) W) and petawatt (10(15) W) laser interaction facilities being built, the need for a detailed understanding of the potential radiological hazards is required and their impact on personnel is of major concern. Experiments at a number of facilities are being undertaken to achieve this aim. This paper describes the recent work completed on the Vulcan petawatt laser system at the CCLRC Rutherford Appleton Laboratory, where photon doses of up to 43 mSv at 1 m per shot have been measured during commissioning studies. It also overviews the shielding in place on the facility in order to comply with the Ionising Radiation Regulations 1999 (IRR99), maintaining a dose to personnel of less than 1 mSv yr(-1) and as low as reasonably practicable (ALARP).

Time-resolved x-ray spectra from solid targets irradiated by the VULCAN Petawatt laser focused to 1020Wcm−2 show that material at solid density is heated to temperatures above 500 eV to a depth of about 15 μm and for a duration of more than 30 ps. Modeling with the implicit hybrid plasma code LSP shows that the heating is sensitive to the laser prepulse through resistive inhibition of the laser accelerated electrons in the blow off layer.

Introduction Atomic clusters are well known for their ability to absorb a very high fraction of the laser energy incident upon them (>90%). Consequently, a radically different laser interaction occurs in comparison to that found when gas targets or solid targets are used. Gases, which typically absorb <1% of the incident laser energy, produce relatively low temperature plasma, while solid density targets are heated far more efficiently through a variety of heating mechanisms.

Summary form only given. Petawatt lasers have several important applications including fast ignition of fusion targets and the development of compact X-ray and charged particle sources. Understanding the transport and energy deposition of the relativistic electron beam produced by the absorption from ultra-intense lasers is a crucial part of these applications. We have used the thermal X-ray emission of aluminium tracer layers in a CH substrate to diagnose the temperature as a function of depth. With laser intensities around 10/sup 20/ W cm/sup -2/ and a pulse length of /spl sim/800 fsec we find temperatures of 650 eV-450 eV at depths of 8 micron to 17 micron. Deeper layers show strongly non-thermal emission characteristic of 'hollow atoms' with multiple inner shell vacancies. We have used the hybrid plasma simulation code LSP to model the transport and energy deposition from the relativistic electron beam and find broad agreement with our measurements which is improved if some laser pre-pulse is added to the model which has the effect of inhibiting the penetration of the relativistic electrons. The LSP simulations also show that the aluminium tracer layer should be significantly hotter than the CH substrate due to enhanced resistive heating, but with very thin tracer layers the electrons responsible for exciting the X-ray emission are not in equilibrium at the higher temperature due to finite mean free path effects (non-local transport).

Measurements of energetic electron beams generated from ultrahigh intensity laser interactions (I>10(19) W/cm(2)) with dense plasmas are discussed. These interactions have been shown to produce very directional beams, although with a broad energy spectrum. In the regime where the beam density approaches the density of the background plasma, we show that these beams are unstable to filamentation and "hosing" instabilities. Particle-in-cell simulations also indicate the development of such instabilities. This is a regime of particular interest for inertial confinement fusion applications of these beams (i.e., "fast ignition").

We are studying the feasibility of utilizing Kalpha x-ray sources in the range of 20 to 100 keV as a backlighters for imaging various stages of implosions and high aerial density planar samples driven by the NIF laser facility. The hard x-ray Kalpha sources are created by relativistic electron plasma interactions in the target material after a radiation by short pulse high intensity lasers. In order to understand Kalpha source characteristics such as production efficiency and brightness as a function of laser parameters, we have performed experiments using the 10 J, 100 fs JanUSP laser. We utilized single-photon counting spectroscopy and x-ray imaging diagnostics to characterize the Kalpha source. We find that the Kalpha conversion efficiency from the laser energy at 22 keV is similar to3 x 10(-4).

A method of measuring the temperature of the fast electrons produced in ultraintense laser-plasma interactions is described by inducing photonuclear reactions, in particular (gamma,n) and (gamma,3n) reactions in tantalum. Analysis of the gamma rays emitted by the daughter nuclei of these reactions using a germanium counter enables a relatively straightforward near real-time temperature measurement to be made. This is especially important for high temperature plasmas where alternative diagnostic techniques are usually difficult and time consuming. This technique can be used while other experiments are being conducted. (C) 2002 American Institute of Physics.

The application of high intensity laser-produced gamma rays is discussed with regard to picosecond resolution deep-penetration radiography. The spectrum and angular distribution of these gamma rays is measured using an array of thermoluminescent detectors for both an underdense (gas) target and an overdense (solid) target. It is found that the use of an underdense target in a laser plasma accelerator configuration produces a much more intense and directional source. The peak dose is also increased significantly. Radiography is demonstrated in these experiments and the source size is also estimated. (C) 2002 American Institute of Physics.

The Atomic Weapons Establishment at Aldermaston, U.K., has a number of pulsed-power-driven flash X-ray machines for diagnosing the hydrodynamics of explosively-driven high-Z materials. The most powerful of these machines is Mogul-E, which operates at about 10 MV and 30 kA, delivering about 450 R @ 1 m in a 5 mm spot. Longer-term plans envisage the upgrading of existing facilities through the construction of a multi-axis Hydrodynamic Research Facility (HRF). It is proposed that the HRF will be furnished initially with three inductive voltage adder (IVA) machines operating at /spl sim/14 MV, each giving 600 R @ 1 m in a 5 mm spot. It is envisaged that, following further research, the outputs will be increased towards 1000 R, with, it is hoped, a reduction in X-ray spot size. More speculative proposals involve increasing the number of machines from 3 to 5, and/or the splitting of the output end of one or more machines to drive more than one X-ray source per machine. An overview of the research programme necessary to achieve these aims is presented.

Summary form only given, as follows. When a high power laser is focused onto a solid or gaseous target at very high intensities the electron's motion in the electric field of the laser becomes relativistic and MeV electrons and ions are observed both from interactions with gaseous and solid targets. The most powerful lasers have been able to focus the laser light to intensities in excess of 10/sup 20/ WCM/sup -2/ with pulses containing up to several hundred Joules of laser radiation on target. Experiments investigating short pulse length, high intensity laser beams on the Vulcan Laser at the Rutherford Appleton Laboratory have yielded significant X-ray doses which are in the energy regime of interest to the flash radiography community at AWE. Such laser driven X-ray sources have specific applications to the radiographing of very high velocity, high line of site mass, high atomic number materials (core punching). The advantages of laser sources are their small X-ray source size, typically 10's of microns compared with conventional flash X-ray source sizes of millimeters. These series of experiments, conducted at the Rutherford Appleton Laboratories, measured the magnitude and spectral content of the radiation flux output from the Vulcan laser. We will also show how such a Laser driven X-ray source could be applied to core punching.

The generation of MeV electron and ion beams using lasers with intensities of up to 1020 W cm−2 is reported. Intense ion beams with high energies (up to 40 MeV and to 3×1012 protons >5 MeV) are observed. The properties of these particle beams were measured in considerable detail and the results are compared to current theoretical explanations for their generation.

Ultra-short, ultra-intense laser pulses can be used to generate MeV-class x-ray photons. As a laser can be focused to a spot less than a tenth of a millimetre the source size of these x-rays promises to be of a similar size, far better than can presently be achieved with current electron beam machines. In collaboration with Imperial College, London, and the Rutherford Appleton Laboratory we have carried out experiments to characterise the x-ray yield, spectrum and source size on the Vulcan Laser. We also attempted a crude radiograph of a relatively thick object.

The Pulsed Power Group at the Atomic Weapons Establishment (AWE) is interested in the generation of small, intense, multimegavolt X-ray. sources for radiographic applications. For this paper, research has been carried out into electron beam transport and focusing studies on one of our single pulse forming line flash X-ray machines.Experiments were undertaken on E Minor to improve the radiographic spot size generated by our "paraxial diode."' This is a novel anode/cathode assembly designed to produce a small-diameter electron beam focused onto a high-Z target. Electrons are propagated through a gas-filled tone such that their electrostatic repulsive and magnetic attractive forces are almost cancelled. The cone's length and gas pressure were initially optimized and then specific gas species applied to the drift cone. Helium gas improved spot size reproducibility with respect to variations in drift gas pressure when compared with dry air, The addition of a "secondary cell" to increase the neutralization of the electron beam's self-electric forces yielded a 30% improvement in measured radiographic spot size.