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In the last 3 decades, giant steps in technology and simulations capability have been made for the benefit of all magnetic fusion concepts. This is especially true for virtually a one-of-a-kind device, a microwave-driven bumpy-torus magnetic-fusion-energy system. In the 1980s, the prototype experiment was technology limited, and it was judged based on unrealistic expectations from an incomplete understanding of the machine performance. For those experiments, the machine did not achieve the theoretical stability threshold to demonstrate good plasma confinement. This paper examines the premise that the experimental platform was underpowered, which prevented acceptance of its value for fusion. In this paper, the experimental plasma scaling data with power are reviewed. If, with the advancements of technology and simulations capability of the last 30 years, stable operation can be proven, a much improved device competitive with tokamak and stellarator performance may be possible. The advantages of this concept include steady-state operation, gentle shut down, modular construction for fabrication and maintenance, and the natural diversion of impurities.

© Published under licence by IOP Publishing Ltd. We perform relativistic-intensity laser experiments using the Omega EP laser to investigate channeling phenomena and particle acceleration in underdense plasmas. A fundamental understanding of these processes is of importance to the hole-boring fast ignition scheme for inertial confinement fusion. Proton probing was used to image the electromagnetic fields formed as the Omega EP laser pulse generated a channel through underdense plasma. Filamentation of the channel was observed, followed by self-correction into a single channel. The channel radius as a function of time was found to be in reasonable agreement with momentum- conserving snowplough models.

Experiments were performed on the Omega EP laser facility to study laser pulse propagation, channeling phenomena and electron acceleration from high-intensity, high-power laser interactions with underdense plasma. A CH plasma plume was used as the underdense target and the interaction of the laser pulse channeling through the plasma was imaged using proton radiography. High-energy electron spectra were measured for different experimental laser parameters. Structures observed along the channel walls are interpreted as having developed from surface waves, which are likely to serve as an injection mechanism of electrons into the cavitated channel for acceleration via direct laser acceleration mechanisms. Two-dimensional particle-in-cell simulations give good agreement with these channeling and electron acceleration phenomena. © IOP Publishing and Deutsche Physikalische Gesellschaft.

This paper reports on recent results of a series of experiments on laser-generated ion beams. The experiments were done at the 30 TW ‘Trident’ laser system at the Los Alamos National Laboratories in New Mexico, USA, and we demonstrated the first accelerated ions at the 10 TW beamline of the PHELIX laser system at Gesellschaft fur Schwerionenforschung, Darmstadt, Germany. The experiments show the dependence of the Target Normal Sheath Acceleration Process (TNSA) on laser imprint and target parameters. The results are compared to a simple model for the ion propagation. It shows that TNSA-driven protons form an ion beam with superior beam quality, following the versatile spatial beam-shaping approaches.

It has become apparent in the last few years that the surface contamination on laser-acceleration targets is a major impediment to the acceleration of the actual target ions. To this end we have performed experiments at the Los Alamos Trident Laser facility using one arm of the Trident laser at 150 ps to ablatively clean targets that are subsequently irradiated by the Trident TW Short-pulse arm to accelerate the bulk target ions to high energies. The 150 ps ablation pulse rids the rear of the target of its omnipresent surface contamination layer allowing the short-pulse to illuminate the target and accelerate ions via the Target Normal Sheath Acceleration (TNSA) mechanism. Our experimental results are compared to the LASNEX code to validate and improve our predictive capabilities for future acceleration experiments.

We report on measurements of source sizes and charge state distributions of ions accelerated from thin foils irradiated by ultrashort (100–300 fs) high-intensity (1-6×1019 W/cm2) laser pulses. The source sizes of proton and carbon ion beams originating from hydrocarbon contaminants on the surfaces of 5 μm thick aluminum foils were investigated using the knife-edge method. For low-energy protons and low-carbon charge states, the source area was found to exceed the focal spot area by a factor of 104. For the determination of charge state distributions, sandwich targets consisting of a 25 μm thick tungsten layer, a 2-nm thin beryllium layer, and again a tungsten layer whose thickness was varied were used. These targets were resistively heated to remove the light surface contaminants. Peaked energy spectra of oxygen and argon ions corresponding to the equilibrium distribution after propagation through matter were observed.

A cyclic shearing interferometer has been employed to characterize a laser-produced plasma with 180 ps resolution. Counterpropagation maintains an equal path length for the probe and reference beams, and the shear is provided solely by the plasma, which appears within the circuit after the reference beam has passed the laser focal spot. The background is virtually fringe free because of the overlapping of the reference and probe beams so that analysis is simplified. The plasma, which is formed by a line focus, is seen to expand in a cylindrical manner away from the line focus with an exponential density profile. In addition, the interferometer shows evidence of a bow shock when an interaction beam is introduced into the plasma parallel to the direction of the line focus.

Laser-accelerated beams of Mega-electron volt protons have been produced at the Los Alamos Trident laser facility and used for high-resolution point-projection proton radiography of Au grids. The effective proton source size affords an inherent resolution of 2–3 μm in the object plane. The proton beam is characterized by ion time-of-flight Faraday cup measurements and nuclear particle track detectors. Laser-driven proton radiography appears promising as a valuable research tool for probing plasmas or modest density objects.

Single hot spot experiments offer several unique opportunities for developing a quantitative understanding of laser-plasma instabilities. These include the ability to perform direct numerical simulations of the experiment due to the finite interaction volume, isolation of instabilities due to the nearly ideal laser intensity distribution, and observation of fine structure due to the homogeneous plasma initial conditions. Experiments performed at Trident in the single hot spot regime have focused on the following issues. First, the intensity scaling of stimulated Raman scattering (SRS) for classically large damping regimes (kλD=0.35) was examined, and compared to classical SRS theory. SRS onset was observed at intensities much lower than expected (2×1015 W/cm2), from which nonclassical damping is inferred. Second, Thomson scattering was used to probe plasma waves driven by SRS, and structure was observed in the scattered spectra consistent with multiple steps of the Langmuir decay instability. Finally, sca...

The results from experiments in quasihomogeneous plasmas to evaluate the potential threat of high laser reflectivity from stimulated Raman scattering (SRS) to inertial-confinement fusion (ICF) are presented. The SRS laser reflectivity is observed to be sizable (up to 50%) and very weakly dependent on electron density (and kλD), over a large range of density that corresponds to a large variation in Landau damping of plasma waves. In contrast, the reflectivity increases monotonically over time, along with ion temperature, until gross hydrodynamic activity interferes with SRS. This is consistent with previous observations of SRS reflectivity scaling with the damping rate of ion acoustic waves [Fernandez et al., Phys. Rev. Lett. 77, 2702 (1996); Kirkwood et al., ibid. 77, 2706 (1996)]. The data from plasmas with the highest kλD values indicate anomalously low damping rates for the SRS plasma wave.

An unusual enhancement of two normally-weak and density-stable satellite spectral lines resulting from 2s 2 –1s2p and 1s2s 2 –1s 2 2p transitions in He- and Li-like ions of silicon has been observed in laser-produced plasma experiments at the TRIDENT facility. Space-resolved intensities compared to other more-intense satellites formed by dielectronic recombination are increased by a factor as high as 8 over code predictions at low density (coronal limit). The data were obtained using temporally- and spatially resolved X-ray spectroscopic measurements, supported by Thomson scattering diagnostics. One explanation considered is that the more-intense satellite lines are opacity limited. This suggests a method of determining radiative transfer on the more intense lines, by comparison measurements. Also coincident with these two enhanced features is a K α blend from low stages of ionization, which suggests some alternate interpretation. A complete understanding of the observed anomalies awaits further experimentation.

Ion acoustic and electron plasma waves, associated with backward-propagating stimulated Brillouin scattering and stimulated Raman scattering, have been diagnosed in a long-scale-length, nearly homogenous plasma with transverse flow. Thomson scattered light from a probe beam is employed to show that these waves are well localized in space and for a time much shorter than the laser pulse duration. These plasma conditions are relevant to hohlraum design for the National Ignition Facility inertial confinement fusion laser system. [R. Sawicki et al., Fusion Technol. 34, 1097 (1998)].

The TRIDENT laser system at the Los Alamos National Laboratory is being used for fundamental experiments which study the interaction of self-focusing, stimulated Raman scattering (SRS) and stimulated Brillouin scattering (SBS) in a near-diffraction-limited (single) laser hot spot in order to better understand the coupling between these plasma instabilities. The diffraction limited beam mimics a single hot spot found in speckle distributions that are typical of random or kinoform phase plates (RPP or KPP) used for spatial smoothing of laser beams. A long scale length, hot plasma (∼1 mm, ∼0.6 keV) is created by a separate heater beam, and the single hot spot beam is used to drive parametric instabilities. The focal plane distribution and wave-front of the interaction beam are characterized, and its intensity can be varied between 1014–1016 W/cm2. The plasma density, temperature, and flow profiles are measured using a gated imaging spectroscopy of collective Thomson scattering from the heater beam. Results of the laser and plasma characterization, and initial results of backscattered SRS, SBS, and beam steering in a flowing plasma are presented.

We have designed and produced hot, millimeter-scale, high-{ital Z} plasmas of interest for National Ignition Facility hohlraum target design. Using a high-{ital Z} gas fill produces electron temperatures in the 3.5{endash}6-keV range, the highest temperatures measured to date for high-density (10{sup 21} e/cm{sup 3}) laser-heated plasmas, and much higher than the 3 keV found for low-{ital Z} (neopentane) fills. These measurements are in good agreement with the target design calculations, and the {ital L}-shell spectroscopic approach used to estimate the electron temperature has certain advantages over traditional {ital K}-shell approaches. {copyright} {ital 1999} {ital The American Physical Society}

A preformed plasma simulating the corona of a fast ignitor target has been probed with 527 nm and 1054 nm lasers exceeding the critical power for ponderomotive electron cavitation. For both colors, the f number of the probe beam is increased as it propagates through the plasma. Transmission of the diffraction-limited beams is higher for the green than for the 1 μm case.

The reflectivity of laser light due to stimulated Brillouin scattering (SBS) from long-scale plasmas normally saturates when the laser intensity is increased sufficiently. Nevertheless a significant increase in the SBS reflectivity back into the beam cone results from a subtle change in the target geometry, done for the purpose of seeding SBS. The key element is apparently the injection into the plasma of a modest external electromagnetic seed at a wavelength near that of the scattered light. {copyright} {ital 1998} {ital The American Physical Society}

Data from a pinhole camera and a transmission grating spectrograph are used in multi-TW laser irradiance of thin metal films to assess the maximum laser spot size and to show tenths of a percent conversion of laser light to K-, L-, and M-band x rays. The distribution of target debris, an operational issue for the survivability of an unshielded parabola in a large laser system, is revealed by x-ray fluorescence measurements of witness samples. At the 25-J, 30-TW level, we find little evidence of damage to the f/3 parabola with an angle of incidence on target greater than 22°.

Two types of satellite lines are studied in laser-produced plasmas as potential diagnostic tools. One consists of a pair of lines straddling the wavelength of a dipole-forbidden line and displaced from it by the laser frequency. The relative intensities are a measure of the local laser electric field in the plasma. Possible satellites of this sort associated with He-like and Li-like magnesium n = 2 to n = 3 transitions are indicated in the data. The second type of satellite arises from an innershell transition in Li-like aluminum (and magnesium) and the lines occur adjacent to the He-like ls2 1S-ls3p 1P x-ray resonance line. The upper level configuration for one satellite does not readily autoionize, and hence is populated mainly by electron collisions in a high density plasma. It is an electron density indicator, and in the present case the relative intensity is consistent with electron densities ~ 1020 cm−3, according to atomic physics modeling. The wavelengths of these Li-like innershell satellites appear to be shifted shorter by ~ 13 mA when compared to those of nearby He-like resonance lines. The sequence of such ionic x-ray lines from streak data are in agreement with a numerical code.

In an experiment relevant to the fast ignitor fusion concept, a preformed plasma simulating the corona of a fusion target has been probed with laser intensities exceeding 1018 W/cm2. It is seen that the f number of the probe beam is increased as it propagates through the target plasma—a channeling of the power. The transmission and backscatter of the probe beam have been examined, and the analysis suggests anomalous absorption of laser light in shorter scale length plasmas.

A 2-D Eulerian code with a turbulent mix model was used for the first time to model a set of plastic (CH) ablator capsules with 15 μm thick CH shells. Our simulations of these capsules do a reasonable job of matching the implosion radius versus time, self-emitting core radius, and have an experiment/simulation yield ratio that is about 0.24.

Los Alamos National Laboratory is contributing to the core science and technology of the inertial confinement fusion program leading to the National Ignition Facility. Short summaries of a sample o...

The onset of stimulated Brillouin scattering (SBS) has been examined by varying the effective F number (lens focal length/incident beam diameter) of the optical system used to irradiate a performed 1 mm long, longitudinally uniform hydrocarbon (CH) plasma. SBS onset occurs at higher average laser intensity for smaller F, in qualitative agreement with theory. Quantitative comparison between theory and experiment, and implications for the National Ignition Facility [Phys. Plasmas 2, 2480 (1995)] are discussed.

A spatially discriminating optical streaked spectrograph is employed as a plasma diagnostic on the Nova laser. The instrument, which makes use of a spectrometer coupled to a streak camera with CCD readout, observes a small region of Nova target plasmas with a Cassegrain telescope. It yields simultaneous temporal and spectral information about emission and scattered light from the small plasma region.

Development of robust instrumentation has shown evidence for a multi-μC expulsion of relativistic electrons from a sub-μm-thick foil, laser illuminated with 60–70 J on target at 2 × 1020 W/cm2. From previous work and with electron spectroscopy, it is seen that an exponential electron energy distribution is accurate enough to calculate the emitted electron charge and energy content. The 5–10-μC charge for the >100-TW Trident Laser represents the first active measurement of the >50% laser-light-to-electron conversion efficiency. By shorting out the TV/m electric field usually associated with accelerating multi-MeV ions from such targets, one finds that this charge is representative of a multi-MA current of relativistic electrons for diverse applications from electron fast ignition to advanced radiography concepts. Included with the details of the discoveries of this research, shortcomings of the diagnostics and means of improving their fidelity are discussed.

Capsules driven with polar drive [1, 2] on the National Ignition Facility [3] are being used [4] to study mix in convergent geometry. In preparation for experiments that will utilize deuterated plastic shells with a pure tritium fill, hydrogen-filled capsules with copper- doped deuterated layers have been imploded on NIF to provide spectroscopic and nuclear measurements of capsule performance. Experiments have shown that the mix region, when composed of shell material doped with about 1% copper (by atom), reaches temperatures of about 2 keV, while undoped mixed regions reach about 3 keV. Based on the yield from these implosions, we estimate the thickness of CD that mixed into the gas as between about 0.25 and 0.43 μm of the inner capsule surface, corresponding to about 5 to 9 μg of material. Using 5 atm of tritium as the fill gas should result in over 1013 DT neutrons being produced, which is sufficient for neutron imaging [5].

We have measured the conversion efficiency, as well as the spectral and temporal x‐ray output of H‐ and He‐like carbon line emission, from a thin foil of polypropylene that has been irradiated with subpicosecond KrF laser pulses. The effect of amplified spontaneous emission prepulse on the x‐ray conversion process, as well as the application of these x‐ray ‘‘flashlamps’’ toward pumping soft x‐ray lasers, is discussed.

Experiments were performed using the Omega EP laser, operating at 740 J of energy in 8 ps (90 TW), which provides extreme conditions relevant to fast ignition studies. A carbon and hydrogen plasma plume was used as the underdense target and the interaction of the laser pulse propagating and channeling through the plasma was imaged using proton radiography. The early time expansion, channel evolution, filamentation, and self-correction of the channel was measured on a single shot via this method. A channel wall modulation was observed and attributed to surface waves. After around 50 ps, the channel had evolved to show bubblelike structures, which may be due to postsoliton remnants. © 2011 American Physical Society.

Laser‐plasma accelerated ion and electron beam sources are an emerging field with vast prospects, and promise many superior applications in a variety of fields such as hadron cancer therapy, compact radioisotope generation, table‐top nuclear physics, laboratory astrophysics, nuclear forensics, waste transmutation, Special Nuclear Material (SNM) detection, and inertial fusion energy. LANL is engaged in several projects seeking to develop compact high‐current and high‐energy ion and electron sources. We are especially interested in two specific applications: ion fast ignition/capsule perturbation and radiation oncology. Laser‐to‐beam conversion efficiencies of over 10% are needed for practical applications, and we have already shown inherent efficiencies of >5% from flat foils, on Trident using only a 5th of the intensity [1] and energy of the Nova Petawatt laser [2]. With clever target designs, like structured curved cone targets, we have also been able to achieve major ion energy gains, leading to the highest energy laser‐accelerated proton beams in the world [3]. These new target designs promise to help usher in the next generation of particle sources realizing the potential of laser‐accelerated beams.

The Neutron Imaging System (NIS), currently under development at Los Alamos National Laboratory, will be a phase 2 diagnostic for the National Ignition Facility at Lawrence Livermore National Laboratory. It is designed to provide neutron fluence images of imploded ICF capsule targets with neutron yields above 10^12, with a spatial resolution of 15–20 microns. These images are time-integrated through the period of TN burn.

The high contrast front-end for the 200 TW Trident laser has shown in recent experiments the importance roles that Amplified Spontaneous Emission (ASE) and prepulse contrast play in laser-ion acceleration. Ion energies above 58 MeV with efficiencies of greater than 5% into ions above 4 MeV have been observed even at modest intensities, on par with the Nova Petawatt results2 at half the intensity1, and a fifth of the energy and power, at an intrinsic laser ASE contrast of ≫ 10−7. Scalings for, laser energy, intensity, and target thickness are presented and compared to other empirical scalings and theories, including results of the new ultra-high contrast ≫10−10 Optical Parametric Chirped-Pulse Amplification (OPCPA) front-end system3.

Inertial confinement fusion research at Los Alamos National Laboratory is focused on high‐leverage areas of thermonuclear ignition to which LANL can apply its historic strengths and that are complementary to high‐energy‐density‐physics topics. Using the Trident and Omega laser facilities, experiments are pursued in laser‐plasma instabilities, symmetry, Be technologies, neutron and fusion‐product diagnostics, and defect hydrodynamics.

The newly upgraded TRIDENT high-energy-density (HED) facility provides high-energy short-pulse laser-matter interactions with powers in excess of 200 TW and energies greater than 120 J. In addition, TRIDENT retains two long-pulse (nanoseconds to microseconds) beams that are available for simultaneous use in either the same experiment or a separate one. The facility's flexibility is enhanced by the presence of two separate target chambers with a third undergoing commissioning. This capability allows the experimental configuration to be optimized by choosing the chamber with the most advantageous geometry and features. The TRIDENT facility also provides a wide range of standard instruments including optical, x-ray, and particle diagnostics. In addition, one chamber has a 10 in. manipulator allowing OMEGA and National Ignition Facility (NIF) diagnostics to be prototyped and calibrated.

With the completion of the Trident laser facility upgrade, 200 TW high-energy laser pulses are now capable of producing x-ray pulses with energies in the range of 15-40 keV, which will be used for high-spatial resolution radiography. A diagnostic suite is being developed on the laser system to investigate and characterize the x-ray emission from high-Z targets. This includes charge coupled device based single-photon counters, imaging plates, a high-energy electronic imager, spectral diagnostics, and optical and x-ray spot size diagnostics. We describe recent x-ray results from a commissioning campaign as well as describe the development and design of a high-energy spectrometer. X-ray radiographs taken at 22 keV with a spatial resolution of 25 mum are a first demonstration on this facility of high-energy, high-spatial resolution capability.

The sub-ps Trident laser is upgraded to deliver >100 J on target. We are prepared to measure conversion efficiencies of 200-TW laser light to K-shell emission. X-ray diagnostics include a simple, inexpensive Laue X-ray spectrograph and a set of Ross filter pairs. The sensitivity of Si p-i-n diodes is adequate to record X-ray emission up to 100 keV. With carefully matched Ross filter pairs, the diodes permit estimation of the signal between the filter edges of two channels through subtraction of signals. Estimates suggest that the signal-to-noise ratio of the K-shell signal to X-ray continuum and leakage from filter mismatch is adequate to determine the conversion efficiency. These instruments will be employed to optimize the efficiency of X-ray backlighters in this energy range.

Polar-direct-drive experiments conducted at the National Ignition Facility [E. I. Moses, Fusion Sci. Technol. 54, 361 (2008)] performed at laser irradiance between 1 and 2×1015 W/cm2 exhibit increased hard x-ray emission, decreased neutron yield, and reduced areal density as the irradiance is increased. Experimental x-ray images at the higher irradiances show x-ray emission at the equator, as well as degraded symmetry, that is not predicted in hydrodynamic simulations using flux-limited energy transport, but that appear when non-local electron transport together with a model to account for cross beam energy transfer (CBET) is utilized. The reduction in laser power for equatorial beams required in the simulations to reproduce the effects of CBET on the observed symmetry also reproduces the yield degradation consistent with experimental data.

We present a general expression for the maximum ion energy observed in experiments with thin foils irradiated by high-intensity laser pulses. The analytical model is based on a radially confined surface charge set up by laser accelerated electrons on the target rear side. The only input parameters are the properties of the laser pulse and the target thickness. The predicted maximum ion energy and the optimal laser pulse duration are supported by dedicated experiments for a broad range of different ions.

Acceleration of particles by intense laser-plasma interactions represents a rapidly evolving field of interest, as highlighted by the recent demonstration of laser-driven relativistic beams of monoenergetic electrons. Ultrahigh-intensity lasers can produce accelerating fields of 10 TV m(-1) (1 TV = 10(12) V), surpassing those in conventional accelerators by six orders of magnitude. Laser-driven ions with energies of several MeV per nucleon have also been produced. Such ion beams exhibit unprecedented characteristics--short pulse lengths, high currents and low transverse emittance--but their exponential energy spectra have almost 100% energy spread. This large energy spread, which is a consequence of the experimental conditions used to date, remains the biggest impediment to the wider use of this technology. Here we report the production of quasi-monoenergetic laser-driven C5+ ions with a vastly reduced energy spread of 17%. The ions have a mean energy of 3 MeV per nucleon (full-width at half-maximum approximately 0.5 MeV per nucleon) and a longitudinal emittance of less than 2 x 10(-6) eV s for pulse durations shorter than 1 ps. Such laser-driven, high-current, quasi-monoenergetic ion sources may enable significant advances in the development of compact MeV ion accelerators, new diagnostics, medical physics, inertial confinement fusion and fast ignition.

Summary form only given. An understanding of the material dynamics and EoS characteristics of copper-doped beryllium (Be-Cu) ablators is critical for several ignition designs for the National Ignition Facility (NIF). Beryllium offers several advantages as an ablator: (a) high density, (b) low heat capacity, and (c) low opacity. In addition, dopants can be used to optimize these characteristics, for example, copper increases the density and opacity. In such a design, the Be-Cu ablator is subjected to thermal and soft X-ray radiation, delivering a sequence of shocks which compress a deuterium-tritium capsule. The first shock is expected to be between 0.5 and 8.0 Mbar. Be-Cu is predicted to melt on the Hugoniot between 1 and 2 Mbar and may depend upon the time scale. The anisotropic mechanical and thermal expansion properties of Be-Cu may introduce velocity fluctuations as the microstructure is loaded, and may then seed Rayleigh-Taylor instabilities. The uncertainty in Be-Cu melt and instability-growth dependence upon microstructure impacts the predictive capabilities for capsule performance. We have developed and fielded a series of experiments at the Omega laser facility that closely replicate the NIF-foot hohlraum conditions expected for a Be-Cu ablator. The experiments aim to investigate the seeding of instabilities by microstructure. In these experiments, a holhraum is rapidly brought up to a radiation temperature of 70-90 eV and held there for 2.5-3.2 ns. After ~3.0 ns, the temperature is raised to 120-150 eV in order to drive instabilities. Using 25-70 micron thick Be-0.9%Cu samples mounted on one end of the hohlraum, we performed free-surface velocimetry and pyrometry measurements during the foot of the pulse. We will present the velocity and pyrometry data along with inferred pressure, and discuss potential implications for Be-Cu capsule performance at NIF

Thomson scattering is used to measure Langmuir waves (LW) driven by stimulated Raman scattering (SRS) in a diffraction limited laser focal spot. For SRS at wave numbers klambda(D) less similar 0.29, where k is the LW number and lambda(D) is the Debye length, multiple waves are detected and are attributed to the Langmuir decay instability (LDI) driven by the primary LW. At klambda(D) greater similar 0.29, a single wave, frequency-broadened spectrum is observed. The transition from the fluid to the kinetic regime is qualitatively consistent with particle-in-cell simulations and crossing of the LDI amplitude threshold above that for LW self-focusing.

The laminarity of high current multi‐MeV proton beams produced by irradiating thin metallic foils with ultra‐intense lasers has been measured. For proton energies >10 MeV, the transverse and longitudinal emittance are respectively 10 MeV. Magnetic stripping of the co‐moving electrons out of the beam after a few cm of debunching is not observed to induce emittance growth.

Order-of-magnitude anomalously high intensities for two-electron (dielectronic) satellite transitions, originating from the He-like 2s(2) 1S0 and Li-like 1s2s(2) (2)S(1/2) autoionizing states of silicon, have been observed in dense laser-produced plasmas at different laboratories. Spatially resolved, high-resolution spectra and plasma images show that these effects are correlated with an intense emission of the He-like 1s3p 1P-1s(2) 1S lines, as well as the K(alpha) lines. A time-dependent, collisional-radiative model, allowing for non-Maxwellian electron-energy distributions, has been developed for the determination of the relevant nonequilibrium level populations of the silicon ions, and a detailed analysis of the experimental data has been carried out. Taking into account electron density and temperature variations, plasma optical-depth effects, and hot-electron distributions, the spectral simulations are found to be not in agreement with the observations. We propose that highly stripped target ions (e.g., bare nuclei or H-like 1s ground-state ions) are transported into the dense, cold plasma (predominantly consisting of L- and M-shell ions) near the target surface and undergo single- and double-electron charge-transfer processes. The spectral simulations indicate that, in dense and optically thick plasmas, these charge-transfer processes may lead to an enhancement of the intensities of the two-electron transitions by up to a factor of 10 relative to those of the other emission lines, in agreement with the spectral observations.

The proton probing technique is used to image quasi-static electromagnetic fields present in the wake of a high-intensity short-pulse laser propagating through an underdense plasma. Bubblelike field structures form along the channel filaments and expand in time. © 2006 IEEE.

Temporally, spatially, and spectrally resolved x-ray image data from direct-drive implosions on OMEGA were interpreted with the aid of radiation-hydrodynamic simulations. Neither clean calculations nor those using a turbulent mix model can explain fully the observed migration of shell-dopant material (titanium) into the core. Shell-dopant migration was observed via time-dependent, spatially integrated spectra, and spatially and spectrally resolved x-ray images of capsule implosions and resultant dopant emissions. The titanium emission was centrally peaked in narrowband x-ray images. In post-processed clean simulations, the peak titanium emission forms in a ring in self-emission images as the capsule implodes. Post-processed simulations with mix reproduce trends in time-dependent, spatially integrated spectra, as well having centrally peaked Ti emission in synthetic multiple monochromatic imager. However, mix simulations still do not transport Ti to the core as is observed in the experiment. This suggests that phenomena in addition to the turbulent mix must be responsible for the transport of Ti. Simple diffusion estimates are unable to explain the early Ti mix into the core. Mechanisms suggested for further study are capsule surface roughness, illumination non-uniformity, and shock entrainment.

A diffraction-limited laser interacts with a plasma whose conditions are uniform on the scale of the focused laser spot. Two distinct, narrow waves are observed in the backscattered spectrum with phase velocities of ${v}_{\ensuremath{\varphi}}{/v}_{e}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1.4\ifmmode\pm\else\textpm\fi{}0.08$ and $4.2\ifmmode\pm\else\textpm\fi{}0.1$, where ${v}_{e}$ is the electron thermal speed. The high-velocity wave is ordinary stimulated Raman scattering (SRS) from a Langmuir wave. The low-velocity wave corresponds to stimulated scattering from an electron-acoustic wave (SEAS), and implies strong electron trapping. Previous SRS data from low-density plasmas are reinterpreted in terms of SEAS.

An x‐ray streak camera is used to diagnose a laser‐produced Al plasma with time resolution of ∼10 ps. A streak record of filtered emission and a time‐integrated transmission grating spectrum reveal that the plasma radiation is dominated by emission from He‐ and H‐like resonance lines.

The conversion efficiency into kilovolt line radiation for 248‐nm light at 1017 W/cm2 on an aluminum target is measured. The x‐ray yield is found to increase with the scale length of the target plasma. The interaction is modeled as resonance absorption, and the plasma scale length is determined from the prelase energy and irradiance.

The transmitted angular distribution of a 527 nm nearly diffraction-limited laser is measured after it propagates through a plasma with supersonic transverse flow. The laser beam is deflected by as much as 10 degrees and exhibits bowlike features in the flow direction, which is attributed to flow-induced beam steering. The finite interaction volume allows for direct comparison with a 3D hydrodynamic simulation, which is in good agreement with details of the experiment.

SDOSS is employed to study broadband laser scattering encompassing SBS, SRS, and the 3/2‐ω signature of two plasmon decay for ns‐scale laser‐plasma experiments with 351‐ or 527‐nm drive. It uses a Cassegrain telescope to image scattered light from a laser plasma onto a field stop. The telescope magnification and the stop aperture provide spatial discrimination of target plane scatter. A UV lens relays the image to a 0.25‐m spectrograph which is lens coupled to a streak camera with an S‐1 photocathode. The streak output is imaged onto a CCD camera. In its 512×480 pixel array, the CCD covers a spectral range from 200 to 800 nm with 4‐nm resolution and can be adjusted to look from 350 to 1060 nm. The sweep speed is variable with full window values of 30, 12, 6 ns, and faster. An optical fiducial provides a spectral and temporal marker. On the Livermore Nova laser, SDOSS has been used to determine spatial density in gas‐filled hohlraums from SRS signals. At Trident in Los Alamos, it has been employed for similar measurements with long scale length plasmas in SBS and SRS seeding experiments. It has proven to be a versatile tool for studying the physics of laser‐generated plasmas.