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The National Ignition Facility (NIF) diagnostic instrument manipulator (DIM) - based high resolution (dHIRES) x-ray spectrometer was used to measure the time evolution of the electron density (n e) and temperature (T e) in the hot spot of four NIF compressed capsules with 25 ps time resolution during the ‘stagnation’ phase. The electron density was inferred by comparing the measured Stark broadening of the krypton (Kr) Heβ spectral complex with theoretical calculations that include ion dynamic effects, and the electron temperature was inferred by comparing the measured ratio of the intensity of a dielectronically excited Li-like Kr line to the intensity of the Kr Heβ resonance line with calculations using the spectroscopic collisional radiative atomic model (SCRAM) and CRETIN collisional-radiative models. The inferred, time averaged n e values mainly agree with n e values from neutron diagnostics within uncertainties, but the neutron time-of-flight values of T ion are consistently higher than dHIRES T e values by 200–700 eV. The dHIRES measurements and measurement techniques, method of uncertainty analysis, and discussion of comparisons with measurements from neutron diagnostics are presented.

At the completion of the National Ignition Campaign (NIC), the National Ignition Facility (NIF) had about 36 different types of diagnostics. These were based on several decades of development on No...

The principal approach to ignition on the National Ignition Facility (NIF) is indirect drive. A schematic of an ignition target is shown in Figure 1. The laser beams are focused through laser entrance holes at each end of a high-Z cylindrical case, or hohlraum. The lasers irradiate the hohlraum walls producing x-rays that ablate and compress the fuel capsule in the center of the hohlraum. The hohlraum is made of Au, U, or other high-Z material. For ignition targets, the hohlraum is {approx}0.5 cm diameter by {approx}1 cm in length. The hohlraum absorbs the incident laser energy producing x-rays for symmetrically imploding the capsule. The fuel capsule is a {approx}2-mm-diameter spherical shell of CH, Be, or C filled with DT fuel. The DT fuel is in the form of a cryogenic layer on the inside of the capsule. X-rays ablate the outside of the capsule, producing a spherical implosion. The imploding shell stagnates in the center, igniting the DT fuel. NIC has overseen installation of all of the hardware for performing ignition experiments, including commissioning of approximately 50 diagnostic systems in NIF. The diagnostics measure scattered optical light, x-rays from the hohlraum over the energy range from 100 eV tomore » 500 keV, and x-rays, neutrons, and charged particles from the implosion. An example of a diagnostic is the Magnetic Recoil Spectrometer (MRS) built by a collaboration of scientists from MIT, UR-LLE, and LLNL shown in Figure 2. MRS measures the neutron spectrum from the implosion, providing information on the neutron yield and areal density that are metrics of the quality of the implosion. Experiments on NIF extend ICF research to unexplored regimes in target physics. NIF can produce more than 50 times the laser energy and more than 20 times the power of any previous ICF facility. Ignition scale hohlraum targets are three to four times larger than targets used at smaller facilities, and the ignition drive pulses are two to five times longer. The larger targets and longer pulse lengths produce unique plasma conditions for laser-plasma instabilities that could reduce hohlraum coupling efficiency. Initial experiments have demonstrated efficient coupling of laser energy to x-rays. X-ray drive greater than 300 eV has been measured in gas-filled ignition hohlraum and shows the expected scaling with laser energy and hohlraum scale size. Experiments are now optimizing capsule implosions for ignition. Ignition conditions require assembling the fuel with sufficient density and temperature for thermonuclear burn. X-rays ablate the outside of the capsule, accelerating and spherically compressing the capsule for assembling the fuel. The implosion stagnates, heating the central core and producing a hot spot that ignites and burns the surrounding fuel. The four main characteristics of the implosion are shell velocity, central hot spot shape, fuel adiabat, and mix. Experiments studying these four characteristics of implosions are used to optimize the implosion. Integrated experiments using cryogenic fuel layer experiments demonstrate the quality of the implosion as the optimization experiments progress. The final compressed fuel conditions are diagnosed by measuring the x-ray emission from the hot core and the neutrons and charged particles produced in the fusion reactions. Metrics of the quality of the implosion are the neutron yield and the shell areal density, as well as the size and shape of the core. The yield depends on the amount of fuel in the hot core and its temperature and is a gauge of the energy coupling to the fuel. The areal density, the density of the fuel times its thickness, diagnoses the fuel assembly, which is measured using the fraction of neutrons that are down scattered passing through the dense shell. The yield and fraction of down scattered neutrons, or shell rho-r, from the cryogenic layered implosions are shown in Figure 3. The different sets of data represent results after a series of implosion optimization experiments. Both yield and areal density show significant increases as a result of the optimization. The experimental Ignition Threshold Factor (ITFX) is a measure of the progress toward ignition. ITFX is analogous to the Lawson Criterion in Magnetic Fusion. Implosions have improved by over a factor of 50 since the first cryogenic layered experiments were done in September 2010. This increase is a measure of the progress made toward the ignition goal in the past year. Optimization experiments are planned in the coming year for continued improvement in implosion performance to achieve the ignition goal. In summary, NIF has made significant progress toward ignition in the 30 months since project completion. Diagnostics and all of the supporting equipment are in place for ignition experiments. The Ignition Campaign is under way as a national collaborative effort of all the National Nuclear Security Administration (NNSA) science laboratories as well as international partners.« less

Indirect-drive inertial confinement fusion (ICF) uses high-Z cavities, or hohlraums, to confine x rays for compressing and igniting deuterium-tritium fuel contained in spherical capsules. For laser-driven ICF, the intense laser beams enter the hohlraum through small laser entrance holes (LEHs), heating the high-Z hohlraum walls. The laser-produced radiation heats the unirradiated high-Z walls producing a nearly isotropic radiation environment for spherically compressing the lCF capsule. The radiation flux on the capsule is not completely isotropic, however, because the laser-irradiated area is generally brighter than the surrounding x-ray heated walls and the LEHs do not radiate. Furthermore, the angular distribution of flux on the capsule is time dependent because the unilluminated walls become hotter and more emissive as a function of time, and plasma dynamics cause the laser-irradiated area to move. Symmetric implosions are obtained by dynamically balancing the effects of the LEHs, wall heating, and laser-spot motion.

In order to prevent high‐Z plasma from filling in the hohlraum in indirect drive experiments, a low‐Z material, or tamper is introduced into the hohlraum. This material, when fully ionized is typically less than one‐tenth of the critical density for the laser light used to illuminate the hohlraum. This tamper absorbs little of the laser light, thus allowing most of the laser energy to be absorbed in the high‐Z material. However, the pressure associated with this tamper is sufficient to keep the hohlraum wall material from moving a significant distance into the interior of the hohlraum. In this paper we discuss measurements of the motion of the interface between the tamper and the high‐Z hohlraum material. We also present measurements of the effect the tamper has on the hohlraum temperature.

Soft x-ray projection lithography (SXPL) systems are designed to operate with narrow bandwidths around 130Å, where the highest reflectivity mirrors have been demonstrated1. Several different sources are under consideration. One possibility is the laser-produced plasma, in which Intense visible laser light incident on a solid metal surface in vacuum generates an x-ray emitting plasma. An important question is whether sufficient x-ray radiation is generated at 130Å. Although much work has been performed at the very high laser intensities used in fusion applications, no experiments existed at the pulse widths and intensities necessary for SXPL systems. In this work a comprehensive soft x-ray database for laser plasma lithographic sources was developed. We determined the absolute conversion efficiency from laser light into x-rays for various target materials, laser wavelengths {1.064μm & 532nm),pulse lengths (7.5-30ns), incident intensities{1x109W/cm2 - 1x1013W/cm), and spot sizes(15μm-2mm).

X ray production in the region around 130 Å from laser-produced plasmas has been investigated for using them as a possible source for projection x-ray lithography. The dependence of production efficiency on target material, intensity, and pulse length has been extensively studied using a 0.53 µm wavelength laser with a maximum output of 0.3 J. Production efficiency of 1% into a 3 Å bandwidth has been demonstrated from a Sn target for intensities around 1011 W/cm2 using an 8 ns pulse. Absolute x-ray production in the region around 130 Å is measured using two different techniques for wavelength discrimination. A broad band channel defined by a grazing incidence carbon x-ray mirror and a Be transmission filter coupled with a Si XUV solid state diode measures x-rays in the 177 Å to 111 Å region. We also measure x-ray production in a narrow band around 130 Å defined by a near normal incidence synthetic multilayer mirror. Filters, mirrors, and detectors have been absolutely calibrated at synchrotrons to obtain absolute yields. In addition, we measure spectra using a transmission grating spectrometer. The spectra show that a relatively narrow feature in Sn near 130 Å enhances x-ray production making this element an optimum choice for this wavelength region. The intensity scaling data suggest that laser spot size and two-dimensional expansion of the plasma play an important role in optimizing x-ray production for these sub-joule irradiation conditions. In future experiments we plan to extend these measurements to larger spot sizes using a higher power laser to better understand the effects of two-dimensional plasma expansion on x-ray production. We also plan to extend these studies using a 1 µm laser to investigate the wavelength dependence on conversion efficiency.

Laser‐produced plasmas are investigated as a source for soft x‐ray projection lithography. The dependence of conversion efficiency on target material, intensity, wavelength, and pulse width is determined using absolutely calibrated detectors. Conversion efficiency greater than 1% into a 2.2 eV bandwidth is demonstrated for Sn targets, fulfilling the system source requirements.

The backscattered energy spectrum of a beam of MeV ions incident along a major axial direction of a single crystal displays a high energy peak which represents the interaction of the beam with the surface region of the solid. Measurements under U.H.V. conditions, on well characterized surfaces, yield information on the thermal vibration amplitude, relaxation and reconstruction of the first monolayer(s) of the solid; this information is not easily obtainable by standard surface physics techniques. Such studies are of importance in the field of catalysis and semiconductors as well as the fundamental understanding of surfaces. An U.H.V. system for surface analysis studies couple to a 3.75 MeV Van de Graaff accelerator shall be described. Measurements of the surface peak intensity for W(100) are presented and shown to be in good agreement with theoretical models of the scattering process. The interpretation of such measurements in terms of surface physics parameters will be discussed.

The surface peak, observed in backscattering-channeling experiments, has been measured as a function of projectile (He/sup +/) energy on a clean W(100) crystal. We show that the intensity of the surface peak is in good agreement with classical models of channeling. Furthermore, we deduce an upper limit of 6% for the relaxation of the W(100) surface.

We present results of a laser Doppler‐shift technique which gives the velocity profiles of ablatively accelerated targets. Measurements of the effects of laser beam nonuniformity on the target acceleration are presented and interpreted in the context of laser pellet fusion.

Auger, Rutherford backscattering, and x‐ray‐diffraction measurements show that plasma‐grown oxide films on Ga0.64Al0.36As are amorphous, uniform in composition with depth, and possess very sharp oxide‐semiconductor interfaces. The electrical properties (I‐V, C‐V) of these films are such that they may be used for surface passivation of optoelectronic devices and as dielectric layers in electronic device fabrication.

Thin oxide films of GaAs grown in a plasma have been analyzed using Rutherford backscattering and ion‐induced x rays. Films whose thicknesses are greater than 1000 A have a composition of O:Ga:As of 3:1.07:1. For the thinner films, the oxygen content is less indicating an incomplete oxidation.

We have made absolute measurements of x‐ray spectra from 0.1–1.5 keV produced by plasmas from targets irradiated by the Lawrence Livermore National Laboratory Nova laser. These measurements were made using a 15‐channel K‐ and L‐edge filtered x‐ray diode system. Valid interpretation of the results from this type of diagnostic requires some care in eliminating the effect of channel response at photon energies higher than the absorption edge. Significant errors can occur if this is disregarded. We will discuss the techniques used and the magnitude of the effects observed. Integrated x‐ray energy in the 1.5–3‐keV region is inferred from the results.

The K X-ray spectrum from a 30 MeV chlorine ion beam was measured as it was stopped in aluminium. The spectrum exhibits six lines located approximately half way between the Kalpha 1,2 and Kbeta 1,3 lines of chlorine. These lines can be interpreted as Kalpha transitions with various 2p shell vacancies and with the M shell electrons partially stripped.

We have begun investigating the production of an XUV/soft x‐ray laser, using our high‐powered glass lasers as drivers. A major diagnostic for lasing is the measure of the absolute power produced in the lasing line. I have developed a spectrography to time‐resolve lasing lines in the energy range from 50 eV to greater than 200 eV. The spectrograph combines a transmission grating and x‐ray streak camera to produce a flat field in the energy range from 50 eV to greater than 200 eV. The spectrograph combines a transmission grating and x‐ray streak camera to produce a flat field instrument. A cylindrical mirror is used in front of the grating to image the source and act as a collecting optic. The efficiency of the components is calibrated so that absolute intensities can be measured. I will compare the performance of this instrument with reflection grating systems. I will also discuss planned improvements to the system which should increase total throughput, image quality, and resolving power.

We have built an x-ray streaked crystal spectrograph for making time-resolved x-ray spectral measurements. This instrument can access Bragg angles from 11/sup 0/ to 38/sup 0/ and x-ray spectra from 200 eV to greater than 10 keV. We have demonstrated resolving powers, E/..delta..E > 200 at 1 keV and time resolution less than 20 psec. A description of the instrument and an example of the data is given.

We have made time-resolved spectral measurements above 80 A from laser-produced plasmas. These are made using a transmission grating spectrograph whose primary components are a cylindrically-curved x-ray mirror for light collection, a transmission grating for spectral dispersion, and an x-ray streak camera for temporal resolution. A description of the instrument and an example of the data are given. We have built a spectrograph to time resolve the spectrum above 80 A from laser-produced plasmas. Several possible schemes using high-powered lasers have been identified that produce x-ray lasing lines in the 80 A to 300 A range.1 This spectrograph has been built to measure the output from these targets. The principal components of the spectrograph are a cylindrically-curved x-ray mirror for light collection, a transmission grating for wavelength dispersion, and a soft x-ray streak camera for x ray detection. These have been combined to produce an instrument having high spectral resolution, E/tL > 200, continuous wavelength coverage from 80 A to 300 A, good time resolution, 1,20 psec, and high sensitivity, 1,10 photons/sec-sr. In addition, because an application is to measure x-ray lasing output, we have devised an optical alignment system which can accurately point the instrument to the target with an accuracy of less than one milliradian. A schematic of the instrument design is shown in Fig. 1. X rays from the target are collected and focused at the detection plane by a cylindrically-curved grazing incidence x-ray mirror. The mirror acts like one element of a Kirkpatrick-Baez x-ray microscope producing a line focus perpendicular to the plane of dispersion. 2 The mirror has an eight meter radius of curvature and operates at an angle of incidence of 4°. It is 68 cm from the target midway between the target and detection circle. This produces a magnification of unity. Spherical aberrations for these conditions are estimated to be less than 10 μm, which is much less than target sizes.© (1984) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.