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The generation of accelerated electrons in the X-pinch minidiode is studied experimentally. It is well known that the explosion of an X-pinch consisting of two or more wires is accompanied by the formation of a minidiode, in which electrons are accelerated. The subsequent slowing down of electrons in the products of wire explosion causes the generation of hard X-ray (HXR) emission with photon energies higher than 10 keV. In this work, the spatial and temporal characteristics of X-pinch HXR emission are studied, the specific features of HXR generation are discussed, and the capability of applying this radiation to point-projection X-ray imaging of various plasma and biological objects is considered. The parameters of the electron beam produced in the X-pinch are measured using a Faraday cup and X-ray diagnostics. The experiments were performed with the XP generator (550 kA, 100 ns) at Cornell University (United States) and the BIN generator (270 kA, 150 ns) at the Lebedev Physical Institute (Russia).

The experiments reported here were designed to test X-pinch wire-loading configurations using a simple plastic frame that might enable the X-pinch wires to be changed under vacuum after a pulse. Several frame configurations and materials were tested, some of which suffered from early surface flashover and current shunting away from the X-pinch. Fiberglass frames proved to be successful both in minimizing the current shunting up to the time of the X-pinch X-ray burst and, in most tests, in substantially reducing X-ray emission from energetic electrons and secondary soft X-ray bursts following the first X-ray burst. Both of these features are beneficial for using X-pinches for point-projection radiography as well as for recording X-ray spectra from the X-pinches or other nearby plasmas

X pinch plasmas produced from fine metal wires can reach near solid densities and temperatures of 1 keV or even more. Plasma conditions change on time scales as short as 5–10 ps as determined using an x-ray streak camera viewing a focusing crystal spectrograph or directly viewing the plasma through multiple filters on a single test. As a result, it is possible to determine plasma conditions from spectra with ∼10 ps time resolution. Experiments and theory are now coming together to give a consistent picture of the dynamics and kinetics of these high energy density plasmas with very high temporal and spatial precision. A set of diagnostic techniques used in experiments for spectrally, temporally, and spatially resolved measurements of X pinch plasmas is described. Results of plasma parameter determination from these measurements are presented. X ray backlighting of one x- pinch by another with ∼30 ps x-ray pulses enables the dynamics and kinetics to be correlated in time.

The X pinch is a dense plasma X-ray source that is known to emit subnanosecond bursts of X-rays in the 2.5-8 keV energy range from a very small (/spl sim/1 /spl mu/m) source commonly referred to as a micropinch. As such, it has been successfully used as a point source for X-ray radiographic imaging of small biological samples with spatial resolution as good as 1-2 /spl mu/m. Recent experiments show that the soft X-ray emission from a micropinch extends out to as high as 15 keV, and that there is also harder radiation from a slightly displaced /spl sim/100 /spl mu/m source with photon energies reaching above 60 keV that appears to be due to the presence of several-nanosecond electron-beam pulse. Both of these harder X-ray sources are potentially useful X-ray sources for high-resolution radiography of thicker biological samples than we have previously imaged. A characterization of these two hard X-ray radiation sources from X pinch plasmas using a slit camera with different filters, as well as imaging of a variety of biological objects on each pulse, revealed the energy range and source size of the micropinch radiation separate from the larger electron-beam source. High-resolution images (1-10 /spl mu/m scale resolution) of samples, such as a boron fiber with tungsten core (2.5-12 keV) as well as a several-millimeter-thick chicken wing with bone (>10 keV), will be presented.

Time-resolved spectroscopic measurements of the radiation emitted from Al, Ti, and Mo X pinches have been made with ps time resolution. The radiation is emitted from micropinch plasmas with sizes of order 1 μm in times in the 10– 100 ps range. Spectra implied that dense, ∼1 keV plasmas were produced, such as a 90 ps lifetime, 1.5– 1.8 keV electron temperature and near solid-density Ti plasma. The experimental systems and analysis methods are described in detail, including line ratio calculations for μm-scale Ti and Al plasmas with ion densities of 1019–1024 cm−3 and ∼1 keV electron temperatures.

We present a focusing spectrograph configuration, the Focusing Spectrograph with Crossed Dispersion (FSCD), that enables us to solve the problem in a crystal spectrograph of reflected radiation in many orders. In the FSCD, the x-ray radiation from a small source is dispersed by a transmission grating placed in front of the Bragg reflector (mica crystal). This configuration retains the advantages of a spherically bent mica crystal spectrograph while enabling the analysis of the radiation in a number of spectral bands simultaneously and independently. Results using a 150 mm radius spherically bent mica crystal combined with 0.5 μm period gold transmission gratings in X pinch experiments are presented.

A new type of x-ray refractive lens, the refractive bubbles-in-capillary lens (RBC lens), for plasma diagnostics is presented. The lens consists of a glass capillary filled with a large number of biconcave microlenses. The fabrication technique for the lens is described. It is shown that the microlenses have a spherical shape and can focus x-ray radiation with photon energies E>4 keV. Ray-tracing and analytical calculations of lens properties have been performed and have predicted high efficiency and good spatial resolution for RBC lenses. Real lenses were tested using Cr Kα x-ray radiation (λ=2.29 A), and spatial resolution of about 10 μm was obtained. In plasma experiments, x-ray radiation from a Ti X pinch (λ=2.62 A) was focused by a lens with 35 bubbles in a 100 μm diam capillary (focal length of about 8 cm) to a spot with diameter less than 6 μm. The shape of the hot plasma could be seen. Possibilities for RBC lens applications to plasma measurements are discussed.

X-pinch plasmas, produced by exploding two or more 10–50 μm metal wires that cross and touch in the middle in the form of an X, have been successfully developed as point sources of soft x rays for radiography. However, the parameters of the x-ray source as a function of time, space and wavelength band are not well understood. To determine the X-pinch plasma characteristics, time-resolved x-ray spectra produced by two- and multiwire X pinches made from different wire materials were recorded using an x-ray streak camera. A spherically bent mica crystal spectrograph was used with a ∼10 ps time resolution x-ray streak camera in a slitless configuration. Some spectra were dominated by continuum and others by line radiation, and observed spectral features varied on time scales ranging from 10 to 1000 ps, depending on the wire material. Electron temperatures and densities in Ti X pinches were estimated from line ratios based upon collisional-radiative calculations, and from the time delay between the appearance ...

The plasma parameters in hot spots of an X-pinch are determined by using time-resolved data from X-ray spectroscopy in experiments on the implosion of crossed Ti wires in the XP device with a current of 480 kA and pulse duration of 100 ns. The electron densities and temperatures calculated from these data are in the ranges (0.8–3)×1023cm–3 and 1–2.5 keV, respectively. An analysis performed shows that the plasma processes are highly nonequilibrium.

Bright, ∼1 μm x-ray sources (micropinches) produced within exploding wire X pinches are found to be near solid density and ∼1 keV electron temperature. For example, with a Ti X pinch, a 90 ps lifetime, 1.5–1.8 keV electron temperature, ∼1023/cm3 electron density plasma was observed. These plasma characteristics were determined using time-resolved x-ray spectra produced by 2- and 4-wire X pinches and collected by an x-ray streak camera with

The energy deposited by a submicrosecond, /spl sim/1-kA current pulse in a 25-/spl mu/m diameter metal wire prior to its explosion, correlates directly with the expansion rate of the wire after the explosion. Energy deposition by resistive heating is terminated by the formation of plasma around the wire and a collapse of the voltage along the wire, and is evidently facilitated by the desorption of gases from the wire and/or the evaporation of the wire material (or impurities within it) as it heats up. Data presented here implies that the relationship between materials with the lowest resistivities and high exploding wire expansion rates found in earlier work (D. B. Sinars et al. 2000) is a result of the reduced voltage delaying the gas breakdown along such wires. This, in turn, increases the energy deposited resistively in the wire before the current shifts to the surrounding plasma. If gas breakdown does not occur until close to the full vaporization energy is deposited in the wire, the expansion rate will be more rapid than if a small fraction of the vaporization energy is deposited before voltage collapse.

An X pinch plasma is produced using two or more fine metal wires arranged so that they cross and touch at a single point, in the form of an "X," as the load of a pulsed power generator (pulser). X pinches produce very bright, small, short-lived sources of X-rays in the 1-10 keV range. The X-ray source size, pulse duration and photon energy spectra depend upon the wire material and diameter, and the current waveform from the pulser. Those with /spl sim/1 /spl mu/m source size can be used as point sources of X-ray radiation for point-projection radiography with high spatial resolution. We report experiments with a variety of different wire materials, including Al, Ti, Mo, W, among others, all of which produced high resolution images, and all of which have subnanosecond X-ray pulses for X-rays /spl ges/3 keV. X pinches produced using all of these materials had common development stages. However, the wire material and the rate of rise of the current pulse influenced the details of the dynamics, leading to variation in the timing of the X-ray burst(s) relative to the start of the current pulse. For a given wire material, wire diameter had only a small effect on X-ray emission timing. Final X pinch neck implosion speeds as high as 66-75 /spl mu/m/ns were estimated.

The X pinch has proved to be an excellent source of 2.5–10 keV radiation for point-projection radiography with spatial resolution of 2 μm or even better. The pulse duration of the x-ray bursts has been investigated for a wide variety of wire materials in the 1.5–10 keV energy range using a set of fast diamond photoconducting detectors with different filters, and using an x-ray streak camera to observe the source through four different filters on each pulse. All wires tested have intense continuum up to at least 6 keV, and the duration of the pulse is shorter for the harder radiation component for all materials. However, there are substantial differences between materials. For example, the pulse duration for Al with filtering for energy ⩾1.5 and ⩾5 keV are about 1 and 0.5 ns, respectively. By contrast, for Mo with filtering for energy ⩾2.5 and ⩾5 keV, the pulse durations are about 200 ps and ⩽80 ps, respectively.

Wire-array Z-pinch implosion experiments begin with wire heating, explosion, and plasma formation phases that are driven by an initial 50–100 ns, 0–1 kA/wire portion of the current pulse. This paper presents expansion rates for the dense, exploding wire cores for several wire materials under these conditions, with and without insulating coatings, and shows that these rates are related to the energy deposition prior to plasma formation around the wire. The most rapid and uniform expansion occurs for wires in which the initial energy deposition is a substantial fraction of the energy required to completely vaporize the wire. Conversely, wire materials with less energy deposition relative to the vaporization energy show complex internal structure and the slowest, most nonuniform expansion. This paper also presents calibrated radial density profiles for some Ag wire explosions, and structural details present in some wire explosions, such as foam-like appearance, stratified layers and gaps.

Using an X pinch as a source of radiation for point-projection radiography, it is possible to project a high-resolution (1–10 μm) shadow image of dense plasma or test objects onto x-ray-sensitive film. The emission characteristics of X pinches composed of a wide variety of materials have been studied using several diagnostics. The pulse duration and shape of the x-ray bursts were measured in the 1.5–6 keV band using fast diamond PCDs and an x-ray streak camera with sweep speeds as fast as 10 ns for the full sweep (3.5 cm). To investigate the line and continuum radiation emitted by the X pinches, a convex spectrograph using a mica or KAP crystal, and a spectrograph based on a spherically bent mica crystal were used. Summarizing the data, including radiography results, wires known to have slower expansion rates and high boiling temperatures (NiCr, Ti, Nb, Mo, Pd, Ta, W, and Pt) appeared to yield the smallest x-ray source sizes, i.e., gave the best spatial resolution in radiographs and provided subnanosecond...

Substantial increases are reported in the expansion rates of exploding, dense wire cores under conditions simulating the prepulse phase of wire array z-pinch experiments [R. B. Spielman et al., Phys. Plasmas 5, 2105 (1998)] using wires with insulating coatings. The insulation apparently allows additional wire heating by delaying the formation of plasma around the wires. Once plasma is formed it terminates significant current flow in the residual wire cores. This effect is demonstrated for 25-μm diameter W and 25-μm diameter Ag wires.

Radiative properties of plasmas from X pinches with nichrome and conichrome wires have been studied using the presented diagnostic arrangement. The experimental results have been produced at the Cornell XP facility with a peak current of 450 kA and a full width at half maximum pulse duration of 100 ns. The spatially resolved, time-integrated x-ray line spectra from the region of the X-pinch cross point have been recorded using different crystal spectrometers. In particular, K-shell and L-shell x-ray spectra of Ni and Cr have been recorded through different filters in the same pulses for X pinches from two different wire alloys. A nonlocal thermodynamic equilibrium collisional–radiative atomic kinetic model of Ni has been developed to identify the useful diagnostic spectroscopic features and to model experimental spectra. The results of the modeling and radiative properties of different materials from nichrome and conichrome alloys are compared and discussed.

Electron beams in 400 kA peak current Mo and W X-pinches have been studied using 1 ns time-resolution Si diodes to monitor x rays >9 keV. Softer x rays were monitored by photoconducting detectors (PCDs). Three different types of higher energy x-ray bursts were observed. The first type appears to be produced by electrons generated starting at the moment of, or immediately after, the first thermal x-ray burst (typically 40–50 ns after the current start), and Si detector signals last 1–2 ns. The second type of harder x-ray burst occurs 50–80 ns after the current start, lasts 2.5–10 ns, and is typically not correlated with a thermal x-ray burst. These two types of bursts were generated near the cross-wire region. The third type of x-ray burst occurs 70–100 ns after the current start, and is also uncorrelated with PCD signals. The energetic electrons responsible for these x rays are generated for 10–30 ns, and the radiation is produced in the anode region.

A transmission grating spectrometer (TGS) with one dimensional spatial resolution was used to investigate the radiative properties of X-pinch plasmas produced using wires made of NiCr and CoNiCr alloys, and Mo. Experiments were carried out on the Cornell XP machine. The TGS was used to estimate of the energy yields of L-shell Cr and Ni, and M-shell Mo radiation. The absolute energy yields in the wavelength range 10 42 A. The results are compared with data obtained previously with the TGS on a 1 MA...

We present diagnostic images taken of an X-pinch plasma x-ray source driven by the XP pulser (100 ns, 500 kA) at Cornell University using an x-ray bubble compound refractive lens. The lens consists of a 200 μm inside diameter glass capillary that contains about 100 biconcave microlenses formed by a string of bubbles in epoxy. A precise system for lens alignment with of 3–5 arcmin accuracy is described. X-ray images of four-wire X pinches were obtained with a spatial resolution of approximately 2 μm.

A new focusing spectrograph configuration with crossed dispersion (FSCD) has been developed for use in X pinch experiments. This device solves the problem in a crystal spectrograph of the overlapping of reflected radiation in many orders. The x-ray radiation from a small source is dispersed by a transmission grating before it reaches the Bragg reflector (mica crystal). A large aperture (10 mm×10 mm), 0.5 μm period gold transmission grating was made on a 0.5 μm thick Si3N4 substrate and combined with spherically bent mica crystals with radii of curvature of 100 mm or 186 mm. Results of FSCD application to plasma experiments with X pinch x-ray sources is presented.

Radial wire arrays offer the potential for higher energy density of radiated x-rays compared to cylindrical arrays. Higher radiated energy density would allow for more compact hohlraums thus easing power requirements for ICF. In an effort to explore how radiated power scales with the rise-rate of the current we performed experiments on two 1 MA pulsed power generators with very different rise rates∔ MAGPIE at Imperial College with about 300 ns rise time and COBRA at Cornell with about 100 ns rise time. Comparisons of radiated power from 16-wire Al and Cu arrays over a range of masses are presented. Results from these initial experiments suggest that radiated power for a given material is similar when implosion times are matched to the current rise time. We also present comparisons of radiated power from modified array geometries such as wire length and cathode diameter. Some results from Ti/Ni and Fe/Ni arrays are also presented.

Summary form only given. X-pinches are produced by driving a high current through two, four, or more thin wires that cross and touch in the middle of the load region of a pulsed power generator. An X pinch produces a high temperature and high density plasma in the vicinity of the cross point that generates one or a few bursts of soft X-ray emission. The experiments to be discussed have been carried out at the Cornell COBRA facility with a peak current of 1 MA and a rise time of 100 ns. Four-wire X pinches were placed in the return current positions of COBRA and the duration of the X-ray burst emitted from the central cross point region of the X-pinch during implosion was observed using an X-ray streak camera in direct-view mode. Various filters and objects to be imaged placed in front of the entrance slit of the streak camera enable us to obtain source size and spectral information on the incoming radiation and to measure the duration of the radiation as a function of photon energy. The results of these experiments will be discussed

Summary form only given. X pinch experiments with a streak camera have shown that the X pinch X-ray burst starts with strong continuum in the 1-5 keV spectral band. The plasma conditions at that initial moment are still unknown and are difficult to determine. In this stage most X pinches do not radiate intense spectral lines of multicharged ions, and so plasma spectroscopic techniques based on emission lines are not applicable. Measurements based on the X pinch continuum radiation are potentially useful. The common way to do this is to determine the exact shape of the continuum spectrum and compare it with calculated spectra for different plasma conditions. There are several experimental problems in such measurements. First of all, spectrally well calibrated detectors covering wide spectral bands are required. Secondly, the initial stage must be "extracted" from the total micropinch radiation. That can be done in space, in time or in spectrum. Spatially, the radiating area (source size) in the first stage is very small (~1 mum) and devices with extremely high spatial resolution would have to be used. In this paper we describe a new technique of plasma temperature determination based on the use of a device called a slit-step-wedge camera (SSW-camera) that is based upon spectrum and source size. The SSW-camera enables a comparison of intensities of X-ray radiation passed through filters with K-edges in the spectral band being studied. This technique enables us to avoid absolute detector calibration and to increase temperature measurement accuracy. Experimental results of micropinch temperature determination for X pinches made from different wire materials are presented. It is shown that with the assumption of a Planckian spectrum for the micropinch radiation, the value of the temperature typically lies in the interval 400-800 eV, and sometimes reaches 1 keV

Time‐resolved L‐shell x‐ray spectra from single X pinches at 400 kA and two X pinches in parallel with about 225 kA each have been obtained from medium Z materials (Z=40–47) using a new, specially designed Kentech x‐ray streak camera combined with a Focussing Spectrograph with Spatial Resolution (FSSR) mica crystal spectrograph. The beginning of an X pinch x‐ray pulse usually started with a strong radiation burst containing continuum radiation only. After a very short time (tens of ps), the radiation from the spectral lines of N‐like ions appeared. Line radiation appeared during the entire time of following x‐ray bursts if more than one burst appeared in the x‐ray output pulse. New feature, namely narrow time dip after continuum burst, was observed in some experiments. Possible explanation of this phenomenon is discussed.

Summary form only given. The X pinch has proven itself to be both an extraordinary X-ray back lighting source and an interesting high energy density plasma for plasma dynamics and X-ray spectroscopy studies. However, some of the most interesting physics of an X pinch happens on a few ns, or even subnanosecond, time scale. The X pinch has been estimated to approach solid density on a size scale of 1 micron and achieve temperatures greater than 1 keV for a period of about 0.1 ns during which there is an intense X-ray burst. The final stages of implosion leading to the formation of the X-ray burst last only a few nanoseconds. Therefore, images of the X pinch taken with an apparatus that integrates over a few ns are not sufficient to resolve the dynamics of the X pinch during the last critical stages of implosion. Here, we report experiments using a sub-200 ps laser pulse to record several frames of each X pinch pulse with both shadow and interference images. We expect to show images that are of interest both as observations of X pinch dynamics for materials such as Al, Mo, and W and for comparison with code calculations used to model the X pinch

Summary form only given. The plasma formation and implosion characteristics, as well as the energy in X-ray radiation, from two and multiwire X pinches have been investigated and compared using the XP and COBRA pulsed power generators at Cornell University. The XP generator (40-50 ns rise time, 450 kA peak current) has been used for the X pinch studies and applications for several years. The rebuilt COBRA generator, which has a variable current pulse waveform and amplitude (95-150 ns rise time, 0.9-1 MA peak current), has extended the range of current pulse parameters available at Cornell for X pinch studies. X pinches with 2 to 12 wires, with diameters from 10 to 75 mum, and made of several different wire materials (from Al to W) have been tested. The influence of the rate of rise of current and the X pinch wire mass on X pinch plasma formation, radiated energy and pinch implosion dynamics has been investigated using a broad range of diagnostics with spatial and/or temporal resolution. Two or multiwire X pinches were placed in the diode center and/or one or two X pinches were placed in one or two of the four parallel return current posts of the diode. Radiographic images of different test objects, wires in wire-array Z-pinches and the X pinches, themselves, were obtained with mum scale spatial resolution. Differences between 2 and multiwire X pinch implosion dynamics and X-ray energy yield were studied in the experiments. The substantially higher energy yield and harder radiation spectrum from multiwire X pinches than from two wire X pinches enables imaging of thicker (more absorbing) objects without increasing the load current. The multiwire X pinches also have more predictable behavior that is almost independent of the wire material

We present a system for diagnostic imaging of x-ray sources using a compound refractive lens. Such a system can be built at a low cost, yet image at resolutions of 2 μm or better. The essential components of the system are the source to be imaged, a compound refractive lens and imaging detector (either electronic or film). In addition, spatial and spectral filters can be added to improve resolution and a laser alignment system can be used to rapidly align the source, lens and camera.

Two methods of using the X pinch as a source of X-ray radiation for the radiography of dense plasmas and other objects are presented. These methods do not use pinholes, instead taking advantage of the small source size (

Summary form only given. Time-resolved L-shell X-ray spectra from single X pinches at 400 kA, and two X pinches in parallel, each with about 225 kA, have been obtained from medium Z materials (Z=40-47). This was accomplished using a new, specially designed Kentech X-ray streak camera combined with a focusing spectrograph with spatial resolution (FSSR) mica crystal spectrograph. The experiments were carried out on the 450 kA, 100 ns (full width at half maximum) XP pulser at Cornell University. A very short delay triggering system makes it possible to record the beginning of an X-ray burst with a temporal resolution of about 10 ps. The streak camera sweep is triggered either by the UV generated during the X-pinch breakdown process or by the XUV pulse radiated just before the main X-ray pulse. An X-ray pulse from an X pinch usually begins with a strong burst of continuum radiation. After a very short time, on the order of tens of ps, the continuum burst will subside, and radiation from the spectral lines of Ne-like ions will appear. This line radiation will continue for the remainder of the overall X-ray output pulse, becoming superimposed upon any subsequent continuum bursts that should occur. Line widths were observed to change with time, indicating a change in ion velocity and/or plasma density. There was no evidence of energetic electrons in the initial part of the X-ray pulse. In fact, spectral lines corresponding to transitions in relatively cold, weakly ionized wire material, and excited by electrons with energies of more than 10 keV, were generally observed in the X-ray radiation more than 100 ps after the initial "thermal" X-ray burst. The fine structure of Ne-like spectra along the isoelectronic sequence for Z=40-47 is currently being investigated

Summary form only given. X-pinch plasmas are formed when an X pinch (made by crossing two or more fine wires in the form of an "X"), is driven by a 450 kA current pulse in Cornell's XP pulser. We've obtained time-resolved spectra from the plasma of 4 wire 25 mum diameter Cu and 4 wire 25 mum diameter Manganin (86% Cu, 14% Mn) X pinches using an X-ray streak camera together with a spherically bent mica crystal spectrometer. Time integrated spectra have also been obtained using a focusing spectrometer with spatial resolution (FSSR) with a spherically bent mica crystal. Both streak camera spectra and FSSR spectra of Cu K-shell and Cu L-shell line emission from Cu and Manganin have been recorded and analyzed. A simple Gabriel model has been developed to model the experimental spectra and to extract the electron temperature as a function of time. An electron temperature of ~200 eV has been inferred from Cu L-shell spectra and 2 keV has been inferred from Cu K-shell spectra from both the time-integrated and time-dependent experiments. The results of the experiments as well as the application of the model are discussed

Summary form only given. The X-pinch plasma has established itself as an extraordinarily useful tool for studying the dynamics and kinetics of hot, dense plasmas as well as for high resolution imaging. An X-pinch plasma is formed when two or more fine wires, which cross at a point to form an "X," are used as the load of a pulse power machine. When this configuration is exploded to form a plasma, a Z-pinch forms near the original cross point of the wires. This process produces small, bright plasmas that emit nanosecond scale X-ray bursts in the 1-15 keV range. For our experiments the X pinches were driven with Cornell's XP pulser, which reaches a peak current of about 450 kA in 40-50 ns. The small (micron scale) X-ray sources produced are useful for point projection X-ray imaging. Thus, in order to maximize the usefulness of X pinches we must find ways to control the unstable process that produces the X-ray bright spots. Furthermore, in order to advance the study of X-pinch plasmas it would be helpful to find a way to increase the rate at which X-pinch pulses can be taken. Consequently, we have devised a setup to improve both of these situations. Initially, we designed an X-pinch "frame" to increase the repetition rate for X-pinch pulses since many frames can be loaded in advance, reducing the setup time for each experiment. In addition, we imagine using several frames chained together in order to change the load under vacuum. In testing we found that many of the frame materials used would conduct too much of the current as result of UV induced flashover. We found that of the materials tested, fiberglass was able to hold off the UV flashover the longest without a need for additional shielding. The fiberglass frames allowed enough load current to produce a high quality bright spot while the conduction due to UV flashover prevented subsequent bursts and minimized the production of energetic electrons. All of these conditions lead to increased image quality. We also found that the intensity of higher energy X-rays (above 8 keV) was significantly reduced. Therefore, these X pinches are most useful for soft X-ray imaging. Additionally, we tested various geometries, including several X pinches in series, which can give us information from multiple X pinches in a single shot

Summary form only given. Radiographs of X-pinches driven by ~400 kA current pulses show jets of matter extending along the anode-cathode axis from both sides of the crossing point of the X pinch wires. The jets, formed by ablation of material from the heated wires of the X pinch, extend over a few mm of the 15 mm anode-cathode gap and persist over tens of ns during the X-pinch implosion. Spatially resolved spectra of Ti X-pinches show that while emission from highly ionized Ti is localized in a 10-100 mum region near the crossing point of the wires, K-alpha emission from Ti I to Ti XIII extends over several mm on the anode side of the hot, dense central portion of the X-pinch plasma. Streak camera measurements show ns-scale bursts of K-alpha emission following the sub-ns bursts of X-ray emission from H- and He-like Ti. We present spectroscopic modeling of the spatially and temporally resolved K-alpha emission measurements, giving ionization balance and electron temperature estimates resolved in space and time. We show that the electron energies required for excitation of inner-shell K-alpha transitions from low charge states of Ti are much greater than the thermal temperatures that can support such charge states, indicating that beams of hot electrons play an important role in the X-ray emission from the jets

Summary form only given. X-pinch plasmas are produced by using two or more fine wires that cross and touch in the middle, in the form of an X, as the load in the anode-cathode gap of a pulsed power generator. They have proved to be very useful for studying high energy density plasmas ranging in Z from Mg to W. The z-pinch process that takes place near the cross point of the wires undergoes m=0 (sausage) instabilities that produce a cascade of smaller and smaller "necks" in the plasma until one or more micropinches form, emit an X-ray burst, and then explosively disassemble. From the X-ray spectra emitted by Mo, Ti and other wire X pinches, together with X-ray backlighting, these micropinches have been determined to be near solid density and in the keV temperature range for times of the order of 10-100 ps. The object of the experiments presented here was to test wireloading configurations that might accomplish three purposes: 1) enable the load to be changed under vacuum after a pulse using a simple plastic holder, 2) Reliably reduce the number of bright emission spots produced by an X pinch to one, and 3) reduce the number of energetic electrons produced shortly after an X-ray burst. The first of these would allow more pulses per day, the second would allow cleaner X-ray spectroscopy data to be collected (both time-integrated and time-dependent), and the third would reduce the X-ray background when soft (2-8 keV) X-rays are used for imaging on film. There is also the possibility that reproducible loading of holders would produce more reproducible timing of X-pinch X-ray bursts to enable the best possible temporal resolution with time-depended X-ray spectra obtained with an X-ray streak camera.

Summary form only given. Experiments using 4-wire brass (Cu and Zn) X pinches were carried out using Cornell's XP facility with a peak current of up to 470 kA and 100 ns pulse duration. Time-integrated line spectra from the radiating plasma at the cross point were obtained with convex mica spectrometers and an FSSR. The results of the experiments, as well as the radiative properties of Cu and Zn in the K-shell and L-shell spectral regions are discussed. The time duration of the X-ray bursts of the brass X pinch was also obtained using an X-ray streak camera in direct mode with Be and Ti filters, and the results are presented.

Mo wire $X$ pinches typically emit several x-ray bursts from a bright spot near the crossing of the $X$-pinch wires. Streak camera images of $L$-shell line emission from Mo wire $X$ pinches have been analyzed using a non-local thermodynamic equilibrium (NLTE) collisional-radiative atomic kinetics model, providing temperature and density profiles with $\ensuremath{\sim}50\phantom{\rule{0.3em}{0ex}}\mathrm{ps}$ time resolution over the $\ensuremath{\sim}350\phantom{\rule{0.3em}{0ex}}\mathrm{ps}$ x-ray bursts. In conjunction with nonspectroscopic measurements, the analysis is used to propose a picture of the dynamic evolution of the $X$-pinch plasma. The $L$-shell spectra from the first x-ray burst indicate an electron density near ${\mathrm{10}}^{\mathrm{22}}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$ and an electron temperature near $1\phantom{\rule{0.3em}{0ex}}\mathrm{keV}$; subsequent x-ray bursts have $L$-shell spectra that indicate electron temperatures slightly above $1\phantom{\rule{0.3em}{0ex}}\mathrm{keV}$ and electron densities near ${10}^{20}$ and ${\mathrm{10}}^{\mathrm{21}}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$. The size of the $L$-shell line-emitting region is estimated to be near $10\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{m}$ for the first x-ray burst and much larger for the later bursts. It is proposed that inner-shell excitation of low ionization stages of Mo in a $\ensuremath{\mu}\mathrm{m}$-scale plasma region contributes to the observed radiation from the first micropinch, which typically emits a short burst of $g3\phantom{\rule{0.3em}{0ex}}\mathrm{keV}$ radiation and has $L$-shell spectra characterized by broad spectral lines overlaying an intense continuum.

Mo wire X pinches typically emit several x-ray bursts from a bright spot near the crossing of the X -pinch wires. Streak camera images of L -shell line emission from Mo wire X pinches have been analyzed using a non-local thermodynamic equilibrium (NLTE) collisional-radiative atomic kinetics model, providing temperature and density profiles with approximately 50 ps time resolution over the approximately 350 ps x-ray bursts. In conjunction with nonspectroscopic measurements, the analysis is used to propose a picture of the dynamic evolution of the X -pinch plasma. The L -shell spectra from the first x-ray burst indicate an electron density near 10(22) cm(-3) and an electron temperature near 1 keV; subsequent x-ray bursts have L -shell spectra that indicate electron temperatures slightly above 1 keV and electron densities near 10(20) and 10(21) cm(-3). The size of the L -shell line-emitting region is estimated to be near 10 microm for the first x-ray burst and much larger for the later bursts. It is proposed that inner-shell excitation of low ionization stages of Mo in a microm -scale plasma region contributes to the observed radiation from the first micropinch, which typically emits a short burst of3 keV radiation and has L -shell spectra characterized by broad spectral lines overlaying an intense continuum.

X pinch radiation produced by electron beams accelerated in the X pinch minidiode ranging in energy from 10 to 100 keV has been studied and used to image a variety of different objects. The experiments have been carried out using the XP pulser (470 kA, 100 ns) at Cornell University and the BIN pulser (280 kA, 120 ns) at the P.N. Lebedev Physical Institute. This electron-beam-generated x-ray source's geometric, temporal and spectral properties have been studied over different energy ranges between 10 and 100 keV. The imaging was carried out in a low magnification scheme, and spatial resolution of a few tens of μm was demonstrated.

The X pinch plasma emits subnanosecond bursts of x-rays in the 3 - 10 keV energy range from a very small source. As such, it has been used for high-resolution point-projection imaging of small, dense, rapidly changing plasmas, as well as submillimeter thick biological samples. The very small x-ray source size of the X pinch provides high spatial coherence of the x-rays, enabling the X pinch to be used for imaging low absorption, low contrast objects with excellent spatial resolution by incorporating wave-optics effects. The reverse procedure has been used to determine the X pinch x-ray source size: well-defined micro-fabricated slits were imaged by point-projection radiography, and the detailed patterns were compared with wave-optics calculations of the expected image patterns on film as a function of x-ray source size and energy band. In addition, an x-ray streak camera was used to study the X pinch source size as a function of time. Dynamic shadow images of a boron fiber with a tungsten core and glass fiber sheathed in plastic were compared with a time-integrated radiographic image. Source sizes as small as 1.2 μm (full width at half maximum, assuming a Gaussian spatial intensity profile for the source) have been inferred.

Summary form only given, as follows. Experiments have been carried out using the XP pulser (470 kA peak current, 100 ns fwhm pulse duration) at Cornell University to investigate the geometric and spectral parameters of the X pinch x-ray source for photon energy E > 10 keV. The X pinch is known to emit sub-ns bursts of x-ray radiation in the 1.5-5 keV energy range from /spl sim/1 micron dense plasma sources. Using a pinhole camera with different filters to image a variety of objects on each pulse has shown that X pinches radiated up to 100 keV, and that the source size and duration of radiation vary with the photon energy range. For example, several mm thick metal objects have been imaged with 30 keV x-rays in a low magnification scheme, and the /spl sim/10 micron scale image resolution implies a source size for this radiation of at most a few tens of microns. This radiation is believed to be due to electron beams accelerated across the minidiode that forms just as an X pinch emits its soft x-ray burst.

Summary form only given, as follows. The X-pinch is a very small radiation source in the 3-10 keV X-ray band. It has been used successfully to obtain micron scale resolution point-projection images of rapidly varying plasmas with subnanosecond temporal resolution, such as other X-pinches and exploding wire arrays, as well as to image /spl les/2 mm thick biological samples, such as small insects and beet seeds.

Summary form only given, as follows. To investigate the influence of X-pinches, driven by 225 kA each, on each other as a function of their separation distance, several distances between the X-pinches were tested with various wire materials. Pinhole images, interferometry data, and soft x-ray images of interacting X-pinches were collected. Time integrated radiographs of two X-pinches show, when the X-pinches are less than 10 mm apart, the merging of the jet-like plasmas that form between the legs, implying a strong magnetic interaction between the jets sometime during the pulse. Possible explanations of these observations, including the influence of the plasma surrounding the X-pinches on bright spot formation, will be discussed. These results also have implications for x-ray backlighting and for time-dependent x-ray spectroscopy experiments.

Summary form only given, as follows. An X-pinch plasma is produced by exploding two or more fine metal wires that cross and touch at a single point (in the form of an X) using a 200-400 kA, 100 ns current pulse. Near the original cross point of the wires, one or more micron scale micropinches form and emit subnanosecond bursts of 1-10 keV x-rays from very small source regions. From time-dependent x-ray streak camera measurements of the >1 keV radiation from X-pinches made with, for example, Mo wires, the basic shape of the continuum radiation spectrum has been studied. One method of estimating the shape of the continuum spectrum is to use a filter technique. The method is based on comparison of measured ratios of signals from x-ray detectors covered by different spectral filters with calculated ratios. Using a set of Be, Al, and Ti filters over the energy range of 1-10 keV, the intensity of the x-ray radiation from Mo X-pinches was obtained as a function of energy. This technique was realized using a fast Kentech streak camera. Calculations of the camera response have been made for bremsstrahlung and plankian x-ray spectra. The shape of the spectrum provides information about the X pinch plasma parameters.

Summary form only given. X pinch plasmas are produced by exploding two metal wires that cross and touch at a single point (in the form of an X) using a 200-400 kA, 100 ns (FWHM) current pulse. A magnetically driven implosion near the original cross point of the wires leads to the emission of one or more 2.5 keV are emitted; the duration of these bursts can be 10/sup 28/eV/cm/sup 3/ at the moment of the X-ray burst. Furthermore, their volume power density is >10/sup 21/ W/cm/sup 3/ with a surface flux of >10/sup 16/ W/cm/sup 2/. Radiographs of the X pinch implosion process show that a z-pinch forms in the region of the original wire cross point about 2 ns before the characteristic X-ray bursts occur. The z-pinch implodes and gaps develop in the radiographic images coincident in time and space with the X-ray burst(s). Immediately following the moment of X-ray burst emission, explosive disassembly of the z-pinch occurs on a 1 ns time scale, accompanied by the launching of shockwaves into the surrounding material. Time-integrated spectroscopic measurements of X pinch radiation indicate electron temperatures of 500-1300 eV, depending of the wire material, and in some cases densities in excess of 10/sup 22//cm/sup 3/. Time-resolved spectroscopic measurements using an X-ray streak camera are presently underway that may reveal the physical mechanisms which lead to the generation of the X-ray bursts.

Summary form only given, as follows. An important question associated with z-pinch implosion experiments using fine wire arrays concerns the effect on the implosion of the plasma formed around and between the wires during the expansion phase. Heating and expansion occurs early on in the pulse, before the current is so high (>10 kA/wire) that the global magnetic fields are strong enough to initiate the implosion. We report on our initial results to study the dynamics of plasma expansion and inter-wire merging as well as the early stages of implosion. The intent of the work is to better understand how the wire material is swept away from the initial wire positions by the global magnetic field forces. Our experiments were conducted using Cornell's XP pulsed power generator (450 kA peak current, 100 ns) and an LC current pulser (4.5 kA peak current, 10 A/ns rise rate). Multi-wire arrays (2-8 wires) driven by currents ranging from 1 kA/wire to 100 kA/wire were studied. Consequently, both the expansion and early implosion regimes could be investigated. We used W, Al, and Ag wires, 1 cm in length, and 7.5-25 mm in diameter. Plasma densities were measured using both a shearing interferometer (l=532 nm) and X-ray backlighting. The optical interferometer was especially useful for observing relatively low electron densities present during plasma formation, expansion and inter-wire merging. X-ray backlighting was used to image the high density wire cores and the relatively high density merged plasma that occurred late in the expansion phase. Some X-ray imaging was also possible during the early stages of implosion.

Summary form only given. The X pinch is an intense source of X-ray radiation in the 1.5-8 keV range. Individual x-ray sources produced within an X pinch exist for 10/sup 21/ W/cm/sup 3/ and a surface flux > 10/sup 16/ W/cm/sup 2/ for the X-ray source. Time-resolved spectroscopic measurements of the radiation from X pinches will be presented that use a spherically bent mica crystal (R = 100-186 mm) and a Kentech X-ray streak camera with time resolution of

Summary form only given. An X-pinch plasma is produced by exploding two 10-50 micron metal wires that cross and touch at a single point (in the form of an X) using a 200-400 kA, 100 ns (FWHM) current pulse. In the region of the original cross point of the wires, a magnetically driven plasma implosion occurs, and one or more

Summary form only given. In previous work (Sinars et al., 2000) we investigated the significant impact of thin insulating coatings on the explosion of 25 /spl mu/m Ag and W wires driven by a pulsed current source with a rate of current rise of 10/sup 10/ A/s per wire. This range is similar to the prepulse conditions of wire-array experiments on the Saturn and Z accelerators at Sandia National Laboratories in Albuquerque, NM. Our studies have found that most of the energy deposition in wires under these conditions occurs during an initial resistive heating phase lasting

In previous work on the X pinch (XP) facility (470 kA, 100 ns), we found that an on-axis z pinch forms in the cross point region during the final few ns prior to the radiation bursts. The rapid collapse of the z pinch results in a gap in the observable mass distribution, which we refer to as a minidiode. Improved measurements of the collapse of this z pinch have been made, allowing more reliable estimates of the pinch velocities prior to the radiation burst, and the expansion velocities after the radiation burst. We have also observed "self-similar" structure in different stages of the z pinch collapse. In addition, the source of the radiation bursts was localized to within 10 microns within the observed z pinch structure using a technique reported during ICOPS 1999. Using three X pinches to backlight one another, two images of each X pinch can be obtained. Thus, the hot spot of one of the X pinches and the z-pinch structure both prior to and after its radiation burst can be determined. These results should enable us to better understand the role of the X-ray source in the dynamics of the X pinch.