The radiation from plasmas hotter than 106 K falls in the x-ray region. Such plasmas are required for fusion power generation. They can also be used as x-ray sources. Measurements of x-ray emission from high temperature plasma yields (a) diagnostic information on the plasma conditions and (b) the characteristics of plasma x-ray sources which determine their applications. Hence, measurements of x-rays from plasmas are finding widespread use.

Measurements of x-rays emitted by hot plasmas provide a powerful diagnostic method of determining important plasma parameters and suggest certain types of plasmas as possibly useful x-ray sources. Instrumentation to accomplish these measurements for various types of plasmas are reviewed. State-of-the-art x-ray spectrometers, calorimeters, and source-imaging devices, designed especially for plasmas generated by focused, nanosecond laser pulses are described. Possibilities of time-resolved measurements on such short-lived plasmas are discussed.

X-ray fluorescence analysis has been used for some years at two Institutes of the Karlsruhe Nuclear Research Center to determine routinely thorium, uranium, and plutonium in unirradiated and irradiated nuclear fuels. It has "been used in addition to assay neptunium, americium and curium contained in irradiated samples. The method excels because it is versatile, rapid, tamperproof, and efficient. As a rule, fission products, pollutions, and foreign activities do not interfere with the determination which can be made in a direct way without chemical separation. In practice, the nuclear fuels are dissolved prior to the analysis and a given amount of an appropriate element as an “internal standard” is added. The accuracies attainable (1 σ RSD better than 1 %) are comparable with the mass spectrometric isotope dilution analysis so that in the input analysis of reprocessing plants X-ray fluorescence analysis constitutes a true alternative to the mass spectrometric isotope dilution analysis.

Within the efforts to automate the method the prototype of the fully automated system is presently tested with non-active material. A first, not yet fully automated, development stage is being installed in the Karlsruhe Reprocessing Plant. It is anticipated that it will be tested soon under operating conditions. Complete automation of the system is scheduled to be completed at a later date.

Presented here is a report on the development of practical techniques for laboratory spectroscopy in the 5 to 150 A wavelength region as may be applied, for example, to light element and surface state analysis, high temperature plasma diagnostics and to the design and calibration of x-ray astronomy measurements.

The dynamic behavior of a test sample during and shortly after it has been irradiated by an intense relativistic electron beam (REB) is of great interest to the study of beam energy deposition. Since the sample densities are far beyond the cutoff in the optical region, flash x-radiography techniques have been developed to diagnose the evolution of the samples. The conventional approach of analyzing the dynamic behavior of solid densities utilizes one or more short x-ray bursts to record images on photographic emulsion. This technique is not useful in the presence of the intense x-rays from the REB interacting with the sample. We report two techniques for isolating the film package from the REB x-ray pulse.

One arrangement employs a microchannel plate electron multiplier array (CEMA) to convert the incident x-ray linage to an amplified electron “image,” This image is proximity focused onto an aluminized plastic scintillator held at 5-10 kV relative to the CEMA output face. A streak camera shielded from the x-rays is used to record the time varying image on the 2 ns persistence scintillator. The resolution limitation is primarily that of the image converter, i.e., 5 ns and 5 line pairs/mm.

To achieve higher sensitivity and resolution, an arrangement employing two microchannel plates has been developed. In this device, two channel plates are immersed in a long uniform solenoidal magnetic field; the electrons generated by the first plate are guided by the magnetic field lines to the second plate which increases the system gain by > 103. Placed a few mm behind the second plate is a phosphor screen which in turn is directly connected to film via a fiber optic face plate. In this way, isolation of the x-ray burst from the long persistence phosphor and film is achieved by using a long solenoid. The temporal resolution (approximately 3 ns) can be gained by the appropriate gating of the channeltron plates and/or grids. The spatial resolution is governed by the channel plate “pores” size, by electron orbit characteristics in the solenoidal magnetic field, and by the effective x-ray source geometry.

By using these two methods, nanosecond time resolved x-ray pinhole photographs and flash x-ray radiograph of REB initiated events have been achieved.

Soft X-ray, vacuum ultraviolet diagnostics of high temperature, high density plasmas are used to determine the temporal, spatial, spectral and total fluence of radiation emitted from plasmas. Some of the radiation diagnostics used to characterize these plasmas are: metallic photocathodes with thin anodes; Ross filter - PIN detector combination; time-resolved pinhole cameras; metallic calorimeter; bent crystal and grazing incidence spectrographs; and differentially pumped, windowless, Samson-type ionization chambers.

We investigate the possibilities of amplification of soft x rays in a low Z plasma produced by a picosecond laser. Inversion of population could take place between metastable and fundamental state of lithium-like ions.

A pinhole camera has been used to record low-energy x rays produced from CD2 microsphere irradiation with Sandia Laboratories four-beam, pulsed laser system. Camera useful energy range, spatial resolution, and x-ray energy sensitivity are discussed. Camera x-ray energy sensitivity which was determined by laboratory calibration is compared with measurements obtained with a multi-channel x-ray spectrometer. X-ray photographs of laser-irradiated microspheres are presented. Spatial information about the x-ray source derived from these photographs is discussed.

The x-ray spectroscopy of laser-generated plasmas can be applied to photon energies of less than 1 keV, provided calibrations of the response of energy discriminators and detectors are performed in the sub-kilovolt region. In our application we use photographic film to monitor the intensity of radiation dispersed by a curved lead stearate crystal. We have determined the response to sub-kilovolt x-rays of two types of film, Kodak No-Screen and the special vacuum ultra-violet Kodak type 101-01. This calibration was obtained by exposing samples of film to continuous beams of nearly monochromatic characteristic radiation from an array of targets. The fluorescent radiations were the K series of carbon and magnesium and the L series of titanium, nickel, cobalt and copper. The response data are presented as a series of characteristic curves, plotting for each film type and photon energy the net diffuse photographic density as a function of the photon flux incident on the film. The processing of all film was in accordance with the manufacturer's suggestions. We attempt to characterize the accuracy and reproducibility of these data. The data demonstrate the greater sensitivity of the type 101-01 to sub-kilovolt x-rays.

The intensity and spectral purity of the incident fluorescent beams were monitored by a thin-window gas proportional counter that used flowing propane gas at sub-atmospheric pressures. We describe the procedures and results of a determination of the quantum efficiency of this counter as a function of photon energy.

Laser interaction experiments have been conducted on Sandia Laboratories' four-beam laser system. In these experiments, pulses of 1.06 μm light of up to 50 J each were focused in a tetrahedral geometry onto CD2 microspheres. A 22-channel x-ray spectrometer which utilises silicon diodes with appropriate K-edge prefilters was used for x-ray measurements. Typically, bremsstrahlung-recombination spectra were observed in the photon regime below about 5 keV. The electron temperatures for this part of the spectrum ranged from a few hundred eV to 1 keV with up to 15 percent of the total laser energy converted to x-rays. Less than one percent of the total energy emitted as x-rays appeared in the spectral range above 5 keV.

The use of CaF2 (Dy) thermoluminescent dosimeters to diagnose the X-radiation from 1.06 μ laser-produced plasmas is described. The TLD's have been used in various cassettes to measure total X-ray yield and the X-ray continuum out to ∼100 kev. Described are experiments pertaining to maintenance and recovery of TLD soft X-ray response, their linearity, insensitivity to 1.06 μ laser light, and energy calibration. Also, described are the TLD attenuation experiments in the “soft” and “hard” components of the laser plasma X-ray spectrum.

The plasma focus device, a form of linear pinch discharge, produces an intense x-ray and neutron (D2) burst from a magnetically heated dense plasma. Rapidly changing magnetic fields at pinch time generate large axial electric fields which accelerate electrons and ions. In the experiments reported here the x-ray production during the plasma pinch of a 96 kilojoule (at 20 kV) plasma focus device was measured.

The purpose of these experiments was to evaluate the energy in accelerated electrons in the plasma focus device and to learn how to enhance these electron hursts. Well focused, megampere electron beams at a few hundred kilovolts, lasting less than 10 nanoseconds have applications in fusionable pellet heating experiments. (1) X-rays were monitored to evaluate these electron bursts using a defocusing bent crystal spectrometer, doubly diffused silicon (PIN) detectors, with Ross filters, thermoluminescent dosimeters (TLDs) with filters, and x-ray pinhole photography.

Thermoluminescent dosimeters indicated maximum x-ray yields of 140 joules above 3 keV at 57.3 kilojoules stored energy (16 kV) for a conversion efficiency to x-rays of 0.2%. 40 joules are above 60 keV and 15 joules above 80 keV. The hard x-ray pulse typically rises in 3 ns and frequently has a pulse width less than 10 ns. The low energy x-ray spectrum consists almost entirely of lines from the high Z anode insert, and the high energy spectrum is characteristic of a nonthermal power law distribution with an exponent of 2.2 ± 0.8. Peak hard x-ray production is obtained at 1 torr deuterium in contrast to peak neutron production (3 x 1010) at 5 torr. The addition of argon reduces total x-ray yield and increases the relative fraction of soft x-rays.

These measurements suggest that the plasma focus produces 1200 joules of electrons with an average energy of 150 keV, in 10 nanoseconds with a stored energy of 57.3 kilojoules. This is a power of 1.2 × 1011 watts and power density of 1.5 × 1013 watts cm−2.

A time dependent x-ray diagnostic technique based on the fast rise time characteristics of unitary crystals is demonstrated, and a correction for decay time is determined for anthracene crystals. The method has a probable time resolution capability better than 10 picoseconds. The shape of the x-ray pulse emitted by laser-generated plasmas is measured by this method and found to be similar to the shape of the laser pulse for laser pulse widths of 1.5-3.5 nanoseconds.

The x-ray energy emitted from laser-produced plasmas has been measured under various experimental conditions. Two Nd-glass lasers were used in separate experiments to focus pulsed laser light on planar targets. X-ray fluences were measured with newly developed silicon detector calorimeters. Results for various experimental conditions are reported in terms of the efficiency with which the laser light was converted to x-ray energy by plasma production.

The instrumentation for measuring x-ray yields from laser produced plasma is described. This new type of calorimeter is composed of a silicon detector, a charge-sensitive preamplifier and an analog-to-digital readout scheme for multiplexing up to ten detector outputs.

X-rays interacting with the detector produce hole-electron pairs in proportion to the total energy lost in the detector (∼1012 eV). In this application the detector can be characterized as a solid-state ionization chamber. The detector signal is coupled to a charge-sensitive preamplifier which generates a voltage pulse proportional to the x-ray energy absorbed. In this way the x-ray energy is measured by “direct conversion” rather than measuring the temperature rise due to an energy flux.

Experiments were conducted on two underground nuclear tests with the primary objective of determining if high-intensity x-ray exposures can cause a failure of the photographic reciprocity law. The results of the experiments, which included exposures at intensities up to 1020 photons/cm2-sec, were in good agreement with standard diagnostic experiments. Thus, these results show that films receiving x-ray exposures do not experience high-intensity reciprocity failure, and, in so doing confirm photographic theory on this point.

Measured latent-image regression curves and x-ray spectral sensitivity curves for commercially available films, obtained under laboratory-ambient condition and under a vacuum of 10−4 torr are presented. Anomalies in the film response are described, and the dependence of the response characteristics on the exposure environment and the emulsion characteristics is discussed. Suggestions are made for the use of films for x-ray measurements.

A low energy x-ray radiography apparatus has been developed primarily for the nondestructive inspection of LiD laser fusion targets. Exposure times of 15 minutes at 6 keV have been found satisfactory for the detection of voids in nominal 100 micron diameter spheres.