Takeshi Yanagidaira

A simple, quantitative method for measuring pulsed soft x rays

A simple quantitative image processing system for pulsed soft x rays with time and spatial resolution is described. The system consists of easily obtained commercial components including a microchannel plate–phosphor screen combination, a charge coupled device camera, an image memory board, and a personal computer. To make a quantitative measurement possible, the image processing is used in conjunction with measurement of the ‘‘phosphor screen current.’’ Performance of the system is examined using a soft x‐ray source generated with a plasma focus device. The order of intensity, ∼1012 photons/su2009mm2u2009mrad2u20090.01% BW of Ar K lines is observed for about 20 ns from the pinched plasma in which 3% of Ar is added to the 6 Torr H2.

Quantitative measurement of x-ray images with a gated microchannel plate system in a z-pinch plasma experiment

A multiframe, gated pinhole system capable of quantitative acquisition for pulsed soft x rays is described and tested. The system based on a gated microchannel plate (MCP) is employed to observe the evolution of z-pinch plasma in a plasma focus facility with a time resolution of similar to 220 ps. The quantitative relationship between x-ray source intensity and the recorded images has been investigated. To make a quantitative measurement, the phosphor screen current was measured to calculate the total electrons output from the MCP, which is proportional to both the incident x-ray intensity and the intensity of the recorded images. Furthermore, by taking into account the pinhole geometry, MCP gain and system spectral response, a quantitative calibration of the x-ray images has been established. We have employed the system to observe the plasma evolution in a plasma focus facility. An order of similar to 10(16) photons/(s mm(2) mrad(2)) soft x-ray emission within 6-14 Angstrom was observed in a neon puffed experiment with time resolved four successive frames

Soft X-Ray Hot Spots Observation in an Argon Admixed Plasma Focus Experiment

Hot spots in a dense plasma focus are investigated with a time-resolved and filtered pinhole camera system through Ar K-lines emission. A Moire Schlieren technique is used to observe the macroscopic plasma behavior conjunctly. The hot spots are generated at the disruption of the plasma column with growth of macroscopic instabilities. At the disrupted regions, the hot spots appear and emit intense K-lines of argon approximately for 15 ns. A spatial distribution of Ar K-line emission is quantitatively obtained using the pinhole camera system. The maximum intensity, ∼9.8×10 11 -50% +170% (photons/(s·mm 2 ·(mrad) 2 ·0.01%BW)) is observed when 6% of argon is added to the 4 Torr hydrogen.

A Streak Mode Soft X-ray Imaging System

A streak mode soft X-ray imaging system was newly developed. The system is composed of a combination of a six-channel scintillator-photomultiplier array and a pinhole camera. In this system, the pinhole camera was used to obtain the spatial distribution of the impulsive soft X-ray source quantitatively. Analog signals from the photomultiplier array were provided to obtain the time variation of the source intensity. Software was developed to perform a streak mode display consisting of a 25×20 mesh (3.2 ns/div and 1 mm/div). This system has been successfully employed to observe the time evolution of X-ray emission in plasma focus discharges with puffed Ar. The lifetime and the intensity of the soft X-ray emitting spots around 4 A were found typically to be ~5 ns and ~1016 photons/(mrad2mms), respectively.

An imaging spectrometer with a convex crystal for pulsed x rays in plasma experiments

An imaging spectrometer with a convex rubidium acid phthalate (RbAP) crystal is designed and examined. Using the ray tracing technique based on the kinematical theory of diffraction, resolution power, dispersion, linearity, spatial resolution and dynamic range of the monochromatic image are discussed. Broadening by a rocking curve is also taken into account. Performance of the spectrometer is successfully examined using the so-called hot spots as the soft x-ray source which are generated in the pinched plasma by the plasma focus facility with an additional gas puff.

Soft x-ray emission in the neon gas puff plasma focus

Correlation between soft x-ray emission and dynamic plasma behavior is discussed for a plasma focus device with injected neon. Intense H-like and He-like lines from neon are radiated during an interval when the plasma appears from a visible-light streak camera to be stable. However, data from a multiframing soft x-ray camera indicate the growth of m=0 macroscopic instabilities during this period. The peak of the soft x-ray signal coincides with the micropinch generated in the plasma column, and the emission ends simultaneously with the extinction of the visible light. The electron temperature and density, which are obtained from spectroscopic analysis, are ∼0.5 keV and ∼1022u200acm−3, respectively.

Spectroscopic Investigation of Z-Pinch with a Spatial and Temporal Resolution

Soft X-rays generated by a plasma focus device with an Ar gas puff are studied using a composite system which consists of an imaging Bragg spectrometer and a soft X-ray high speed imaging system. Two modes of soft X-ray emitting sources in Z-pinch plasma, filamentary and scattered spots, are generated in this experiment depending on the delay time from the gas puff to the main discharge. Spectroscopic observation revealed that even the case of the filamentary mode is not really filamentary but is actually X-ray emitting spots (hot spots) densely arranged in a column along the electrode axis. By using the soft X-ray high speed imaging system, the streak mode display is restructured from the data obtained in a single shot, Temporally resolved observations in streak mode showed that a spot appeared at a point near the electrode face first, then different hot spots appeared successively along the axis and in a direction away from the electrode face. It is clarified that the hot spot is a small region from which intense H-like and He-like spectral lines are emitted. The size and the distance between spots are from 0.1 to 0.5 mm in radius and similar to 0.5 mm in length, respectively. The lifetime of the spots is 5 similar to 10 ns. The average electron temperature and density calculated from the intensity ratio of those spectral lines are similar to 1.8 keV and 1.7 x 10(22) /cm(3), respectively. They did not show a notable change along the axis.

An image converting system in framing and streak mode for impulsive soft x-ray observation

A high-speed image converting system is described. The system is capable of display both in multiframing- and streak-mode image for a pulsed x-ray source. The system relies on a new concept without employing an image converter tube. To achieve both temporally and spatially resolved display, the image of the x-ray source is acquired with a pinhole camera and with multichannel arrayed scintillator–photomultiplier combinations, which are used complementarily. The temporal resolution is 3 ns. This system is successfully used to observe the time evolution of soft x-ray emissions around 4 A in plasma focus discharges with puffed Ar.

Spectroscopic Study of Soft X-Ray Sources Generated in a Plasma Focus with Neon Gas Puffing

Soft X-ray emitting spots (hot spots) generated in a plasma focus with a gas puffing are investigated using a streak mode imaging system for the soft X-ray region and a convex Bragg spectrometer wh...

System for time-resolved observation of impulsive soft X-ray sources and its application to plasma focus experiment

A soft X-ray pinhole camera system for time-resolved, one-dimensional (1D) measurement of an impulsive source whose energy is in the range from 1 keV to 20 keV is developed. The system is based on the filtered pinhole camera. The pinhole image is divided into six channels in the direction of the electrode axis through slits and bundled fiber optics. Each channel is detected with a scintillator-photomultiplier combination. The temporal resolution of this system is 5.2 ns. The absolute sensitivity of the channel is ~4.2×10-20 A/[photons/(mrad2s)]. This system was successfully used to observe the time evolution of the soft X-ray source generated with a plasma focus device with a gas-puffed target.