Maximum X-ray Yield Research Articles

Measurement of Femtosecond Laser Plasma X-ray Spectra Using a Medipix Detector

A method for measuring the bremsstrahlung X-ray spectra of electrons accelerated in a laser plasma using Medipix matrices has been developed. The application of the matrix provides the spectrum accumulation in a much shorter time, as compared to detectors based on a scintillator and a photomultiplier commonly used for such measurements. This ensures dynamic monitoring of the X-ray characteristics and prompt adjustment of the laser source parameters to obtain the maximum X-ray yield and energy. The results of measurements of the X-ray spectra at the ILC MSU terawatt femtosecond-laser complex for various laser-plasma interaction regimes are presented.

Свойства керамического пироэлектрического генератора рентгеновского излучения в зависимости от давления остаточного газа

AbstractThe properties of X-ray emission from a pyroelectric accelerator based on ferroelectric ceramics have been experimentally studied, including the maximum energy of X-ray photons and their maximum yield generated by accelerated electrons at various pressures of residual gas in the generator chamber. The maximum X-ray yield and maximum energy of X-ray photons and accelerated electrons have been observed at a residual-gas pressure of around several millitorr.

Properties of a Ceramic Pyroelectric X-Ray Generator as Dependent on Residual-Gas Pressure

The properties of X-ray emission from a pyroelectric accelerator based on ferroelectric ceramics have been experimentally studied, including the maximum energy of X-ray photons and their maximum yield generated by accelerated electrons at various pressures of residual gas in the generator chamber. The maximum X-ray yield and maximum energy of X-ray photons and accelerated electrons have been observed at a residual-gas pressure of around several millitorr.

Characterization of laser-driven electron and photon beams using the Monte Carlo code FLUKA

AbstractWe present a new simulation method to predict the maximum possible yield of X-rays produced by electron beams accelerated by petawatt lasers irradiating thick solid targets. The novelty of the method lies in the simulation of the electron refiluxing inside the target implemented with the Monte Carlo code Fluka. The mechanism uses initial theoretical electron spectra, cold targets and refiluxing electrons forced to re-enter the target iteratively. Collective beam plasma effects are not implemented in the simulation. Considering the maximum X-ray yield obtained for a given target thickness and material, the relationship between the irradiated target mass thickness and the initial electron temperature is determined, as well as the effect of the refiluxing on X-ray yield. The presented study helps to understand which electron temperature should be produced in order to generate a particular X-ray beam. Several applications, including medical and security imaging, could benefit from laser generated X-ray beams, so an understanding of the material and the thickness maximizing the yields or producing particular spectral characteristics is necessary. On the other more immediate hand, if this study is experimentally reproduced at the beginning of an experiment in which there is an interest in laser-driven electron and/or photon beams, it can be used to check that the electron temperature is as expected according to the laser parameters.

Estimation of electron temperature and radiation emission of a low energy (2.2 kJ) plasma focus device

Radiation emission in a 2.2 kJ Mather-type plasma focus device is investigated using a five channel BPX65 PIN diode spectrometer. At optimum condition, radiation emission from the system is found to be strongly influenced in hollow anode and filling gas pressure. Maximum X-ray yield in 4p sr has been obtained in case of hollow anode in argon gas medium due to interaction of electron beam. Results indicate that an appropriate design of anode can enhance radiation emission by more intense interaction of expected electron beam with hollow anode. The outcome is helpful to design a plasma focus with enhanced X-ray generation with improved shot-to-shot reproducibility in plasma focus device.

Effect of Cathode Designs on Radiation Emission of Compact Diode (CD) Device

A comparative study on the radiation emission such as X-ray yield and efficiency has been carried out in compact diode device. Two different designs of cathode having sharp-edged razor blade (of 0.5 mm thickness with width 2 mm) and a sewing machine needle (of 0.5 mm diameter at tip with length of 39 mm) have been tested for this study. The radiation emission (X-ray yield) was determined by employing two set of PIN diodes at fixed positions. The maximum X-ray yield depends on cathode designs and electrodes separation in few mm. The yield of X-ray is small in the case of sharp-edged razor blade cathode than the sewing machine needle cathode. The X-ray yield, measured by 4π-geometry, shows its dependence on the cathode designs. The maximum X-ray yield is found to be 939.2 ± 65.7 mJ with efficiency of 0.4142 ± 0.0289%. This study indicates that the compact diode device could be optimized to a great extent for optimal X-ray yield by using an appropriate cathode design.

The correlation of x-ray emission with pinch energy in a 1.5 kJ plasma focus

Correlation of x-ray emission with pinch energy from a 1.5 kJ Mather-type plasma focus device for Ag and Sn inserts at the Cu tapered anode tip is reported. The space and time resolved x-ray emission characteristics are investigated by using a simple pinhole camera with appropriate filters and a multichannel pin-diode spectrometer. High voltage probe and Rogowski coil signals are used to estimate the pinch energy. At optimum conditions, the maximum x-ray yield in 4π-geometry is found to be 9 and 8 J/shot with efficiency of 0.6% and 0.5% for Sn and Ag inserted anodes. This is despite the fact that input energy converted to pinch energy is lower at 8% for Sn insert compared with 15% for the Ag insert. An increase in x-ray yield with an increase in pinch energy is observed for Sn as well as Ag. Pinhole images reveal that x-rays of energy less than 5 keV are emitted from the focus region and the high-energy x-rays are emanated from the anode tip.

Catalytic action of β source on x-ray emission from plasma focus

The influence of preionization around the insulator sleeve by a mesh-type β source (Ni6328) for the x-ray emission from a (2.3-3.9 kJ) plasma focus device is investigated. Quantrad Si p-i-n diodes along with suitable filters are employed as time-resolved x-ray detectors and a multipinhole camera with absorption filters is used for time-integrated analysis. X-ray emission in 4π geometry is measured as a function of argon and hydrogen gas filling pressures with and without β source at different charging voltages. It is found that the pressure range for the x-ray emission is broadened, x-ray emission is enhanced, and shot to shot reproducibility is improved with the β source. With argon, the CuKα emission is estimated to be 27.14 J with an efficiency of 0.7% for β source and 21.5 J with an efficiency of 0.55% without β source. The maximum x-ray yield in 4π geometry is found to be about 68.90 J with an efficiency of 1.8% for β source and 54.58 J with an efficiency of 1.4% without β source. With hydrogen, CuKα emission is 11.82 J with an efficiency of 0.32% for β source and 10.07 J with an efficiency of 0.27% without β source. The maximum x-ray yield in 4π geometry is found to be 30.20 J with an efficiency of 0.77% for β source and 25.58 J with an efficiency of 0.6% without β source. The x-ray emission with Pb insert at the anode tip without β source is also investigated and found to be reproducible and significantly high. The maximum x-ray yield is estimated to be 46.6 J in 4π geometry with an efficiency of 1.4% at 23 kV charging voltage. However, degradation of x-ray yield is observed when charging voltage exceeds 23 kV for Pb insert. From pinhole images it is observed that the x-ray emission due to the bombardment of electrons at the anode tip is dominant in both with and without β source.

Anode length optimization in a modified plasma focus device for optimal x-ray yields

The effect of anode length and operating gas pressure on the x-ray emission from a nitrogen-filling modified plasma focus device has been investigated. The time-resolved investigation of x ray was carried out by using a five-channel photodiode x-ray spectrometer. The maximum x-ray yield is seen to increase with the increase in the anode length from 110 to 125 mm. Further increase in the anode length to 130 mm causes the x-ray yields to decrease. The highest x-ray yield of 4.5 J into 4πsr was found for 125 mm anode length, which is 0.2% of the input energy. The average x-ray photon energy was estimated by using half-value thickness method and found to be 8.4 keV. The electron temperature of the plasma was estimated to be around 3 keV by x-ray intensity ratio method. The space-resolved x-ray-emitting zones for all the anodes were captured by a pinhole-based x-ray imaging camera and the images were scanned for different gray levels by using a MATLAB computing software. These gray level spectra show that the image for a 125 mm anode length is more intense than that for the other anode. In addition to this, the gray level spectrum shows some highly dense spot inside the image, which is the so-called hot spot, emitting relatively higher energy x rays. Our results indicate that the plasma focus device could be optimized to a great extent for optimal x-ray yield by using an appropriate anode length.

Comparative studies of X-ray emission from a plasma focus with different metal inserts at the anode tip

X-rays emission from a low energy (1.4–5.3 kJ) Mather-type plasma focus device with different (Cu, Mo, W and Pb) inserts at the anode tip is reported. The space and time resolved X-ray emission characteristics are investigated by using a multichannel pindiode spectrometer and a simple pinhole camera with appropriate filters. The variation of total X-ray yield and corresponding efficiency with discharge current, charging voltage and stored energy is investigated. At optimum conditions, the maximum X-ray yield in 4 π-geometry is found to be 67.6, 62.4, 64 and 46.5 J/shot with Cu tip, Mo, W and Pb inserted anodes, respectively, and corresponding efficiencies for X-ray generation are 1.5, 1.4, 1.2 and 1.4%. In case of Pb inserted anode X-ray yield deterioration is observed for charging voltages grater than 23 kV. Pinhole images of the X-ray emitting sites reveal that soft X-rays are emitted from focus region, whereas hard X-rays are emanated from anode tip.

Study of tungsten wire array Z-pinch implosion on Qiang-Guang I facility

The main results of investigation on the tungsten wire array Z-pinch implosion experiment performed on Qiang-Guang I facility in 2003 are reported in this paper. A set of diagnostic equipments including an x-ray power meter (XRPM), a 1D spatial-temporal x-ray meter and a pinhole camera was used to study implosion process and x-ray radiation characteristics of the tungsten wire array. In the experiment, the maximum x-ray yield of 36.6kJ was obtained for an optimizing load with a diameter of 8mm and a length of 20mm, which consists of 32 5-μm-diameter tungsten wires. The experimental results show that the region of x-ray emission decreased at a rate of 6.4×106cm/s by analysing the data of the 1D spatial-temporal x-ray meter. It also shows that the peak time of x-ray radiation was prior to the time when plasmas were compressed into a near-axis region.

Study of x-ray emission from a table top plasma focus and its application as an x-ray backlighter

A study of a 2 kJ, 200 kA, table top plasma focus device as an intense x-ray source is reported. The x-ray yield from a number of gases, (deuterium, nitrogen, neon, argon, and xenon) is measured as a function of filling pressure and in neon as a function of anode length. In gases with Z<18, the plasma implodes to form a uniform cylindrical column, whereas for Z⩾18, the plasma consists of a number of hot spots. A maximum x-ray yield of 16.6 J and pulse length of 10–15 ns was obtained in neon. The x-ray emission was established to be due to H- and He-like line radiation. The temperature estimated from spectroscopic observations was about 300–400 eV at an electron density of (3–5)×1020 cm−3 in neon. At low pressures in neon, hard x-ray radiation, presumably due to electron beams was dominant. Mesh images of different wire materials were recorded at the optimum pressure in neon as a proof of principle for x-ray backlighting.