X-ray Pinhole Camera Research Articles

Study of uniformity of elongated plasma channels formed in gas puff targets using extreme ultraviolet and soft X-ray radiation

AbstractThe results of formation of elongated krypton/helium plasma channels are presented. Two laser pulses were used: one to produce plasma channels and the second one for conversion to soft X rays. The soft X-ray radiation was in turn used for backlighting the channels and their visualization. The study of their formation and uniformity was performed using a combination of soft X-ray shadowgraphy and pinhole camera imaging. The plasma channels, with various lengths and various densities, were visualized and the results of their characterization are presented. Using moderate laser pulse energy quite uniform channels, up to 9 mm in length, were demonstrated.

Wire array experiments in a low impedance and low current generator

In this work, a preliminary study about the behavior of a low impedance generator on different wire array configurations is reported. The experimental measurements were carried out on a small multi-purpose generator (1.2μF, 345J, 47.5nH, T/4 = 375 ns and Z = 0.2Ω in short circuit) which produces currents up to 122 kA with 500 ns quarter period, when a charging voltage of 24kV and a wire load are used. Two types of configurations were tested: parallel wires (two and four) and X-pinch configurations. The experiments were carried out on W, Al, and Cu wires with different diameters. The discharge was characterized by means of a set of diagnostics which included: Rogowski coil; filtered PCD detector; filtered PIN diode; gated VUV/soft X-ray pinhole camera, Shadow diagnostic and dark field Schlieren technique. From the set of experimental results, the following observations can be established: (i) The generator is highly sensitive to the changes of load impedance due to its low impedance design. (ii) Every shot shows a dip in the current derivative signal shortly after the discharge onset time (from 6 to 40 ns), which is inversely related to the load resistance. (iii) Both configurations show a similar dynamic to those observed in experiments of higher current and shorter quarter period. (iv) At the X-pinch experiments, two or more hard X-ray bursts are detected, around 200 ns from the current onset time. These X-ray bursts are correlated with the dips observed in the current derivative signal.

Measurement of jet evolution and electron energy spectrum during the process of laser-driven magnetic reconnection

Magnetic reconnection (MR) is a universal physical process in plasma, in which the stored magnetic energy is converted into high-velocity flows and energetic particles. It is believed that MR plays an important role in many plasma phenomena such as solar fare, gamma-ray burst, fusion plasma instabilities, etc.. The process of MR has been studied in detail by dedicated magnetic-driven experiments. Here, we report the measurements of magnetic reconnection driven by Shenguang II lasers and Gekko XVII lasers. A collimated plasma jet is observed along the direction perpendicular to the reconnection plane with the optical probing. The present jet is very different from traditional magnetic reconnection outflows as known in the two-dimensional reconnection plane. In our experiment, by changing the delay of optical probing beam, we measure the temporal evolution of jet from 0.5 ns to 2.5 ns and its velocity around 400 km/s is deduced. Highcollimated jet is also confirmed by its strong X-ray radiation recorded by an X-ray pinhole camera. With the help of optical interferograms we calculate the jet configuration and its density distribution by using Abel inverting technique. A magnetic spectrometer with an energy range from hundred eV up to one MeV is installed in front of the jet, in the direction perpendicular to the reconnection plane, to measure the accelerated electrons. Two cases are considered for checking the acceleration of electrons. The results show that more accelerated electrons can be found in the reconnection case than in the case without reconnection. We propose that the formation and collimation of the plasma jet, and the electron energy spectrum may be possible directly influenced by the reconnection electric field, which is very important for understanding the energy conversion in the process of MR and establishment of the theoretical model. Finally the electron energy spectra of three different materials Al, Ta and Au are also shown in our work. The results indicate that the higher atomic number material can obtain a better signal-noise ratio, which provides some helpful references for our future work.

Macro and micro full field x-ray fluorescence with an X-ray pinhole camera presenting high energy and high spatial resolution.

This work describes a tabletop (50 cm × 25 cm × 25 cm) full field X-ray pinhole camera (FF-XPC) presenting high energy- and high spatial-resolution. The FF-XPC consists of a conventional charge-coupled device (CCD) detector coupled, in a coaxial geometry, to a pinhole collimator of small diameter. The X-ray fluorescence (XRF) is induced on the samples with an external low-power X-ray tube. The use of the CCD as an energy dispersive X-ray detector was obtained by adopting a multi-image acquisition in single photon counting and by developing a processing algorithm to be applied in real-time to each of the acquired image-frames. This approach allowed the measurement of X-ray spectra with an energy resolution down to 133 eV at the reference value of 5.9 keV. The detection of the X-ray fluorescence through the pinhole-collimator allowed the two-dimensional elemental mapping of the irradiated samples. Two magnifications (M), determined by the relative sample-pinhole-CCD distances, are used in the present setup. A low value of M (equal to 0.35×) allows the macro-FF-XRF of large area samples (up to 4 × 4 cm(2)) with a spatial resolution down to 140 μm; a large magnification (M equal to 6×) is used for the micro-FF-XRF of small area samples (2.5 × 2.5 mm(2)) with a spatial resolution down to 30 μm.

Generation and characterization of plasma channels in gas puff targets using soft X-ray radiography technique

We present our recent results of a formation and characterization of plasma channels in elongated krypton and xenon gas puff targets. The study of their formation and temporal expansion was carried out using a combination of a soft X-ray radiography (shadowgraphy) and pinhole camera imaging. Two high-energy short laser pulses were used to produce the channels. When a pumping laser pulse was shaped into a line focus, using cylindrical and spherical lenses, the channels were not produced because much smaller energy density was deposited in the gas puff target. However, when a point focus was obtained, using just a spherical lens, the plasma channels appeared. The channels were up to 9 mm in length, had a quite uniform density profile, and expanded in time with velocities of about 2 cm/μs.

Determination of the ReA Electron Beam Ion Trap electron beam radius and current density with an X-ray pinhole camera.

The Electron Beam Ion Trap (EBIT) of the National Superconducting Cyclotron Laboratory at Michigan State University is used as a charge booster and injector for the currently commissioned rare isotope re-accelerator facility ReA. This EBIT charge breeder is equipped with a unique superconducting magnet configuration, a combination of a solenoid and a pair of Helmholtz coils, allowing for a direct observation of the ion cloud while maintaining the advantages of a long ion trapping region. The current density of its electron beam is a key factor for efficient capture and fast charge breeding of continuously injected, short-lived isotope beams. It depends on the radius of the magnetically compressed electron beam. This radius is measured by imaging the highly charged ion cloud trapped within the electron beam with a pinhole camera, which is sensitive to X-rays emitted by the ions with photon energies between 2 keV and 10 keV. The 80%-radius of a cylindrical 800 mA electron beam with an energy of 15 keV is determined to be r(80%) = (212 ± 19)μm in a 4 T magnetic field. From this, a current density of j = (454 ± 83)A/cm(2) is derived. These results are in good agreement with electron beam trajectory simulations performed with TriComp and serve as a test for future electron gun design developments.

An X-ray pinhole camera using metallic radioisotopes emitting only characteristic X-rays

We developed an X-ray pinhole camera using a radio-isotope source that emits only X-rays.We investigated the performance of this system using a 55Fe source with phantom samples. We then applied it to investigate the movement of a 55Fe tracer in Japanese mustard spinach. We obtained X-ray images of the 55Fe tracer in the spinach samples, and found that 55Fe accumulated in the plant.

Gold planar wire array radiation sources at university scale generators and their applications

Various configurations of planar wires arrays (PWA) made from wires in a broad range of atomic numbers up to 74 (W) have been extensively tested on Zebra generator at the University of Nevada, Reno. In this work, we present the results of our experiments with PWA made of the wires with an even higher atomic number, specifically 79 ( Au ). Two different configurations (single and double PWAs) are considered. The diagnostic set included: x-ray detectors, laser shadowgraphy, time-gated and time-integrated x-ray pinhole cameras, time-integrated spatially resolved and time-gated spatially integrated x-ray spectrometers, and a bolometer. The total x-ray yield was measured along and perpendicular to the load plane and reached the highest value measured on Zebra so far for the single PWA (perpendicular to the plane, 32 kJ). Theoretical tools included non-LTE kinetic and wire ablation dynamic models. The full set of data using aforementioned diagnostics is analyzed and specific implosion and radiative characteristics of Au PWAs. The application of gold PWAs in compact hohlraum configurations on Zebra is highlighted. VisRad (Prism Computational Sciences), a 3-D view factor code, is used to simulate the multi-dimensional radiation environment with a special emphasis on radiation temperature calculations and uniformity at the re-emission target surface.

New method for measuring beam profiles using a parametric X-ray pinhole camera

We propose a new method for measuring electron beam profiles using parametric X-ray radiation. In this method, a pinhole is placed between the source of parametric X-ray radiation and a two-dimensional X-ray detector, and the beam profile can be reconstructed on the detector, i.e., based on the principle of a pinhole camera. The profiles are in good agreement with the results obtained using a standard method with optical transition radiation. This method may prove useful to measure profiles of electron beams with short bunch lengths in recent advanced linear accelerators. • We propose a new method for measuring beam profiles using parametric X-ray radiation. • The proposed method is based on the principle of a pinhole camera. • We have succeeded in performing a proof-of-principle experiment. • The proposed method may be useful for beam monitors in recent advanced accelerators.

A new X-ray pinhole camera for energy dispersive X-ray fluorescence imaging with high-energy and high-spatial resolution

A new X-ray pinhole camera for the Energy Dispersive X-ray Fluorescence (ED-XRF) imaging of materials with high-energy and high-spatial resolution, was designed and developed. It consists of a back-illuminated and deep depleted CCD detector (composed of 1024×1024pixels with a lateral size of 13μm) coupled to a 70μm laser-drilled pinhole-collimator, positioned between the sample under analysis and the CCD. The X-ray pinhole camera works in a coaxial geometry allowing a wide range of magnification values.The characteristic X-ray fluorescence is induced on the samples by irradiation with an external X-ray tube working at a maximum power of 100W (50kV and 2mA operating conditions).The spectroscopic capabilities of the X-ray pinhole camera were accurately investigated. Energy response and energy calibration of the CCD detector were determined by irradiating pure target-materials emitting characteristic X-rays in the energy working-domain of the system (between 3keV and 30keV).Measurements were performed by using a multi-frame acquisition in single-photon counting. The characteristic X-ray spectra were obtained by an automated processing of the acquired images. The energy resolution measured at the Fe–Kα line is 157eV.The use of the X-ray pinhole camera for the 2D resolved elemental analysis was investigated by using reference-patterns of different materials and geometries. The possibility of the elemental mapping of samples up to an area of 3×3cm2 was demonstrated.Finally, the spatial resolution of the pinhole camera was measured by analyzing the profile function of a sharp-edge. The spatial resolution determined at the magnification values of 3.2× and 0.8× (used as testing values) is about 90μm and 190μm respectively.

神光Ⅱ升级装置X光针孔相机研制

The pinhole camera is an important device for inspecting of laser focal spot and target pointing in inertial confinement fusion experiments. In this paper, the X-ray pinhole camera has been developed for ShengguangⅡ-up equipment. This study focuses on parameter and configuration optimization. And the devices have been designed, manufactured, assembled and tested. The results of test experiments show that the energy range is 1.0-5.5 keV, the spatial resolution is better than 20 m, and the magnification ratio is 5.13-9.99. That proves that the pinhole camera can be applied on ShengguangⅡ-up equipment.

Preliminary result of an advanced tangential X-ray pinhole camera system with a duplex MWPC on KSTAR plasma

An advanced tangential X-ray pinhole camera (TXPC) has been developed for KSTAR by utilizing a 2-D duplex multi-wire proportional counter (MWPC) detector. The KSTAR MWPC employs a 2-D parallel type readout system for high temporal resolution and adopts a duplex type for the capability of electron temperature measurement via the multi-color method. This paper presents the performance test result of the developed MWPC system utilizing a Fe-55 X-ray source. As a preliminary experimental result from the 2012 KSTAR campaign, the clear presentation of sawtooth activities and its frequency change, and 2-D plasma images during the vertical disruption event are given.

Optimization of the configuration of pixilated detectors based on the Shannon-Nyquist theory

The configurations of pixilated detectors for x-ray imaging crystal spectrometers and x-ray pinhole cameras can be optimized based on the Shannon-Nyquist sampling and interpolation theory, since the observed spectra are typically oversampled. The degree of oversampling is quantified and alternative uses for redundant pixels are proposed.

Novel energy resolving x-ray pinhole camera on Alcator C-Mod

A new energy resolving x-ray pinhole camera has been recently installed on Alcator C-Mod. This diagnostic is capable of 1D or 2D imaging with a spatial resolution of ≈1 cm, an energy resolution of ≈1 keV in the range of 3.5-15 keV and a maximum time resolution of 5 ms. A novel use of a Pilatus 2 hybrid-pixel x-ray detector [P. Kraft et al., J. Synchrotron Rad. 16, 368 (2009)] is employed in which the lower energy threshold of individual pixels is adjusted, allowing regions of a single detector to be sensitive to different x-ray energy ranges. Development of this new detector calibration technique was done as a collaboration between PPPL and Dectris Ltd. The calibration procedure is described, and the energy resolution of the detector is characterized. Initial data from this installation on Alcator C-Mod is presented. This diagnostic provides line-integrated measurements of impurity emission which can be used to determine impurity concentrations as well as the electron energy distribution.

六通道掠入射软X射线针孔照相技术

六通道掠入射软X射线针孔照相技术

The beam-based calibration of an X-ray pinhole camera at SSRF

A pinhole camera for imaging X-ray synchrotron radiation from a dipole magnet is now in operation at the Shanghai Synchrotron Radiation Facility (SSRF) storage ring. The electron beam size is derived by unfolding the radiation image and the point spread function (PSF) with deconvolution techniques. The performance of the pinhole is determined by the accuracy of the PSF measurement. This article will focus on a beam-based calibration scheme to measure the PSF system by varying the beam images with different quadrupole settings and fitting them with the corresponding theoretical beam sizes. Applying this method at SSRF, the PSF value of the pinhole is revised from 37 to 44 μm. The deviation in beam size between the theoretical value and the measured value is minimized to 4% after calibration. This optimization allows us to observe the horizontal disturbance due to injection down to as small as 0.5 μm.

Methods of Generation and Detailed Characterization of Millimeter-Scale Plasmas Using a Gasbag Target

Gasbag targets are useful for the research of laser-plasma interactions in inertial confinement fusion, especially in the laser overlapping regime. We report that on the Shengguang-II laser facility, millimeter-scale plasmas are successfully generated by four 0.35 μm laser beams using a gasbag target. Multiple diagnostics are applied to characterize the millimeter-scale plasmas in detail. The images from the x-ray pinhole cameras confirm that millimeter-scale plasmas are indeed created. An optical Thomson scattering system diagnoses the electron temperature of the CH filling plasmas by probing the thermal ion-acoustic fluctuations, which indicates that the electron temperature has a 600 eV flat roof in 0.7–1.3 ns. Another key parameter, i.e. the electron density of the millimeter-scale plasmas, is inferred by the spectrum of the back stimulated Raman scattering of an additional 0.53 μm laser beam. The inferred electron density keeps stable at 0.1nc in early time consistent with the controlled filling pressure and splits into a higher density in late time, which is attributed to the blast wave entering into the SRS interaction region.

Interaction of a laser-produced copper plasma jet with ambient plastic plasma

This work is aimed at the investigation of mutual interaction of plastic (CH) and copper axially symmetric plasmas, and the dependence on the ratio of their ablated masses. For that purpose we irradiated a plastic target with a Cu cylindrical insert of diameter 400 µm with a laser beam of radius exceeding that of the insert. In such an arrangement we were able to control the volumes and masses of interacting CH and Cu plasmas by varying the laser beam diameter. The experiment was carried out at the Prague Asterix Laser System (PALS) iodine laser. The laser provided a 250 ps pulse with an energy of 130 J at the third harmonic frequency (i.e. a wavelength of λ3 = 0.438 µm). The interaction of the laser-driven plasma jet with ambient plasma was studied by means of a three-frame interferometric system and a four-frame x-ray pinhole camera. For simulation of the experiment we used the two-dimensional hydrodynamic code ATLANT-HE. The reported results demonstrated that there is an optimal ratio of Cu and plastic plasma masses, at which stable extended Cu plasma jets can be created. Even a relatively thin plastic plasma envelope can compress the Cu plasma and control the jet formation. Thicker plastic plasma layers, however, lead to complex hydrodynamic motion accompanied by generation of transverse shock waves, which can completely suppress the jet formation. The pressure of the plastic plasma was found to be 1.35 times higher than that of the copper plasma. A theoretical analysis of the experimental results allows us to conclude that this difference in pressures follows from the essential differences in expansion dynamics of plasmas with low and high atomic numbers.

Note: Diagnosing femtosecond laser-solid interactions with monochromatic K α imager and x-ray pinhole camera

An x-ray pinhole camera and a monochromatic K(α) imager are used to measure the interactions of intense femtosecond laser pulses with Cu foil targets. The two diagnostics give different features in the spot size and the laser energy scaling, which are resulted from different physical processes. Under our experimental conditions, the K(α) emission is mainly excited by the fast electrons transporting inside the cold bulk target. In contrast, the x-ray pinhole signals are dominated by the broadband thermal x-ray emission from the hot plasma at the front target surface.

Charge-injection-device performance in the high-energy-neutron environment of laser-fusion experiments

Charge-injection devices (CIDs) are being used to image x rays in laser-fusion experiments on the University of Rochester's OMEGA Laser System. The CID cameras are routinely used up to the maximum neutron yields generated (∼10(14) DT). The detectors are deployed in x-ray pinhole cameras and Kirkpatrick-Baez microscopes. The neutron fluences ranged from ∼10(7) to ∼10(9) neutrons/cm(2) and useful x-ray images were obtained even at the highest fluences. It is intended to use CID cameras at the National Ignition Facility (NIF) as a supporting means of recording x-ray images. The results of this work predict that x-ray images should be obtainable on the NIF at yields up to ∼10(15), depending on distance and shielding.