Continuous X-ray Sources Research Articles

Experimental investigations of hard x-ray source produced by picosecond laser-irradiated solid target

Measurements of Kα line and bremsstrahlung continuous x-ray emission from high-intensity laser-irradiated thin targets are presented. The experiments were performed at the SG-II UP Petawatt laser. Self-standing Sn foils varying thicknesses and Sn foils backed by the thick substrate were irradiated by the laser pulses up to 300 J of energy with peak intensity higher than 1018 W/cm2. A transmission curved crystal spectrometer and a filter-stack spectrometer were used to measure the Kα line and bremsstrahlung x-ray spectral distribution, respectively. Both Kα and 70–200 keV x-ray yields decrease 3- to 5-fold for target backed by the substrate. 2- to 4-fold reduction of Kα and 70–200 keV x-ray yields for the 8.5 μm targets relative to 50 μm targets was observed. Moreover, a significant background x-ray emission generated from the target holder reduces the ratio of signal to noise. Adopting a low-Z material holder can mitigate the x-ray background noises. This study is instructive to optimize target design for the high-intensity laser-driven Kα or continuous x-ray sources.

Spectroscopic analysis with tender X-rays: SpAnTeX, a new AP-HAXPES end-station at BESSY II

We present a newly developed end-station at BESSY II dedicated to in situ Spectroscopic Analysis with Tender X-rays (SpAnTeX). The core of the end-station is a new SPECS PHOIBOS 150 HV NAP electron spectrometer. First, we show that the system has successfully achieved high electron transmission and detection efficiency under gas pressures up to 30 mbar and photon energies ranging between 200 eV and 10 keV. Second, using two features of this spectrometer (a new lateral resolution lens and a 3D delay line detector), we show that the endstation enables collection of the photoelectron spatial distribution under realistic working conditions (p ≥ 20 mbar) with a resolution better than 30 μm and the possibility to perform time resolved studies using a continuous tender X-ray source. We conclude by reporting an example of the possible experiments that can be performed using this new endstation using the Dip-and-Pull technique.Although mainly focused on the characterization of solid/liquid interfaces using AP-HAXPES, the end-station can be used at soft X-ray beamlines for more traditional AP-XPS experiments. The Dip-and-Pull module also demonstrates good electrochemical performance. The wide pressure and photon energy range covered by this end-station also enables investigations of solid/solid, solid/gas, liquid/vapor and liquid/liquid interfaces at pressures up to 30 mbar with tender X-rays.

Pulsed X-ray source with the pulse duration of 50 ns and the peak power of 70 MW for capturing moving objects.

Traditionally, X-ray systems for capturing moving objects consist of a continuous X-ray source and a detector that operates at a predetermined frame rate. This study investigates the possibility of using pulsed X-ray source with an inductive energy storage device and a semiconductor opening switch for shooting moving objects. The study uses a high-voltage pulse generator that has the following parameters namely, the pulse voltage amplitude up to 320 kV, the pulse current up to 240 A, the current pulse duration of about 50 ns, and the pulse repetition rate up to 2 kHz. The duration and intensity of glow for standard CsI:Tl and Gd2O2S:Tb X-ray phosphors after their irradiation with X-ray flashes of about 50 ns duration are investigated. After X-ray radiation is converted into light, the signal is recorded using semiconductor detectors. We acquired several images of an object moving at a speed of about 20 m/s. A semiconductor detector with phosphor, which operates in the mode of continuous signal accumulation, is used. When using the pulsed X-ray source and phosphors with a short afterglow, the individual frames can be obtained at the pulse repetition rate of several kilohertz, and the detector does not contain the residual luminescence from the previous frame by the arrival of the next frame. The X-ray source shows good pulse-to-pulse reproducibility of X-rays, and can be used to capture objects in motion at a frame rate of several kHz.

Foil backlighter development at the OMEGA laser facility for extended x-ray absorption fine structure experiments.

Extended x-ray absorption fine structure (EXAFS) measurements require a bright and continuous x-ray source and a detection system with high spectral resolution to capture the modulations of the absorption coefficient above the material absorption edge. When performing EXAFS measurements under laser-driven dynamic compression, it is hence critical to optimize the backlighter x-ray emission. A series of experiments has been conducted at the OMEGA laser facility to characterize titanium (Z = 22), iron (Z = 26), germanium (Z = 32), molybdenum (Z = 42), silver (Z = 47), and gold (Z = 79) foil backlighters irradiated with 3 kJ-12 kJ of laser energy. The spectra have been recorded using a dual crystal spectrometer (DCS), a two-channel transmission spectrometer covering 11 keV-45 keV and 19 keV-90 keV energy bands. The DCS has been calibrated so that the spectral intensities can be compared between different campaigns.

Use of a priori spectral information in the measurement of x-ray flux with filtered diode arrays.

Filtered x-ray diode (XRD) arrays are often used to measure x-ray spectra vs. time from spectrally continuous x-ray sources such as hohlraums. A priori models of the incident x-ray spectrum enable a more accurate unfolding of the x-ray flux as compared to the standard technique of modifying a thermal Planckian with spectral peaks or dips at the response energy of each filtered XRD channel. A model x-ray spectrum consisting of a thermal Planckian, a Gaussian at higher energy, and (in some cases) a high energy background provides an excellent fit to XRD-array measurements of x-ray emission from laser heated hohlraums. If high-resolution measurements of part of the x-ray emission spectrum are available, that information can be included in the a priori model. In cases where the x-ray emission spectrum is not Planckian, candidate x-ray spectra can be allowed or excluded by fitting them to measured XRD voltages. Examples are presented from the filtered XRD arrays, named Dante, at the National Ignition Facility and the Laboratory for Laser Energetics.

X-ray opacity measurements in mid-Z dense plasmas with a new target design of indirect heating

X-ray transmission spectra of copper, nickel and aluminum laser produced plasmas were measured at the LULI2000 laser facility with an improved target design of indirect heating. Measurements were performed in plasmas close to local thermodynamic equilibrium at temperatures around 25 eV and densities between 10−3 g/cm3 and 10−2 g/cm3. This improved design provides several advantages, which are discussed in this paper. The sample is a thin foil of mid-Z material inserted between two gold cavities heated by two 300J, 2ω, nanosecond laser beams. A third laser beam irradiates a gold foil to create a spectrally continuous X-ray source (backlight) used to probe the sample. We investigate 2p–3d absorption structures in Ni and Cu plasmas as well as 1s–2p transitions in an additional Al plasma layer to infer the in-situ plasma temperature. Geometric and hydrodynamic calculations indicate that the improved geometry reduces spatial gradients during the transmission measurements. Experimental absorption spectra are in good agreement with calculations from the hybrid atomic physics code SCO-RCG.

A power–voltage scaling law for liquid anode X-ray tubes

An analysis is presented of the relative magnitudes of factors affecting the specific loadability (Wmm−2K−1) of liquid metal anode X-ray sources (LIMAX). These factors are to a certain extent analogous to those, such as focus width, focus-anode relative sweep velocity and the anode thermal conductivity, of importance in solid-state (e.g. rotating anode) X-ray tubes.It is shown that in general, convection cooling of the electron window by the liquid metal stream represents the least efficient thermal transport process in LIMAX. As the energy deposited in the electron window through inelastic electron scattering is approximately inversely proportional to electron energy, the power loadability of a LIMAX source operated under constant conditions scales to first approximation with the square of the tube potential. This power–voltage scaling law of liquid metal anode X-ray sources is without analogue in solid-state X-ray sources.A summary is presented of potential applications of high continuous power X-ray sources operating in the high-voltage region of several 100kV.

Measurement of granular flow in a silo using Digital Speckle Radiography

In this paper, the flow of a powder through a silo is investigated using Digital Speckle Radiography (DSR). This technique allows displacement measurements to be made on the sub-mm scale to an accuracy of 0.06 μm and a spatial resolution of 26 μm. The method performs an image cross-correlation on a random seeding of X-ray opaque material as it flows out of the silo with the powder. The flow is captured digitally using a continuous X-ray source and an image intensifier and Charge Coupled Device (CCD) camera to give real time measurements. The powder used is Al 2O 3 with an average particle size of 50 μm and the seeding material is tungsten powder, also with an average particle size of 50 μm. Clear flow behaviour is observed for two different sizes of outlet and the flow rate and strains occurring during the flow are also investigated.

On the Possible Mechanisms of Activation Changes of Enzymes under Pulsed Irradiation

Classical radiation biology, radiation treatment of patients, and pulsed radiation chemistry usually deal with weak beams of radiation and operate in terms of dose (D). In this case, only the absolute number of ionizing particles or photons interacting with the object independently of one another is important. In this work, we resume our previous investigations of enzyme activation/inactivation produced by pulsed ionizing radiation from a dense plasma focus (DPF) device at a very short and intense irradiation process, when the concentrations of spurs and blobs are sufficiently dense to allow the micro-volumes to overlap each other. The time interval is small compared with the corresponding biochemical process. It is shown that the irradiation of biological objects for a few nanoseconds by beams of x-ray photons with a low dose (D ∼ 10-6–10-3 Gy) but at a high dose power (D/τ∼103–105 Gy/s) may be of a collective nature and result in synergetic effects. In particular, it was found that a remarkable activation/inactivation of enzymes (horseradish peroxidase, angiotensin-converting-enzyme) takes place at low doses in these regimes. The results of irradiating the above-mentioned enzymes in vitro with x-rays of nanosecond pulse duration coming from a dense plasma focus are presented here. Neutrons (2.5 MeV, 103–105 n/cm2 and x-ray photons of different energy ranges (7–9 keV and 20–200 keV) together with dose power factors are analyzed as possible reasons for the activation/inactivation of enzymes in various dose ranges. Our results are compared to those of the same experiments conducted with continuous x-ray sources based on a classical x-ray tube and on a 137Cs-isotope source (D∼10-3–102 Gy).

High speed x-ray radiography diagnostic of current interruption in circuit breakers

High-speed x-ray radiography is used for the imaging of internal components of a low-voltage air circuit breaker during fast current interruption events. A continuous x-ray source was used to irradiate the circuit breaker during interruption, while a fast camera imaging system recorded the output visible light from the x-ray image intensifier up to a maximum rate of 4000 frames per second. Detailed time-resolved images were obtained of the movable contact position and tripping mechanism components of the circuit breaker during the interruption event. Experimental observations were used to validate numerical simulation results obtained using electromagnetics and dynamics/kinematics analysis software. In addition to imaging of the circuit breaker mechanism, molten metal streams and droplets ejected from the electrodes were also observed. Tracking of these metallic particles can provide valuable information about contact phenomena and gas flow fields in circuit breakers.

Count-Rate Statistics for Drift Detectors.

Synchrotron light sources are low-duty-cycle pulsed X-ray sources, a fact that is often neglected in estimating the count-rate capabilities of photon-counting detectors in synchrotron-based experiments. In this paper, we demonstrate the effect that this has on the pileup statistics of drift detectors. We derive expressions for the cases of continuous and pulsed X-ray sources. We consider a pulsed source with period that is either much less than the shaper support time or much less than the average drift time. We also consider a pulsed source with a period that is long or comparable to both the shaper support and the drift time. These conditions correspond to normal and reduced bunch fill patterns of synchrotrons.

Characterization of a subpicosecond x-ray streak camera for ultrashort laser-produced plasmas experiments

We present results of the characterization of an ultrafast x-ray streak camera, based on Photonis (formerly Philips Photonics) P860 tube, developed for use in ultrashort laser-produced plasma research. The streak camera presented here (called PX1) has been extensively characterized with continuous and pulsed x-ray sources. Time resolution of 350 fs in the keV x-ray range has been achieved, while maintaining a high spatial resolution of 40 μm along a direction perpendicular to the time dispersion axis. It is shown that the streak camera response is lower when the photocathode is illuminated by a pulsed source than when used with a continuous one. This effect seems to be related to a change in the phosphor response. The camera has been used to achieve high-resolution subpicosecond time-resolved spectroscopy of ultrashort laser plasmas allowing the measurements of K-shell line emission durations of 700 fs.

The soft X-ray and extremely ultraviolet filters with negligible pinholes transmittance

It is proposed to fabricate two-layer thin film filters without pinholes transmittance of visible and UV light. We describe the design and performance of these filters. Filter consists of two layers of thin metal films fixed to each side of porous membrane with thorough pores or transmission diffraction grating as support. As examples it was made Al or Rh two-layer thin film filters on metallized porous track membrane supports with the 10 −9–10 −10 level of visible and UV light rejection at transmittance T∼0.1 ÷ 0.01 in the Extreme ultraviolet region. Proposed filter is appropriate in the optical experiments with strong continuous X-ray and Extreme ultraviolet radiation sources such as laser plasma, SR sources and the Sun.

X-ray calibration of Kodak SB film in the 1.5–2.2-keV region

The relative response of Kodak SB film has been measured with a pulsed-laser Al plasma x-ray source in the energy region delimited by the absorption edges of Br (1599 eV) and of Ag (3351 eV) in the photographic emulsion. The data of optical density versus exposure were obtained by recording spectra at different exposures which were controlled by placing stepped Be filters. A significant variation has been observed with earlier results obtained with continuous x-ray sources at high optical densities. The data may be fit with a simple expression of exposure L determined with an arbitrary constant L0 as a function of optical density D with only two parameters, Dsat and k: L = L0/(Dsat/D − 1)1/k. It is found that Dsat=3.45 and k=0.92 over the entire energy range.

Use of Bremsstrahlung in the Measurement of the Efficiency of Solid State Detectors below 5 keV

Atomic-field bremsstrahlung produced by the bombardment of atoms by an electron beam of 5-10 keV energy provides a continuous x-ray source which is suitable for the measurement of the relative efficiency of solid state detectors in the energy region below 5 keV. The relative efficiency as a function of photon energy can be obtained by normalizing the observed spectrum to the theoretical bremsstrahlung cross section. In this paper we will present an example of this technique using a thin film target and a gas beam target to illustrate some of the problems and to demonstrate the potential of this technique.

Transmission Scanning Using a Continuous X-ray Source

A system of rectilinear scanning has been developed which senses the presence of particular elements by measuring the differential attenuation of x-ray photons about a specific absorption edge. A continuous x-ray spectrum generated from a side-window 50 kVcp tube is used and the transmitted beam is detected by an energy selective Ge(HP) semiconductor detector. Measurements on phantoms with absorbers up to 10 cm thick indicate sensitivity to middle Z elements such as iodine, down to the range of 1 mg/cm2 in reasonable scanning times. Little effect was seen by additional 1" absorbers, and the effects of in-line voids can be minimized. Scans were taken of rabbit kidneys and bileary tracts as an iodated contrast agent was infused, and of rabbit lungs while the animal breathed a xenon/oxygen mixture. Future directions for this technique of transmission scanning are discussed.