Maria Pia Valdivia

Maria Pia Valdivia
University of California, San Diego | UCSD · Center for Energy Research (CER)

PhD

About

43
Publications
3,246
Reads
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221
Citations
Citations since 2016
18 Research Items
191 Citations
20162017201820192020202120220102030405060
20162017201820192020202120220102030405060
20162017201820192020202120220102030405060
20162017201820192020202120220102030405060
Additional affiliations
January 2013 - September 2021
Johns Hopkins University
Position
  • Associate Research Scientist

Publications

Publications (43)
Article
Talbot–Lau x-ray interferometry is a refraction-based diagnostic that can map electron density gradients through phase-contrast methods. The Talbot–Lau x-ray deflectometry (TXD) diagnostics have been deployed in several high energy density experiments. To improve diagnostic performance, a monochromatic TXD was implemented on the Multi-Tera Watt (MT...
Article
Full-text available
Interferometry is one of the most sensitive and successful diagnostic methods for plasmas. However, owing to the design of most common interferometric systems, the wavelengths of operation, and therefore the range of densities and temperatures that can be probed, are severely limited. Talbot-Lau Interferometry offers the possibility of extending in...
Article
Talbot-Lau X-ray Deflectometry (TXD) enables refraction-based imaging for high-energy-density physics (HEDP) experiments, and thus, it has been studied and developed with the goal of diagnosing plasmas relevant to Inertial Confinement and Magnetic Liner Inertial Fusion. X-pinches, known for reliably generating fast (~1 ns), small (~1 µm) x-ray sour...
Article
Talbot-Lau x-ray interferometry has been implemented to map electron density gradients in High Energy Density Physics (HEDP) experiments. X-ray backlighter targets have been evaluated for Talbot-Lau X-ray Deflectometry (TXD). Cu foils, wires, and sphere targets have been irradiated by 10–150 J, 8–30 ps laser pulses, while two pulsed-power generator...
Article
Wire X-pinches (WXPs) have been studied comprehensively as fast ( ∼ 1 ns pulse width), small ( ∼ 1 μm) x-ray sources, created by twisting two or more fine wires into an “X” to produce a localized region of extreme magnetic pressure at the cross-point. Recently, two alternatives to the traditional WXP have arisen: the hybrid X-pinch (HXP), composed...
Article
Full-text available
Talbot-Lau x-ray interferometry is a grating-based phase-contrast technique, which enables measurement of refractive index changes in matter with micrometric spatial resolution. The technique has been established using a variety of hard x-ray sources, including synchrotron, free-electron lasers, and x-ray tubes, and could be used in the optical ran...
Article
Full-text available
A Talbot–Lau x-ray deflectometer can map electron density gradients in high energy density plasmas, as well as provide information about plasma elemental composition through single-image x-ray refraction and attenuation measurements. A new adaptation to a pulsed power environment used backlighting from copper X-pinches, allowing for electron densit...
Article
A Talbot–Lau X-ray Deflectometer (TXD) was implemented in the OMEGA EP laser facility to characterize the evolution of an irradiated foil ablation front by mapping electron densities >10²² cm⁻³ by means of Moiré deflectometry. The experiment used a short-pulse laser (30–100 J, 10 ps) and a foil copper target as an x-ray backlighter source. In the f...
Article
Full-text available
We describe a platform developed on the LULI2000 laser facility to investigate the evolution of Rayleigh-Taylor instability (RTI) in scaled conditions relevant to young supernova remnants (SNRs) up to 200 years. An RT unstable interface is imaged with a short-pulse laser-driven (PICO2000) x-ray source, providing an unprecedented simultaneous high s...
Article
Talbot-Lau x-ray interferometers can map electron density gradients in High Energy Density (HED) samples. In the deflectometer configuration, it can provide refraction, attenuation, elemental composition, and scatter information from a single image. X-ray backlighters in Talbot-Lau deflectometry must meet specific requirements regarding source size...
Article
Talbot-Lau x-ray interferometry uses incoherent x-ray sources to measure refraction index changes in matter. These measurements can provide accurate electron density mapping through phase retrieval. An adaptation of the interferometer has been developed in order to meet the specific requirements of high-energy density experiments. This adaptation i...
Article
Talbot-Lau X-ray deflectometry (TXD) has been developed as an electron density diagnostic for High Energy Density (HED) plasmas. The technique can deliver x-ray refraction, attenuation, elemental composition, and scatter information from a single Moiré image. An 8 keV Talbot-Lau interferometer was deployed using laser and x-pinch backlighters. Grat...
Article
We present the development and advancement of the Talbot-Lau X-ray deflectometry (TXD) single-image phase-retrieval technique, for high-energy density (HED) plasma diagnostics. The Talbot-Lau interferometer has been benchmarked as an electron density diagnostic for low-Z objects (Z < 13 ) at the X-ray energies of 8 and 17 keV. A laser driven X-ray...
Article
X-ray phase-contrast techniques can measure electron density gradients in high-energy-density plasmas through refraction induced phase shifts. An 8 keV Talbot-Lau interferometer consisting of free standing ultrathin gratings was deployed at an ultra-short, high-intensity laser system using K-shell emission from a 1-30 J, 8 ps laser pulse focused on...
Article
Full-text available
Electron beams produced by the hollow cathode effect are studied in a compact gas filled 24-kV, 5-kA capillary discharge. The characteristics and role of electron beams on X-ray production are studied in order to better understand their impact on X-ray production. X-ray plasma emission is analyzed with a spectrometer, while wideband diodes and Fara...
Article
Full-text available
Moiré fringe deflectometry with grating interferometers is a technique that enables refraction-based x-ray imaging using a single exposure of an object. To obtain the refraction image, the method requires a reference fringe pattern (without the object). Our study shows that, in order to avoid artifacts, the reference pattern must be exactly matched...
Conference Paper
Phase-contrast x-ray diagnostics can detect density gradients in low-Z matter with the sensitivity and spatial resolution required in High Energy Density (HED) plasma experiments. Talbot-Lau interferometry measures x-ray beam deviations due to refraction index gradients in its path. It can simultaneously provide x-ray attenuation, refraction, eleme...
Conference Paper
For the first time an x-ray Talbot-Lau moire deflectometer is being developed that will use a flash tube source and fast detector for dynamic density gradient measurements. In Talbot-Lau moire deflectometry, an x-ray grating makes an image of itself on a second grating (the Talbot effect) to produce a moire pattern on a detector. The test object is...
Article
Full-text available
The Talbot–Lau x-ray moiré deflectometer is a powerful plasma diagnostic capable of delivering simultaneous refraction and attenuation information through the accurate detection of x-ray phase shift and intensity. The diagnostic can provide the index of refraction n=1−δ+iβ of an object (dense plasma, for example) placed in the x-ray beam by indepen...
Article
We report on results from experiments using laser-cut X shaped foils (or foil X-pinches) driven by the 250 kA, 150 ns rise-time GenASIS Linear Transformer Driver. Optical probing of the laser-cut foil X-pinches shows considerable dynamic and qualitative similarity with the more traditional wire X-pinches. Results demonstrate excellent quality X-ray...
Article
Full-text available
The highly localized density gradients expected in High Energy Density (HED) plasma experiments can be characterized by x-ray phase-contrast imaging in addition to conventional attenuation radiography. Moiré deflectometry using the Talbot-Lau grating interferometer setup is an attractive HED diagnostic due to its high sensitivity to refraction indu...
Article
Full-text available
We present results from a pulsed capillary ns discharge source, operated in Nitrogen and N/He mixtures, in an alumina capillary 2.1mm long with outer diameter of 6.3mm and inner diameter of 1.6mm. The electrical energy stored is 0.5J with peak current of 6kA. Fast charging from an IGBT based pulsed power circuit allows operation at 35-600 Hz with v...
Article
Full-text available
A fast nanosecond capillary discharge for fast repetition rate operation has been designed and tested. Operated in Ar and Ar/He mixtures X-ray emission from ionization stages from Ar VIII to XII have been observed according to capillary dimensions and operating voltages. Intense electron beams are formed as a result of the transient hollow cathode...
Conference Paper
Phase-contrast x-ray diagnostics can detect density gradients in low-Z matter with the sensitivity and spatial resolution necessary to characterize High Energy Density Plasma (HEDP) experiments. Talbot-Lau interferometry measures x-ray beam angular deviations due to refraction index gradients along its path and can simultaneously provide x-ray atte...
Article
Full-text available
X-ray phase-contrast radiography could better characterize highly localized density gradients expected in High Energy Density (HED) plasma experiments than conventional attenuation radiography. In particular, the Talbot-Lau (TL) grating interferometer, which works with extended and polychromatic x-ray sources, is a potentially attractive HED diagno...
Article
Full-text available
We report on experimental observations of pulsed capillary discharges aimed at soft x-ray production within the water-window range. Through systematical studies of capillary tube characteristics and discharge conditions, radiation emission was analysed. Plasma properties were studied by means of spectrometry, wide-band PIN diode signals and plasma...
Conference Paper
Phase-contrast x-ray imaging techniques can detect density gradients in low-Z matter with the sensitivity and spatial resolution necessary to characterize High Energy Density Laboratory Plasma (HEDLP) experiments. The Talbot-Lau interferometer measures x-ray beam angular deviations due to refraction index gradients along its path, thus making it an...
Conference Paper
form only given. We present results examining the dynamics of low current (25kA), long rise-time (400 ns) X-pinches. These are the lowest parameters yet used for X-pinch experiments. The X-pinches comprised either 2 or 4 wires of 5μm tungsten. We analyze coronal and axial plasma dynamics, cross-point evolution, X-ray emission, and post-pinching dis...
Article
We report on experiments examining the dynamics of low current (25 kA), long rise-time (400 ns) X-pinches. The experiments used two- and four-wire 5 μm tungsten X-pinches. We discuss coronal plasma dynamics, X-ray emission, cross-point evolution, and axial column dynamics. We show that the pinch dynamics are akin to those in X-pinches driven by 0.1...
Conference Paper
form only given. A series of observations using soft X-rays and optical techniques diagnose key plasma parameters in a low inductance large aspect ratio fast capillary discharge. The capillary discharge is operated with less than 1 Joule of stored electrical energy and is designed for fast repetition rate operation. Peak current is between 5 and 8...
Article
Full-text available
We present observations of the emission characteristics of the plasma processes of a low inductance, sub Joule, compact capillary discharge, when operated in nitrogen at up to 600 Hz. A quarter period of under 10 ns is achieved allowing currents of order 5 kA. Four geometries are explored: two lengths, 21 and 36 mm, and two internal diameters, 1.6...
Article
We report on experiments with two planar arrays consisting of four nickel wires in each array to study advection of current to the precursor plasma. The linear transformer driver GenASIS was used to deliver a peak current of 200 kA with 150 ns rise-time. Laser probing along and across the wire arrays provided time evolution information of the varia...
Article
We present experimental data from laser cut X-pinches in an effort to develop a reliable and efficient X-ray backlighting source for the characterization of ICF capsules. Temporal and spatial resolution of the pinch is resolved using wideband Si diodes and time integrated x-ray pinhole cameras respectively. A comparison is made between laser cut an...
Article
form only given. Soft x-ray emission characteristics from a compact pulsed capillary ns discharge are described for a hollow cathode discharge operating in N/He gas mixtures. Different configurations with alumina and nitride capillaries of 21 and 36 mm in length and inner diameters of 1.6 and 3.2 mm were studied. Fast charging from an IGBT based pu...
Article
Full-text available
We present the experimental details and results from a low energy but high repetition rate compact plasma capillary source for extreme ultraviolet and soft x-ray research and applications. Two lengths of capillary are mounted in two versions of a closely related design. The discharge operates in 1.6 and 3.2 mm inner diameter alumina capillaries of...
Article
Full-text available
We analyze experimental results of radiation emission from a compact pulsed capillary ns discharge source, designed for soft x-ray applications, operated in Nitrogen and N/He mixtures at voltages in the range of 18-24kV. The discharge operates in an alumina capillary of length 21mm and 1.6mm inner diameter. The electrical energy stored is ~0.5 J wi...
Article
The capillary discharge is a very bright radiation source. When operated as a ns discharge at a peak current of order 10 kA and at a high repetition rate of order 200 Hz a very bright source at 13.5 nm is obtained. We present a series of observations that will extend the use of the discharge as a source of He-like nitrogen emission at 2.89 nm as a...
Article
We present experimental observations on a z-pinch plasma formed within a conducting coil. The experiment aims to produce a single component x-ray emitting titanium plasma. The z-pinch is formed inside a thin wall titanium coil, which act as the load of a small pulsed power generator, with a nominal 150 kA, 120 ns pulse. The coil pitch is chosen so...
Article
Full-text available
We present experimental results on the formation of a Titanium z-pinch plasma inside a thin wall Titanium coil, which is the load of a small pulsed power generator, with a nominal 180 kA pulse. The coil pitch is such that the inductive impedance is high enough on the time scale of the experiment for a current path along the pinch axis to be preferr...

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