High-pressure synchrotron x-ray diffraction and vibrational spectroscopy (infrared absorption and Raman) in a diamond-anvil cell have been performed for polyethylene samples at pressures up to ∼10 GPa. These two techniques yield complementary information on the inter- and intra-molecular bonds and how they change as a function of volume. Three different samples of polyethylene were examined, including a high-density polyethylene, an ultra-high molecular weight polyethylene, and a crosslinked polyethylene. The diffraction peaks for the common orthorhombic Pnam phase continuously decreases in intensity as the pressure is increased and become unobservable at high pressure, while those for a monoclinic A2/m impurity phase initially present in all three samples remain relatively constant in intensity. The monoclinic A2/m phase has two chains per unit cell, as does the ambient pressure orthorhombic Pnam phase, which is consistent with the lack of a change in the vibrational mode splitting patterns as pressure is increased and the monoclinic phase becomes dominant. In addition, the pressure-induced correlation splitting of the infrared active C–H stretching vibrational modes has been observed for the first time.

Gas puff Z-pinches are intense sources of X-rays and neutrons but are highly susceptible to the magneto-Rayleigh-Taylor instability (MRTI). MRTI mitigation is critical for optimal and reproducible yields, motivating significant attention toward various potential mitigation mechanisms. One such approach is the external application of an axial magnetic field, which will be discussed here in the context of recent experiments on the Zebra generator (1 MA, 100 ns) at the University of Nevada, Reno. In these experiments, an annular Kr gas liner is imploded onto an on-axis deuterium target with a pre-embedded axial magnetic field Bz0 ranging from 0 to 0.3 T. The effect of Bz0 on the stability of the Kr liner is evaluated with measurements of plasma radius, overall instability amplitude, and dominant instability wavelength at different times obtained from time-gated extreme ultraviolet pinhole images. It was observed that the external axial magnetic field does not affect the implosion velocity significantly and that it reduces the overall instability amplitude and the presence of short-wavelength modes, indicating improved pinch stability and reproducibility. For the highest applied Bz0=0.3 T, the stagnation radius measured via visible streak images was found to increase. These findings are consistent with experiments reported in the literature, but here, the Bz0 required for stability, Bz0=0.13 Ipk/R0 (where Ipk is the driver peak current and R0 is the initial radius), is lower. This could be attributed to the smaller load geometry, both radially and axially. Consistent with other experiments, the cause of decreased convergence cannot be explained by the additional axial magnetic pressure and remains an open question.

We offer a theoretical and experimental study of the single-photon photoionization of Ne III. The high photon flux and the high-resolution capabilities of the Advanced Light Source at the LBNL were employed to measure absolute photoionization cross sections. The resulting spectrum has been benchmarked against high accuracy relativistic Breit-Pauli R-matrix calculations. A large close-coupling wave function expansion which comprises up to 58 fine-structure levels of the residual ion Ne IV of configurations 2s22p3, 2s2p4, 2p5, 2s22p23s, 2s22p23p and 2s22p23d was included. A complete identification of the measured features was achieved by considering seven low-lying levels of Ne III. We found that the photoionization cross-section (σPI) exhibits the presence of prominent resonances in the low-energy region near the ionization thresholds that correspond to low-lying levels. These include high-peak narrow resonances with almost zero background introduced by relativistic effects. However, there does not exist a significant contribution to σPI from relativistic effects at the high-energy interval of the present study.

Recent experiments on the 1 MA, 100 ns Zebra driver at the Nevada Terawatt Facility at the University of Nevada, Reno, investigated the compression of a deuterium target by a high-atomic-number (Ar or Kr) gas-puff liner. Pinch stability improved with axial premagnetization of 1–2 kG observed as a decrease in magneto-Rayleigh-Taylor instability growth. Implosion dynamics and stagnation conditions were studied computationally with the radiation-MHD code MACH2 using initial conditions that approximate those in the experiment. Typical average and peak implosion velocities exceeded 300 and 400 km/s, respectively, which raised the target adiabat by shock heating as the front converges on axis, at which time the target is adiabatically compressed to stagnation. Experimental fusion yields of up to 2 × 109 for Ar liner on D target implosions were measured, while with a Kr liner yields up to 1 × 1010 were measured. Higher yields in Kr compared to Ar were also calculated in 2-D MACH2 simulations. These observations will be further tested with other radiation-MHD codes, and experiments on the 1 MA LTD-III machine at UC San Diego.

Aluminum oxide (Al2O3) plasma was generated using the Ti:Sapphire/Nd:glass laser and Z-pinch pulse-power generator at the University of Nevada, Reno, Nevada Terawatt Facility. To determine the electron temperature, we use the Boltzmann plot method for the transitions (Al III 4d 2D3/2 → 4p 2P1/2) at 451.2564 nm, (Al III 4d 2D5/2 → 4p 2P3/2) at 452.9194 nm, (Al III 4p 2P3/2 → 4s 2S1/2) at 569.6603, and (Al III 4p 2P1/2 → 4s 2S1/2) at 572.2728 nm. Simultaneously, Mach–Zehnder laser interferometry was used to measure the electron number density. We compared simulated spectra obtained from PrismSPECT with electron number density and temperature measurements, and the electron temperature was found to range from 1.8 to 2.8 eV, while the electron number density was found to range from 2.3 × 1017 to 6.9 × 1017 cm−3 early in the pinched plasma formation.

We present the first experimental measurement of temperature and density of a warm dense plasma produced by a pulsed power driver at the Nevada Terawatt Facility (NTF). In the early phases of discharge, most of the mass remains in the core, and it has been challenging to diagnose with traditional methods, e.g. optical probing, because of the high density and low temperature. Accurate knowledge of the transport coefficients as well as the thermodynamic state of the plasma is important to precisely test or develop theoretical models. Here, we have used spectrally resolved non-collective X-ray Thomson scattering to characterize the dense core region. We used a graphite load driven by the Zebra current generator (0.6 MA in 200 ns rise time) and the Ti He-α line produced by irradiating a Ti target with the Leopard laser (30 J, 0.8 ns) as an X-ray probing source. Using this configuration, we obtained a signal-to-noise ratio ~2.5 for the scattered signal. By fitting the experimental data with predicted spectra, we measured T = 2±1.9 eV, ρ = 0.6±0.5 gr/cc, 70 ns into the current pulse. The complexity of the dense core is revealed by the electrons in the dense core that are found to be degenerate and weakly coupled, while the ions remain highly coupled.

The objectives of this tutorial are as follows: 1) to help students and researchers develop a basic understanding of how pulsed-power systems are used to create high-energy-density (HED) matter; 2) to develop a basic understanding of a new, compact, and efficient pulsed-power technology called linear transformer drivers (LTDs); 3) to understand why LTDs are an attractive technology for driving HED physics (HEDP) experiments; 4) to contrast LTDs with the more traditional Marx-generator/ pulse-forming-line approach to driving HEDP experiments; and 5) to briefly review the history of LTD technology as well as some of the LTD-driven HEDP research presently underway at universities and research laboratories across the globe. This invited tutorial is part of the Mini-Course on Charged Particle Beams and High-Powered Pulsed Sources, held in conjunction with the 44th International Conference on Plasma Science in May of 2017.

In many Z-pinch experiments, the magneto Rayleigh-Taylor instability and other MHD instabilities are potentially disruptive to the pinch. It has been demonstrated that multi -shell Z- pinch loads and an externally-applied axial magnetic field can mitigate these instabilities 1 . An external magnetic field has been applied in Staged Z-pinch 2 (SZP), where a high-atomic-number gas liner (Ar or Kr) implodes onto a deuterium target in cylindrical geometry.

This report compiles multiple articles describing activities developed and performed under the Site-Directed Research and Development Program for the benefit the Nation during Fiscal Year 2018. Sustained investment and ongoing core innovation are the keys to successful research and development programs. These elements drive the Site-Directed Research and Development (SDRD) Program and provide solutions to some of the most challenging problems our nation and our allies face. Our Nevada enterprise, consisting of both our management and operating entity and our NNSA field office, is aggressively investing in SDRD and injecting innovation through strategic partnerships. Our partnerships with universities, industry, and our sister institutions within the National Nuclear Security Administration (NNSA) build upon our core capabilities and allow us to create innovative solutions to support our mission requirements. In 2018, we raised the investment level of SDRD for only the second time in the history of the program. Nearly at our congressionally authorized limit, SDRD has substantial resources to successfully address numerous issues. Investment is only one part of the equation; innovation is generated through collaborations that bring discovery and provide the “technical differentiation” and the return on investment we seek. This report demonstrates an enduring theme of how partnerships help us drive the best outcomes and provide the maximum impact possible, while using our resources efficiently.

An experimental platform for the studying of high-intensity laser plasma interactions in strong magnetic fields has been developed based on the 1 MA Zebra pulsed power generator coupled with the 50-TW Leopard laser. The Zebra generator produces 100-300 T longitudinal and transverse magnetic fields with different types of loads. The Leopard laser creates plasma at an intensity of 1019 W/cm2 in the magnetic field of coil loads. Focusing and targeting systems are integrated in the vacuum chamber of the pulsed power generator and protected from the plasma debris and strong mechanical shock. The first experiments with plasma at laser intensity >2 × 1018 W/cm2 demonstrated collimation of the laser produced plasma in the axial magnetic field strength >100 T.

Recent experiments at the Nevada Terawatt Facility at UNR show evidence of uniform compression of a deuterium plasma target compressed by a high-Z, Argon or Krypton gas-puffed liner. Pinch stability is improved by seeding the implosion with a 0.1-0.2 T axial magnetic field. Implosion dynamics and stagnation conditions are also studied computationally with the radiation-MHD code MACH2, using in itial conditions similar to those in the experiment. Simulations show that magnetic field diffuses through the outer shell and piles up at the interface providing narrow profile, high intensity current that Ohm-icly preheats the target. This secondary piston launches a shock wave in the target plasma that heats the several 100 eV. Finally, the preheated target is adiabatically compressed to stagnation. Simulations show: (a) more pronounced preheating with Kr than Ar, (b) the axial magnetic field is compressed only in the shocked target and in the liner plasma, providing greater magneto-Rayleigh-Taylor mitigation during run-in compared to the self-similar model. For typical Ar liner on D target experiments we measured neutron yield up to 2x 10 9 and for Kr liner, up to 9x 10 9 .

Relative cross sections for the valence shell photoionisation (PI) of S-2 ground level and 2D metastable Ca+ ions were measured with high energy resolution by using the ion-photon merged-beams technique at the Advanced Light Source. Overview measurements were performed with a full width at half maximum bandpass of Delta E = 17 meV, covering the energy range 20-56. eV. Details of the PI spectrum were investigated at energy resolutions reaching the level of Delta E = 3.3 meV. The photon energy scale was calibrated with an uncertainty of +/- 5. meV. By comparison with previous absolute measurements the present experimental high-resolution data were normalized to an absolute cross-section scale and the fraction of metastable Ca+ ions that were present in the parent ion beam was determined to be 18% +/- 4%. Large-scale R-matrix calculations using the Dirac Coulomb approximation and employing 594 levels in the closecoupling expansion were performed for the Ca+(3s(2)3p(6)4s S-2(1/2)) and Ca+(3s(2)3p(6)3d D-2(3/2,5/2))levels. The experimental data are compared with the results of these calculations and previous theoretical and experimental studies.

An experimental and theoretical study of the single photoionization cross section of the P+ cation of phosphorus is presented. Photoionization (PI) cross sections are instrumental for the determination of abundances in the interstellar medium. The experiment was performed by merging an ion beam with a photon beam. The photon beam was nearly monochromatic and had an energy resolution of 24meV. Calculations were carried out using the Breit–Pauli R-matrix method. The combined study was developed in the photon energy interval from 18eV (68.9nm) to 50eV (24.8nm). Comparison between the measured and the calculated cross section shows good agreement in general and identifies features of the process and existence of states in the experimental beam. The present results should provide for more accurate modeling of P+.

We are developing a novel diagnostic for measurement of bulk fluid motion in materials, that is particularly applicable to very hot, x-ray emitting plasmas in the High Energy Density Physics (HEDP) regime. The X-ray Doppler Velocimetry (XDV) technique relies on monochromatic imaging in multiple x-ray energy bands near the center of an x-ray emission line in a plasma, and utilizes bent imaging crystals. Higher energy bands are preferentially sensitive to plasma moving towards the viewer, while lower energy bands are preferentially sensitive to plasma moving away from the viewer. Combining multiple images in different energy bands allows for a reconstruction of the fluid velocity field integrated along the line of sight. We review the technique, and we discuss progress towards benchmarking the technique with proof-of-principle HEDP experiments.