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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,639 records · Page 91
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Calculating shock Hugoniot and isentropes using multiphase equation of state tables and application to shock and release of diamond ablators in inertial confinement fusion implosions

Advances in shock and ramp compression techniques now allow experimental access to unprecedented extreme conditions of pressure and temperature, providing a means to test theoretical models. Here, we describe a simple methodology to compute multi-phase shock Hugoniot and isentropes using multiphase equation of state tables. We treat explicitly the phase coexistence along the phase boundary to reveal the evolution of the sample as it undergoes the phase transformation in adiabatic conditions. We illustrate the method by calculating the predicted shock and shock-and-release behavior of diamond at conditions relevant for the initial stage of inertial confinement fusion implosions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Surface, structural and mechanical properties of zirconium ablated by KrF excimer laser radiation

We study the effect of the ambient – dry (air) and wet (propanol) – environment on the surface, structural and mechanical properties of zirconium samples after irradiation with a KrF excimer laser (wavelength of 248 nm, pulse duration of 20 ns and repetition rate of 20 Hz). The samples are exposed to an increasing number of laser pulses varying from 500 to 2000 in both media. Various features of the treated targets such as surface morphology, chemical composition, crystalline structure and hardness are analysed by complementary characterisation techniques, such as scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), Raman spectroscopy and Vickers hardness tester, respectively. Surface morphology and hardness are explained on the basis of modifications in crystalinity, residual pressures and chemical properties of the sample surface after its irradiation. (interaction of laser radiation with matter)

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Humidity determines snowpack ablation under a warming climate

Significance Changes in the amount and timing of snowmelt have large effects on water for society and ecosystems. Using long-term records from across the western United States, we demonstrate that atmospheric humidity is a major control on how seasonal snow responds to warming temperatures. Specifically, we observe an increase in the frequency and magnitude of episodic winter melt events under higher humidity that may alter the timing of water availability. In lower-humidity regions, however, warming is associated with increased sublimation and/or evaporation from the snowpack further reducing the amount of available water in these dry regions. Management approaches to address these changes in snowmelt water resources from continued warming will require improved estimation of variable and changing atmospheric humidity.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

Systematic Source Determination and X-Ray Radiography Detection of Nonuniformities on High-Density Carbon Ablators

Recent deuterium-tritium (D-T)–layered implosion experiments at the National Ignition Facility have achieved a burning plasma and >1-MJ neutron yield. A series of repeat experiments have shown that the degree of performance is very likely dependent on capsule quality, including the quantity of what are collectively termed “high- Z particles.” These particles are detected on a custom-built radiography system, known as the Sagometer, during the final target qualification process. The term particles is misleading, as the source of these nonuniformities in the capsule images is uncertain; the term detection will be used instead. An increased number of D-T targets have been rejected at the final stages of production due to Sagometer detections. Late detections are deleterious in terms of loss of production parts, effort, and overall operating efficiency. In response, we undertook an effort to determine the origin of these detections and to ultimately mitigate target losses caused by them. Through careful testing and analysis, we have determined neither insufficient production cleanliness nor hohlraum shedding is responsible for the detections on the capsule. Here, we determined that the detections are inherent to the capsule and have made efforts to use the Zeiss Xradia to identify them earlier in the production process. While testing revealed the Xradia is not currently sufficient for identifying such particles using radiography images, we continue to look to other forms of metrology to down select the capsules early in the process.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2013

Observation of Self-Similarity in the Magnetic Fields Generated by the Ablative Nonlinear Rayleigh-Taylor Instability

Magnetic fields generated by the nonlinear Rayleigh-Taylor growth of laser-seeded three-dimensional broadband perturbations were measured in laser-accelerated planar targets using ultrafast proton radiography. The experimental data show self-similar behavior in the growing cellular magnetic field structures. These observations are consistent with a bubble competition and merger model that predicts the time evolution of the number and size of the bubbles, linking the cellular magnetic field structures with the Rayleigh-Taylor bubble and spike growth.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Dosimetric comparison of flattened and unflattened beams for stereotactic ablative radiotherapy of stage I non-small cell lung cancer

Purpose: To compare contribution and accuracy of delivery for two flattening filter free (FFF) beams of the nominal energy 6 and 10 MV and a 6 MV flattened beam for early stage lung cancer. Methods: For each of 11 patients with stage I nonsmall cell lung cancer three volumetric modulated arc therapy plans were prepared utilizing a 6 MV flattened photon beam (X6FF) and two nonflattened beams of nominal energy 6 and 10 MV (X6FFF, X10FFF). Optimization constraints were set to produce dose distributions that meet the criteria of the RTOG-0915 protocol. The radiation schedule used for plan comparison in all patients was 50 Gy in five fractions. Dosimetric parameters of planning target volume (PTV) and organs-at-risk and delivery times were assessed and compared. All plans were subject to verification using Delta{sup 4} unit (Scandidos, Sweden) and absolutely calibrated gafchromic films in a thorax phantom. Results: All plans had a qualitatively comparable outcome. Obtained dose distributions were conformal (CI < 1.17) and exhibited a steep dose fall-off outside the PTV. The ratio of monitor units for FFF versus FF plans in the authors' study ranged from 0.95 to 1.21 and from 0.93 to 1.25 for X6FFF/X6FF and X10FFF/X6FF comparisons, respectively. The ratio systematically increased with increasing size of the PTV (up to +25% for 150 cm{sup 3} PTV). Yet the integral dose to healthy tissue did not follow this trend. Comparison of cumulative dose volume histograms for a patient's body showed that X6FFF plans exhibit improved conformity and reduced the volume of tissue that received more than 50% of the prescription dose. Parameters related to dose gradient showed statistically significant improvement. CI{sub 50%}, CI{sub 60%}, CI{sub 80%}, and CI{sub 100%} were on average reduced by 4.6% (p < 0.001), 4.6% (p = 0.002), 3.1% (p = 0.002), and 1.2% (p = 0.039), respectively. Gradient measure was on average reduced by 4.2% (p < 0.001). Due to dose reduction in the surrounding lung tissue, the V{sub 20} {sub Gy} and V{sub 12.5} {sub Gy} were reduced by 5.5% (p = 0.002) and 4.5% (p < 0.001). These dosimetric improvements in the fall-off were not observed for the X10FFF plans. Differences in sparing of normal tissues were not found to be statistically significant for either of the two FFF beams. Mean beam-on times were 111 s (2SD = 11 s) for X10FFF, 128 s (2SD = 19 s) for X6FFF, and X6FF plans required on average 269 s (2SD = 71 s). While the mean dose rate was 1555 ± 264 and 1368 ± 63 MU/min, for X10FFF and X6FFF, plans using the conventional X6FF were delivered with the constant maximum dose rate of 600 MU/min. Verification of all plans showed acceptable and comparable results for all plans in homogeneous as well as heterogeneous phantoms. Mean GS (3%, 2 mm) using the Delta{sup 4} phantom were 98.9% (2SD = 3.2%), 99.2% (2SD = 2.3%), and 99.2% (2SD = 2.3%) for X6FFF, X6FF, and X10FFF modalities. Verification using a thorax phantom showed GS > 98% in all cases. Conclusions: The use of FFF beams for stereotactic radiation therapy of nonsmall cell lung cancer patients yielded dose distributions qualitatively comparable to flattened beams and significantly reduced treatment delivery time. Utilizing the X6FFF beam improved conformity of dose distribution. On the other hand, X10FFF beam offered a slight improvement in treatment efficiency, and lower skin and peripheral dose. All effects were relatively small.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2014

Simulation study of the effects of near- and far-field heating during focused ultrasound uterine fibroid ablation using an electronically focused phased array: A theoretical analysis of patient safety

Purpose: Assess the feasibility of using large-aperture, flat ultrasonic transducer arrays with 6500 small elements operating at 500 kHz without the use of any mechanical components for the thermal coagulation of uterine fibroids. This study examines the benefits and detriments of using a frequency that is significantly lower than that used in clinical systems (1–1.5 MHz). Methods: Ultrasound simulations were performed using the anatomies of five fibroid patients derived from 3D MRI. Using electronic steering solely, the ultrasound focus from a flat, 6500-element phased array was translated around the volume of the fibroids in various patterns to assess the feasibility of completing full treatments from fixed physical locations. Successive temperature maps were generated by numerically solving the bioheat equation. Using a thermal dose model, the bioeffects of these simulations were quantified and analyzed. Results: The simulations indicate that such an array could be used to perform fibroid treatments to 18 EM{sub 43} at an average rate of 90 ± 20 cm{sup 3}/h without physically moving the transducer array. On average, the maximum near-field thermal dose for each patient was below 4 EM{sub 43}. Fibroid tissue could be treated as close as 40 mm to the spine without reaching temperatures expected to cause pain or damage. Conclusions: Fibroids were successfully targeted and treated from a single transducer position to acceptable extents and without causing damage in the near- or far-field. Compared to clinical systems, treatment rates were good. The proposed treatment paradigm is a promising alternative to existing systems and warrants further investigation.

60 APPLIED LIFE SCIENCES↗