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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 973 records · Page 54
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Experimental verification of the capillary plasma triggered long spark gap under the extremely low working coefficient in air

The paper has proposed a new triggering method for long spark gap based on capillary plasma ejection and conducted the experimental verification under the extremely low working coefficient, which represents that the ratio of the spark gap charging voltage to the breakdown voltage is particularly low. The quasi-neutral plasma is ejected from the capillary and develops through the axial direction of the spark gap. The electric field in the spark gap is thus changed and its breakdown is incurred. It is proved by the experiments that the capillary plasma ejection is effective in triggering the long spark gap under the extremely low working coefficient in air. The study also indicates that the breakdown probabilities, the breakdown delay, and the delay dispersion are all mainly determined by the characteristics of the ejected plasma, including the length of the plasma flow, the speed of the plasma ejection, and the ionization degree of the plasma. Moreover, the breakdown delay and the delay dispersion increase with the length of the long spark gap, and the polarity effect exists in the triggering process. Lastly, compared with the working patterns of the triggering device installed in the single electrode, the working pattern of the devices installed in both the two electrodes, though with the same breakdown process, achieves the ignition under longer gap distance. To be specific, at the gap length of 14 cm and the working coefficient of less than 2%, the spark gap is still ignited accurately.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Verification of BOUT++ by the method of manufactured solutions

BOUT++ is a software package designed for solving plasma fluid models. It has been used to simulate a wide range of plasma phenomena ranging from linear stability analysis to 3D plasma turbulence and is capable of simulating a wide range of drift-reduced plasma fluid and gyro-fluid models. A verification exercise has been performed as part of a EUROfusion Enabling Research project, to rigorously test the correctness of the algorithms implemented in BOUT++, by testing order-of-accuracy convergence rates using the Method of Manufactured Solutions (MMS). We present tests of individual components including time-integration and advection schemes, non-orthogonal toroidal field-aligned coordinate systems and the shifted metric procedure which is used to handle highly sheared grids. The flux coordinate independent approach to differencing along magnetic field-lines has been implemented in BOUT++ and is here verified using the MMS in a sheared slab configuration. Finally, we show tests of three complete models: 2-field Hasegawa-Wakatani in 2D slab, 3-field reduced magnetohydrodynamics (MHD) in 3D field-aligned toroidal coordinates, and 5-field reduced MHD in slab geometry.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Calculation and experimental verification of a collimator with a Kerr lens for fibre laser mode locking

We present the calculation and experimental verification of the operation of a collimator coupling a light beam into an optical fibre with an As{sub 2}S{sub 3} nonlinear plate. It is shown that a Kerr lens formed in the plate with an increase in the peak pulse power leads to an increase in the output coupling ratio by about 15%, which can be used for the passive mode locking of a fibre laser. (lasers)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Experimental demonstration of an isotope-sensitive warhead verification technique using nuclear resonance fluorescence

Significance We present an experimental demonstration of an isotope-sensitive warhead verification protocol. The measurement is capable of detecting tampering with a warhead’s material or geometry with high statistical confidence in realistically attainable measurement times, while simultaneously protecting sensitive warhead design information. Such a protocol could enable the verifiable elimination of nuclear warheads under a future arms reduction treaty.

45 MILITARY TECHNOLOGY, WEAPONRY, AND NATIONAL DEF↗
DOE OSTI2015

A HYDROCHEMICAL HYBRID CODE FOR ASTROPHYSICAL PROBLEMS. I. CODE VERIFICATION AND BENCHMARKS FOR A PHOTON-DOMINATED REGION (PDR)

A two-dimensional hydrochemical hybrid code, KM2, is constructed to deal with astrophysical problems that would require coupled hydrodynamical and chemical evolution. The code assumes axisymmetry in a cylindrical coordinate system and consists of two modules: a hydrodynamics module and a chemistry module. The hydrodynamics module solves hydrodynamics using a Godunov-type finite volume scheme and treats included chemical species as passively advected scalars. The chemistry module implicitly solves nonequilibrium chemistry and change of energy due to thermal processes with transfer of external ultraviolet radiation. Self-shielding effects on photodissociation of CO and H{sub 2} are included. In this introductory paper, the adopted numerical method is presented, along with code verifications using the hydrodynamics module and a benchmark on the chemistry module with reactions specific to a photon-dominated region (PDR). Finally, as an example of the expected capability, the hydrochemical evolution of a PDR is presented based on the PDR benchmark.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Prompt gamma timing range verification for scattered proton beams

Range verification is a very important point in order to fully exploit the physical advantages of protons compared to photons in cancer irradiation. Recently, a simple method has been proposed which makes use of the time of fight of protons in tissue and the promptly emitted secondary photons along the proton path (Prompt Gamma Timing, PGT). This has been considered so far for monoenergetic pencil beams only. In this work, it has been studied whether this technique can also be applied in passively formed irradiation fields with a so called spread out Bragg peak. Time correlated profiles could be recorded, which show a trend that is consistent with theoretical predictions. (authors)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Studies of a Proton Bunch Phase Monitor for Range Verification in Proton Therapy

A primary subject of the present research in particle therapy is to ensure the precise irradiation of the target volume. The prompt gamma timing (PGT) method provides one possibility for in vivo range verification during the irradiation of patients. Prompt gamma rays with high energies are emitted promptly due to nuclear reactions of protons with tissue. The arrival time of these gammas to the detector reflects the stopping process of the primary protons in tissue and is directly correlated to the range. Due to the time resolution of the detector and the proton bunch time spread, as well as drifts of the bunch phase with respect to the accelerator frequency, timing spectra are smeared out and compromise the accuracy of range information intended for future clinical applications. Nevertheless, counteracting this limitation and recovering range information from the PGT measured spectra, corrections using a bunch phase monitor can be performed. A first prototype of bunch phase monitor was tested at GSI Darmstadt, where measurements of the energy correlation profile of the ion bunches were performed. At the ELBE accelerator at Helmholtz-Zentrum Dresden-Rossendorf (HZDR), set up to provide bremsstrahlung photons in very short pulses, a constant fraction algorithm for the incoming digital signals was evaluated, which is used for optimizing the time resolution. Studies of scattering experiments with different thin targets and detector positions are accomplished at Onco Ray Dresden, where a clinical proton beam is available. These experiments allow a basic characterization of the proton bunch structure and the detection yield. (authors)

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2021

Electrical Measurement and Verification of Energy in DC Buildings

Today's selection of DC buildings features a diverse set of electrical topologies and turnkey solutions, and each has specific design trade-offs and optimizations. Designers desperately need standardized metrics and procedures for measurement and verification (M&V) to analyze and compare the advantages of each DC solution to traditional AC building networks. This work develops the Measurement-Informed Modeling (MIM) method, which can be used to determine full-building efficiency and energy savings. The MIM M&V procedure develops a building model, and refines the model with metered data. This work demonstrates the MIM method by measuring the full-building efficiency of two DC buildings operated by the Institute of Building Research in Shenzhen, China. The MIM procedure can ultimately be used to compare and improve the efficiency of various DC topologies.

buildings↗
DOE OSTI2013

A Run-Time Verification Framework for Smart Grid Applications Implemented on Simulation Frameworks

Smart grid applications are implemented and tested with simulation frameworks as the developers usually do not have access to large sensor networks to be used as a test bed. The developers are forced to map the implementation onto these frameworks which results in a deviation between the architecture and the code. On its turn this deviation makes it hard to verify behavioral constraints that are de- scribed at the architectural level. We have developed the ConArch toolset to support the automated verification of architecture-level behavioral constraints. A key feature of ConArch is programmable mapping for architecture to the implementation. Here, developers implement queries to identify the points in the target program that correspond to architectural interactions. ConArch generates run- time observers that monitor the flow of execution between these points and verifies whether this flow conforms to the behavioral constraints. We illustrate how the programmable mappings can be exploited for verifying behavioral constraints of a smart grid appli- cation that is implemented with two simulation frameworks.

Architecture baed testing↗
DOE OSTI2016

The escape of high explosive products: An exact-solution problem for verification of hydrodynamics codes

This paper documents the escape of high explosive (HE) products problem. The problem, first presented by Fickett & Rivard, tests the implementation and numerical behavior of a high explosive detonation and energy release model and its interaction with an associated compressible hydrodynamics simulation code. The problem simulates the detonation of a finite-length, one-dimensional piece of HE that is driven by a piston from one end and adjacent to a void at the other end. The HE equation of state is modeled as a polytropic ideal gas. The HE detonation is assumed to be instantaneous with an infinitesimal reaction zone. Via judicious selection of the material specific heat ratio, the problem has an exact solution with linear characteristics, enabling a straightforward calculation of the physical variables as a function of time and space. Lastly, implementation of the exact solution in the Python code ExactPack is discussed, as are verification cases for the exact solution code.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2011

In vivo real-time dosimetric verification in high dose rate prostate brachytherapy

Purpose: To evaluate the performance of a diode array in the routine verification of planned dose to points inside the rectum from prostate high dose rate (HDR) brachytherapy using a real-time planning system. Methods: A dosimetric study involving 28 patients was undertaken where measured doses received during treatment were compared to those calculated by the treatment planning system (TPS). After the ultrasound imaging required for treatment planning had been recorded, the ultrasound probe was replaced with a geometric replica that contained an 8 mm diameter cylindrical cavity in which a PTW diode array type 9112 was placed. The replica probe was then positioned inside the rectum with the individual diode positions determined using fluoroscopy. Dose was then recorded during the patients' treatment and compared to associated coordinates in the planning system. Results: Factors influencing diode response and experimental uncertainty were initially investigated to estimate the overall uncertainty involved in dose measurements, which was determined to be {+-}10%. Data was acquired for 28 patients' first fractions, 11 patients' second fractions, and 13 patients' third fractions with collection dependent upon circumstances. Deviations between the diode measurements and predicted values ranged from -42% to +35% with 71% of measurements experiencing less than a 10% deviation from the predicted values. If the {+-}10% measurement uncertainty was combined with a tolerated dose discrepancy of {+-}10% then over 95% of the diode results exhibited agreement with the calculated data to within {+-}20%. It must also be noted that when large dose discrepancies were apparent they did not necessarily occur for all five diodes in the one measurement. Conclusions: This technique provided a method that could be utilized to detect gross errors in dose delivery of a real-time prostate HDR plan. Limitations in the detection system used must be well understood if meaningful results are to be achieved.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2011

Spatial correlation of proton irradiation-induced activity and dose in polymer gel phantoms for PET/CT delivery verification studies

Purpose: This work demonstrates a novel application of BANG3-Pro2 polymer gel dosimeter as a dosimetric phantom able to accurately capture both dose and induced activity. Methods: BANG3-Pro2 dosimeters were irradiated with a clinical proton beam using an unmodulated beam and a spread-out Bragg peak (SOBP) modulation, the latter with a Lucite compensator to introduce a range offset in one quadrant of the circular field. The dosimeters were imaged in a nearby positron emission tomography/computed tomography (PET/CT) unit starting within 5 min of beam-off. Induced positron emission (PE) activity along the central axis of the beam was compared to analytical calculations. Dose distributions were read out using an optical CT scanner and were validated against ion chamber measurements and the treatment plan. The offset between the distal fall-off of dose and activity (50% level) was determined over the entire irradiated field. Lateral profiles of PE were correlated to measured dose for the unmodulated beam delivery. Results: Measured profiles of PE activity along the central beam axis were found to be within 10% of the predictions of analytical calculations. The depth-dose profiles agreed with the reference values (ion chamber or treatment plan) within 3%. The offset between the depth profiles of dose and activity for the unmodulated beam was 8.4 {+-} 1.4 mm. For the compensator-based SOBP delivery, the distribution of offsets throughout the field was found to be bimodal, with the mean of 8.9 {+-} 2.8 mm for the thinner region of the compensator and 4.3 {+-} 2.5 mm for the thicker region. For the pristine beam delivery, lateral profiles of dose and activity were found to exhibit fair spatial correlation throughout the beam range, with the mean 2D gamma index of 0.42 and 91% of the evaluated pixels passing the test. Conclusions: This work presents the first demonstration of simultaneous and accurate experimental measurement of three-dimensional distributions of dose and induced activity and lays the groundwork for further investigations using BANG3-Pro2 as a dosimetric phantom in PET/CT delivery verification studies.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2012

Investigation of the spatial resolution of an online dose verification device

Purpose: The aim of this work is to characterize a new online dose verification device, COMPASS transmission detector array (IBA Dosimetry, Schwarzenbruck, Germany). The array is composed of 1600 cylindrical ionization chambers of 3.8 mm diameter, separated by 6.5 mm center-to-center spacing, in a 40 x 40 arrangement. Methods: The line spread function (LSF) of a single ion chamber in the detector was measured with a narrow slit collimator for a 6 MV photon beam. The 0.25 x 10 mm{sup 2} slit was formed by two machined lead blocks. The LSF was obtained by laterally translating the detector in 0.25 mm steps underneath the slit over a range of 24 mm and taking a measurement at each step. This measurement was validated with Monte Carlo simulation using BEAMnrc and DOSXYZnrc. The presampling modulation transfer function (MTF), the Fourier transform of the line spread function, was determined and compared to calculated (Monte Carlo and analytical) MTFs. Two head-and-neck intensity modulated radiation therapy (IMRT) fields were measured using the device and were used to validate the LSF measurement. These fields were simulated with the BEAMnrc Monte Carlo model, and the Monte Carlo generated incident fluence was convolved with the 2D detector response function (derived from the measured LSF) to obtain calculated dose. The measured and calculated dose distributions were then quantitatively compared using {chi}-comparison criteria of 3% dose difference and 3 mm distance-to-agreement for in-field points (defined as those above the 10% maximum dose threshold). Results: The full width at half-maximum (FWHM) of the measured detector response for a single chamber is 4.3 mm, which is comparable to the chamber diameter of 3.8 mm. The pre-sampling MTF was calculated, and the resolution of one chamber was estimated as 0.25 lp/mm from the first zero crossing. For both examined IMRT fields, the {chi}-comparison between measured and calculated data show good agreement with 95.1% and 96.3% of in-field points below {chi} of 1.0 for fields 1 and 2, respectively (with an average {chi} of 0.29 for IMRT field 1 and 0.24 for IMRT field 2). Conclusions: The LSF for a new novel online detector has been measured at 6 MV using a narrow slit technique, and this measurement has been validated by Monte Carlo simulation. The detector response function derived from line spread function has been applied to recover measured IMRT fields. The results have shown that the device measures IMRT fields accurately within acceptable tolerance.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2012

Automated radiotherapy treatment plan integrity verification

Purpose: In our clinic, physicists spend from 15 to 60 min to verify the physical and dosimetric integrity of radiotherapy plans before presentation to radiation oncology physicians for approval. The purpose of this study was to design and implement a framework to automate as many elements of this quality control (QC) step as possible. Methods: A comprehensive computer application was developed to carry out a majority of these verification tasks in the Philips PINNACLE treatment planning system (TPS). This QC tool functions based on both PINNACLE scripting elements and PERL sub-routines. The core of this technique is the method of dynamic scripting, which involves a PERL programming module that is flexible and powerful for treatment plan data handling. Run-time plan data are collected, saved into temporary files, and analyzed against standard values and predefined logical rules. The results were summarized in a hypertext markup language (HTML) report that is displayed to the user. Results: This tool has been in clinical use for over a year. The occurrence frequency of technical problems, which would cause delays and suboptimal plans, has been reduced since clinical implementation. Conclusions: In addition to drastically reducing the set of human-driven logical comparisons, this QC tool also accomplished some tasks that are otherwise either quite laborious or impractical for humans to verify, e.g., identifying conflicts amongst IMRT optimization objectives.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2012

EPID-based verification of the MLC performance for dynamic IMRT and VMAT

Purpose: In advanced radiotherapy treatments such as intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT), verification of the performance of the multileaf collimator (MLC) is an essential part of the linac QA program. The purpose of this study is to use the existing measurement methods for geometric QA of the MLCs and extend them to more comprehensive evaluation techniques, and to develop dedicated robust algorithms to quantitatively investigate the MLC performance in a fast, accurate, and efficient manner. Methods: The behavior of leaves was investigated in the step-and-shoot mode by the analysis of integrated electronic portal imaging device (EPID) images acquired during picket fence tests at fixed gantry angles and arc delivery. The MLC was also studied in dynamic mode by the analysis of cine EPID images of a sliding gap pattern delivered in a variety of conditions including different leaf speeds, deliveries at fixed gantry angles or in arc mode, and changing the direction of leaf motion. The accuracy of the method was tested by detection of the intentionally inserted errors in the delivery patterns. Results: The algorithm developed for the picket fence analysis was able to find each individual leaf position, gap width, and leaf bank skewness in addition to the deviations from expected leaf positions with respect to the beam central axis with sub-pixel accuracy. For the three tested linacs over a period of 5 months, the maximum change in the gap width was 0.5 mm, the maximum deviation from the expected leaf positions was 0.1 mm and the MLC skewness was up to 0.2 Degree-Sign . The algorithm developed for the sliding gap analysis could determine the velocity and acceleration/deceleration of each individual leaf as well as the gap width. There was a slight decrease in the accuracy of leaf performance with increasing leaf speeds. The analysis results were presented through several graphs. The accuracy of the method was assessed as 0.01 mm for both the gap size and peak position determination. Conclusions: This study provides fast, easy, and accurate test methods for routine QA of the MLC performance and helps in faster troubleshooting of MLC problems in both IMRT and VMAT treatments.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2012

The effects of incidence angle on film dosimetry and their consequences in IMRT dose verification

Purpose: The dosimetric accuracy of EDR2 radiographic film has been rigorously assessed in regular and intensity modulated beams for various incidence angles, including the parallel and perpendicular orientation. There clearly exists confusion in literature regarding the effect of film orientation. The primary aim is to clarify potential sources of the confusion and to gain physical insight into the film orientation effect with a link to radiochromic film as well. Methods: An inverse pyramid IMRT field, consisting of six regular and elongated 3 Multiplication-Sign 20 cm{sup 2} field segments, was studied in perpendicular and parallel orientation. Assessment of film self-perturbation and intrinsic directional sensitivity were also included in the experiments. Finally, the authors investigated the orientational effect in composite beams in the two extreme orientations, i.e., perpendicular and parallel. Results: The study of an inverse pyramid dose profile revealed good agreement between the perpendicular film and the diamond detector within 0.5% in the low-scatter regions for both 6 and 18 MV. The parallel oriented film demonstrated a 3% under-response at 5-cm (6 MV) depth against the perpendicular orientation, but both orientations over responded equally in the central region, which received only scattered dose, at both 5- and 20-cm depths. In a regular 6-MV 5 Multiplication-Sign 5 cm{sup 2} field, a 4.1% lower film response was observed in the parallel orientation compared to perpendicular orientation. The under response gradually increased to 6% when reducing the field size to 0.5 Multiplication-Sign 5 cm{sup 2}. On the other hand, the film showed a 1.7% lower response in parallel orientation for the large field size of 20 Multiplication-Sign 20 cm{sup 2} at 5-cm depth but the difference disappeared at 10 cm. At 18 MV, similar but somewhat lower differences were found between the two orientations. The directional sensitivity of the film diminishes with increasing field size and depth. Surprisingly a composite IMRT beam consisting of 20 adjacent strip segments also produced a significant orientational dependence of film response, notwithstanding the large total field size of 20 Multiplication-Sign 20 cm{sup 2}. Conclusions: This analysis allowed the development of a hypothesis about the physics behind the orientational dependence of film response in general and to formulate precautions when using film dosimetry in the dosimetric verification of multibeam treatments.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2012

Verification of dosimetric accuracy on the TrueBeam STx: Rounded leaf effect of the high definition MLC

Purpose: The dosimetric leaf gap (DLG) in the Varian Eclipse treatment planning system is determined during commissioning and is used to model the effect of the rounded leaf-end of the multileaf collimator (MLC). This parameter attempts to model the physical difference between the radiation and light field and account for inherent leakage between leaf tips. With the increased use of single fraction high dose treatments requiring larger monitor units comes an enhanced concern in the accuracy of leakage calculations, as it accounts for much of the patient dose. This study serves to verify the dosimetric accuracy of the algorithm used to model the rounded leaf effect for the TrueBeam STx, and describes a methodology for determining best-practice parameter values, given the novel capabilities of the linear accelerator such as flattening filter free (FFF) treatments and a high definition MLC (HDMLC). Methods: During commissioning, the nominal MLC position was verified and the DLG parameter was determined using MLC-defined field sizes and moving gap tests, as is common in clinical testing. Treatment plans were created, and the DLG was optimized to achieve less than 1% difference between measured and calculated dose. The DLG value found was tested on treatment plans for all energies (6 MV, 10 MV, 15 MV, 6 MV FFF, 10 MV FFF) and modalities (3D conventional, IMRT, conformal arc, VMAT) available on the TrueBeam STx. Results: The DLG parameter found during the initial MLC testing did not match the leaf gap modeling parameter that provided the most accurate dose delivery in clinical treatment plans. Using the physical leaf gap size as the DLG for the HDMLC can lead to 5% differences in measured and calculated doses. Conclusions: Separate optimization of the DLG parameter using end-to-end tests must be performed to ensure dosimetric accuracy in the modeling of the rounded leaf ends for the Eclipse treatment planning system. The difference in leaf gap modeling versus physical leaf gap dimensions is more pronounced in the more recent versions of Eclipse for both the HDMLC and the Millennium MLC. Once properly commissioned and tested using a methodology based on treatment plan verification, Eclipse is able to accurately model radiation dose delivered for SBRT treatments using the TrueBeam STx.

60 APPLIED LIFE SCIENCES↗