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Title: Physics V&V L2 Milestone

Abstract

This presentation describes the verification assessments measures used at LANL.

Authors:
 [1]
  1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA), Office of Defense Programs (DP) (NA-10)
OSTI Identifier:
1394961
Report Number(s):
LA-UR-17-28612
DOE Contract Number:
AC52-06NA25396
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
97 MATHEMATICS AND COMPUTING

Citation Formats

Woods, Nathan. Physics V&V L2 Milestone. United States: N. p., 2017. Web. doi:10.2172/1394961.
Woods, Nathan. Physics V&V L2 Milestone. United States. doi:10.2172/1394961.
Woods, Nathan. 2017. "Physics V&V L2 Milestone". United States. doi:10.2172/1394961. https://www.osti.gov/servlets/purl/1394961.
@article{osti_1394961,
title = {Physics V&V L2 Milestone},
author = {Woods, Nathan},
abstractNote = {This presentation describes the verification assessments measures used at LANL.},
doi = {10.2172/1394961},
journal = {},
number = ,
volume = ,
place = {United States},
year = 2017,
month = 9
}

Technical Report:

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  • This milestone has been accomplished. The Heavy Ion Fusion Science Virtual National Laboratory has completed simulations of a fast correction scheme to compensate for chromatic and time-dependent defocusing effects in the transport of ion beams to the target plane in the NDCX-1 facility. Physics specifications for implementation in NDCX-1 and NDCX-2 have been established. This milestone has been accomplished. The Heavy Ion Fusion Science Virtual National Laboratory has completed simulations of a fast correction scheme to compensate for chromatic and time-dependent defocusing effects in the transport of ion beams to the target plane in the NDCX-1 facility. Physics specifications formore » implementation in NDCX-1 and NDCX-2 have been established. Focal spot differences at the target plane between the compressed and uncompressed regions of the beam pulse have been modeled and measured on NDCX-1. Time-dependent focusing and energy sweep from the induction bunching module are seen to increase the compressed pulse spot size at the target plane by factors of two or more, with corresponding scaled reduction in the peak intensity and fluence on target. A time-varying beam envelope correction lens has been suggested to remove the time-varying aberration. An Einzel (axisymmetric electric) lens system has been analyzed and optimized for general transport lines, and as a candidate correction element for NDCX-1. Attainable high-voltage holdoff and temporal variations of the lens driving waveform are seen to effect significant changes on the beam envelope angle over the duration of interest, thus confirming the utility of such an element on NDCX-1. Modeling of the beam dynamics in NDCX-1 was performed using a time-dependent (slice) envelope code and with the 3-D, self-consistent, particle-in-cell code WARP. Proof of concept was established with the slice envelope model such that the spread in beam waist positions relative to the target plane can be minimized with a carefully designed Einzel lens waveform and transport line. WARP simulations have verified the efficacy of the Einzel lens while including more detailed beam physics. WARP simulations have also indicated some unpredicted transittime effects, and methods are currently being explored to compensate and reduce this complication. We have explored the use of an Einzel lens, or system of Einzel lenses, to compensate for chromatic aberrations in the beam focal spot in the NDCX-2 target plane. The final beam manipulations in NDCX-2 (linear velocity ramp, charge neutralization, high field final focus solenoid) are similar to NDCX-1 though the NDCX-2 beam has much higher energy and current. The most relevant distinctions are that the pulse duration at the entrance to the drift compression section is tenfold shorter, and that the beam energy tenfold higher, than in NDCX-1. Placing a time-dependent, envelope angle correcting element at the neutralized drift region entrance presents a very significant challenge to voltage holdoff and voltage swing V(t) in a single Einzel lens. Placing the Einzel lens(es) further upstream reduces the required voltage risetime V'(t) to effect the necessary envelope correction, while increasing the duration over which the timedependent voltage must vary. While this simplifies the technological challenge of designing and operating a Einzel lens in NDCX-2, it does require much finer control of the correcting waveform and measurements of its effect on space-charge dominated beams over a much longer axial path length to target than in the NDCX-1.« less
  • The Los Alamos Physics and Engineering Models (PEM) program has developed a model for Richtmyer-Meshkov instability (RMI) based ejecta production from shock-melted surfaces, along with a prescription for a self-similar velocity distribution (SSVD) of the resulting ejecta particles. We have undertaken an effort to validate this source model using data from explosively driven tin coupon experiments. The model’s current formulation lacks a crucial piece of physics: a method for determining the duration of the ejecta production interval. Without a mechanism for terminating ejecta production, the model is not predictive. Furthermore, when the production interval is hand-tuned to match time-integrated massmore » data, the predicted time-dependent mass accumulation on a downstream sensor rises too sharply at early times and too slowly at late times because the SSVD overestimates the amount of mass stored in the fastest particles and underestimates the mass stored in the slowest particles. The functional form of the resulting m(t) is inconsistent with the available time-dependent data; numerical simulations and analytic studies agree on this point. Simulated mass tallies are highly sensitive to radial expansion of the ejecta cloud. It is not clear if the same effect is present in the experimental data but if so, depending on the degree, this may challenge the model’s compatibility with tin coupon data. The current implementation of the model in FLAG is sensitive to the detailed interaction between kinematics (hydrodynamic methods) and thermodynamics (material models); this sensitivity prohibits certain physics modeling choices. The appendices contain an extensive analytic study of piezoelectric ejecta mass measurements, along with test problems, excerpted from a longer work (LA-UR-17-21218).« less
  • During the first two years of radioactive operation of the Defense Waste Processing Facility process, several areas for improvement in melter design were identified. Due to the need for a process that allows continuous melter operation, the down time associated with disruption to melter operation and pouring has significant cost impact. A major objective of this task is to address performance limitations and deficiencies identified by the user.
  • A presentation was made to the Milestone review committee on September 18, 2009 that outlined the efforts making up the achievement of the Campaign 2, Level 2 Milestone No.3132. After the presentation and review of the collective work, the committee determined that the milestone was successfully completed. Highlights from this review are discussed here. A brief summary of the discussion points includes: (1) It was clear that this work represents a comprehensive collection of experimental, modeling, literature review, and analysis activities with a thorough attention to the details. The deliverables include 2 technical presentations and 5 written reports describing thismore » work. (2) This is a joint LLNL/LANL milestone led by Campaign 2 with leveraging effort from other campaigns and activities at LLNL: (a) The contributing programs included Enhanced Surveillance Campaign (ESC) and Readiness Campaign. Key technical elements of this work were built on scientific advances from the Laboratory Directed Research and Development (LDRD) program. (b) Part of this work covers activities associated with the Enhanced Collaboration (EC) with the Atomic Weapons Establishment (AWE). (3) This Milestone work has supported a high-level Directed Stockpile Work (DSW) Joint DoD/DOE TATB Production Initiative. This is an example of the strong relevance of this Milestone research to current stockpile issues. A summary of the future direction in this research area includes: (1) The Ionic Liquid (IL) re-crystallization process has been demonstrated to improve the performance of recrystallized TATB molecule. However, lower thermal stability of the IL crystallized material (compared to conventional TATB) warrants further study to understand the source of this effect. (2) The compatibility issue needs to be addressed in upcoming work. One concern is how the new solvent and ionic liquid used in the formulation process might behave in the nuclear explosive assembly. Similarly, compatibility studies for the candidate binder must be performed. The future focus on R&D and additional scientific tools to address these areas is technically sound. (3) Currently there is no defined process for advancing this milestone's research and development successes into a production scale effort. The committee recognizes that other campaigns (Readiness Campaign, Enhanced Surveillance Campaign) will need to consider additional leverage resources for that scale-up effort. (4) We recommend that this effort continues to use modeling and experiment as complimentary paths to strengthen the scientific approach.« less
  • The milestone reviewed on Sept. 16, 2009 was 'High-fidelity simulation of shock initiation of high explosives at the grain scale using coupled hydrodynamics, thermal transport and chemistry'. It is the opinion of the committee that the team has satisfied the milestone. A detailed description of how the goals were met is provided. The milestone leveraged capabilities from ASC Physics and Engineering Materials program combined with experimental input from Campaign 2. A combined experimental-multiscale simulation approach was used to create and validate the various TATB model components. At the lowest length scale, quantum chemical calculations were used to determine equations ofmore » state, thermal transport properties and reaction rates for TATB as it is decomposing. High-pressure experiments conducted in diamond anvil cells, gas guns and the Z machine were used to validate the EOS, thermal conductivity, specific heat and predictions of water formation. The predicted reaction networks and chemical kinetic equations were implemented in Cheetah and validated against the lower length scale data. Cheetah was then used within the ASC code ALE3D for high-resolution, thermo-mechanically coupled simulations of pore collapse at the micron size scale to predict conditions for detonation initiation.« less