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Modelling multi-ion plasma gun simulations of Tokamak disruptions

Description: The effect of impurity ions in plasma gun ablation tests of various targets is considered. Inclusion of reasonable amounts of impurity ({approximately}10%) is adequate to explain observed energy transmission and erosion measurements. The gun tests and the computer code calculations are relevant to the parameter range expected for major disruptions on large tokamaks.
Date: August 1, 1995
Creator: Ehst, D.A.
Partner: UNT Libraries Government Documents Department

Studies of impurity mode and ITG mode in toroidal plasmas

Description: The impurity mode and {eta}{sub i} mode driven by impurity ions with outwardly peaked density profiles, just as it is at the boundary of tokamak plasmas, and the ion temperature gradient, respectively, are studied in high temperature toroidal plasmas. The gyrokinetic theory is applied and finite Larmor radius effects of both hydrogenic and impurity ions are included. It is found that the impurity mode is enhanced by the ion temperature gradient. In addition, the impurity ions with outwardly peaked density profiles are demonstrated to have destabilizing effects on the {eta}{sub i} mode. These two modes are strongly coupled to each other so that it is impossible to distinguish between them when both the driving mechanisms axe strong enough to drive the corresponding mode unstable independently. The correlation of the results with nonlinear simulations and the experimental observations are discussed.
Date: April 1, 1995
Creator: Dong, J.Q. & Horton, W.
Partner: UNT Libraries Government Documents Department

The Absence of Plasma in"Spark Plasma Sintering"

Description: Spark plasma sintering (SPS) is a remarkable method for synthesizing and consolidating a large variety of both novel and traditional materials. The process typically uses moderate uni-axial pressures (<100 MPa) in conjunction with a pulsing on-off DC current during operation. There are a number of mechanisms proposed to account for the enhanced sintering abilities of the SPS process. Of these mechanisms, the one most commonly put forth and the one that draws the most controversy involves the presence of momentary plasma generated between particles. This study employees three separate experimental methods in an attempt to determine the presence or absence of plasma during SPS. The methods employed include: in-situ atomic emission spectroscopy, direct visual observation and ultra-fast in-situ voltage measurements. It was found using these experimental techniques that no plasma is present during the SPS process. This result was confirmed using several different powders across a wide spectrum of SPS conditions.
Date: April 10, 2008
Creator: Hulbert, Dustin M.; Anders, Andre; Dudina, Dina V.; Andersson, Joakim; Jiang, Dongtao; Unuvar, Cosan et al.
Partner: UNT Libraries Government Documents Department

Final Report - Investigation of Intermittent Turbulence and Turbulent Structures in the Presence of Controlled Sheared Flows

Description: Final Report for grant DE-FG02-06ER54898. The dynamics and generation of intermittent plasma turbulent structures, widely known as "blobs" have been studied in the presence of sheared plasma flows in a controlled laboratory experiment.
Date: June 27, 2013
Creator: Gilmore, Mark A.
Partner: UNT Libraries Government Documents Department

Experimental Investigation of Active Feedback Control of Turbulent Transport in a Magnetized Plasma

Description: A new and unique basic plasma science laboratory device - the HelCat device (HELicon-CAThode) - has been constructed and is operating at the University of New Mexico. HelCat is a 4 m long, 0.5 m diameter device, with magnetic field up to 2.2 kG, that has two independent plasmas sources - an RF helicon source, and a thermionic cathode. These two sources, which can operate independently or simultaneously, are capable of producing plasmas with a wide range of parameters and turbulence characteristics, well suited to a variety of basic plasma physics experiments. An extensive set of plasma diagnostics is also operating. Experiments investigating the active feedback control of turbulent transport of particles and heat via electrode biasing to affect plasma ExB flows are underway, and ongoing.
Date: July 7, 2013
Creator: Gilmore, Mark Allen
Partner: UNT Libraries Government Documents Department

Control of laser plasma instabilities in hohlraums

Description: Laser plasma instabilities are an important constraint on the operating regime for inertial fusion. Many techniques have been developed to control the various laser-driven instabilities. Experiments with long scale length plasmas are testing these instability levels, the nonlinear regimes, and the control mechanisms.
Date: December 1, 1996
Creator: Kruer, W.L.
Partner: UNT Libraries Government Documents Department

Collaborative Research: Experimental and Theoretical Study of the Plasma Physics of Antihydrogen Generation and Trapping

Description: Ever since Dirac predicted the existence of antimatter in 1928, it has excited our collective imagination. Seventy-four years later, two collaborations at CERN, ATHENA and ATRAP, created the first slow antihydrogen. This was a stunning achievement, but the most important antimatter experiments require trapped, not just slow, antihydrogen. The velocity, magnetic moment, and internal energy and state of the antihydrogen depend strongly on how it is formed. To trap antihydrogen, physicists face two broad challenges: (1) Understanding the behavior of the positron and antiprotons plasmas from which the antihydrogen is synthesized; and (2) Understanding the atomic processes by which positrons and antiprotons recombine. Recombination lies on the boundary between atomic and plasma physics, and cannot be studied properly without employing tools from both fields. The proposed collaborative research campaign will address both of these challenges. The collaboration members have unique experience in the relevant fields of experimental and theoretical non-neutral plasma physics, numerical modeling, nonlinear dynamics and atomic physics. This expertise is not found elsewhere amongst antihydrogen researchers. The collaboration members have strong ties already, and seek to formalize them with this proposal. Three of the four PIs are members of the ALPHA collaboration, an international collaboration formed by most of the principal members of the ATHENA collaboration.
Date: March 29, 2013
Creator: Robicheaux, Francis
Partner: UNT Libraries Government Documents Department

Generator powered plasma focus

Description: An earlier set of experiments will be described briefly, in which plate flux compression generators were used to power a Plasma Focus. Currents, voltages and 'rundown times' obtained in these experiments are shown to agree well with a simple model. This same model is then used to show how dramatic operational improvements could be obtained with use of an appropriate fuse, provided the model remained valid.
Date: January 1, 2002
Creator: Fowler, C. M.
Partner: UNT Libraries Government Documents Department

Gyrokinetic Theory for Arbitrary Wavelength Electromagnetic Modes in Tokamaks

Description: A linear gyrokinetic system for arbitrary wavelength electromagnetic modes is developed. A wide range of modes in inhomogeneous plasmas, such as the internal kink modes, the toroidal Alfvén eigenmode (TAE) modes, and the drift modes, can be recovered from this system. The inclusion of most of the interesting physical factors into a single framework enables us to look at many familiar modes simultaneously and thus to study the modifications of and the interactions between them in a systematic way. Especially, we are able to investigate self-consistently the kinetic MHD phenomena entirely from the kinetic side. Phase space Lagrangian Lie perturbation methods and a newly developed computer algebra package for vector analysis in general coordinate system are utilized in the analytical derivation. In tokamak geometries, a 2D finite element code has been developed and tested. In this paper, we present the basic theoretical formalism and some of the preliminary results.
Date: October 1, 1997
Creator: Qin, H.; Rewoldt, G. & Tang, W.M.
Partner: UNT Libraries Government Documents Department

DUST-PLASMA INTERACTIONS

Description: The objective of our theoretical research under this grant over the past 3 years was to develop new understanding in a range of topics in the physics of dust-plasma interactions, with application to space and the laboratory. We conducted studies related to the physical properties of dust, waves and instabilities in both weakly coupled and strongly coupled dusty plasmas, and innovative possible applications. A major consideration in our choice of topics was to compare theory with experiments or observations, and to motivate new experiments, which we believe is important for developing this relatively new field. Our research is summarized, with reference to our list of journal publications.
Date: January 5, 2010
Creator: Rosenberg, Dr. M.
Partner: UNT Libraries Government Documents Department

Tapered plasma channels to phase-lock accelerating and focusing forces in laser-plasma accelerators

Description: Tapered plasma channels are considered for controlling dephasing of a beam with respect to a plasma wave driven by a weakly-relativistic, short-pulse laser. Tapering allows for enhanced energy gain in a single laser plasma accelerator stage. Expressions are derived for the taper, or longitudinal plasma density variation, required to maintain a beam at a constant phase in the longitudinal and/or transverse fields of the plasma wave. In a plasma channel, the phase velocities of the longitudinal and transverse fields differ, and, hence, the required tapering differs. The length over which the tapered plasma density becomes singular is calculated. Linear plasma tapering as well as discontinuous plasma tapering, which moves beams to adjacent plasma wave buckets, are also considered. The energy gain of an accelerated electron in a tapered laser-plasma accelerator is calculated and the laser pulse length to optimize the energy gain is determined.
Date: May 17, 2010
Creator: Rittershofer, W.; Schroeder, C.B.; Esarey, E.; Gruner, F.J. & Leemans, W.P.
Partner: UNT Libraries Government Documents Department

Final Report for Grant No. DE-FG02-03ER54706 "Support for the 7th Workshop on The Interrelationship between Plasma Experiment in Laboratory and Space"

Description: We describe the support given to support the 7th IPELS meeting which brings together space and laboratory based physicists. The meeting was a great success with more than 80 attendees and a significant number of young scientists. The major topics of discussion were magnetic reconnection, plasma turbulence, and waves in plasmas.
Date: September 13, 2005
Creator: Kletzing, C.
Partner: UNT Libraries Government Documents Department

Efficient electron injection into plasma waves using higher-orderlaser modes

Description: Using higher-order transverse laser modes as drivers forplasma wave excitation, and, in particular, using a ring laser beam withmaximum intensity off-axis, results in reversal of the focusinganddefocusing phase regions in a laser wakefield accelerator. Thisresults in improved performance of self-trapping and laser injectionschemes. Specifically, the trapping threshold required foropticalinjection is decreased and the maximum energy gain of the trappedelectrons is increased. This scheme could also be of interest for thegeneration of ring electron beams or for beam conditioning.
Date: August 2, 2006
Creator: Michel, P.; Esarey, E.; Schroeder, C.B.; Shadwick, B.A. & Leemans,W.P.
Partner: UNT Libraries Government Documents Department

Thermal effects in plasma-based accelerators

Description: Finite plasma temperature can modify the structure of thewake field, reduce the wave-breaking field, and lead to self-trappedelectrons, which can degrade the electron bunch quality in a plasma-basedaccelerator. A relativistic warm fluid theory is used to describe theplasma temperature evolution and alterations to the structure of anonlinear periodic wave exited in a warm plasma. The trapping thresholdfor a plasma electron and the fraction of electrons trapped from athermal distribution are examined using a single-particle model.Numerical artifacts in particle-in-cell models that can mimic the physicsassociated with finite momentum spread are discussed.
Date: January 9, 2007
Creator: Esarey, E.; Schroeder, C.B.; Michel, E.; Shadwick, B.A.; Geddes,C.G.R. & Leemans, W.P.
Partner: UNT Libraries Government Documents Department

Spatial filter issues

Description: Beamlet measurements show that cone pinholes outperform other types tested with regard to both closure and back reflections. A ±150 µrad stainless steel cone remained open for a 15.5 kJ, 10:1 contrast shaped pulse with ±7.5 µrad of SSD divergence, which more than meets the requirements for a NIF ignition pulse. Measurements also showed the maximum tolerable pressures in the NIF spatial filters to be a few milliTorr, leading to recommendations of 0.1 and 0.6 mTorr for the NIF transport and cavity spatial filters, respectively.
Date: July 23, 1998
Creator: Boley, C. D.; Bonneau, F.; Estabrook, K. G.; Milam, D. & Murray, J. E.
Partner: UNT Libraries Government Documents Department

Nested Well Plasma Traps

Description: Criteria for the confinement of plasmas consisting of a positive and negative component in Penning type traps with nested electric potential wells are presented. Computational techniques for the self-consistent calculation of potential and plasma density distributions are developed. Analyses are presented of the use of nested well Penning traps for several applications. The analyses include: calculations of timescales relevant to the applications, e.g. reaction, confinement and relaxation timescales, self-consistent computations, and consideration of other physical phenomenon important to the applications. Possible applications of a nested well penning trap include production of high charge state ions, studies of high charge state ions, and production of antihydrogen. In addition the properties of a modified Penning trap consisting of an electric potential well applied along a radial magnetic field are explored.
Date: August 2000
Creator: Dolliver, Darrell
Partner: UNT Libraries

Dynamics of an Isolated Blob in the Presence of the X-Point

Description: The interplay of X-point shearing and axial plasma redistribution along a moving flux tube is discussed. Blobs limited to the main scrape-off-layer and the blobs entirely confined in the divertor region are identified. A strong effect of the radial tilt of the divertor plate on ''divertor'' blobs is found.
Date: October 10, 2005
Creator: Cohen, R H & Ryutov, D D
Partner: UNT Libraries Government Documents Department

An estimate of collisional beam scattering during final focus in NDCX-II

Description: The final focus of NDCX-II contains a region with quite high plasma density. We estimate here how much collisional scatter we expect from transit through this plasma. A separate question, not explored here, is how much scatter there might be off of collective fluctuations in the neutralizing plasma, including those driven by the passage of the beam.
Date: March 23, 2010
Creator: Cohen, R.H.
Partner: UNT Libraries Government Documents Department

DEVELOPMENT OF WATER JET PLASMA MIRROR FOR STAGING OF LASER PLASMA ACCELERATORS

Description: Staging Laser Plasma Accelerators (LPAs) is necessary in order to reach beam energies of 100 GeV and above. This requires incoupling of additional laser beams into accelerating stages. In order to maintain the high average accelerating gradient of a staged LPA, it is imperative to minimize the distance that is needed for laser incoupling. A plasma mirror is proposed as the final coupling optic reducing the coupling distance from tens of meters, using a conventional optic, to as small as a few cm. Both a planar water jet and a nitrocellulose foil are used as reflecting surfacesand characterized. A maximum reflectivity of 70percent was obtained using both surfaces.
Date: May 4, 2009
Creator: Panasenko, Dmitriy; Gonsalves, Anthony J.; Leemans, Wim; Nakamura, Kei; Shu, Anthony & Toth, Csaba
Partner: UNT Libraries Government Documents Department