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Compact torus studies: Final report

Description: The compact torus (CT) device has been proposed for use in some applications which are of interest in Laboratory programs in the areas of pulsed power and inertial confinement fusion. These applications involve compression and acceleration of CT plasmas. The RACE (Ring Accelerator Experiment) experimental program at Livermore has been initiated to study these applications. The work reported here involves studies of plasma physics and other aspects of these compact torus applications. The studies conducted identify specific problem areas associated with the CT device and examine these areas in some detail. This report contains studies of three particular problem areas of the CT applications. These three areas are: the general nonlinear properties of the CT as a magnetohydrodynamic (MHD) equilibrium, particle simulation of the compression of the CT, with a focus on the non-MHD effects, and nonlinear RF interaction problems in the CT.
Date: June 1, 1987
Creator: Morse, E.C.
Partner: UNT Libraries Government Documents Department

Stability of the field-reversed mirror

Description: The stability of a field reversed mirror plasma configuration is studied with an energy principle derived from the Vlasov equation. Because of finite orbit effects, the stability properties of a field-reversed mirror are different from the stability properties of similar magnetohydrodynamic equilibria. The Vlasov energy principle developed here is applied to a computer simulation of an axisymmetric field-reversed mirror state. It has been possible to prove that the l = 0 modes, called tearing modes, satisfy a sufficient condition for stability. Precessional modes, with l = 1, 2, are found to be unstable at low growth rate. This suggests possible turbulent behavior (Bohm confinement) in the experimental devices aiming at field reversal. Techniques for suppressing these instabilities are outlined, and the applicability of the Vlasov energy principle to more complicated equilibrium models is shown.
Date: January 1, 1979
Creator: Morse, E.C.
Partner: UNT Libraries Government Documents Department

Stability of the field-reversed mirror

Description: The stability of a field reversed mirror plasma configuration is studied with an energy principle derived from the Vlasov equation. Because of finite orbit effects, the stability properties of a field-reversed mirror are different from the stability properties of similar magnetohydrodynamic equilibria. The Vlasov energy principle developed here is applied to a computer simulation of an axisymmetric field-reversed mirror state. It has been possible to prove that the l = 0 modes, called tearing modes, satisfy a sufficient condition for stability. Precessional modes, with l = 1, 2, are found to be unstable at low growth rate. This suggests possible turbulent behavior (Bohm confinement) in the experimental devices aiming at field reversal. Techniques for suppressing these instabilities are outlined, and the applicability of the Vlasov energy principle to more complicated equilibrium models is shown.
Date: January 1, 1979
Creator: Morse, E. C.
Partner: UNT Libraries Government Documents Department

Blanket optimization studies for Cascade

Description: A nonlinear, multivariable, blanket optimization technique is applied to the Cascade inertial confinement fusion reactor concept. The thickness of a two-zone blanket, which consists of a BeO multiplier region followed by a LiAlO/sub 2/ breeding region, is minimized subject to constraints on the tritium breeding ratio, neutron leakage, and heat generation rate in Al/SiC tendons that support the chamber wall.
Date: February 28, 1985
Creator: Meier, W.R. & Morse, E.C.
Partner: UNT Libraries Government Documents Department

Compact torus accelerator: a driver for ICF. Revision 1

Description: We have carried out further investigations of technical issues associated with using a compact torus (CT) accelerator as a driver for inertial confinement fusion (ICF). In a CT accelerator, a magnetically-confined torus-shaped plasma is compressed, accelerated and focused by two concentric electrodes. Here, we evaluate an accelerator point design with a capacitor bank energy of 9.2 MJ. Modeled by a O-D code, the system produces a xenon plasma ring with a radius of 0.73 cm, a velocity of 4 x 10/sup 7/ m/s, and a mass of 4.4 ..mu..g. The plasma ring energy available for fusion is 3.8 MJ, a 40% driver efficiency. Ablation and magnetic pressures of the point design, a due to CT acceleration, are analyzed. Pulsed-power switching limitations and driver cost analysis are also presented. Our studies confirm the feasibility of producing a ring to induce fusion with acceptable gain. However, some uncertainties must be resolved to establish viability.
Date: July 31, 1986
Creator: Tobin, M.T. & Morse, E.C.
Partner: UNT Libraries Government Documents Department

Stability of field-reversed mirrors

Description: The stability of the field-reversed mirror configuration to acoustic modes in the low-frequency regime is analyzed. While previous work has been done using field-reversed configurations in the geometrical limit of infinite length, or zero plasma width, the attempt here is to analyze an equilibrium that has order unity aspect ratio. Further, while previous efforts have concentrated on fluid equilibrium or a specific distribution function, the approach here is to develop a formalism that can be used for an arbitrary distribution that is a function of the constants of motion.
Date: January 1, 1978
Creator: Morse, E.C. & Miley, G.H.
Partner: UNT Libraries Government Documents Department

Operation of a quasioptical electron cyclotron maser

Description: The electron cyclotron maser or gyrotron concept has been developed to produce sources producing 200 kW at 28 GHz continuously, and higher power outputs and frequencies in pulsed mode. These sources have been useful in electron cyclotron resonance heating (ECRH) in magnetically confined fusion devices. However, higher frequencies and higher power levels will be required in reactor-grade fusion plasmas, with likely requirements of 1.0 MW or more per source at 140 GHz. Conventional gyrotrons follow a trend of decreasing power for increasing frequency. In order to circumvent this problem, the quasioptical electron cyclotron maser was proposed. In this device, the closed resonator of the conventional gyrotron is replaced with an open, Fabry-Perot type resonator. The cavity modes are then the TEM-type modes of an optical laser. The advantage of this configuration is that the cavity size is not a function of frequency, since the length can be any half-integer number of wavelengths. Furthermore, the beam traverses across the cavity transverse to the direction of radiation output, and thus the rf window design is less complicated than in conventional tubes. The rf output, if obtained by diffraction coupling around one of the mirrors, could be in a TEM mode, which would allow for quasioptical transmission of the microwaves into the plasma in fusion devices. 4 references, 1 figure.
Date: December 1, 1984
Creator: Morse, E.C. & Pyle, R.V.
Partner: UNT Libraries Government Documents Department

Stability of field reversed mirrors

Description: The field-reversed mirror (FRM) concept potentially offers and extremely interesting small fusin power plant. For example, current studies of the SAFFIRE device suggest that nearly ignited, self-sustained operation might be feasible. Perhaps the key unanswered question is the stability forces. The present work employs an energy principle to demonstrate stability of low frequency modes and derive limiting conditions of importance to design stability studies such as SAFFIRE.
Date: January 1, 1978
Creator: Morse, E.C.; Condit, W.C. & Miley, G.H.
Partner: UNT Libraries Government Documents Department

Diffusion of alkali species in porous tungsten substrates used in contact ionization sources

Description: Contact ionization (doped) sources used in current Heavy Ion Fusion experiments consist of a porous tungsten substrate doped with an alkali carbonate. In the early stages of the heating cycle (T - 600 C), the carbonate breaks down and releases the alkali atoms that then diffuse through the substrate. At the emitter surface there is a balance between the fast desorption rate of the alkali atoms (mostly as neutrals) and the slower replenishment rate from the substrate by diffusion. Time-resolved measurements of neutral particle evaporation rates at the emitter surface have been used to estimate the effective diffusion coefficient (D) that characterizes the migration of alkali species in the substrate. These estimates are consistent with the observed source lifetimes (tens of hrs.) and establish the alkali migration in the bulk as a diffusion-limited process. The measurements suggest that the faster migration rates (D {approx} 10{sup -5} - 10{sup -6} cm2/s) occur early during the heating cycle when the dominant species are the neutral alkali atoms. At operating temperatures there is a slower migration rate (D x 10-7cm2/sd) ue to the dominance of ions, which difise by a slower surface diffusion process.
Date: January 1, 2002
Creator: Chacon-Golcher, E. (Edwin); Kwan, J. (Joe) & Morse, E. C. (Edward C.)
Partner: UNT Libraries Government Documents Department

Studies of finite gyro-radius effects in a field reversed mirror configuration

Description: The field-reversed mirror (FRM) is characterized by a small size such that finite gyro-radius effects must be considered in both stability and transport analyses. Consequently, such effects are important to the interpretation of both ongoing experiments and extrapolation to future reactor concepts. The present work employs an energy principle to study stability of low-frequency (..omega.. << ..cap omega../sub ce/, ..omega.. approx. = ..cap omega../sub ci/) acoustic modes. Also a Monte Carlo technique has been developed for study of high energy-ion transport.
Date: January 1, 1979
Creator: Miley, G.H.; Gilligan, J.G.; Driemeyer, D.E.; Morse, E.C. & Condit, W.C.
Partner: UNT Libraries Government Documents Department

Imploded Capsule Fuel Temperature and Density Measurement by Energy-Dependent Neutron Imaging

Description: Neutron imaging systems measure the spatial distribution of neutron emission from burning inertial confinement fusion (ICF) targets. These systems use a traditional pinhole geometry to project an image of the source onto a two-dimensional scintillator array, and a CCD records the resulting scintillation image. The recent history of ICF neutron images has produced images with qualities that have improved as the fusion neutron yields have increased to nearly 10{sup 14} neutrons. Anticipated future neutron yields in excess of 10{sup 16} at the National Ignition Facility and LMJ have raised the prospect of neuron imaging diagnostics which simultaneously probe several different characteristics of burning fusion targets. The new measurements rely on gated-image recording to select images corresponding to specific bands of neutron energies. Gated images of downscattered neutrons with energies from 5 to 8 MeV can emphasize regions of the target which contain DT fuel which is not burning. At the same time, gated images which select different portions of the 14-MeV spectral peak can produce spatial temperature maps of a burning target. Since the neutron production depends on the DT fuel density and temperature, simultaneous images of temperature and neutron emission can be combined to infer the an image of the source density using an Abel inversion method that is analogous to the method that has been used in x-ray imaging. Thus, with higher-yield sources, neutron imaging offers the potential to record simultaneously several critical features that characterize the performance of an ICF target: the neutron emission distribution, the temperature and density distributions, and the distribution of nonburning fuel within the target.
Date: September 28, 2005
Creator: Moran, M J; Koch, J; Landen, O L; Haan, S W; Barrera, C A & Morse, E C
Partner: UNT Libraries Government Documents Department

Demonstration of Successful X-ray Thomson Scattering Using Picosecond K-(alpha) X-ray Sources for the Characterization of Dense Heated Matter

Description: We discuss the first successful K-{alpha} x-ray Thomson scattering experiment from solid density plasmas for use as a diagnostic in determining the temperature, density, and ionization state of warm dense matter with picosecond resolution. The development of this source as a diagnostic and stringent requirements for successful K-{alpha} x-ray Thomson scattering are addressed. Data for the experimental techniques described in this paper [1] suggest the capability of single shot characterization of warm dense matter and the ability to use this scattering source at future Free Electron Lasers (FEL) where comparable scattering signal levels are predicted.
Date: May 5, 2008
Creator: Kritcher, A; Neumayer, P; Lee, H J; Doeppner, T; Falcone, R; Glenzer, S et al.
Partner: UNT Libraries Government Documents Department

Diffusion of alkali species in porous tungsten substrates used in contact-ionization sources

Description: Contact ionization (doped) sources used in current Heavy Ion Fusion (HIF) experiments consist of a porous tungsten substrate doped with an alkali carbonate. During the early stages of the heating cycle (T {approx} 600 C), the carbonate breaks down and releases the alkali atoms that then diffuse through the substrate. At the emitter surface there is a balance between the fast desorption rate of the alkali atoms (mostly as neutrals) and the slower replenishment rate from the substrate by diffusion. Time-resolved measurements of neutral particle evaporation rates at the emitter surface have been used to estimate the effective diffusion coefficient (D) that characterizes the migration of alkali species in the substrate. These estimates are consistent with the observed source lifetimes (tens of hrs.) and establish the alkali migration in the bulk as a diffusion-limited process. The measurements suggest that the faster migration rates (D {approx} 10{sup -5}-10{sup -6} cm{sup 2}/s) occur early during the heating cycle when the dominant species are the neutral alkali atoms. At operating temperatures there is a slower migration rate (D {approx} 10{sup -7} cm{sup 2}/s) due to the dominance of ions, which diffuse by a slower surface diffusion process.
Date: June 1, 2003
Creator: Chacon-Golcher, E.; Kwan, J.W. & Morse, E.C.
Partner: UNT Libraries Government Documents Department

Highly Efficient Tabletop Optical Parametric Chirped Pulse Amplifier at 1 (micron)m

Description: Optical parametric chirped pulse amplification (OPCPA) is a scalable technology, for ultrashort pulse amplification. Its major advantages include design simplicity, broad bandwidth, tunability, low B-integral, high contrast, and high beam quality. OPCPA is suitable both for scaling to high peak power as well as high average power. We describe the amplification of stretched 100 fs oscillator pulses in a three-stage OPCPA system pumped by a commercial, single-longitudinal-mode, Q-switched Nd:YAG laser. The stretched pulses were centered around 1054 nm with a FWHM bandwidth of 16.5 nm and had an energy of 0.5 nJ. Using our OPCPA system, we obtained an amplified pulse energy of up to 31 mJ at a 10 Hz repetition rate. The overall conversion efficiency from pump to signal is 6%, which is the highest efficiency obtained With a commercial tabletop pump laser to date. The overall conversion efficiency is limited due to the finite temporal overlap of the seed (3 ns) with respect to the duration of the pump (8.5 ns). Within the temporal window of the seed pulse the pump to signal conversion efficiency exceeds 20%. Recompression of the amplified signal was demonstrated to 310 fs, limited by the aberrations initially present in the low energy seed imparted by the pulse stretcher. The maximum gain in our OPCPA system is 6 x 10{sup 7}, obtained through single passing of 40 mm of beta-barium borate. We present data on the beam quality obtained from our system (M{sup 2}=1.1). This relatively simple system replaces a significantly more complex Ti:sapphire regenerative amplifier based CPA system used in the front end of a high energy short pulse laser. Future improvement will include obtaining shorter amplified pulses and higher average power.
Date: December 4, 2001
Creator: Jovanovic, I.; Ebbers, C.A.; Comaskey, B.J.; Bonner, R.A. & Morse, E.C.
Partner: UNT Libraries Government Documents Department