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HIGH SPATIAL RESOLUTION IMAGING OF INERTIAL FUSION TARGET PLASMAS USING BUBBLE NEWTRON DETECTORS

Description: OAK B202 HIGH SPATIAL RESOLUTION IMAGING OF INERTIAL FUSION TARGET PLASMAS USING BUBBLE NEWTRON DETECTORS. Bubble detectors, which can detect neutrons with a spatial resolution of 5 to 30 {micro}, are a promising approach to high-resolution imaging of NIF target plasmas. Gel bubble detectors were used in successful proof-of-principle imaging experiments on OMEGA. Until recently, bubble detectors appeared to be the only approach capable of achieving neutron images of NIF targets with the desired 5 {micro} spatial resolution in the target plane. In 2001, NIF reduced the required standoff distance from the target, so that diagnostic components can now be placed as close as 10 cm to the target plasma. This will allow neutron imaging with higher magnification and may make it possible to obtain 5 {micro}m resolution images on NIF using deuterated scintillators. Having accomplished all that they can hope to on OMEGA using gel detectors, they suggested that the 2002 NLUF shots be used to allow experimental tests of the spatial resolution of the CEA-built deuterated scintillators. The preliminary CEA data from the June 2002 run appears to show the spatial resolution using the deuterated scintillator detector array is improved over that obtained in earlier experiments using the proton-based scintillators. Gel detectors, which consist of {approx} 10 {micro}m diameter drops of bubble detector liquid suspended in an inactive support gel that occupies {approx} 99% of the detector volume, were chosen for the initial tests on OMEGA since they are easy to use. The bubbles could be photographed several hours after the neutron exposure. Imaging NIF target plasmas at neutron yields of 10{sup 15} will require a higher detection efficiency detector. Using a liquid bubble chamber detector should result in {approx} 1000 times higher neutron detection efficiency which is comparable to that possible using scintillation detectors. A pressure-cycled liquid ...
Date: October 1, 2002
Creator: FISHER,RK
Partner: UNT Libraries Government Documents Department

Alpha diagnostics using pellet charge exchange: Results on TFTR and prospects for ITER

Description: Confinement of alpha particles is essential for fusion ignition and alpha physics studies are a major goal of the TFTR, JET, and ITER DT experiments, but alpha measurements remain one of the most challenging plasma diagnostic tasks. The Pellet Charge Exchange (PCX) diagnostic has successfully measured the radial density profile and energy distribution of fast (0.5 to 3.5 MeV) confined alpha particles in TFTR. This paper describes the diagnostic capabilities of PCX demonstrated on TFTR and discusses the prospects for applying this technique to ITER. Major issues on ITER include the pellet`s perturbation to the plasma and obtaining satisfactory pellet penetration into the plasma.
Date: May 1, 1996
Creator: Fisher, R.K.; Duong, H.H. & McChesney, J.M.
Partner: UNT Libraries Government Documents Department

Threshold bubble chamber for measurement of knock-on DT neutron tails from magnetic and inertial confinement experiments

Description: We propose a new {open_quotes}threshold{close_quotes} bubble chamber detector for measurement of knock-on neutron tails. These energetic neutrons result from fusion reactions involving energetic fuel ions created by alpha knock-on collisions in tokamak and other magnetic confinement experiments, and by both alpha and neutron knock-on collisions in inertial confinement fusion (ICF) experiments. The energy spectrum of these neutrons will yield information on the alpha population and energy distribution in tokamaks, and on alpha target physics and {rho}R measurements in ICF experiments. The bubble chamber should only detect neutrons with energies above a selectable threshold energy controlled by the bubble chamber pressure. The bubble chamber threshold mechanism, detection efficiency, and proposed applications to the International Thermonuclear Experimental Reactor (ITER) and National Ignition Facility (NIF) experiments will be discussed.
Date: July 1, 1996
Creator: Fisher, R.K.; Zaveryaev, V.S. & Trusillo, S.V.
Partner: UNT Libraries Government Documents Department

The effect of toroidal field ripple on confined alphas in TFTR D-T plasmas

Description: The Pellet Charge Exchange (PCX) diagnostic on the Tokamak Fusion Test Reactor (TFTR) presently measures trapped alpha distribution functions with very small pitch angle (v {parallel} /v {approximately} 0.05) at the midplane. The measured PCX alpha signal exhibits a depletion region near the outboard region. Results of the alpha energy spectra and radial profile suggest stochastic ripple diffusion is the cause of the depletion. Comparison of the ripple stochastization boundary with Goldston-White-Boozer theory also shows the correct functional dependence on alpha energy and q-profile.
Date: May 1, 1996
Creator: Duong, H.H.; Medley, S.S. & Fisher, R.K.
Partner: UNT Libraries Government Documents Department

Design and operation of the pellet charge exchange diagnostic for measurement of energetic confined alphas and tritons on TFTR

Description: Radially-resolved energy and density distributions of the energetic confined alpha particles in D-T experiments on TFTR are being measured by active neutral particle analysis using low-Z impurity pellet injection. When injected into a high temperature plasma, an impurity pellet (e.g. Lithium or Boron) rapidly ablates forming an elongated cloud which is aligned with the magnetic field and moves with the pellet. This ablation cloud provides a dense target with which the alpha particles produced in D-T fusion reactions can charge exchange. A small fraction of the alpha particles incident on the pellet ablation cloud will be converted to helium neutrals whose energy is essentially unchanged by the charge transfer process. By measuring the resultant helium neutrals escaping from the plasma using a mass and energy resolving charge exchange analyzer, this technique offers a direct measurement of the energy distribution of the incident high-energy alpha particles. Other energetic ion species can be detected as well, such as tritons generated in D-D plasmas and H or He{sup 3} RF-driven minority ion tails. The diagnostic technique and its application on TFTR are described in detail.
Date: May 1, 1996
Creator: Medley, S.S.; Duong, H.H. & Fisher, R.K.
Partner: UNT Libraries Government Documents Department

Development of environmentally advanced hydropower turbine system design concepts

Description: A team worked together on the development of environmentally advanced hydro turbine design concepts to reduce hydropower`s impact on the environment, and to improve the understanding of the technical and environmental issues involved, in particular, with fish survival as a result of their passage through hydro power sites. This approach brought together a turbine design and manufacturing company, biologists, a utility, a consulting engineering firm and a university research facility, in order to benefit from the synergy of diverse disciplines. Through a combination of advanced technology and engineering analyses, innovative design concepts adaptable to both new and existing hydro facilities were developed and are presented. The project was divided into 4 tasks. Task 1 investigated a broad range of environmental issues and how the issues differed throughout the country. Task 2 addressed fish physiology and turbine physics. Task 3 investigated individual design elements needed for the refinement of the three concept families defined in Task 1. Advanced numerical tools for flow simulation in turbines are used to quantify characteristics of flow and pressure fields within turbine water passageways. The issues associated with dissolved oxygen enhancement using turbine aeration are presented. The state of the art and recent advancements of this technology are reviewed. Key elements for applying turbine aeration to improve aquatic habitat are discussed and a review of the procedures for testing of aerating turbines is presented. In Task 4, the results of the Tasks were assembled into three families of design concepts to address the most significant issues defined in Task 1. The results of the work conclude that significant improvements in fish passage survival are achievable.
Date: August 1, 1997
Creator: Franke, G.F.; Webb, D.R. & Fisher, R.K. Jr.
Partner: UNT Libraries Government Documents Department

Fast alpha diagnostics using carbon pellet injection

Description: Charge exchange interactions of alpha particles with the ablation cloud surrounding an injected carbon pellet can be used to measure the energy spectrum of the incident fast confined alpha particles in a fusion plasma. Measurement of helium neutrals from He{sup 2+} + C{sup 4+} {yields} He{sup 0} + C{sup 6+} interactions appears to be the most attractive option. This paper describes progress on developing this diagnostic including measurements during pellet injection into the TEXT tokamak. 14 refs., 2 figs.
Date: September 1, 1990
Creator: Fisher, R.K.; McChesney, J.M.; Howald, A.M.; Parks, P.B.; Thomas, D.M.; McCool, S.C. et al.
Partner: UNT Libraries Government Documents Department

Energy confinement in Doublet III with high-Z limiters

Description: This report describes the experimental measurements and data analysis techniques used to evaluate the energy confinement in noncircular plasmas produced in Doublet III. Major aspects of the confinement measurements and analysis techniques are summarized. Machine parameters, diagnostic systems and discharge parameters relavent to the confinement measurements are given. Magnetic analysis techniques used to determine the plasma shape are reviewed. Scaling of the on-axis values of electron temperature, confinement time and Z/sub eff/ with plasma density is presented. Comparison with scaling results from other circular tokamaks is discussed. Numerical and analytic techniques developed for calculating the plasma energy confinement time and self-consistent profiles of density, temperature, current, and flux in non-circular geometries are described. These techniques are applied to the data and used to determine the central and global electron energy confinement time for a typical doublet plasma. Additional aspects of the confinement such as the radial dependence of the electron thermal conductivity and the estimated ion temperature are explored with the aid of a non-circular transport simulation code. The results of the confinement measurements are summarized and discussed. A brief summary of the theoretically expected effects of noncircularity on plasma confinement is included for reference as Appendix I.
Date: February 1, 1980
Creator: Marcus, F.B.; Adcock, S.J.; Baker, D.R.; Blau, F.P.; Brooks, N.H.; Chase, R.P. et al.
Partner: UNT Libraries Government Documents Department

Confined trapped-alpha behavior in TFTR deuterium-tritium plasmas

Description: Confined trapped-alpha energy spectra and differential radial density profiles in TFTR D-T plasmas are obtained with the Pellet Charge-eXchange (PCX) diagnostic which measures high energy (E{sub {alpha}} = 0.5--3.5 MeV), trapped alphas (v{sub {parallel}}/v = - 0.048) at a single time slice ({Delta}t {approximately} 1 msec) with a spatial resolution of {Delta}r {approximately} 5 cm. Tritons produced in D-D plasmas and RF-driven ion tails (H, {sup 3}He or T) were also observed and energetic tritium ion tail measurements will be discussed. PCX alpha and triton energy spectra extending up to their birth energies were measured in the core of MHD-quiescent discharges where the expected classical slowing down and pitch angle scattering effects are not complicated by stochastic ripple diffusion and sawtooth activity. Both the shape of the measured alpha and triton energy distributions and their density ratios are in good agreement with TRANSP predictions, indicating that the PCX measurements are consistent with classical thermalization of the fusion-generated alphas and tritons. From calculations, these results set an upper limit on possible anomalous radial diffusion for trapped alphas of D{sub {alpha}} {le} 0.01 m{sup 2}s{sup {minus}1}. Outside the core, where the trapped alphas are influenced by stochastic ripple diffusion effects, the PCX measurements are consistent with the functional dependence of the Goldston-White-Boozer stochastic ripple threshold on the alpha energy and the q-profile. In the presence of strong sawtooth activity, the PCX diagnostic observes significant redistribution of the alpha signal radial profile wherein alphas are depleted in the core and redistributed to well outside the q = 1 radius, but apparently not beyond the energy-dependent stochastic ripple loss boundary.
Date: October 1, 1997
Creator: Medley, S.S.; Budny, R.V.; Redi, M.H.; Roquemore, A.L.; White, R.B.; Duong, H.H. et al.
Partner: UNT Libraries Government Documents Department

Aspects of trapped confined alpha physics on TFTR

Description: The energy distributions and radial density profiles of the fast-confined trapped alpha particles in DT experiments on TFTR are being measured in the energy range 0.5 to 3.5 MeV using the Pellet Charge Exchange diagnostic developed in a collaboration involving General Atomics, the A.F. Ioffe Physical-Technical Institute, and the Princeton Plasma Physics Laboratory. A brief description of the measurement technique which involves active neutral particle analysis using the ablation cloud surrounding an injected lithium or pellet as the neutralizer is presented. In the core of quiescent TFTR discharges, measured alpha spectra are consistent with classical slowing down. Measured Doppler broadening of alphas near the birth energy is consistent with the effective temperature of interacting deuterium and tritium ions. Outside the core alpha energy spectra and density profiles are influenced by the magnetic field ripple and appear to be consistent with stochastic ripple diffusion. Sawtooth oscillations lead to the significant broadening of alpha density profiles. The experimental data are modeled using a Fokker-Planck Post TRANSP (FTTP) code which includes the effects of the classical slowing down, magnetic field ripple losses, and the sawtooth mixing of alpha particles. The comparison of the experimental data with the FPPT calculations shows that broadening of trapped alpha density profiles after the sawtooth crashes can be explained by the influence of poloidal electric field generated during the crashes.
Date: June 1, 1996
Creator: Petrov, M.P.; Gorelenkov, N.N.; Budny, R.V.; Mansfield, D.K.; Medley, S.S.; Duong, H.H. et al.
Partner: UNT Libraries Government Documents Department

Alpha particle diagnostics using impurity pellet injection

Description: We have proposed using impurity injection to measure the energy distribution of the fast confined alpha particles in a reacting plasma. The ablation cloud surrounding the injected pellet is thick enough that an equilibrium fraction F{sub o}{sup {infinity}}(E) of the incident alphas should be neutralized as they pass through the cloud. By observing neutrals created in the large spatial region of the cloud which is expected to be dominated by the helium-like ionization state, e.g., Li{sup +} ions, we can determine the incident alpha distribution dn{sub He}2+/dE from the measured energy distribution of neutral helium atoms. Initial experiments were performed on TEXT in which we compared pellet penetration with our impurity pellet ablation model, and measured the spatial distribution of various ionization states in carbon pellet clouds. Experiments have recently begun on TFTR with the goal of measuring the alpha particle energy distribution during D-T operation in 1993--94. A series of preliminary experiments are planned to test the diagnostic concept. The first experiments will observe neutrals from beam-injected deuterium ions and the high energy {sup 3}He tail produced during ICH minority heating on TFTR interacting with the cloud. We will also monitor by line radiation the charge state distributions in lithium, boron, and carbon clouds.
Date: May 1, 1992
Creator: Fisher, R.K.; McChesney, J.M.; Howald, A.W.; Parks, P.B. (General Atomics, San Diego, CA (United States)); Snipes, J.A.; Terry, J.L. et al.
Partner: UNT Libraries Government Documents Department