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Use of the TFTR prototype charge exchange neutral analyzer for fast He/sub 3//sup + +/ diagnostics during ICRF heating on PLT

Description: The Charge Exchange Neutral Analyzer (CENA) for TFTR is designed to measure singly charged ion species of atomic mass A = 1, 2, and 3 simultaneously with up to 75 energy channels per mass and an energy range of 0.5 < AE < 600, where AE is in units of AMU.keV. Plans to test the prototype analyzer on PLT prior to installation on TFTR are discussed. The capability of the analyzer to simultaneously measure singly reionized H, D, and He/sub 3/ charge exchange neutrals makes the analyzer of particular interest for recently proposed fast He/sub 3//sup + +/ diagnostics during ICRF heating on PLT.
Date: July 1, 1981
Creator: Medley, S.S.
Partner: UNT Libraries Government Documents Department

Vacuum system design and tritium inventory for the TFTR charge exchange diagnostic

Description: The charge exchange diagnostic for the TFTR is comprised of two analyzer systems which contain a total of twenty independent mass/energy analyzers and one diagnostic neutral beam tentatively rated at 80 keV, 15 A. The associated vacuum systems were analyzed using the Vacuum System Transient Simulator (VSTS) computer program which models the transient transport of multi-gas species through complex networks of ducts, valves, traps, vacuum pumps, and other related vacuum system components. In addition to providing improved design performance at reduced cost, the analysis yields estimates for the exchange of tritium from the torus to the diagnostic components and of the diagnostic working gases to the torus.
Date: May 1, 1979
Creator: Medley, S.S.
Partner: UNT Libraries Government Documents Department

Study of the mass and energy resolution of the E parallel B charge exchange analyzer for TFTR

Description: The charge exchange diagnostic for TFTR requires simultaneous multispecie (H/sup +/, D/sup +/, ..gamma../sup +/) analysis of particles in the energy range of 0.5 - 150 keV. The analyzer design chosen to provide this capability employs a wide gap semi-circular region of superimposed parallel electric and magnetic fields to accomplish mass and energy resolution, respectively. Combined with a large area, multi-anode microchannel plate detector, this arrangement will enable the energy distributions of protons, deuterions, and tritons to be measured concurrently as a function of time during each discharge. A computer simulation program for calculating ion trajectories through the analyzer was written that includes a realistic model of the magnetic and electrostatic fringe fields. This report presents the results of a study of the proposed E parallel B analyzer, and it reveals that the fringe fields are not detrimental to the performance of the analyzer.
Date: September 1, 1979
Creator: Kaita, R. & Medley, S.S.
Partner: UNT Libraries Government Documents Department

Fusion gamma diagnostics for D-T and D-/sup 3/He plasmas

Description: Nuclear reactions of interest in controlled thermonuclear fusion research often possess a branch yielding prompt emission of gamma radiation. In principle, the gamma emission can be exploited to provide a new fusion diagnostic offering measurements comparable to those obtained by the well established neutron diagnostics methods. The conceptual aspects for a fusion gamma diagnostic are discussed in this paper and the feasibility for application to the Tokamak Fusion Test Reactor during deuterium neutral beam heating of a D-T plasma and minority ion cyclotron resonance heating of a D-/sup 3/He plasma is examined.
Date: November 1, 1982
Creator: Medley, S.S. & Hendel, H.
Partner: UNT Libraries Government Documents Department

Visible imaging of edge fluctuations in TFTR

Description: Images of the visible light emission from the inner wall region of TFTR have been made using a rapidly gated, intensified TV camera. Strong ''filamentation'' of the neutral deuterium D..cap alpha.. light is observed when the camera gating time is <100 ..mu..sec during neutral-beam-heated discharges. These turbulent filaments vary in position randomly vs. time and have a poloidal wavelength of approx.3-5 cm which is much shorter than their parallel wavelength of approx.100 cm. A second and new type of edge fluctuation phenomenon, which we call a ''merfe,'' is also described. Merfes are a regular poloidal pattern of toroidally symmetric, small-scale marfes which move away from the inner midplane during the current decay after neutral beam injection. Some tentative interpretations of these two phenomena are presented. 27 refs., 8 figs.
Date: March 1, 1989
Creator: Zweben, S.J. & Medley, S.S.
Partner: UNT Libraries Government Documents Department

Microchannel plate response to high-energy neutrons

Description: The response of a chevron microchannel plate (MCP) to high energy neutrons was measured. The large area (4.6 cm x 13 cm) multi-anode MCP performance characteristics in the saturated pulse counting mode of operation were examined prior to neutron testing. This established a linear operating regime in which the neutron detection efficiency was measured to be 0.17% for 2.5 MeV-DD neutrons and 0.64% for 14 MeV-DT neutrons. The higher response measured for the 14 MeV-DT neutrons is attributed to gamma ray contamination induced by neutron collisions with materials located between the neutron source and the MCP detector. Due to their lower energy, the 2.5 MeV-DD response measurements are expected to be relatively free of gamma contamination and, hence, indicative of actual response of the MCP detector to neutrons in the 1 to 10 MeV energy range.
Date: July 1, 1981
Creator: Persing, R. & Medley, S.S.
Partner: UNT Libraries Government Documents Department

Gamma ray measurements during deuterium and /sup 3/He discharges on TFTR

Description: Gamma ray count rates and energy spectra have been measured in TFTR deuterium plasmas during ohmic heating and during injection of deuterium neutral beams for total neutron source strengths up to 6 x 10/sup 15/ neutrons per second. The gamma ray measurements for the deuterium plasmas are in general agreement with predictions obtained using simplified transport models. The 16.6 MeV fusion gamma ray from the direct capture reaction D(/sup 3/He,..gamma..)/sup 5/Li was observed during deuterium neutral beam injection into /sup 3/He plasmas for beam powers up to 7 MW. The measured yield of the 16.6 MeV gamma ray is consistent with the predicted yield. The observation of this capture gamma ray establishes the spectroscopy of the fusion gamma rays from the D-/sup 3/He reactions as a viable diagnostic of total fusion reaction rates and benchmarks the modeling for extension of the technique to D-T plasmas. 21 refs., 12 figs.
Date: May 1, 1987
Creator: Cecil, F.E. & Medley, S.S.
Partner: UNT Libraries Government Documents Department

Gyro-electron ghost images due to microchannel plate operation in transverse magnetic fields

Description: A multi-anode microchannel plate (MCP) detector was operated in a transverse magnetic field. When a collimated ion beam of approx.4-mm diameter impinged on one area of the plate, ghost images were observed elsewhere on the plate at anodes up to several centimeters from the beam spot. This effect is due to secondary electrons which are emitted from the interstitial surfaces around the MCP pores and returned to the surface of the plate under the influence of E-tilde X B-tilde fields, where E-tilde is the electric field perpendicular to the plate due to the MCP bias potential and B-tilde is the externally applied transverse magnetic field. A regenerative process is observed in which the secondary electrons traverse the surface of the plate in the E-tilde X B-tilde direction by successive gyro-orbit steps. A method for suppressing the ghost images is discussed.
Date: June 1, 1986
Creator: Roquemore, A.L. & Medley, S.S.
Partner: UNT Libraries Government Documents Department

Charge exchange ion temperature measurements during high power neutral beam injection on PLT

Description: A compilation and analysis of charge exchange ion temperature measurements obtained duriang recent high power neutral beam heating experiments on PLT is presented. For titanium gettered discharges using water-cooled carbon limiters (a = 40 cm), PLT produced ion temperatures up to 6.6 keV (T/sub e/ = 3.5 - 4.0 keV) with 2.4 MW-level neutral deuterium injection into low density hydrogen and deuterium plasmas. Over the beam power (P/sub B/ approx. 0.7 - 2.4 MW) and line average electron density (anti n/sub e/ approx. 1.6 - 3.6 x 10/sup 13/ cm/sup -3/) parameter space thus far explored, the ion temperature increase, ..delta..T/sub i/, is observed to scale according to the empirical relation: ..delta..T/sub i/ (keV) = 4.5 +- 0.5 P/sub B/ (MW)/anti n/sub e/(x 10/sup 13/ cm/sup -3/), where anti n/sub e/ is the line average electron density at peak ion temperature.
Date: January 1, 1979
Creator: Medley, S.S. & Davis, S.L.
Partner: UNT Libraries Government Documents Department

A procedure for generating quantitative 3-D camera views of tokamak divertors

Description: A procedure is described for precision modeling of the views for imaging diagnostics monitoring tokamak internal components, particularly high heat flux divertor components. These models are required to enable predictions of resolution and viewing angle for the available viewing locations. Because of the oblique views expected for slot divertors, fully 3-D perspective imaging is required. A suite of matched 3-D CAD, graphics and animation applications are used to provide a fast and flexible technique for reproducing these views. An analytic calculation of the resolution and viewing incidence angle is developed to validate the results of the modeling procedures. The calculation is applicable to any viewed surface describable with a coordinate array. The Tokamak Physics Experiment (TPX) diagnostics for infrared viewing are used as an example to demonstrate the implementation of the tools. For the TPX experiment the available locations are severely constrained by access limitations at the end resulting images are marginal in both resolution and viewing incidence angle. Full coverage of the divertor is possible if an array of cameras is installed at 45 degree toroidal intervals. Two poloidal locations are required in order to view both the upper and lower divertors. The procedures described here provide a complete design tool for in-vessel viewing, both for camera location and for identification of viewed surfaces. Additionally these same tools can be used for the interpretation of the actual images obtained by the actual diagnostic.
Date: May 1, 1996
Creator: Edmonds, P.H. & Medley, S.S.
Partner: UNT Libraries Government Documents Department

Design Study of a Visible/Infrared Periscope for Intense Radiation Applications using Reflective Optics

Description: In magnetically confined fusion devices employing deuterium-tritium (D-T) operation, refractive optical components exposed to neutron and gamma radiation can be subject to degradation of the transmission characteristics, induced luminescence, and altered mechanical properties including dimensional changes. Although radiation resistant refractive optics functioned well for the Tokamak Fusion Test Reactor (TFTR) periscope system during D-T operation, this design approach is unpromising in the much more hostile radiation environment of future D-T devices such as the International Thermonumclear Experimental Reactor (ITER). Under contract to the Princeton Plasma Physics Laboratory, Ball Aerospace of Colorado carried out a periscope design study based on the use of reflective optics. In this design, beryllium reflective input optics supported by a fused silica optical bench were interfaced to a Cassegrain relay system to transfer plasma images to remotely located cameras. This system is also capable of measuring first-wall surface temperatures in the range of 300 - 2,000 degrees C even under projected heating of the reflective optics themselves to several hundred degrees Celsius. Tests of beryllium mirror samples, however, revealed that operation at temperatures above 700 degrees C leads to a loss of specular reflectivity, thus placing an upper limit on the acceptable thermal environment. The main results of this periscope study are presented in this paper.
Date: May 1, 1998
Creator: Medley, S.S.
Partner: UNT Libraries Government Documents Department

Operation of the TFTR Pellet Charge Exchange Diagnostic in the Pulse Counting Mode during H+ RF-minority Heating

Description: The Pellet Charge Exchange technique on TFTR has been used primarily to obtain active charge exchange measurements using a high energy (0.5 - 4.0 MeV) neutral particle analyzer (NPA) in conjunction with impurity pellet injection (Li and B) with the scintillator-photomultiplier detector system operated in the current mode. While passive measurements using pulse counting were also obtained using this instrumentation, operation in this mode was very restrictive with pulse counting rates limited to less than {approximately}10 kHz in the absence of any significant neutron and gamma induced background signal. An upgrade to a specialized pulse counting capability which was developed by the Ioffe Institute was implemented which consisted of CsI(Tl) scintillators having features designed to minimize signals induced by background neutron and gamma rays and 16-channel pulse height analysis electronics on each of the eight NPA energy channels. Passive measurements of RF-driven energetic hydrogen minority ions which served to verify operation of the pulse counting mode are reported. It is shown that in the passive mode the main donors for the neutralization of H+ ions in this energy range are C5+ ions. The measured effective H+ tail temperatures range from 0.15 MeV at an RF power of 2 MW to 0.35 MeV at 6 MW.
Date: May 1998
Creator: Medley, S. S.
Partner: UNT Libraries Government Documents Department

Performance study of the TFTR diagnostic neutral beam for active charge exchange measurements

Description: A neutral beam source will be incorporated in the Tokamak Fusion Test Reactor (TFTR) charge exchange diagnostic to provide a time modulated, spatially localized enhancement of the charge exchange efflux. Two autonomous Charge Exchange Neutral Analyzer (CENA) systems are being designed for the TFTR. One system measures the plasma ion temperature along twelve vertical line-of-sight chords spaced approximately equidistantly across the torus minor diameter. The other system is dedicated primarily to measurement of ion phenomena associated with neutral beam injection heating and has a fan-like field of view along eight sight-lines in the equitorial plane. The neutral beam is steerable in order to access the viewing field of both CENA systems, though in general not simultaneously. The performance of the diagnostic neutral beam is evaluated to determine the optimal beam specifications for active charge exchange measurements. Using the optimal beam design parameters, the efficacy of the neutral doping is examined for both CENA systems over the envisioned range of the TFTR plasma density and temperature.
Date: June 1, 1980
Creator: Medley, S.S.; Goldston, R.J. & Towner, H.H.
Partner: UNT Libraries Government Documents Department

Monte Carlo simulation of ion trajectories in the modified PDX thermal charge exchange analyzer

Description: An improved design for the present PDX thermal charge exchange analyzer (MACE) has been proposed by one of the authors, in which the five cylindrical electrostatic plates for mass separation are replaced by a single flat, electrostatic deflection plate. An existihg Monte Carlo code that simulated the passage of ions through the MACE analyzer was modified to examine the feasibility of this change. The resulting calculations were used to optimize detector positions and collimation requirements. The first analyzer to be placed on PDX will be of the old design, similar to the present PLT analyzer. However, if the design reported here is successful on the test stand, the future PDX analyzers will all be of the new, single electrostatic plate variety. A further advantage will be the ability to install as many as ten detectors instead of the current five, thus providing twice as many energy channels for each shot. Also, both mass species (H, D) can be measured concurrently, if desired.
Date: December 1, 1978
Creator: Kaita, R.; Davis, S.L. & Medley, S.S.
Partner: UNT Libraries Government Documents Department

Technique for measuring the fast /sub 3/He/sup + +/ distribution during /sub 3/He/sup + +/ minority ICRF heating

Description: A technique for measuring the fast /sub 3/He/sup + +/ distribution during /sub 3/He/sup + +/ minority ICRF heating is discussed. The technique involves the use of 10 to 100 keV neutral helium beams to neutralize the fast /sub 3/He/sup + +/ ions by double charge exchange (/sub 3/He/sup + +/ + /sub 4/He/sup 0/ ..-->.. /sub 3/He/sup 0/ + /sub 4/He/sup + +/). The neutralized fast /sub 3/He atoms then escape from the plasma and are detected by conventional neutral particle analyzing apparatus. By the use of such a technique, the effectiveness of the coupling of the ion cyclotron waves to the /sub 3/He/sup + +/ minority could be measured.
Date: December 1, 1981
Creator: Post, D.E.; Grisham, L.R. & Medley, S.S.
Partner: UNT Libraries Government Documents Department

Charge exchange analyzer for mass resolved ion temperature measurements on PLT

Description: A five channel, mass resolved, radially scanning charge exchange diagnostic system was calibrated over an energy range of 0.75 less than or equal to E less than or equal to 40 keV and installed recently on PLT. The system provides either passive measurements with facility to correct for neutral density profile effects or active charge exchange diagnostics using a vertically aimed Berkeley ion source which is normally operated at 15 keV, 5 A. This report describes the analyzer and presents typical measurements obtained during high power neutral beam injection heating.
Date: January 1, 1979
Creator: Davis, S.L.; Medley, S.S. & Brusati, M.
Partner: UNT Libraries Government Documents Department

Method for determining fast-alpha-particle confinement in tokamak plasmas using resonant nuclear reactors

Description: The resonant nuclear reactions D(..cap alpha..,..gamma..)/sup 6/Li, /sup 6/Li(..cap alpha..,..gamma..)/sup 10/B, and /sup 7/Li(..cap alpha..,..gamma..)/sup 11/B are examined as diagnostics of fast-alpha-particle confinement in tokamak plasmas. Gamma rays from these resonant reactions with energies from 2.1 MeV to 9.2 MeV may be used to infer the alpha-particle population between energies of 0.4 MeV and 2.6 MeV. The ratio of these alpha-burnup reactions to the reactions T(D,..gamma..)/sup 5/He and /sup 3/He(D,..gamma..)/sup 5/Li provides a technique for the measurement of alpha confinement.
Date: March 1, 1986
Creator: Cecil, F.E.; Zweben, S.J. & Medley, S.S.
Partner: UNT Libraries Government Documents Department

The TFTR E Parallel B Spectrometer for Mass and Energy Resolved Multi-Ion Charge Exchange Diagnostics

Description: The Charge Exchange Neutral Analyzer diagnostic for the Tokamak Fusion Test Reactor was designed to measure the energy distributions of both the thermal ions and the supra thermal populations arising from neutral-beam injection and ion cyclotron radio-frequency heating. These measurements yield the plasma ion temperature, as well as several other plasma parameters necessary to provide an understanding of the plasma condition and the performance of the auxiliary heating methods. For this application, a novel charge-exchange spectrometer using a dee-shaped region of parallel electric and magnetic fields was developed at the Princeton Plasma Physics Laboratory. The design and performance of this spectrometer is described in detail, including the effects of exposure of the microchannel plate detector to magnetic fields, neutrons, and tritium.
Date: January 1, 1998
Creator: Roquemore, A.L. & Medley, S.S.
Partner: UNT Libraries Government Documents Department

Summary of Alpha Particle Transport

Description: This paper summarizes the talks on alpha particle transport which were presented at the 5th International Atomic Energy Agency's Technical Committee Meeting on "Alpha Particles in Fusion Research" held at the Joint European Torus, England in September 1997.
Date: August 19, 1998
Creator: Medley, S.S.; White, R.B. & Zweben, S.J.
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

Measurements of confined alphas and tritons in the MHD quiescent core of TFTR plasmas using the pellet charge exchange diagnostic

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--3.5 MeV using a Pellet Charge eXchange (PCX) diagnostic. A brief description of the measurement technique which involves active neutral particle analysis using the ablation cloud surrounding an injected impurity pellet as the neutralizer is presented. This paper focuses on alpha and triton measurements in the core of MHD quiescent TFTR discharges where the expected classical slowing down and pitch angle scattering effects are not complicated by stochastic ripple diffusion and sawtooth activity. In particular, the first measurement of the alpha slowing down distribution up to the birth energy, obtained using boron pellet injection, is presented. The measurements are compared with predictions using either the TRANSP Monte-Carlo code and/or a Fokker-Planck Post-TRANSP processor code, which assumes that the alphas and tritons are well confined and slow down classically. Both the shape of the measured alpha and triton energy distributions and their density ratios are in good agreement with the code calculations. The authors conclude that the PCX measurements are consistent with classical thermalization of the fusion-generated alphas and tritons.
Date: May 1, 1996
Creator: Medley, S.S.; Budny, R.V. & Mansfield, D.K.
Partner: UNT Libraries Government Documents Department

Measurements of energetic confined alphas and tritons on TFTR

Description: In a collaboration involving General Atomics, the A. F. Ioffe Physical-Technical Institute, and the Princeton Plasma Physics Laboratory, the energy distribution of the fast-confined alpha particles in DT experiments on TFIR is being measured by active neutral particle analysis using the ablation cloud surrounding an injected impurity pellet as the neutralizer. Recent papers reported the first measurements of the energy distribution fast confined alpha particles and examined the influence of magnetic field ripple and sawtooth oscillations on the behavior of the alpha energy spectra and radial density distributions. This paper focuses on alpha and triton measurements in the core of quiescent TFTR discharges where the expected classical slowing down and pitch angle scattering effects are not complicated by stochastic ripple diffusion and sawtooth activity.
Date: August 1, 1995
Creator: Medley, S.S.; Duong, H.H. & McChesney, J.M.
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

TPX diagnostics for tokamak operation, plasma control and machine protection

Description: The diagnostics for TPX are at an early design phase, with emphasis on the diagnostic access interface with the major tokamak components. Account has to be taken of the very severe environment for diagnostic components located inside the vacuum vessel. The placement of subcontracts for the design and fabrication of the diagnostic systems is in process.
Date: August 1, 1995
Creator: Edmonds, P.H.; Medley, S.S. & Young, K.M.
Partner: UNT Libraries Government Documents Department