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Aspects of stellarator confinement scaling

Description: Extensive discussion has been made concerning stellarator experimental confinement scaling and the extrapolation to reactor systems. Two features are discussed here: (1) The role of hydrogen-impurity interactions. (2) The neoclassical (bootstrap) current has been invoked as an argument against the possibility of optimizing the stellarator magnetic configuration to reach high ..beta... It is felt that significant bootstrap current production under conditions of high ..beta.. will dominate the vacuum fields. In this regard, a brief summary is presented of a comparison made between ISX-B high-..beta.. data and the neoclassical predictions. The non-neoclassical rates of electron pitch-angle scattering serve to destroy this current, and are evidently responsible for a lack of evidence for the bootstrap current under conditions in tokamaks where a large effect is expected.
Date: January 1, 1981
Creator: Hogan, J.
Partner: UNT Libraries Government Documents Department

General principles of magnetic fusion confinement

Description: A few of the areas are described in which there is close interaction between atomic/molecular (A and M) and magnetic fusion physics. The comparisons between predictions of neoclassical transport theory and experiment depend on knowledge of ionization and recombination rate coefficients. Modeling of divertor/scrapeoff plasmas requires better low energy charge exchange cross sections for H + A/sup n+/ collisions. The range of validity of neutral beam trapping cross sections must be broadened, both to encompass the energies typical of present injection experiments and to deal with the problem of prompt trapping of highly excited beam atoms at high energy. Plasma fueling models present certain anomalies that could be resolved by calculation and measurement of low energy (<1 keV) charge exchange cross sections.
Date: January 1, 1980
Creator: Hogan, J.T.
Partner: UNT Libraries Government Documents Department

Effects of low-energy-electron-capture collisions (H/sub 0/ + c/sup n+/) on the particle and energy balance of tokamak plasmas

Description: To illustrate the way in which atomic data provides enlightenment in the search for understandable (and thus extrapolable) confinement models, we restrict our scope to electron capture collisions involving H/sub 0/ and multiply-charged ions. Many such foreign (impurity) multiply-charged ion species are found in plasma discharges, as a result of gas recycling and damage to the surrounding surfaces by energetic plasma particles. Typical low-Z ions are carbon and oxygen; the major constituents of the stainless steel wall (Fe, Ni, Cr) are intermediate impurities, while high-Z impurities (Mo, W) enter from limiter plates which constrict the hot plasma zone to reduce direct plasma-wall contact. In this discussion, however, attention will be given only to applications of data involving H/sub 0/ + C/sup n+/ ..-->.. H/sup +/ + C/sup (n-1)+/ reactions with energy 10 eV to 2 keV. This energy range is typical of the plasma edge in present devices.
Date: January 1, 1981
Creator: Hogan, J.T.
Partner: UNT Libraries Government Documents Department

Model for particle balance in pumped divertors (pre-VORTEX)

Description: An internally consistent model for particle transport in an open divertor geometry has been developed. Embodied in a new code, pre-VORTEX, the model couples the particle balance in the plasma core, the scrape-off layer, the open divertor channels, and the vacuum'' regions. This mutual coupling is particularly important in determining the conditions required for high recycling in the divertor. The plasma core is considered to have a relatively quiescent core region and a less well confined edge-localized mode''(ELM) region. The scrape-off layer is modeled with one-dimensional parallel and perpendicular transport. A two-point divertor channel model is used; it is similar to previous models, but with the addition of new physical processes: hydrogen charge exchange, impurity thermal charge exchange, and flux-limited parallel transport. Wall recycling data are required to describe the differing recycling properties of the wall regions and the divertor plates. Given local plasma diffusivities and wall recycling properties, the model predicts the volume-averaged density and global particle confinement time. The input data are uncertain, and a major use for the model is to permit comparison with data. The final model, VORTEX, is intended for application to the analysis of divertor confinement experiments; it is coupled to a one-and-one-half--dimensional transport code and uses detailed geometric input from equilibrium fitting codes, experimentally measured core profiles, and such parameters as can be measured in the scrape-off layer. The pre-VORTEX model is compared as a stand-alone code with typical data from the DIII-D experiment and applied to the proposed DIII-D Advanced Divertor Project.
Date: August 1, 1990
Creator: Hogan, J.T.
Partner: UNT Libraries Government Documents Department

Impurity beam-trapping instability in tokamaks

Description: The sensitivity of neutron energy production to the impurity trapping of injected neutral beams is considered. This process is affected by inherent low-Z contamination of the tritium pre-heat plasma, by the species composition of the neutral beam, and by the entrance angle of the beam. The sensitivities of the process to these variables, and to the variation of wall material are compared. One finds that successful use of a low-Z, low-sputtering material can appreciably lengthen the useful pulse length. (auth)
Date: January 1, 1976
Creator: Hogan, J.T. & Howe, H.C.
Partner: UNT Libraries Government Documents Department

Fluxes of charged and neutral particles from tokamaks

Description: From surface effects in controlled thermonuclear fusion devices and reactors meeting; Argonne, Illinois, USA (10 Jan 1974). A brief description of a tokamak is given and some related impurity problems are discudsed. The role of neutral particles and their influence on present and future experiments involving larger machines is described. Some experimental and theoretical data are shown. (MOW)
Date: January 1, 1973
Creator: Hogan, J.T. & Clarke, J.F.
Partner: UNT Libraries Government Documents Department

ITER confinement capability

Description: The confinement capability of ITER was examined for a number of operational scenarios. The reference ITER physics baseline scenario (I = 22 MA) allows ignited burn under H-mode conditions ({tau}{sub E}(H-mode) {approximately} 2 {times} {tau}{sub E}(L-mode)). At higher currents (I = 25--28 MA) at which ITER can operate for limited pulse duration, there is an increased ignition margin if low-q operation proves acceptable. About a factor of 2 reduction in helium ash concentration (from the baseline value of 10% to 5%) in the reference ITER scenario has about the same impact on ignition capability as increasing the plasma current by about 15% (from the baseline value of 22 MA to {ge}25 MA). It might be possible to further optimize the ignition capability of ITER if some of the limits on operational boundaries can be relaxed by tailoring plasma profiles. 9 refs., 4 figs.
Date: January 1, 1990
Creator: Uckan, N.A. & Hogan, J.T.
Partner: UNT Libraries Government Documents Department

ITER global stability limits

Description: The MHD stability limits to the ITER operational space have been examined with the PEST ideal stability code. Constraints on ITER operation have been examined for the nominal operational scenarios and for possible design variants. Rather than rely on evaluation of a relatively small number of sample cases, the approach has been to construct an approximation to the overall operational space, and to compare this with the observed limits in high-{beta} tokamaks. An extensive database with {approximately}20,000 stability results has been compiled for use by the ITER design team. Results from these studies show that the design values of the Troyon factor (g {approximately} 2.5 for ignition studies, and g {approximately} 3 for the technology phase) which are based on present experiments, are also expected to be attainable for ITER conditions, for which the configuration and wall-stabilisation environment differ from those in present experiments. Strongly peaked pressure profiles lead to degraded high-{beta} performance. Values of g {approximately} 4 are found for higher safety factor (q {sub {Psi}} {le} 4) than that of the present design (q{sub {Psi}} {approximately} 3). Profiles with q(0) < 1 are shown to give g {approximately} 2.5, if the current density profile provides optimum shear. The overall operational spaces are presented for g-q{sub {Psi}}, q{sub {Psi}}-1{sub i}, q-{alpha}{sub p} and l{sub i}-q{sub {psi}}.
Date: January 1, 1990
Creator: Hogan, J.T. & Uckan, N.A.
Partner: UNT Libraries Government Documents Department

Helium transport and exhaust in tokamaks: A report on the international workshop on helium transport and exhaust experiments held at Gatlinburg, Tennessee, United States of America, April 16--18, 1991

Description: A workshop on helium transport and exhaust in tokamaks was held in Gatlinburg, Tennessee, April 6--18, 1991. The chief purpose of the workshop was to foster discussion of plans for future experiments in the study of adequate helium removal from advanced fusion devices such as the International Thermonuclear Engineering Reactor (ITER). The areas covered at the workshop are outlined, and the results presented are discussed in detail.
Date: December 1, 1991
Creator: Hogan, J.T. & Hillis, D.L.
Partner: UNT Libraries Government Documents Department

Some physics considerations for TEPR designs

Description: A simplified version of the Oak Ridge Tokamak Transport Code is used to assess the implications of confinement scaling, impurity trapping of neutral beam particles and plasma currents driven by neutral injection. The ORNL, ANL and GAC experimental power reactor reference designs are considered. (auth)
Date: January 1, 1975
Creator: Hogan, J.T.; Rome, J.A.; McAlees, D.G. & Attenberger, S.E.
Partner: UNT Libraries Government Documents Department

Plasma-surface interactions with ICRF antennas and lower hybrid grills in Tore Supra

Description: The edge plasma interactions of the actively cooled radio-frequency heating launchers in Tore Supra- ion-cyclotron range-of-frequencies (ICRF) antennas and lower-hybrid (LH) grills-are studied using infrared video imaging. On the two-strap ICRF antennas, operated in fast-wave electron heating or current drive mode, hot spots with temperatures of 500-900{degrees} C are observed by the end of 2-s power pulses of 2 MW per antenna. The distribution and maximum values of temperature are determined principally by the relative phase of the two antenna straps: dipole (heating) phasing results in significantly less antenna heating than does 90` (current drive) phasing. Transient heat fluxes of 1-20 MW/m{sup 2} are measured on the lateral protection bumpers at ICRF turn-on; these fluxes are primarily a function of plasma and radio frequency (rf) control, and are not simply correlated with the strap phasing or the final surface temperature distributions. The remarkable feature of the lower hybrid edge interaction is the production of beams of heat flux in front of the grills; these beams propagate along the helical magnetic field lines and can deliver fluxes of 5-10 MW/m{sup 2} over areas of several cm{sup 2} to plasma-facing components such as the grill or antenna lateral bumpers. Both the ICRF and LH phenomena appear to result from the acceleration of particles by the near fields of the launchers. Modeling of the heat flux deposition on components and its relation to sputtering processes is presented, and possibilities for controlling these interactions are discussed.
Date: October 1, 1996
Creator: Harris, J.H.; Hutter, T. & Hogan, J.T.
Partner: UNT Libraries Government Documents Department

Impurity control studies using SOL flow in DIII-D

Description: Experiments on DIII-D have demonstrated the efficacy of using induced scrape-off-layer (SOL) flow to preferentially enrich impurities in the divertor plasma. This SOL flow is produced through simultaneous deuterium gas injection at the midplane and divertor exhaust. Using this SOL flow, an improvement in enrichment (defined as the ratio of impurity fraction in the divertor to that in the plasma core) has been observed for all impurities in trace-level experiments (i.e., impurity level is non-perturbative), with the degree of improvement increasing with impurity atomic number. In the case of argon, exhaust gas enrichment using a modest SOL flow is as high as 17. Using this induced SOL flow technique and argon injection, radiative ELMing H-mode plasmas have been produced that combine high radiation losses (P{sub rad}/P{sub input} > 70%), low core fuel dilution (Z{sub eff} < 1.9), and good core confinement ({tau}{sub E} > 1.0 {tau}{sub E},ITER93H).
Date: November 1, 1998
Creator: Wade, M.R.; Hogan, J.T. & Isler, R.C.
Partner: UNT Libraries Government Documents Department

Lower-hybrid wave coupling and impurity generation in TORE SUPRA

Description: High power coupling of lower hybrid (LH) waves is affected by the geometry of the coupling region and thermal and impurity effects. The authors have carried out LH coupling experiments on Tore Supra specifically to examine these issues. The paper is divided into 3 areas: effect of plasma shape; LH coupling driving combined LH-ICRF experiments; and effect of LH power on thermal load and impurity generation.
Date: December 1, 1995
Creator: Harris, J.H.; Hogan, J.T. & Goniche, M.
Partner: UNT Libraries Government Documents Department

Observation and interpretation of thermal instabilities at the front face of actively cooled limiters in TORE-SUPRA

Description: In TORE-SUPRA, actively cooled modular limiters (time constant = 2 s) covered with carbon have been used to exhaust the convective heat flux continuously up to 700 kW steady state (design value) without thermal instability, i.e., 4.5 MW/m{sup 2} on average. Steady state surface temperatures in the range 600 C (with 1.45 MW of Lower Hybrid waves) were routinely obtained. However, sudden surface temperature excursions from 600 C to 1,900 C, called ``super-brilliances``, were observed during ohmic or heated plasmas, taking place locally over 20 ms, which led to a new equilibrium. This new equilibrium correspond to a local increased power flux density to the limiter as confirmed by calorimetric measurements. Shot after shot, an increasing number of independent overheated zones (up to 4) were observed on the limiter ridge, the closest location to Last Closed Flux Surface (LCFS). The power extracted by the limiter then was {approximately} 1.1 MW (6.9 MW/m{sup 2} average and 15 MW/m{sup 2} maximum). Experimental data and possible mechanisms leading to a finite increased heat flux to the limiter surface are reviewed and comparisons with modelization are made.
Date: December 1, 1995
Creator: Guilhem, D.; Hogan, J.T.; Mitteau, R. & Phillips, V.
Partner: UNT Libraries Government Documents Department

A quantitative study of the carbon impurity production mechanisms from an inertial limiter in Tore Supra as determined by visible spectroscopy

Description: In a steady-state tokamak, impurity production and transport from plasma facing components will have to be controlled. Recent results from several divertor tokamaks suggest the importance of chemical sputtering as an impurity production mechanism. However, since impurity production is minimized in high recycling divertor configurations, the quantitative characterization of impurity generation is more difficult than in the high heat flux environment of a limiter configuration. A quantitative study of the role of temperature dependent sputtering mechanisms on the outboard limiter in Tore Supra was performed. The methane flux proved to be significantly reduced above surface temperatures of 1,100 C and negligible above 1,300 C. The peak in the methane yield as a function of surface temperature is consistent with lab results. It was determined that chemical sputtering (early in the shot) had a small, to negligible, impact on the C{sup +} flux; while RES (late in the shot) had a strong impact on the C{sup +} flux. However, from the Z{sub eff} measurements, it was concluded that neither process contributed to the core carbon content.
Date: December 1, 1995
Creator: Tobin, S.J.; Kammash, T. & Hogan, J.T.
Partner: UNT Libraries Government Documents Department

Three-dimensional antenna models for fusion experiments

Description: The development of the RANT3D code has permitted the systematic study Of the effect of three-dimensional structures on the launched power spectrum for antennas in the ion cyclotron range of frequencies. The code allows the septa between current straps to be modeled with arbitrary heights and permits the antenna to interact with other structures in the tokamak. In this paper we present comparisons of calculated loading with the Tokamak Fusion Test Reactor and Tore Supra experiments, demonstrate the effects on loading caused by positioning uncertainties for an antenna in Tore Supra, and show electric field patterns near the Tore Supra antenna. A poloidal component in the static magnetic field for the plasma response is included in the near-field calculations using the warm plasma code, GLOSI. Preliminary estimates for the heat flux on the bumper limiters during typical operation in Tore Supra are also presented.
Date: July 1995
Creator: Carter, M. D.; Wang, C. Y. & Hogan, J. T.
Partner: UNT Libraries Government Documents Department

Particle exhaust modeling for the collaborative DIII-D Advanced Divertor Program

Description: A principal objective of the collaborative DIII-D Divertor Program (ADP) is to achieve density control in H-mode discharges with edge biasing and with continuous particle exhaust at a rate determined by the external fueling sources (typically 20 Torr{center dot}L/s). The divertor baffle-bias ring system has been optimized for pumping speeds {approx}50,000 L/s with the neutral transport code DEGAS. With an entrance slot conductance of 50,000 L/s, a pumping speed of the same order is required to remove half of the {approx}40 Torr{center dot}L/s that enters the baffle chamber for typical H-mode discharges. Increasing the exhaust fraction with higher pumping speed is self-limiting, owing to the attendant reduction of the recycling flux. The effects of pumping on the plasma core, scrape-off layer (SOL), and divertor have been estimated with a model that self-consistently couples the transport in these regions. The required {approx}50,000 L/s pumping speed can be achieved with either titanium getter pumps or cryopumps. Evaluation of both systems has led to the conclusion that cryopumps will be more compatible with the environment of the DIII-D divertor. 8 refs., 7 figs.
Date: January 1, 1990
Creator: Mioduszewski, P.K.; Owen, L.W. & Menon, M.M. Hogan, J.T.
Partner: UNT Libraries Government Documents Department

Performance characterization of pneumatic single pellet injection system

Description: The Oak Ridge National Laboratory single-shot pellet injector, which has been used in plasma fueling experiments on ISX and PDX, has been upgraded and extensively instrumented in order to study the gas dynamics of pneumatic pellet injection. An improved pellet transport line was developed which utilizes a 0.3-cm-diam by 100-cm-long guide tube. Pellet gun performance was characterized by measurements of breech and muzzle dynamic pressures and by pellet velocity and mass determinations. Velocities up to 1.4 km/s were achieved for intact hydrogen pellets using hydrogen propellant at 5-MPa breech pressure. These data have been compared with new pellet acceleration calculations which include the effects of propellant friction, heat transfer, time-dependent boundary conditions, and finite gun geometry. These results provide a basis for the extrapolation of present-day pneumatic injection system performance to velocities in excess of 2 km/s.
Date: January 1, 1982
Creator: Schuresko, D.D.; Milora, S.L.; Hogan, J.T.; Foster, C.A. & Combs, S.K.
Partner: UNT Libraries Government Documents Department

Modeling of DIII-D noble gas puff and pump experiments

Description: Previous DIII-D experiments that induced a D{sup +} flow in the scrap-off layer (SOL) showed that this flow increased the divertor concentration of extrinsically injected impurities (neon, argon). These impurity fueling and exhaust (or puff and pump) experiments raise a number of modeling issues: the effect of edge-localized modes (ELMs) in regulating impurity core accumulation; the particle balance of the extrinsic impurities; the relation between divertor and plenum enrichment; and the effect of features unique to the present DIII-D Advanced Divertor configuration, specifically, the localized back-conductance of D{sub 2} and impurities from the baffle plenum in the outboard divertor region. To aid in understanding the relations between these processes, models have been improved: for core impurity transport to include ELM effects, and for divertor models to treat helium, neon, and argon transport with DIII-D--specific configuration effects. The models have been used to analyze a series of experiments in which neon and argon were first continuously injected (in the divertor private flux region) for 1.5 s, and then exhausted by the DIII-D cryopumping system. Deuterium was puffed at rates of 80 Torr L/s and 150 Torr L/s from the midplane and the divertor private region in these experiments. Results of the simulations are given.
Date: August 1, 1997
Creator: Hogan, J.T.; Wade, M.; Maingi, R.; Owen, L.; Schaffer, M. & West, P.
Partner: UNT Libraries Government Documents Department

Development of Green Box sensor module technologies for rail applications

Description: Results of a joint Sandia National Laboratories, University of New Mexico, and New Mexico Engineering Research Institute project to investigate an architecture implementing real-time monitoring and tracking technologies in the railroad industry is presented. The work, supported by the New Mexico State Transportation Authority, examines a family of smart sensor products that can be tailored to the specific needs of the user. The concept uses a strap-on sensor package, designed as a value-added component, integrated into existing industry systems and standards. Advances in sensor microelectronics and digital signal processing permit us to produce a class of smart sensors that interpret raw data and transmit inferred information. As applied to freight trains, the sensors` primary purpose is to minimize operating costs by decreasing losses due to theft, and by reducing the number, severity, and consequence of hazardous materials incidents. The system would be capable of numerous activities including: monitoring cargo integrity, controlling system braking and vehicle acceleration, recognizing component failure conditions, and logging sensor data. A cost-benefit analysis examines the loss of revenue resulting from theft, hazardous materials incidents, and accidents. Customer survey data are combined with the cost benefit analysis and used to guide the product requirements definition for a series of specific applications. A common electrical architecture is developed to support the product line and permit rapid product realization. Results of a concept validation, which used commercial hardware and was conducted on a revenue-generating train, are also reported.
Date: April 1, 1996
Creator: Rey, D.; Breeding, R.; Hogan, J.; Mitchell, J.; McKeen, R.G. & Brogan, J.
Partner: UNT Libraries Government Documents Department