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Heating efficiency of high-power perpendicular neutral-beam injection in PDX

Description: The heating efficiency of high power (up to 7.2 MW) near-perpendicular neutral beam injection in the PDX tokamak is comparable to that of tangential injection in PLT. Collisionless plasmas with central ion temperatures up to 6.5 keV and central electron temperatures greater than 2.5 keV have been obtained. The plasma pressure, including the contribution from the beam particles, increases with increasing beam power and does not appear to saturate, although the parametric dependence of the energy confinement time is different from that observed in ohmic discharges.
Date: March 1, 1982
Creator: Hawryluk, R.J.; Arunasalam, V. & Bell, M.
Partner: UNT Libraries Government Documents Department

Effect of current profile evolution on plasma-limiter interaction and the energy confinement time

Description: Experiments conducted on the PLT tokamak have shown that both plasma-limiter interaction and the gross energy confinement time are functions of the gas influx during the discharge. By suitably controlling the gas influx, it is possible to contract the current channel, decrease impurity radiation from the core of the discharge, and increase the gross energy confinement time, whether the aperture limiters were of tungsten, stainless steel or carbon.
Date: April 1, 1979
Creator: Hawryluk, R.J.; Bol, K. & Bretz, N.
Partner: UNT Libraries Government Documents Department

R.F. heating near the lower hybrid frequency in the FM-1 spherator

Description: Plasma heating experiments at frequencies near the lower hybrid frequency have been carried out at modest powers (.05 to 4kW). The antenna structure operating at 68 MHz was comprised of two plates driven out of phase on the exterior of the plasma. High electron heating efficiency (greater than 40 percent) in both helium and argon plasmas was observed with only a weak density dependence. At low densities (n/sub e/ less than or equal to 1 x 10$sup 11$ cm$sup -3$), the heating was uniform across the plasma while at higher densities the heating was preferentially on the exterior portion of the plasma. The heating of the exterior of the plasma was found not to correspond to absorption at the lower hybrid resonance layer. The electron heating efficiency was found to be a weak function of rf power when the incident rf power was varied from 1 to 15 times the experimentally observed threshold power for parametric instabilities. Ion temperatures were determined by measuring the Doppler broadening of an Argon ion line using a Fabry-Perot interferometer. Low efficiency main body ion heating (1 to 3 percent) was observed. (auth)
Date: December 1, 1975
Creator: Hawryluk, R.J.; Davis, S.L. & Schmidt, J.A.
Partner: UNT Libraries Government Documents Department

Inhibition of the current-driven ion wave instability by electron trapping in the FM-1 spherator

Description: An experimental analysis is made of the scattering of microwaves by the density fluctuations due to the current-driven ion wave instability in a toroidal plasma confinement device, the FM-1 spherator. It is found that the instability exists in the collisional regime and it is inhibited (i.e., quenched by two orders in magnitude) in the trapped-electron (i.e., banana) regime. The inhibition occurs when the electron collision frequency is about equal to the electron bounce frequency between mirror trapping. (auth)
Date: October 1, 1975
Creator: Arunasalam, V.; Okabayaski, M.; Hawryluk, R.J. & Suckewer, S.
Partner: UNT Libraries Government Documents Department

Results from deuterium-tritium tokamak confinement experiments

Description: Recent scientific and technical progress in magnetic fusion experiments has resulted in the achievement of plasma parameters (density and temperature) which enabled the production of significant bursts of fusion power from deuterium-tritium fuels and the first studies of the physics of burning plasmas. The key scientific issues in the reacting plasma core are plasma confinement, magnetohydrodynamic (MHD) stability, and the confinement and loss of energetic fusion products from the reacting fuel ions. Progress in the development of regimes of operation which have both good confinement and are MHD stable have enabled a broad study of burning plasma physics issues. A review of the technical and scientific results from the deuterium-tritium experiments on the Joint European Torus (JET) and the Tokamak Fusion Test Reactor (TFTR) is given with particular emphasis on alpha-particle physics issues.
Date: February 1, 1997
Creator: Hawryluk, R.J.
Partner: UNT Libraries Government Documents Department

Review of D-T Experiments Relevant to Burning Plasma Issues

Description: Progress in the performance of tokamak devices has enabled not only the production of significant bursts of fusion energy from deuterium-tritium (D-T) plasmas in the Tokamak Fusion Test Reactor (TFTR) and the Joint European Torus (JET) but, more importantly, the initial study of the physics of burning magnetically confined plasmas. The TFTR and JET, in conjunction with the worldwide fusion effort, have studied a broad range of topics including magnetohydrodynamic stability, transport, wave-particle interactions, the confinement of energetic particles, and plasma boundary interactions. The D-T experiments differ in three principal ways from previous experiments: isotope effects associated with the use of deuterium-tritium fuel, the presence of fusion-generated alpha particles, and technology issues associated with tritium handling and increased activation. The effect of deuterium-tritium fuel and the presence of alpha particles is reviewed and placed in the perspective of the much large r worldwide database using deuterium fuel and theoretical understanding. Both devices have contributed substantially to addressing the scientific and technical issues associated with burning plasmas. However, future burning plasma experiments will operate with larger ratios of alpha heating power to auxiliary power and will be able to access additional alpha-particle physics issues. The scientific opportunities for extending our understanding of burning plasmas beyond that provided by current experiments is described.
Date: December 21, 2001
Creator: Hawryluk, R.J.
Partner: UNT Libraries Government Documents Department

Low Z impurity transport in tokamaks. [Neoclassical transport theory]

Description: Low Z impurity transport in tokamaks was simulated with a one-dimensional impurity transport model including both neoclassical and anomalous transport. The neoclassical fluxes are due to collisions between the background plasma and impurity ions as well as collisions between the various ionization states. The evaluation of the neoclassical fluxes takes into account the different collisionality regimes of the background plasma and the impurity ions. A limiter scrapeoff model is used to define the boundary conditions for the impurity ions in the plasma periphery. In order to account for the spectroscopic measurements of power radiated by the lower ionization states, fluxes due to anomalous transport are included. The sensitivity of the results to uncertainties in rate coefficients and plasma parameters in the periphery are investigated. The implications of the transport model for spectroscopic evaluation of impurity concentrations, impurity fluxes, and radiated power from line emission measurements are discussed.
Date: October 1, 1978
Creator: Hawryluk, R.J.; Suckewer, S. & Hirshman, S.P.
Partner: UNT Libraries Government Documents Department

Effects of low Z impurities during the startup phase of a large tokamak

Description: The requirements placed on a tokamak ohmic heating system (i.e. loop voltage) to initiate the plasma become more severe as the size increases because of the current density decrease. During the startup phase even small concentrations of low Z impurities can affect the plasma energy balance very substantially and have very important effects on the evolution of the discharge. The startup phase has been studied using a simple zero dimensional computer code. Because the dominant energy loss mechanisms during startup, radiation, and ionization are a volume effect, the zero dimensional code was adequate to treat this phase. The results of this study which have been applied to TFTR indicate that the plasma evolution is a sensitive function of the applied loop voltage, impurity concentration, initial filling pressure and the manner in which gas is fed into the discharge. (auth)
Date: January 1, 1976
Creator: Hawryluk, R. J. & Schmidt, J. A.
Partner: UNT Libraries Government Documents Department

Results from D-T Experiments on TFTR and Implications for Achieving an Ignited Plasma

Description: Progress in the performance of tokamak devices has enabled not only the production of significant bursts of fusion energy from deuterium-tritium plasmas in the Tokamak Fusion Test Reactor (TFTR) and the Joint European Torus (JET) but, more importantly, the initial study of the physics of burning magnetically confined plasmas. As a result of the worldwide research on tokamaks, the scientific and technical issues for achieving an ignited plasma are better understood and the remaining questions more clearly defined. The principal research topics which have been studied on TFTR are transport, magnetohydrodynamic stability, and energetic particle confinement. The integration of separate solutions to problems in each of these research areas has also been of major interest. Although significant advances, such as the reduction of turbulent transport by means of internal transport barriers, identification of the theoretically predicted bootstrap current, and the study of the confinement of energetic fusion alpha-particles have been made, interesting and important scientific and technical issues remain for achieving a magnetic fusion energy reactor. In this paper, the implications of the TFTR experiments for overcoming these remaining issues will be discussed.
Date: July 14, 1998
Creator: Hawryluk, R.J. and the TFTR Group
Partner: UNT Libraries Government Documents Department

Results from D-T experiments on TFTR and implications for achieving an ignited plasma

Description: Progress in the performance of tokamak devices has enable not only the production of significant bursts of fusion energy from deuterium-tritium plasmas in the Tokamak Fusion Test Reactor (TFTR) and the Joint European Torus (JET) but, more importantly, the initial study of the physics of burning magnetically confined plasmas. As a result of the worldwide research on tokamaks, the scientific and technical issues for achieving an ignited plasma are better understood and the remaining questions more clearly defined. The principal research topics which have been studied on TFTR are transport, magnetohydrodynamic stability, and energetic particle confinement. The integration of separate solutions to problems in each of these research areas has also been of major interest. Although significant advances, such as the reduction of turbulent transport by means of internal transport barriers, identification of the theoretically predicted bootstrap current, and the study of the confinement of energetic fusion alpha-particles have been made, interesting and important scientific and technical issues remain. In this paper, the implications for the TFTR experiments for overcoming these remaining issues will be discussed.
Date: July 1, 1998
Creator: Hawryluk, R.J.; Blanchard, W. & Batha, S.
Partner: UNT Libraries Government Documents Department

Low-Z impurities in PLT

Description: Low-Z impurities concentrations (oxygen and carbon) have been measured in different discharges in PLT. The contribution to Z/sub eff/, influx rates and radiation losses by oxygen and carbon were obtained. An inverse correlation was found between the low-Z impurity density (and also the edge ion temperature) and the high-Z impurity (tungsten) density. A one-dimensional computer transport model has been used to calculate the spatial profiles of different oxygen and carbon ionization states. This model predicts that fully stripped oxygen and carbon ions should exist near the plasma periphery.
Date: November 1, 1977
Creator: Hinnov, E.; Suckewer, S.; Bol, K.; Hawryluk, R.; Hosea, J. & Meservey, E.
Partner: UNT Libraries Government Documents Department

Gas injection in PLT: experimental overview

Description: Cold gas injection serves both the obvious role of a particle source at the surface of the plasma and a more subtle role as one element in the process by which the relative impurity concentration and the MHD activity of a discharge are determined. Evidence offered by PLT experiments in support of these two widely recognized roles is considered.
Date: January 1, 1977
Creator: Schmidt, G.L.; Bretz, N.I.; Hawryluk, R.J.; Hosea, J.C. & Johnson, D.W.
Partner: UNT Libraries Government Documents Department

Current penetration in the PLT tokamak

Description: Current penetration in the PLT tokamak is modeled by a one dimensional magnetic field diffusion code assuming neoclassical resistivity. The code uses the measured temperature and density profiles as well as current and voltage measurements to evaluate Z/sub eff/. Under certain conditions, the resulting calculations of Z/sub eff/ during the startup phase have been considerably larger than the Z/sub eff/ determined spectroscopically indicating the presence of an enhanced current penetration mechanism. Furthermore, these calculations indicate that the gross energy confinement time is substantially less during the startup phase than in the quasi-steady state.
Date: January 1, 1980
Creator: Hawryluk, R.J.; Bretz, N.; Dimock, D.; Hinnov, E.; Johnson, D.; Monticello, D. et al.
Partner: UNT Libraries Government Documents Department

New techniques for calculating heat and particle source rates due to neutral-beam injection in axisymmetric tokamaks

Description: A set of numerical techniques are described for calculating heat and particle source rates due to neutral beam injection in axisymmetric tokamaks. While these techniques consume a substantial amount of computer time, they take into account a number of significant, and normally neglected, effects. Examples of these effects are reionization of escaping charge exchanged beam particles, finite fast ion orbit excursions, beam deposition through collisions of beam neutrals with circulating beam ions, and the transport of thermal neutrals in the plasma due to charge changing collisions with beam ions.
Date: February 1, 1981
Creator: Goldston, R.J.; McCune, D.C.; Towner, H.H.; Davis, S.L.; Hawryluk, R.J. & Schmidt, G.L.
Partner: UNT Libraries Government Documents Department

Observations of changes in residual gas and surface composition with discharge cleaning in PLT

Description: Hydrogen discharge cleaning of the PLT vacuum vessel has been studied by mass spectroscopy of desorbed gases and surface analysis of exposed samples. Several modes of vessel conditioning have been studied to date: (1) a high power discharge cleaning (PDC) mode, with a peak power density to the vessel wall P/sub s/ approximately 0.6 w/cm/sup 2/ and a peak electron temperature T/sub e/ approximately 100 ev; (2) low power (Taylor-type) discharge cleaning (TDC) with P/sub s/ approximately 0.05 w/cm/sup 2/ and T/sub e/ equal to or less than 5 eV. The predominant residual gases produced during PDC are CH/sub 4/ (1-5 x 10/sup -6/ torr) and CO (1-10 x 10/sup -7/ torr), whereas TDC produced primarily H/sub 2/O (1-2 x 10/sup -6/ torr) and CH/sub 4/ (1-10 x 10/sup -7/ torr). In situ surface analysis of hydrocarbon-covered stainless steel has shown significant decreases in carbon coverage occurring after 10/sup 3/-10/sup 4/ pulses of either cleaning mode. Observed changes in oxygen coverage are more difficult to interpret because of the presence of the nascent oxide layer on the stainless steel substrates.
Date: October 1, 1978
Creator: Dylla, H.F.; Bol, K.; Cohen, S.A.; Hawryluk, R.J.; Meservey, E.B. & Rossnagel, S.M.
Partner: UNT Libraries Government Documents Department

Production of high density plasma by pellet injection in TFTR

Description: High plasma densities have been produced in ohmic and neutral beam heated discharges on TFTR using a repeating pneumatic pellet injector developed at Oak Ridge National Laboratory (ORNL). Line average plasma densities as high as 1 x 10/sup 14/ cm/sup -3/ have been attained by injection of five 2.7 mm deuterium pellets ..delta..n/sub e/ = 2 x 10/sup 14/ cm/sup -3/ over a one-second interval into a stetched neutral beam pulse. Injection of a single large (4 mm) pellet in ohmic discharge has produced highly peaked profiles with nec(o) = 1.8 x 10/sup 14/ cm/sup -3/, n/sub e/(0) tau/sub E/(a) = 6.7 x 10/sup 13/ cm/sup -3/ and n/sub D/(0)Ti(0)tau/sub E/(a) = 8.8 x 10/sup 13/ cm/sup -3/ sKeV. Global confinement in these discharges approaches 0.45 seconds with a central density decay time of 2 seconds. Based on a neoclassical resistivity model and x-ray pulse-height analysis, zeff is <2 in both ohmic and beam-heated plasmas. The energy confinement properties of intermediate density (n/sub e/ (0) = 1 x 10/sup 14/ cm/sup -3/) full beam power (5.7 MW, 80 KVD/sup 0/) discharge have been studied in detail using the TRANSP code. Although the global energy confinement (approx. =2 oums at IP = 2.2 MA) is comparable to gas-fueled discharges, the confinement in the central core is considerably longer and electron heat conduction losses are smaller.
Date: January 1, 1985
Creator: Milora, S.L.; Schmidt, G.L.; Combs, S.K.; Bush, C.E.; Goldston, R.J.; Grek, B. et al.
Partner: UNT Libraries Government Documents Department

TFTR plasma regimes

Description: Significant extensions in the TFTR plasma operating regimes have been achieved with additional heating-system capability, installation of a multishot pellet injector, and the development of an enhanced confinement regime. In ohmically heated pellet-fueled discharges characterized by highly peaked density profiles, enhancements in tau/sub E/ have resulted in n/sub e/(0)tau/sub E/(a)-values of 1.5 x 10/sup 20/ m/sup -3/s. In neutral-beam-heated discharges, an operating regime has been developed in which substantial improvements in energy confinement time and neutron source strength are observed. Ion temperatures of approx.20 keV and n/sub e/(0)tau/sub E/(a)T/sub i/(0)-values of 2 x 10/sup 20/ m/sup -3/s keV have been achieved. This enhanced confinement regime is characterized by high values of ..beta../sub p/ and low values of collisionality. The observed surface voltage, which is negative during beam injection, is compared with models including beam-driven and bootstrap currents.
Date: February 1, 1987
Creator: Hawryluk, R.J.; Arunasalam, V.; Bell, M.G.; Bitter, M. Blanchard, W.R.; Bretz, N.L.; Budny, R. et al.
Partner: UNT Libraries Government Documents Department

First-wall and limiter conditioning in TFTR

Description: A progress report on the experimental studies of vacuum vessel conditioning during the first year of TFTR operation is presented. A previous paper described the efforts expended to condition the TFTR vessel prior to and during the initial plasma start-up experiments. During the start-up phase, discharge cleaning was performed with the vessel at room temperature. For the second phase of TFTR operations, which was directed towards the optimization of ohmically heated plasmas, the vacuum vessel could be heated to 150/sup 0/C. The internal configuration of the TFTR vessel was more complex during the second phase with the addition of a TiC/C moveable limiter array, Inconel bellows cover plates, and ZrAl getter pumps. A quantitative comparison is given on the effectiveness of vessel bakeout, glow discharge cleaning, and pulse discharge cleaning in terms of the total quantity of removed carbon and oxygen, residual gas base pressures and the resulting plasma impurity levels as measured by visible, uv, and soft x-ray spectroscopy. The initial experience with hydrogen isotope changeover in TFTR is presented including the results of the attempt to hasten the changeover time by using a glow discharge to precondition the vessel with the new isotope.
Date: October 1, 1984
Creator: Dylla, H.F.; Blanchard, W.R.; Hawryluk, R.J.; Hill, K.W.; Krawchuk, R.B.; Mueller, D. et al.
Partner: UNT Libraries Government Documents Department

Particle fueling and impurity control in PDX

Description: Fueling requirements and impurity levels in neutral-beam-heated discharges in the PDX tokamak have been compared for plasmas formed with conventional graphite rail limiters, a particle scoop limiter, and an open or closed poloidal divertor. Gas flows necessary to obtain a given density are highest for diverted discharges and lowest for the scoop limiter. Hydrogen pellet injection provides an efficient alternate fueling technique, and a multiple pellet injector has produced high density discharges for an absorbed neutral beam power of up to 600 kW, above which higher speeds or more massive pellets are required for penetration to the plasma core. Power balance studies indicate that 30 to 40% of the total input power is radiated while approx. 15% is absorbed by the limiting surface, except in the open divertor case, where 60% flows to the neutralizer plate. In all operating configurations, Z/sub eff/ usually rises at the onset of neutral beam injection. Both open divertor plasmas and those formed on a well conditioned water-cooled limiter have Z/sub eff/ less than or equal to 2 at the end of neutral injection. A definitive comparison of divertors and limiters for impurity control purposes requires longer beam pulses or higher power levels than available on present machines.
Date: December 1, 1984
Creator: Fonck, R.J.; Bell, M.; Bol, K.; Budny, R.; Couture, P.; Darrow, D. et al.
Partner: UNT Libraries Government Documents Department

Discharge control and evolution in TFTR

Description: The TFTR tokamak is used to evaluate discharge evolution and control, when these are broken down into discharge, initiation, volt-second consumption, and current and density ramp-up and ramp-down. Control of the current ramp-up using a plasma growing technique will be described, and the advantages of this method compared to using constant major and minor radii will be discussed. The control of density using gas puffing, pellet injection, and neutral beam fueling will be presented, along with a discussion of the density range which is found to increase with plasma current. 23 refs., 11 figs., 2 tabs.
Date: January 1, 1986
Creator: Mueller, D.; Bell, M.; Boody, F.; Bush, C.; Cecchi, J.L.; Davis, S. et al.
Partner: UNT Libraries Government Documents Department

Measurements of the toroidal plasma rotation velocity in TFTR major-radius compression experiments with auxiliary neutral beam heating

Description: The time history of the central toroidal plasma rotation velocity in Tokamak Fusion Test Reactor (TFTR) experiments with auxiliary heating by neutral deuterium beam injection and major-radius compression has been measured from the Doppler shift of the emitted TiXXI-K..cap alpha.. line radiation. The experiments were conducted for neutral beam powers in the range from 2.1 to 3.8 MW and line-averaged densities in the range from 1.8 to 3.0 x 10/sup 19/ m/sup -2/. The observed rotation velocity increase during compression is in agreement with results from modeling calculations which assume classical slowing-down of the injected fast deuterium ions and momentum damping at the rate established in the precompression plasma.
Date: July 1, 1986
Creator: Bitter, M.; Scott, S.; Wong, K.L.; Goldston, R.J.; Grek, B.; von Goeler, S. et al.
Partner: UNT Libraries Government Documents Department

End points in discharge cleaning on TFTR (Tokamak Fusion Test Reactor)

Description: It has been found necessary to perform a series of first-wall conditioning steps prior to successful high power plasma operation in the Tokamak Fusion Test Reactor (TFTR). This series begins with glow discharge cleaning (GDC) and is followed by pulse discharge cleaning (PDC). During machine conditioning, the production of impurities is monitored by a Residual Gas Analyzer (RGA). PDC is made in two distinct modes: Taylor discharge cleaning (TDC), where the plasma current is kept low (15--50 kA) and of short duration (50 ms) by means of a relatively high prefill pressure and aggressive PDC, where lower prefill pressure and higher toroidal field result in higher current (200--400 kA) limited by disruptions at q(a) /approx/ 3 at /approx/ 250 ms. At a constant repetition rate of 12 discharges/minute, the production rate of H/sub 2/O, CO, or other impurities has been found to be an unreliable measure of progress in cleaning. However, the ability to produce aggressive PDC with substantial limiter heating, but without the production of x-rays from runaway electrons, is an indication that TDC is no longer necessary after /approx/ 10/sup 5/ pulses. During aggressive PDC, the uncooled limiters are heated by the plasma from the bakeout temperature of 150/degree/C to about 250/degree/C over a period of three to eight hours. This limiter heating is important to enhance the rate at which H/sub 2/O is removed from the graphite limiter. 14 refs., 3 figs., 1 tab.
Date: July 1, 1989
Creator: Mueller, D.; Dylla, H.F.; Bell, M.G.; Blanchard, W.R.; Bush, C.E.; Gettelfinger, G. et al.
Partner: UNT Libraries Government Documents Department