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Conceptual design study of spheromak reactors

Description: Preliminary design studies are carried out for a spheromak fusion reactor. Simplified circuit theory is applied to obtain characteristic relations among various parameters of the spheromak configuration for an aspect ratio A greater than or equal to 1.6. These relations are used to calculate the parameters for the conceptual designs of three types of fusion reactor: (1) DT two-component, (2) DT ignited, and, (3) catalyzed DD ignited reactors. With a total wall loading of approx. 4 MWm/sup -2/, it is found that edge magnetic fields of only approx. 4T (DT) and approx. 9T (cat. DD) are required for ignited reactors of one-meter plasma (minor) radius with output powers in the gigawatt range. Assessment of various methods of generating reactor-grade spheromak plasmas is discussed briefly.
Date: July 1, 1980
Creator: Katsurai, M. & Yamada, M.
Partner: UNT Libraries Government Documents Department

QED-1 device and measurements of gettering efficiency for a simulated divertor plasma

Description: The QED-1 device at PPL has provided gettering efficiency data for neutralized hydrogen plasma on titanium. The hollow-anode arcjet produces a plasma column 1 cm in diameter with 10/sup 12/ < n/sub e/ < 10/sup 15/ cm/sup -3/ and T/sub i/ approx.< T/sub e/ = 3-10 eV, confined by an axial magnetic field of 1-6 kG. The gettering measurements are based on monitoring neutral gas density with respect to time in the divertor simulation chamber of QED-1. The present results indicate that the plasma particles lose their charge and most of their energy when they strike the neutralizer plate.
Date: March 1, 1980
Creator: Owens, D.K. & Yamada, M.
Partner: UNT Libraries Government Documents Department

Amplification of S-1 Spheromak current by an inductive current transformer

Description: We attempt to predict the consequences of adding an inductive current transformer (OH Transformer) to the present S-1 Spheromak experiment. Axisymmetric modeling with only classical dissipation shows an increase of toroidal current and a shrinking and hollowing of the current channel, conserving toroidal flux. These unstable profiles will undergo helical reconnection, conserving helicity K = ..integral.. A-vector x B-vector d tau while increasing the toroidal flux and decreasing the poloidal flux so that the plasma relaxes toward the Taylor state. This flux rearrangement is modeled by a new current viscosity term in the mean-field Ohm's law which conserves helicity and dissipates energy.
Date: November 1, 1985
Creator: Jardin, S.C.; Janos, A. & Yamada, M.
Partner: UNT Libraries Government Documents Department

Relaxation of spheromak plasmas toward a minimum-energy state through global magnetic fluctuations

Description: Globally coherent modes which are observed during formation in the S-1 Spheromak plasma are shown to be important for flux conversion and plasma relaxation toward a minimum-energy state. A significant finding is the temporal progression through the n = 5, 4, 3, 2; m = 1 mode sequence as q rises through rational fractions m/n, where n and m are defined by the functional dependence e/sup i(nphi + mtheta/) of the fluctuations on toroidal angle phi and poloidal angle theta. Resistive MHD analysis predicts the observed modes and the sequence of occurrence.
Date: July 1, 1985
Creator: Janos, A.; Hart, G.W. & Yamada, M.
Partner: UNT Libraries Government Documents Department

Review of recent experiments on magnetic reconnection in laboratory plasmas

Description: The present paper reviews recent laboratory experiments on magnetic reconnection. Examples will be drawn from electron current sheet experiments, merging spheromaks, and from high temperature tokamak plasmas with the Lundquist numbers exceeding 10{sup 7}. These recent laboratory experiments create an environment which satisfies the criteria for MHD plasma and in which the global boundary conditions can be controlled externally. Experiments with fully three dimensional reconnection are now possible. In the most recent TFTR tokamak discharges, Motional Stark effect (MSE) data have verified the existence of a partial reconnection. In the experiment of spheromak merging, a new plasma acceleration parallel to the neutral line has been indicated. Together with the relationship of these observations to the analysis of magnetic reconnection in space and in solar flares, important physics issues such as global boundary conditions, local plasma parameters, merging angle of the field lines, and the 3-D aspects of the reconnection are discussed.
Date: February 1, 1995
Creator: Yamada, M.
Partner: UNT Libraries Government Documents Department

Ion-beam-driven resonant ion cyclotron instability

Description: The resonant ion-beam-driven electrostatic ion cyclotron instability is identified. Measured dispersion relation and onset vs. beam energy and density agree with numerical calculations based on a theory which includes beam acoustic terms. After amplitude saturation, velocity space diffusion of the beam ions is observed. (auth)
Date: November 1, 1975
Creator: Hendel, H.W.; Yamada, M.; Seiler, S.W. & Ikezi, H.
Partner: UNT Libraries Government Documents Department

Ion acceleration and direct ion heating in three-component magnetic reconnection

Description: Ion acceleration and direct ion heating in magnetic reconnection are experimentally observed during counterhelicity merging of two plasma toroids. Plasma ions are accelerated up to order of the Alfen speed through contraction of the reconnected field-lines with three-components. The large increase in ion thermal energy (from 10 eV up to 200 eV) is attributed to the direct conversion of the magnetic energy into the unmagnetized ion population. This observation is consistent with the magnetohydrodynamic and macro-particle simulations.
Date: March 1, 1996
Creator: Ono, Y.; Yamada, M. & Akao, T.
Partner: UNT Libraries Government Documents Department

Verification of the Taylor (minimum energy) state in the S-1 Spheromak

Description: Experimental measurements of the equilibrium in the S-1 Spheromak by use of magnetic probes inside the plasma show that the final magnetic equilibrium is one which has relaxed close to the Taylor (minimum-energy) state, even though the plasma is far from that state during formation. The comparison is made by calculating the two-dimensional ..mu.. profile of the plasma from the probe data, where ..mu.. is defined as ..mu../sub 0/j/sub parallel//B. Measurements using a triple Langmuir probe provide evidence to support the conclusion that the pressure gradients in the relaxed state are confined to the edge region of the plasma.
Date: September 1, 1985
Creator: Hart, G. W.; Janos, A.; Meyerhofer, D. D. & Yamada, M.
Partner: UNT Libraries Government Documents Department

Experimental investigation of the nonlinear evolution of an impurity-driven drift wave

Description: An impurity-driven drift wave is observed to be destabilized by the reversed density gradient of a singly-ionized heavy-impurity-ion population in a Q-machine plasma. The evolution of the instability is investigated as it progresses from the initial linear exponential growth phase, into a nonlinear saturated state, whereupon strong radially outward anomalous diffusion is observed. The relationship between the anomalous diffusion coefficient and the wave amplitude is in agreement with estimates obtained from the nonlinear drift-wave turbulence theory of Dupree.
Date: April 1, 1982
Creator: Allen, G.R.; Yamada, M.; Rewoldt, G. & Tang, W.M.
Partner: UNT Libraries Government Documents Department

Global magnetic fluctuations in S-1 Spheromak plasmas and relaxation toward a minimum-energy state

Description: Globally coherent modes have been observed during formation in the S-1 Spheromak plasma by analysis of magnetic field fluctuations measured from outside the plasma. The modes are of low n number (2 less than or equal to n less than or equal to 5), where n is defined by the functional dependence e/sup in phi/ of the fluctuation on toroidal angle phi. These modes are shown to be related to flux conversion and plasma relaxation toward a minimum-energy state during the spheromak formation. The modes are active while the q profile is rapidly changing, with q on-axis, q/sub 0/, rising to 0.7. A significant finding is the temporal progression through the n = 5, 4, 3, 2; m = 1 mode sequence as q rises through rational fractions m/n. During formation, peak amplitudes of the n = 2, 3, 4 modes relative to the unperturbed field have been observed as high as 20%, while more typical amplitudes are below 5%.
Date: May 1, 1985
Creator: Janos, A.; Hart, G.W.; Nam, C.H. & Yamada, M.
Partner: UNT Libraries Government Documents Department

Measurements of sputtering yields for low-energy plasma ions

Description: Sputtering yields of various wall/limiter materials of fusion devices have been extensively measured in the relevant plasma environment for low-energy light ions (E < 300eV). As a plasma source we have used an energetic arc device (QED-1 machine) in which hydrogen, deuterium, helium and argon plasma can be generated with a density of up to 10/sup 14/ cm/sup -3/ and electron temperature up to 10eV. Target materials used were C (graphite), Ti, Mo, Ta, W, and Fe (stainless steel). In order to study the dependence of the sputtering yields on the incident energy of ions, the target samples were held at negative bias voltage up to 300V. The sputtering yields were determined by a weight-loss method and by spectral line intensity measurements. The data obtained in the present experiment agree well with those previously obtained at the higher energies (E greater than or equal to 200eV) by other authors using different schemes; the present data also extend to substantially lower energies (E approx. > 30eV) than hitherto.
Date: April 1, 1979
Creator: Nishi, M.; Yamada, M.; Suckewer, S. & Rosengaus, E.
Partner: UNT Libraries Government Documents Department

Experimental control of the spheromak tilting instability

Description: The magnetohydrodynamic (MHD) tilting instability of the spheromak configuration has been experimentally investigated by recording the time evolution of the magnetic field configuration with small magnetic probes. Passive coil systems such as the figure eight and saddle coils have been proven experimentally to be effective against this instability.
Date: July 1, 1983
Creator: Munson, C.; Janos, A.; Wysocki, F. & Yamada, M.
Partner: UNT Libraries Government Documents Department

Method and apparatus for the formation of a spheromak plasma

Description: An inductive method and apparatus for forming detached spheromak plasma using a thin-walled metal toroidal ring are described that uses external current leads and internal poloidal and toroidal field coils located inside a vacuum chamber filled with low density hydrogen gas and an external axial field generating coil. The presence of a current in the poloidal field coils, and an externally generated axial field sets up the initial poloidal field configuration in which the field is strongest toward the major axis of the toroid. The internal toroidal-field-generating coil is then pulsed on, ionizing the gas and inducing poloidal current and toroidal magnetic field into the plasma region in the sleeve exterior to and adjacent to the ring and causing the plasma to expand away from the ring and toward the major axis. Next the current in the poloidal field coils in the ring is reversed. This induces toroidal current into the plasma and causes the poloidal magnetic field lines to reconnect. The reconnection continues until substantially all of the plasma is formed in a separated spheromak configuration held in equilibrium by the initial external field.
Date: March 24, 1981
Creator: Jardin, S.C.; Yamada, M.; Furth, H.P. & Okabayashi, M.
Partner: UNT Libraries Government Documents Department

Gaseous divertor simulation in an arc-jet device

Description: The first experimental simulation of the gaseous tokamak divertor is presented. Significant results are: (1) neutral gas at a pressure of a few mTorr is sufficient to absorb the entire localized flux of plasma thermal energy and reidstribute it over a wide area; (2) elastic ion-neutral collisions constitute the main energy absorbing process (at T/sub e,i/ less than or equal to 5 eV), and (3) a large pressure difference between divertor and main plasma chamber is maintained by plasma pumping in the connecting channel.
Date: December 1, 1982
Creator: Hsu, W.L.; Yamada, M. & Barrett, P.J.
Partner: UNT Libraries Government Documents Department

Nonlinear and Non-ideal Effects on FRC Stability

Description: New computational results are presented which advance the understanding of the stability properties of the Field-Reversed Configuration (FRC). We present results of hybrid and two-fluid (Hall-MHD) simulations of prolate FRCs in strongly kinetic and small-gyroradius, MHD-like regimes. The n = 1 tilt instability mechanism and stabilizing factors are investigated in detail including nonlinear and resonant particle effects, particle losses along the open field lines, and Hall stabilization. It is shown that the Hall effect determines the mode rotation and change in the linear mode structure in the kinetic regime; however, the reduction in the growth rate is mostly due to the finite Larmor radius effects. Resonant particle effects are important in the large gyroradius regime regardless of the separatrix shape, and even in cases when a large fraction of the particle orbits are stochastic. Particle loss along the open field lines has a destabilizing effect on the tilt mode and contributes to the ion spin up in toroidal direction. The nonlinear evolution of unstable modes in both kinetic and small-gyroradius FRCs is shown to be considerably slower than that in MHD simulations. Our simulation results demonstrate that a combination of kinetic and nonlinear effects is a key for understanding the experimentally observed FRC stability properties.
Date: October 21, 2002
Creator: Belova, E.V.; Davidson, R.C.; Ji, H. & Yamada, M.
Partner: UNT Libraries Government Documents Department

Characteristics of confinement and fusion reactivity in JT-60U high-{beta}{rho} and TFTR supershot regimes with deuterium neutral beam injection

Description: The high performance regimes achieved in JT-60U and TFTR have produced peak DD fusion neutron rates up to 5.6 {times} 10{sup 16}/s for similar heating beam powers, in spite of considerable differences in machine operation and plasma configuration. A common scaling for the DD fusion neutron rate (S{sub DD} {proportional_to} P{sub abs}{sup 2.0} H{sub ne} V{sub p}{sup {minus}0.9}) is obtained, where P{sub abs} and H{sub ne} are the absorbed beam power and beam fueling peaking factor, respectively, and V{sub p} is the plasma volume. The maximum stored energy obtained in each machine has been up to 5.4 MJ in TFTR and 8.7 MJ in JT-60U. Further improvements in the fusion neutron rate and the stored energy are limited by the {beta}-limit in Troyon range, {beta}{sub N} {approximately} 2.0--2.5. A common scaling for the stored energy (W{sub tot} {proportional_to} P{sub abs}V{sub p}H{sub ne}{sup 0.2}) is also proposed.
Date: March 1, 1995
Creator: Park, H.K.; Bell, M.G. & Yamada, M.
Partner: UNT Libraries Government Documents Department

Global stability study of the ultra low aspect ratio tokamak, ULART

Description: By introducing a slender current carrying conductor through the geometric center axis of the Tokyo University TS-3 device, the authors have generated ultra low aspect ratio tokamak (ULART) configurations with aspect ratio as low as 1.05. In this extreme limit they study the transition of the spheromak (q{sub edge} = 0, I{sub tf} = 0) to a ULART plasma (q{sub edge} = 2--20). The authors investigate the global MHD characteristics of ULART by comparing theoretical results with the experimental data obtained. A small current in the center conductor (compared with the plasma current) is found to significantly improve the overall MHD stability characteristics of the formed plasmas by effectively stabilizing the global tilt/shift mode. Theoretical calculations of the threshold toroidal field current required for stability and the growth rates of the tilt/shift modes agree well with the TS-3 data.
Date: February 1, 1996
Creator: Yamada, M.; Pomphrey, N.; Morita, A.; Ono, Y. & Katsurai, M.
Partner: UNT Libraries Government Documents Department

Parametric lower-hybrid instability driven by modulated electron beam injection

Description: A modulated electron beam is injected into a low ..beta.. plasma parallel to the confining field to investigate the energy-transfer-rate from the electron beam to the plasma. Parametric excitation of electrostatic lower-hybrid waves and ion cyclotron quasimodes is experimentally identified. The temperature of both ions and electrons is observed to increase significantly concomitant with the growth of the instability.
Date: August 1, 1978
Creator: Allen, G.R.; Owens, D.K.; Seiler, S.W.; Yamada, M.; Ikezi, H. & Porkolab, M.
Partner: UNT Libraries Government Documents Department

Exploration of low-aspect-ratio tokamak regimes in the CDX-U and TS-3 devices

Description: In the low-aspect-ratio tokamak regime, a lower q(a) regime (i.e. q(a) {le} 5, A = R/a {approx} 1.5) has been explored in CDX-U, and the ultra-low-aspect-ratio tokamak regime (1.05 {le} A {le} 1.5) has been explored in TS-3. Using a relatively low toroidal magnetic field, plasma discharges with I{sub p} {le} 53 kA, and q(a) {ge} 4 [q{sub cyl}(a) {ge}1] have been obtained in CDX-U. Low q(a), Ohmic plasmas in CDX-U show increasing MHD activity as the edge safety factor is lowered. These modes appear to reduce the current ramp-up rate and, at present, limit the access to even lower q(a) regimes. An experiment carried out in the ULART regime (A {approx} 1.05 {minus} 1.5) on the TS-3 device identifies a threshold of q(a) {ge} 3 with q{sub cyl}(a) < 1 for stability of global tilt/shift modes.
Date: December 31, 1994
Creator: Hwang, Y. S.; Yamada, M. & Jones, T. G.
Partner: UNT Libraries Government Documents Department

Experimental study of magnetic reconnection during a sawtooth crash in a high temperature tokamak plasma

Description: Magnetic reconnection is investigated in high temperature TFTR tokamak plasmas by a set of non-perturbative diagnostics. During the crash phase of sawtooth oscillations in the plasma discharges, the ECE (electron cyclotron emission) diagnostic measures a fast flattening of the 2-D electron temperature profile in a poloidal plane, an observation consistent with the Kadomtsev reconnection theory. On the other hand motional Stark effect(MSE) measurements indicate that central q values do not relax to unity after the crash, but increase only by 5-10%, typically from 0.7 to 0.75. The latter result is in contradiction with the models of Kadomtsev and/or Wesson. A heuristic model for the magnetic reconnection at the sawtooth crash is also presented.
Date: January 1, 1994
Creator: Yamada, M.; Manickam, J.; Pomphrey, N.; Levinton, F. M. & Nagayama, Y.
Partner: UNT Libraries Government Documents Department

Experimental Verification of the Kruskal-Shafranov Stability Limit in Line-Tied Partial Toroidal Plasmas

Description: The stability properties of partial toroidal flux ropes are studied in detail in the laboratory, motivated by ubiquitous arched magnetic structures found on the solar surface. The flux ropes studied here are magnetized arc discharges formed between two electrodes in the Magnetic Reconnection Experiment (MRX) [Yamada et al., Phys. Plasmas, 4, 1936 (1997)]. The three dimensional evolution of these flux ropes is monitored by a fast visible light framing camera, while their magnetic structure is measured by a variety of internal magnetic probes. The flux ropes are consistently observed to undergo large-scale oscillations as a result of an external kink instability. Using detailed scans of the plasma current, the guide field strength, and the length of the flux rope, we show that the threshold for kink stability is governed by the Kruskal-Shafranov limit for a flux rope that is held fixed at both ends (i.e., qa = 1).
Date: July 19, 2011
Creator: Oz, E.; Myers, C. E.; Yamada, M.; Ji, H.; Kulsrud, R. M. & Xie, J.
Partner: UNT Libraries Government Documents Department

Magnetic Reconnection with Sweet-Parker Characteristics in Two-dimensional Laboratory Plasmas

Description: Magnetic reconnection has been experimentally studied in a well-controlled, two-dimensional laboratory magnetohydrodynamic plasma. The observations are found to be both qualitatively and quantitatively consistent with a generalized Sweet-Parker model which incorporates compressibility, downstream pressure, and the effective resistivity. The latter is significantly enhanced over its classical values in the collisionless limit. This generalized Sweet-Parker model also applies to the case in which an unidirectional, sizable third magnetic component is present.
Date: January 1, 1999
Creator: Carter, T.; Hsu, S.; Ji, H.; Kulsrud, R.; Yamada, M. & al, et
Partner: UNT Libraries Government Documents Department

Measurement of Lower-hybrid Drift Turbulence in a Reconnecting Current Sheet

Description: We present a detailed study of fluctuations in a laboratory current sheet undergoing magnetic reconnection. The measurements reveal the presence of lower-hybrid-frequency range fluctuations on the edge of current sheets produced in the Magnetic Reconnection Experiment (MRX). The measured fluctuation characteristics are consistent with theoretical predictions for the lower-hybrid drift instability (LHDI). Our observations suggest that the LHDI does not provide any significant turbulent resistivity in MRX current sheets.
Date: June 20, 2001
Creator: Carter, T.A.; Ji, H.; Trintchouk, F.; Yamada, M. & Kulsrud, R.M.
Partner: UNT Libraries Government Documents Department

Numerical Study of Global Stability of Oblate Field-Reversed Configurations

Description: Global stability of the oblate (small elongation, E &lt; 1) Field-Reversed Configuration (FRC) has been investigated numerically using both three-dimensional magnetohydrodynamic (MHD) and hybrid (fluid electrons and kinetic ions) simulations. For every non-zero value of the toroidal mode number n, there are three MHD modes that must be stabilized. For n = 1, these are the interchange, the tilt and the radial shift; while for n &gt; 1 these are the interchange and two co-interchange modes with different polarization. It is shown that the n = 1 tilt mode becomes an external mode when E &lt; 1, and it can be effectively stabilized by close-fitting conducting shells, even in the small Larmor radii (MHD) regime. The tilt mode stability improves with increasing oblateness, however at suffciently small elongations the radial shift mode becomes more unstable than the tilt mode. The interchange mode stability is strongly profile dependent, and all n * 1 interchange modes can be stabilized for a class of pressure profile with separatrix beta larger than 0.035. Our results show that all three n = 1 modes can be stabilized in the MHD regime, but the stabilization of the n &gt; 1 co-interchange modes still remains an open question.
Date: October 27, 2000
Creator: Belova, E.V.; Jardin, S.C.; Ji, H.; Yamada, M. & Kulsrud, R.
Partner: UNT Libraries Government Documents Department