ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

X
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    Numerical study of tilt stability of prolate field-reversed configurations (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 4996-5006 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Global stability of the field-reversed configuration (FRC) has been investigated numerically using both three-dimensional magnetohydrodynamic and hybrid (fluid electron and δf particle ion) simulations. The stabilizing effects of velocity shear and finite ion Larmor radius (FLR) on the n=1 internal tilt mode in the prolate FRCs have been studied. Sheared rotation is found to reduce the growth rate, however a large rotation rate with Mach number of M(approximately-greater-than)1 is required in order for significant reduction in the instability growth rate to occur. Kinetic effects associated with large thermal ion orbits have been studied for different kinetic equilibria. The simulations show that there is a reduction in the tilt mode growth rate due to FLR effects, but complete linear stability has not been found, even when the thermal ion gyroradius is comparable to the distance between the field null and the separatrix. The instability existing beyond the FLR theory threshold could be due to the resonant interaction of the wave with ions whose Doppler shifted frequency matches the betatron frequency. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1318929
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    Fast flow phenomena in a toroidal plasma (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 2281-2285 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The bulk fluid velocity is measured spectroscopically with 10 μs time resolution in the Madison Symmetric Torus (MST) reversed-field pinch (RFP) [Fusion Technol. 19, 131 (1991)], a diagnostic capability used to study the fast flow dynamics associated with locked modes and the RFP dynamo. The phase velocity of the tearing modes and the fluid velocity accelerate between sawtooth events, reaching a maximum speed of about 20 km/s in a few ms. Both slow down at the sawtooth crash in ≈100 μs. This deceleration time scale is as calculated for the tearing modes from the action of electromagnetic torque on the magnetic islands, but is much faster than expected from the viscous torque on the bulk fluid. In the RFP, correlated fluctuations in the tearing modes and fluid velocity probably also generate current via the "RFP dynamo,'' 〈u˜×B˜〉, where u is the bulk fluid velocity. Initial data indicate a possible increase in 〈u˜φB˜r〉 during sawtooth events, coincident with toroidal flux generation. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871250
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Experimental study of lower-hybrid drift turbulence in a reconnecting current sheet (2002)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 9 (2002), S. 3272-3288 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The role of turbulence in the process of magnetic reconnection has been the subject of a great deal of study and debate in the theoretical literature. At issue in this debate is whether turbulence is essential for fast magnetic reconnection to occur in collisionless current sheets. Some theories claim it is necessary in order to provide anomalous resistivity, while others present a laminar fast reconnection mechanism based on the Hall term in the generalized Ohm's law. In this work, a thorough study of electrostatic potential fluctuations in the current sheet of the magnetic reconnection experiment (MRX) [Yamada et al., Phys. Plasmas 4, 1936 (1997)] was performed in order to ascertain the importance of turbulence in a laboratory reconnection experiment. Using amplified floating Langmuir probes, broadband fluctuations in the lower hybrid frequency range (fLH∼5–15 MHz) were measured which arise with the formation of the current sheet in MRX. The frequency spectrum, spatial amplitude profile, and spatial correlation characteristics of the measured turbulence were examined carefully, finding consistency with theories of the lower-hybrid drift instability (LHDI). The LHDI and its role in magnetic reconnection has been studied theoretically for decades, but this work represents the first detection and detailed study of the LHDI in a laboratory current sheet. The observation of the LHDI in MRX has provided the unique opportunity to uncover the role of this instability in collisionless reconnection. It was found that: (1) the LHDI fluctuations are confined to the low-beta edge of current sheets in MRX; (2) the LHDI amplitude does not correlate well in time or space with the reconnection electric field, which is directly related to the rate of reconnection; and (3) significant LHDI amplitude persists in high-collisionality current sheets where the reconnection rate is classical. These findings suggest that the measured LHDI fluctuations do not play an essential role in determining the reconnection rate in MRX. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1494433
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 4
    Electronic Resource
    Electronic Resource
    Experimental study of ion heating and acceleration during magnetic reconnection : The 42nd annual meeting of the division of plasma physics of the American Physical Society and the 10th international congress on plasma physics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 1916-1928 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ion heating and acceleration has been studied in the well-characterized reconnection layer of the Magnetic Reconnection Experiment [M. Yamada et al., Phys. Plasmas 4, 1936 (1997)]. Ion temperature in the layer rises substantially during null-helicity reconnection in which reconnecting field lines are anti-parallel. The plasma outflow is sub-Alfvénic due to a downstream back pressure. An ion energy balance calculation based on the data and including classical viscous heating indicates that ions are heated largely via nonclassical mechanisms. The Ti rise is much smaller during co-helicity reconnection in which field lines reconnect obliquely. This is consistent with a slower reconnection rate and a smaller resistivity enhancement over the Spitzer value. These observations show that nonclassical dissipation mechanisms can play an important role both in heating the ions and in facilitating the reconnection process. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1356737
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 5
    Electronic Resource
    Electronic Resource
    Studies of global stability of field-reversed configuration plasmas using a rigid body model (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 3685-3693 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Global stability of field-reversed configuration (FRC) plasmas has been studied using a simple rigid body model in the parameter space of s (the ratio of the separatrix radius to the average ion gyro-radius) and plasma elongation E (the ratio of the separatrix length to the separatrix diameter). Tilt stability is predicted, independent of s, for FRC's with low E (oblate), while the tilt stability of FRC's with large E (prolate) depends on s/E. It is found that plasma rotation due to ion diamagnetic drift can stabilize the tilt mode when s/E(approximately-less-than)1.7. The so-called collisionless ion gyro-viscosity also is identified to stabilize tilt when s/E(approximately-less-than)2.2. Combining these two effects, the stability regime broadens to s/E(approximately-less-than)2.8, consistent with previously developed theories. A small additional rotation (e.g., a Mach number of 0.2) can improve tilt stability significantly at large E. A similar approach is taken to study the physics of the shift stability. It is found that radial shift is unstable when E〈1 while axial shift is unstable when E〉1. However, unlike tilt stability, gyro-viscosity has little effect on shift stability. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872978
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 6
    Electronic Resource
    Electronic Resource
    Measurement of the dynamo effect in a plasma (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 1935-1942 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A series of detailed experiments has been conducted in three laboratory plasma devices to measure the dynamo electric field along the equilibrium field line (the α effect) arising from the correlation between the fluctuating flow velocity and magnetic field. The fluctuating flow velocity is obtained from probe measurement of the fluctuating E×B drift and electron diamagnetic drift. The three major findings are the following: (1) The α effect accounts for the dynamo current generation, even in the time dependence through a "sawtooth'' cycle; (2) at low collisionality the dynamo is explained primarily by the widely studied pressureless magnetohydrodynamic (MHD) model, i.e., the fluctuating velocity is dominated by the E×B drift; (3) at high collisionality, a new "diamagnetic dynamo'' is observed, in which the fluctuating velocity is dominated by the electron diamagnetic drift. In addition, direct measurements of the helicity flux indicate that the dynamo activity transports magnetic helicity from one part of the plasma to another, but the total helicity is roughly conserved, verifying Taylor's [Phys. Rev. Lett. 33, 1139 (1974); Rev. Mod. Phys. 58, 741 (1986)] conjecture. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871989
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 7
    Electronic Resource
    Electronic Resource
    Ambipolar magnetic fluctuation-induced heat transport in toroidal devices (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 1999-2005 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The total magnetic fluctuation-induced electron thermal flux has been determined in the Madison Symmetric Torus (MST) reversed-field pinch [Fusion Technol. 19, 131 (1991)] from the measured correlation of the heat flux along perturbed fields with the radial component of the perturbed field. In the edge region the total flux is convective and intrinsically ambipolar constrained, as evidenced by the magnitude of the thermal diffusivity, which is well approximated by the product of ion thermal velocity and the magnetic diffusivity. A self-consistent theory is formulated and shown to reproduce the experimental results, provided nonlinear charge aggregation in streaming electrons is accounted for in the theory. For general toroidal configurations, it is shown that ambipolar constrained transport applies when remote magnetic fluctuations (i.e., global modes resonant at distant rational surfaces) dominate the flux. Near locations where the dominant modes are resonant, the transport is nonambipolar. This agrees with the radial variation of diffusivity in MST. Expectations for the tokamak are also discussed. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871996
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 8
    Electronic Resource
    Electronic Resource
    Transport reduction by current profile control in the reversed-field pinch (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 2440-2446 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An auxiliary poloidal inductive electric field applied to a reversed-field pinch (RFP) plasma reduces the current density gradient, slows the growth of m=1 tearing fluctuations, suppresses their associated sawteeth, and doubles the energy confinement time. This experiment attacks the dominant RFP plasma loss mechanism of parallel streaming in a stochastic magnetic field. The auxiliary electric field flattens the current profile and reduces the magnetic fluctuation level. Since a toroidal flux change linking the plasma is required to generate the inductive poloidal electric field, the current drive is transient to avoid excessive perturbation of the equilibrium. To sustain and enhance the improved state, noninductive current drivers are being developed. A novel electrostatic current drive scheme uses a plasma source for electron injection, and the lower-hybrid wave is a good candidate for radio-frequency current drive. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871268
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 9
    Electronic Resource
    Electronic Resource
    Numerical study of global stability of oblate field-reversed configurations (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 1267-1277 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Global stability of the oblate (small elongation, E〈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 nonzero 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〉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〈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 sufficiently 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〉1 co-interchange modes still remains an open question. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1355027
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 10
    Electronic Resource
    Electronic Resource
    Magnetic fluctuation induced transport in MST (abstract)a) : Proceedings of the tenth topical conference on high temperature plasma diagnostics (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 812-812 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We made local measurements of the magnetic fluctuation induced transport of particles and energy in the outer region (r/a(approximately-greater-than)0.75) of the MST reversed field pinch plasma. These measurements allow comparison with the Rochester–Rosenbluth stochastic diffusion coefficients. An electrostatic electron energy analyzer and fast pyrobolometer were employed in combination with magnetic pickup coils to directly measure the correlated products 〈J˜θB˜r〉 and 〈q˜(parallel)B˜r〉, respectively. Magnetic fluctuation induced transport of both particles and energy is negligible at the extreme edge of MST (r/a(approximately-greater-than)0.9), but increases to a level consistent with estimates of the entire particle and energy flux as the core is approached (5×1021 m−2 s−1 and 105 W m−2). Stochastic particle transport is limited by an apparent ambipolar electric field to the ion stochastic diffusion rate (D=50 m2 s−1), the electron transport being dominated by the energetic component of the distribution (E(approximately-greater-than)50 eV). The measured heat transport is consistent with the convective energy transport carried by the fast electron component (Teffective=100 eV). © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146229
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...