GLORIA

GEOMAR Library Ocean Research Information Access

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
Filter
Document type
Publisher
Years
  • 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 Limitation Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    Ponderomotive feedback stabilization of external kinks and disruptions in tokamaks (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 3429-3439 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A novel mechanism for feedback stabilization of external kink modes and disruptions is proposed in which modulated radio-frequency (RF) antennas apply a stabilizing ponderomotive force (PF) to the plasma. The RF power required for n=1 kink stabilization in the Princeton Beta Experiment-Modified (PBX-M) [Phys. Fluids B 2, 1271 (1990)] is estimated, and it is shown that the idea can be tested with the existing antenna system. A simulation of a preliminary n=0 modulation experiment on PBX-M also shows that the PF can balance applied vertical field oscillations. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871448
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    The prospects for magnetohydrodynamic stability in advanced tokamak regimesf| (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 1601-1605 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Stability analysis of advanced regime tokamaks is presented. Here advanced regimes are defined to include configurations where the ratio of the bootstrap current, IBS, to the total plasma current, Ip, approaches unity, and the normalized stored energy, βN* = 80π〈p2〉1/2a/IpB0, has a value greater than 4.5. Here, p is the plasma pressure, a the minor radius in meters, Ip is in mega-amps, B0 is the magnetic field in Tesla, and 〈⋅〉 represents a volume average. Specific scenarios are discussed in the context of Toroidal Physics Experiment (TPX) [Proceedings of the 20th European Physical Society Conference on Controlled Fusion and Plasma Physics, Lisbon, 1993, edited by J. A. Costa Cabral, M. E. Manso, F. M. Serra, and F. C. Schuller (European Physical Society, Petit-Lancy, 1993), p. I-80]. The best scenario is one with reversed shear, in the q profile, in the central region of the tokamak. The bootstrap current obtained from the plasma profiles provides 90% of the required current, and is well aligned with the optimal current profile for ideal magnetohydrodynamic stability. This configuration is stable up to βN*≈ 6.8, if the external boundary conditions are relaxed to those corresponding to an ideal structure at a moderate distance of approximately 1.3 times the minor radius.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870660
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 4
    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 Limitation Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 5
    Electronic Resource
    Electronic Resource
    High poloidal beta equilibria in the Tokamak Fusion Test Reactor limited by a natural inboard poloidal field null (1991)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 2277-2284 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Recent operation of the Tokamak Fusion Test Reactor (TFTR) [Plasma Phys. Controlled Nucl. Fusion Research 1, 51 (1986)] has produced plasma equilibria with values of Λ≡βp eq+li/2 as large as 7, εβp dia≡2μ0ε〈p⊥〉/〈〈Bp〉〉2 as large as 1.6, and Troyon normalized diamagnetic beta [Plasma Phys. Controlled Fusion 26, 209 (1984); Phys. Lett. 110A, 29 (1985)], βNdia≡108〈βt⊥〉aB0/Ip as large as 4.7. When εβp dia(approximately-greater-than)1.25, a separatrix entered the vacuum chamber, producing a naturally diverted discharge that was sustained for many energy confinement times, τE. The largest values of εβp and plasma stored energy were obtained when the plasma current was ramped down prior to neutral beam injection. The measured peak ion and electron temperatures were as large as 24 and 8.5 keV, respectively. Plasma stored energy in excess of 2.5 MJ and τE greater than 130 msec were obtained. Confinement times of greater than 3 times that expected from L-mode predictions have been achieved. The fusion power gain QDD reached a value of 1.3×10−3 in a discharge with Ip=1 MA and εβp dia=0.85. A large, sustained negative loop voltage during the steady-state portion of the discharge indicates that a substantial noninductive component of Ip exists in these plasmas. Transport code analysis indicates that the bootstrap current constitutes up to 65% of Ip. Magnetohydrodynamic (MHD) ballooning stability analysis shows that, while these plasmas are near, or at the βp limit, the pressure gradient in the plasma core is in the first region of stability to high-n modes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859647
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 6
    Electronic Resource
    Electronic Resource
    Control of plasma shape and performance of the PBX-M tokamak experiment in high-βt /high-βp regimes (1990)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 2 (1990), S. 1271-1279 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The highly indented plasmas of the PBX-M tokamak experiment [Plasma Physics and Controlled Nuclear Fusion Research (IAEA, Vienna, 1989), Vol. 1, p. 97] have reached plasma regimes of both high volume-averaged beta (βt), and high-beta poloidal (βp), and show evidence of the suppression of external surface modes by the passive stabilizing system. Values of βt up to 4.0 I/aB (% MA/m T) with Ti(0)≈4 keV have been obtained. A magnetohydrodynamic analysis of plasmas with βp=2.0 indicates that these plasmas are near the threshold of the second stability regime. A value of βt of 6.8% has been reached with Ti(0)〉5 keV and an indentation of 28%. Control of plasma shape is accomplished with a feedback system that uses a moment expansion about a single equilibrium and is augmented by time-dependent waveforms to redefine plasma shape. Diagnostics to measure the safety factor q have been developed and used to make accurate measurements of q(r) and to verify changes made in q(0).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859542
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 7
    Electronic Resource
    Electronic Resource
    Stability of elongated cross-section tokamaks to axisymmetric even poloidal mode number deformations (1989)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 1 (1989), S. 2349-2352 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In a recent paper, Nakayama, Sato, and Matsuoka [Phys. Fluids 31, 630 (1988)] suggested that elliptical cross-section tokamaks with aspect ratio R/a=3.2 and with elongation κ=2.6 are unstable to a splitting (m=2, n=0) instability for plasma β〉5%, and that κ≥4.0 plasmas are unstable to a splitting for β≥1%. The magnetohydrodynamic evolution code tsc [J. Comput. Phys. 66, 481 (1986)] indicates, however, that such plasmas are robustly stable with respect to this splitting. In fact, a κ=3.7 plasma with β=23.0% shows no tendency to split. However, the addition of pinching coils at the waist will cause the plasma to split if the current in these coils exceeds a critical value Ic, which decreases with increasing beta.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859054
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 8
    Electronic Resource
    Electronic Resource
    Numerical drift orbit calculations for force-free spheromak configurations (1990)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 2 (1990), S. 554-560 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A numerical analysis was performed of guiding-center (gc) orbits in a variety of spheromak-type force-free, numerically determined equilibria including the normal spherical configurations as well as configurations that are more prolate and oblate, and others having hollow or peaked current profiles. The calculated drift orbits differ significantly from the well-known drift orbits in tokamaks. In particular, the results indicate (i) the existence of particles trapped in separate hemispheres, (ii) the orbit widths d are about proportional to the Larmor radius ρ of the particle (calculated for the field maximum) up to ρ≈0.01–0.02 of the major separatrix dimension, (iii) many orbits, in particular on the outer flux lines, have their maximum normalized width dmax/ρL(ρL= local Larmor radius) away from the midplane of the configuration, and (iv) these maximum normalized widths are about 2–4 over most of the volume for all configurations except for prolate ones with a peaked current profile; in the latter configurations, orbits on outer field surfaces show dmax≤ρL.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859292
    Location Call Number Limitation 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...