Finite Larmor radius effects on the stability properties of internal modes of a<i>Z</i>-pinch

Åkerstedt, Hans O.

doi:10.1088/0031-8949/37/1/017

Cited by 16 publications

(3 citation statements)

References 18 publications

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“…Interchange (m = 0) modes seem to play a minor role in Extrap. Large Larmor radius (LLR) effects can reduce linear growth rates of short-axial-wavelength m = 0 modes by up to about 80%, but cannot provide complete stability [15,16]. It is known that peaked pressure profiles and finite edge pressure, which are characteristic for Extrap mode discharges, favours m = 0 stability [17].…”

Section: Stability Theorymentioning

confidence: 99%

Extrap mode confinement in Extrap T1-U

Scheffel¹,

Brzozowski²,

Hellblom³

et al. 1997

Plasma Phys. Control. Fusion

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An extensive series of experiments in the Extrap mode has been carried out on Extrap T1-U in an attempt to obtain hot, collisionless discharges. Using no external axial magnetic field, performance has been limited to low temperatures ( 15 eV) and low currents ( 20 kA) at high loop voltages 1.4 kV, leading to energy confinement times of only a few µs or Alfvén times. The discharge length is typically of the order of greater than 100 Alfvén times.Imposing a weak axial field (q(a) 0.15 at peak current) the temperature could be increased to 40 eV at toroidal currents 60 kA. Energy confinement times up to 15 Alfvén times (≈10 µs) were then obtained.The poor confinement is attributed to the weak axial magnetic field, generating strong instability-induced fluctuations and related radial transport in the core plasma. A turbulence core plasma transport model is suggested, based on theoretical evidence of linear instability in the kinetic regime.Self-generation of axial magnetic field is observed when the magnetic X-points, generated by the plasma current and an external octupole field, approach or pass beyond the wall.Edge transport appears to be dominated by line radiation and heat conduction to the wall along open field lines.

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Section: Stability Theorymentioning

confidence: 99%

Extrap mode confinement in Extrap T1-U

Scheffel¹,

Brzozowski²,

Hellblom³

et al. 1997

Plasma Phys. Control. Fusion

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“…The prime candidate, however, was finite (or large) Larmor radius effects. Due to the inherent complexity of kinetic models, early studies focused on finite Larmor radius modified-fluid models and somewhat optimistic results emanated [7,8]. Recently we have been able to study the fully kinetic ion dynamics, which unfortunately results in only a moderate improvement of ideal growth rates [9,10].…”

Section: Introductionmentioning

confidence: 99%

Kinetic stability of the finite electron temperatureZ-pinch

Scheffel

Arber

Coppins

et al. 1997

Plasma Phys. Control. Fusion

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Large Larmor radius (LLR) stability of linear m = 0 and m = 1 modes in a Z-pinch has been studied using the Vlasov-fluid model (Arber et al 1994 Phys. Rev. Lett. 72 2399 Phys. Rev. Lett. 74 2698. Ions have been modelled fully kinetically through the Vlasov equation, and electrons are treated as a zero temperature, massless fluid. In the present work an improved Vlasov-fluid model is used to investigate the effect of finite electron temperature on m = 0 modes. An electron energy equation is introduced, and results for both adiabatic and isothermal dynamics are presented. It is found that finite electron temperature has a destabilizing effect in general. As a result, the Z-pinch is only weakly stabilized by LLR effects.

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“…34 Generally speaking, FLR effects are stabilizing for weakly unstable low-/? systems, 33 and even more stabilizing as p approaches l. 35 ' 36 For the Z pinch Akerstedt, 31 using an FLR expansion technique, finds absolute stability above a critical value of ka (e.g., ka «4.7 at a//a=0.15) which decreases with increasing dj/a (but see the discussion below concerning the validity of the FLR approach).…”

mentioning

confidence: 99%

Universal diagram for regimes ofZ-pinch stability

Haines

Coppins

1991

Phys. Rev. Lett.

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The regimes for the applicability of various theoretical models for the stability of a Z pinch under pressure balance are shown to be clearly delineated in a diagram of ln(/ 4 a) vs InTV, where /, a, and TV are the current, pinch radius, and line density, respectively. In particular, the most unstable regime where ideal magnetohydrodynamics applies is shown to be restricted to a small-wedge-shaped region bounded by resistive, viscous, anisotropic, and finite-Larmor-radius effects. Recent experimental results of anomalous stability can be interpreted in terms of resistive or large-ion Larmor-radius effects.

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Finite Larmor radius effects on the stability properties of internal modes of aZ-pinch

Cited by 16 publications

References 18 publications

Extrap mode confinement in Extrap T1-U

Extrap mode confinement in Extrap T1-U

Kinetic stability of the finite electron temperatureZ-pinch

Universal diagram for regimes ofZ-pinch stability

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