摘要:

Resistive ballooning modes are analyzed in the neighborhood of the magnetic axis. There are two mode branches, one connecting to the usual tearing mode and the other to the magnetohydrodynamic ballooning mode. Unstable modes satisfy the generalized tearing dispersion relation. Resistive ballooning modes can be unstable for a wide range of beta, but may be stabilized by interchange effects and finite sound speed. The analytic results are in qualitative agreement with low mode number numerical solutions.

ISSN:0031-9171    

DOI:10.1063/1.863285

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

A hybrid fluid‐gyrokinetic derivation of the kinetic modifications to the ballooning‐interchange eigenmode equation is presented which removes the large and small wave frequency restrictions of Tang and Catto. The derivation employs a long‐thin ordering and an eikonal ansatz, but otherwise allows arbitrary asymmetry, beta, pressure anisotropy, and unperturbed parallel and perpendicular electrostatic field.

ISSN:0031-9171    

DOI:10.1063/1.863286

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

A ballooning mode equation that includes full finite Larmor radius effects has been derived from the Vlasov equation for circular tokamak equilibrium. A numerical solution of this equation shows that finite Larmor radius effects are stabilizing.

ISSN:0031-9171    

DOI:10.1063/1.863287

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Electron currents can be driven in a linear plasma by the absorption of lower‐hybrid waves excited primarily in one direction. Current‐drive has been demonstrated both for collisional and resonant‐electron absorption. The magnitude of the excited current is compared with the predictions from an electron kinetic equation with a Lorentz collision operator in the regimek∥vte/&ohgr;≪1.

ISSN:0031-9171    

DOI:10.1063/1.863298

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Instead of using the uniform warm plasma dispersion relation with an inverse Fourier transform to form the mode conversion‐tunneling equation, the equation is developed directly from the Vlasov equation and Maxwell’s equations. The plasma is assumed uniform parallel to B0. The expansion parameters are the Larmor orbit and the scale length, keeping terms to order &rgr;2LandL−1= (1/&ohgr;c)(d&ohgr;c/dx). For the special case with &ohgr;≃2&ohgr;cin a single species plasma, the asymptotic form of the mode conversion‐tunneling equation is unchanged, but localized third and first derivative terms appear even as absorption vanishes.

ISSN:0031-9171    

DOI:10.1063/1.863299

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The axisymmetric, negative energy branch of the Doppler‐shifted electron cyclotron eigenmode has been excited on an unneutralized, 15 kA, 2.25 MV, relativistic electron beam propagating along a guide magnetic field interior to a vacuum conducting wave guide. Large amplitude waves have been generated by means of a traveling wave interaction with helical slow wave structures. The growth process has been identified as the resonant coupling of the negative energy cyclotron mode with the positive energy helix modes. The large amplitude wave produced was propagated on the beam and then identified to be the desired symmetric, negative energy cyclotron wave by direct measurement of its azimuthal symmetry, wavelength, and phase velocity direction. The on‐axis axial electric field component of the wave was inferred to be in excess of 10 MV/m. Finally, as is necessary for collective ion acceleration by these waves, the cyclotron wave phase velocity has been controlled, in the range 0.20–0.06 times the speed of light, by spatially changing the guide magnetic field strength.

ISSN:0031-9171    

DOI:10.1063/1.863300

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The single‐mode time‐asymptotic nonlinear saturation of the drift‐cyclotron loss‐cone instability is considered. In this model, there is a uniform magnetic field as well as mirror losses. The linear stability boundary, and the saturation levels of unstable oscillations and floating potential near this boundary, are determined. The theory is then compared with observations on the PR‐6 mirror experiment. Good agreement is obtained using a simple energy model for the slow time variation of the equilibrium distribution function.

ISSN:0031-9171    

DOI:10.1063/1.863301

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The boundary value problem involving a magnetized plasma half‐space confined by a perfectly reflecting interface is solved using the relativistic Vlasov–Maxwell system. The external field is assumed to be constant and along the normal of the boundary, and only the linear responses to obliquely incident vacuum waves are considered. When the incidence is normal, only a pair of purely transversal modes, similar to the ordinary and extraordinary modes of the infinite systems, can be excited. When the incidence is oblique, two additional hybridpandsmodes may exist, which are decoupled into the longitudinal and transversal parts only when there is no external field. Thepmode vanishes if the field at the boundary, B(0), is in the plane of incidence, and thesmode is zero if B(0) is in the plane which is perpendicular to both the interface and the plane of incidence. Reflection, transmission, and absorption coefficients are calculated for the case of normal incidence.

ISSN:0031-9171    

DOI:10.1063/1.863302

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Equilibrium, stability, and confinement properties of compact toroids produced in field‐reversed theta‐pinch experiments (FRX) are reported. Two experimental facilities, FRX‐A and FRX‐B, have been used to study highly elongated compact toroid plasmas confined in a purely poloidal field geometry. Spatial scans and fill pressure scaling of the equilibrium plasma parameters are presented. Plasma conditions range fromTe∼150 eV,Ti∼800 eV,nm∼1×1015cm−3toTe∼100 eV,Ti∼150 eV,nm∼4×1015cm−3. Typical confined plasma dimensions are: major radiusR∼4 cm, minor radiusa∼2 cm, and total length 35–50 cm. The plasma configuration remains in a stable equilibrium for up to 50 &mgr;sec followed by the destructiven= 2 rotational instability. The stable period prior to the onset of the rotational mode is up to one hundred times greater than characteristic Alfve´n transit times of the plasma. This stable period increases and the mode growth rate decreases with increaseda/&rgr;i(where &rgr;iis the ion gyroradius). Agreement of experimental and theoretical mode frequencies for the instability is observed. Preferential particle loss has been proposed as a likely cause of rotation. The particle inventory at the onset of the instability is consistent with this hypothesis. The particle loss rate is also consistent with the predicted anomalous transport near the separatrix. Contributions to rotational instability from diffusion, end‐shorting, equipartition, and compression are also discussed.

ISSN:0031-9171    

DOI:10.1063/1.863303

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

In a small theta pinch, a density pulse propagating to the end is found to form after the compression phase. Doppler‐shift measurements of the He ii, &lgr; = 4686 A˚ line indicate that axial particle flow is present only during the implosion, thermal conduction being the dominant end‐loss mechanism at later times. Comparison of the actual heat flux with that expected from classical theory, the presence of an enhanced forbidden component as well as plasma satellites of the He i, &lgr; = 4922 A˚ line outside the coil region, and a flat‐top electron distribution function obtained by Thomson scattering, lead to the conclusion that thermal conduction is anomalous. The concept of a replacement wave is successfully applied to account for the observed phenomena.

ISSN:0031-9171    

DOI:10.1063/1.863304

出版商:AIP    

年代:1981

数据来源: AIP