摘要:

A self‐consistent theory of the free electron laser instability is developed for a hollow electron beam propagating through an undulator (multiple mirror) magnetic field. The stability analysis is carried out within the framework of the linearized Vlasov–Maxwell equations. It is assumed that the beam is thin, with radial thickness much smaller than the mean beam radius, and that &ngr;/&ggr;b≪1, where &ngr; is Budker’s parameter and &ggr;bmc2is the characteristic energy of the electron beam. The dispersion relation describing the free electron laser instability in a hollow relativistic electron beam is obtained for an equilibrium distribution function in which all electrons have the same value of transverse energy and the same value of canonical angular momentum, and a Lorentzian distribution in axial momentum. It is shown that the influence of finite radial geometry plays a critical role in determining the detailed stability behavior. Moreover, the growth rate and bandwidth of the instability can be expressed in terms of Budker’s parameter &ngr;, instead of the plasma frequency as in the case of a uniform density beam. Furthermore, it is found that free electron laser stability properties exhibit a sensitive dependence on axial momentum spread.

ISSN:0031-9171    

DOI:10.1063/1.863569

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The Vlasov–Maxwell equations are used to investigate the stability of azimuthally symmetric perturbations (e.g., sausage and hollowing modes) of an electron or ion beam immersed in a resistive plasma. The perturbed space charge and plasma current are treated self‐consistently for any value of the plasma conductivity. A similar analysis of the hose instability is also carried out. It is assumed that &ngr;/&ggr;b≪1, where &ngr; is Budker’s parameters and &ggr;bmc2is the characteristic beam electron energy. The analysis is carried out for the ’’loss‐cone’’ distribution function in which all of the beam electrons have the same value of energy (in a frame of reference rotating with angular velocity &ohgr;b) and the same value of axial canonical momentum. In the high conductivity regime, the system is shown to be strongly destabilized by a sufficiently large value of the fractional current neutralization.

ISSN:0031-9171    

DOI:10.1063/1.863570

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Ordinary electromagnetic waves can be employed to heat electrons in magnetized plasmas through parametric instabilities if the power level exceeds a certain threshold. Around the electron cyclotron second harmonic frequency band, ordinary waves can decay into upper hybrid waves and other ordinary waves with lower frequency and wavenumber. Depending on the pump wavelength and power, both forward and backward scattering processes can take place. The decay waves ultimately fed energy into electrons through turbulent heating. Only bulk heating has been observed in the simulation.

ISSN:0031-9171    

DOI:10.1063/1.863571

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

It is shown that the interaction of pulse modulated radio frequency waves of suitable amplitude, with the population of trapped particles in a tokamak may develop the features of the so‐called stochastic instability, eventually leading to a systematic increase in the energy of the particles and to their detrapping.

ISSN:0031-9171    

DOI:10.1063/1.863572

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

A linear theory of electrostatic ion cyclotron normal modes with moderate wavenumber (k⊥ &rgr;i≲1) which can exist in a sheared magnetic field is given. Such modes have been seen in a scattering experiment on the TFR tokamak. A novel mode with fluid electron behavior is found, and the Drummond and Rosenbluth current‐driven mode with kinetic electron behavior is recovered. Toroidal effects are considered. The kinetic modes offer the most natural explanation for the experimental frequency spectrum. However, numerical solutions of the dispersion relations predict that current drifts three to ten times larger than those in TFR are needed for instability.

ISSN:0031-9171    

DOI:10.1063/1.863573

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

A vortex ring version of the Ka´rma´n vortex street is observed through flow visualization. A remarkably stable configuration of discrete vortex shedding is recognized with a distinction from the two‐dimensional case that the spacing between the alternating vortices is not equal.

ISSN:0031-9171    

DOI:10.1063/1.863574

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

One‐dimensional diffusion is considered for a system in which the diffusion coefficientDhas a rapid oscillation in the spatial variable as well as a slow variation. For long times, the distribution function evolves diffusively with an effective diffusion coefficient given by averaging 1/D.

ISSN:0031-9171    

DOI:10.1063/1.863575

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The linear stability of low‐frequency, long‐wavelength longitudinal modes in a collisionless single‐ended Q machine is investigated using self‐consistent velocity distribution functions. The so‐called ion‐acoustic instability occurring at positive biases is shown to actually be of the Buneman type.

ISSN:0031-9171    

DOI:10.1063/1.863548

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The linear Vlasov theory of electrostatic drift instabilities is considered using the slab model and the local approximation. The effects of magnetic field curvature on the lower hybrid density drift instability are studied. Magnetic curvature does not significantly affect the growth rate at low beta.

ISSN:0031-9171    

DOI:10.1063/1.863545

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Comment on parametric instability in an inhomogeneous plasma is made.(AIP)

ISSN:0031-9171    

DOI:10.1063/1.863546

出版商:AIP    

年代:1981

数据来源: AIP