1,721,102 research outputs found
Large-amplitude oscillations and chaos in a Hamiltonian plasma system with many degrees of freedom
Full text linkTaking the beam-plasma system as a reference Hamiltonian system with many degrees of freedom, the connection between the development of large amplitude oscillations and stochasticity of the system (measured through the time-dependent maximum Lyapunov exponent) is investigated. It is found that the development of self-consistent large amplitude oscillations occurs in correspondence with the onset of chaos, and is related to a well defined change of topology of the phase space of the system. It is also shown that in a (Hamiltonian) linearly stable regime the development of large amplitude oscillations can occur when weakly dissipative processes are introduced
Non-resonant dynamic stabilization of the m=1 diocotron mode
No full textThe m=1 diocotron mode of a nonneutral plasma column confined in a Malmberg-Penning trap, i.e. the rotation of the plasma center-of-charge around the longitudinal symmetry axis, is experimentally found to be unstable. We have investigated in the ELTRAP device a control mechanism of the radial drift of the column based on a Radio Frequency drive applied on an azimuthally sectored electrode of the trap. Systematic experiments show the characteristic features of the mechanism, namely the presence of amplitude and frequency thresholds as well as the non-resonant behavior, whose interpretation invokes the concept of dynamic stabilization
Development of diagnostic and manipulation systems for space-charge dominated electron beams and confined electron plasmas in ELTRAP
No full textModifications have been implemented in the Penning-Malmberg device ELTRAP aimed
at performing studies on the dynamics of space-charge dominated nanosecond electron bunches traveling along the magnetic field. In particular, a Thomson backscattering apparatus has been developed where an infrared (IR) laser pulse collides with the bunched electron beam. The frequency-shifted
backscattered radiation, acquired by means of a photomultiplier (PMT), can be exploited to evaluate information on energy, energy spread and density of the bunch. The achievable sensitivity
of the diagnostics has been estimated, and valuable information on the main parameters affecting the signal-to-noise (S/N) ratio has been obtained [B. Paroli, F. Cavaliere, M. Cavenago, F. De Luca, M. Ikram, G. Maero, C. Marini, R. Pozzoli, and M. Romé, JINST 7, P01008 (2012)]. A series of upgrades are under way, aimed at increasing the S/N ratio through the use of a new laser for the electron source, the insertion of a stray light shield, and the optimization of the detection electronics. Moreover, electromagnetic simulations relevant to the design and implementation of a microwave
heating system are presented. The generation of an electron plasma in ELTRAP by means of a low-power radio frequency (RF) drive in the MHz range applied on one of the trap electrodes and under ultra-high vacuum (UHV) conditions has previously been demonstrated [B. Paroli, F. De Luca,
G. Maero, F. Pozzoli, and M. Romé, Plasma Sources Sci. Technol. 19, 045013 (2010)]. The new heating system will allow the extension of the RF studies to the GHz range and in particular the
production of a more energetic electron plasma via cyclotron resonant excitation
Ionization adiabat
No full textAn equation of state interrelating density and temperature is derived for a thermally insulated ideal gas undergoing an adiabatic transformation with a varying fraction of ionized atoms
Diocotron instability in non-neutral plasmas with a stationary point in the rotation frequency profile
No full textA new analytical solution to the problem of the l=1 diocotron mode instability in a hollow density non-neutral plasma column with finite lenght is presented. The starting point of the analysis is the paper of Finn [J. M. Finn, D. del-Castillo-Negrete, and D. C. Barnes, Phys. Plasmas 6, 3744 (1999)], where the instability mechanism involves compression of the plasma in the direction parallel to the magnetic field, with conservation of its line-integrated density. In the limit of small curvature of the plasma end-fronts, the method presented here provides both eigenvalue and eigenfunction for the unstable l=1 "extreme mode." (C) 2005 American Institute of Physics
MEP: a 3D PIC Code for the Simulation of the Dynamics of a Non-Neutral Plasma
No full textThe three-dimensional evolution of a pure electron plasma is studied by means of a newly developed particle-in-cell code which solves the drift-Poisson system where kinetic effects in the motion parallel to the magnetic field are taken into account. Different results relevant to the non-linear dynamics of trapped plasmas and low-energy electron beams are presented. [All rights reserved Elsevier]
Multiresolution analysis of the two-dimensional free decaying turbulence in a pure electron plasma
Full text linkThe two-dimensional (2D) freely decaying turbulence is investigated
experimentally in an electron plasma confined in a Malmberg–Penning trap
and studied using a wavelet-based multiresolution analysis. The coherent and
incoherent parts of the flow are extracted using a recursive denoising algorithm
with an adaptive self-consistent threshold. Only a small number of wavelet
coefficients (but corresponding to the greatest part of the enstrophy or energy
contents) turns out to be necessary to represent the coherent component. The
remaining small amplitude coefficients represent the incoherent component,
which is characterized by a near Gaussian vorticity PDF. Scale contributions to
the measured enstrophy and energy distributions are inferred, and the results are
compared with recent experiments and theoretical pictures of the 2D turbulence.
The results suggest that the computational complexity of 2D turbulent flows may
be reduced in simulations by considering only coherent structures interacting
with a statistically modeled background
Relativistic cold fluid radial equilibrium of an annular nonneutral plasma
No full textThe relativistic radial equilibrium of a nonneutral plasma confined in a cylindrical trap is considered for the general case in which a coaxial inner
charged conductor is present. Both rigid and sheared modes of plasma rotation in crossed self-consistent electric and magnetic fields are analyzed.
It is found that relativistic effects can limit the outer radius of an annular nonneutral plasma column for the fast sheared rotational mode. For the
particular case of a uniform plasma density, the outer radius cannot exceed √3ric/|Ω| if the inner radius of the plasma column ri is smaller than
3c/|Ω|, where Ω is the cyclotron frequency. On the contrary, radially unlimited equilibria are found when ri > 3c/|Ω|. The Brillouin density
limit is also analyzed and a class of sheared equilibria is found where the limit valid for the case of rigid rotation can be overcome
On the relativistic cold fluid radial equilibrium of a nonneutral plasma
No full textt is shown that relativistic effects strongly modify the equilibrium of nonneutral plasmas even if the linear velocity of plasma rotation in crossed electric and magnetic fields is small as compared to the speed of light. The change is especially pronounced for the fast rigid-rotor equilibrium, when the frequency of the azimuthal rotation is close to the cyclotron frequency, and the radial density profile becomes approximately parabolic rather than stepwise as predicted by the non-relativistic theory. It is argued that such effects could be detected in experiments similar to those performed by Theiss et al. [A.J. Theiss, R.A. Mahaffey, A.W. Trivelpiece, Phys. Rev. Lett. 35 (1975) 1436]. The relativistic modification of the Brillouin density limit is also addressed
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