Search results for "PLASMA"
showing 10 items of 4043 documents
Total absorption studies of high priority decays for reactor applications: 86Br and 91Rb
2017
Preliminary results from beta decay studies of nuclei that are important for reactor applications are presented. The beta decays have been studied using the total absorption technique (TAS) and the pure beams provided by the JYFLTRAP system at the IGISOL facility of the University of Jyväskylä. peerReviewed
Strong-field-ionization suppression by light-field control
2012
In recent attempts to control strong-field phenomena such as molecular dissociation, undesired ionization sometimes seriously limited the outcome. In this work we examine the capability of quantum optimal control theory to suppress the ionization by rational pulse shaping. Using a simple model system and the ground-state occupation as the target functional, we show that optimal control generally leads to a significant suppression of the ionization, although the fluence and the pulse length are kept fixed. In the low-frequency regime the ionization is reduced mainly by avoiding high peaks in the intensity and thus preventing tunneling. In contrast, at high frequencies in the extreme ultravio…
Limitation of the ECRIS performance by kinetic plasma instabilities (invited).
2016
Electron cyclotron resonance ion source (ECRIS) plasmas are prone to kinetic instabilities due to anisotropic electron velocity distribution. The instabilities are associated with strong microwave emission and periodic bursts of energetic electrons escaping the magnetic confinement. The instabilities explain the periodic ms-scale oscillation of the extracted beam current observed with several high performance ECRISs and restrict the parameter space available for the optimization of extracted beam currents of highly charged ions. Experiments with the JYFL 14 GHz ECRIS have demonstrated that due to the instabilities the optimum Bmin-field is less than 0.8BECR, which is the value suggested by …
Transverse distribution of beam current oscillations of a 14 GHz electron cyclotron resonance ion source
2014
The temporal stability of oxygen ion beams has been studied with the 14 GHz A-ECR at JYFL (University of Jyvaskyla, Department of Physics). A sector Faraday cup was employed to measure the distribution of the beam current oscillations across the beam profile. The spatial and temporal characteristics of two different oscillation “modes” often observed with the JYFL 14 GHz ECRIS are discussed. It was observed that the low frequency oscillations below 200 Hz are distributed almost uniformly. In the high frequency oscillation “mode,” with frequencies >300 Hz at the core of the beam, carrying most of the current, oscillates with smaller amplitude than the peripheral parts of the beam. The result…
Powerful neutron generators based on high current ECR ion sources with gyrotron plasma heating
2017
This article has no abstract. peerReviewed
Limitations of electron cyclotron resonance ion source performances set by kinetic plasma instabilities.
2015
Electron cyclotron resonance ion source (ECRIS) plasmas are prone to kinetic instabilities due to anisotropy of the electron energy distribution function stemming from the resonant nature of the electron heating process. Electron cyclotron plasma instabilities are related to non-linear interaction between plasma waves and energetic electrons resulting to strong microwave emission and a burst of energetic electrons escaping the plasma, and explain the periodic oscillations of the extracted beam currents observed in several laboratories. It is demonstrated with a minimum-B 14 GHz ECRIS operating on helium, oxygen, and argon plasmas that kinetic instabilities restrict the parameter space avail…
Detuning-induced robustness of a three-state Landau-Zener model against dissipation
2019
A three-state system subjected to a time-dependent Hamiltonian whose bare energies undergo one or more crossings, depending on the relevant parameters, is considered, also taking into account the role of dissipation in the adiabatic following of the Hamiltonian eigenstates. Depending on the fact that the bare energies are equidistant or not, the relevant population transfer turns out to be very sensitive to the environmental interaction or relatively robust. The physical mechanisms on the basis of this behavior are discussed in detail.
Numerical simulations of turbulent flow in an electromagnetically levitated metallic droplet using k-Ω SST and Reynolds stress models
2020
International audience; Electromagnetic levitation of a metallic droplet in the microgravity conditions is modelled accounting for the droplet shape variation, its displacement and turbulent character of the flow in the system. Three different models are applied for description of turbulent flow in the droplet: k − ω SST model and two models based on Reynolds stresses (RSM), all of them resulted in a qualitatively similar flow inside a droplet. Use of RSM-based models leads to a sharper interface of a droplet in volume-of-fluid calculations compared to the k − ω SST model. Two RSM models predict value of the surface tension close to a theoretical one, yet, both fail in predicting of viscosi…
Solving the heat-flow problem with transient relativistic fluid dynamics
2014
Israel-Stewart theory is a causal, stable formulation of relativistic dissipative fluid dynamics. This theory has been shown to give a decent description of the dynamical behavior of a relativistic fluid in cases where shear stress becomes important. In principle, it should also be applicable to situations where heat flow becomes important. However, it has been shown that there are cases where Israel-Stewart theory cannot reproduce phenomena associated with heat flow. In this paper, we derive a relativistic dissipative fluid-dynamical theory from kinetic theory which provides a good description of all dissipative phenomena, including heat flow. We explicitly demonstrate this by comparing th…
Laboratory astrophysics survey of key x-ray diagnostic lines using a microcalorimeter on an electron beam ion trap
2000
Cosmic plasma conditions created in an electron beam ion trap (EBIT) make it possible to simulate the dependencies of key diagnostic X-ray lines on density, temperature, and excitation conditions that exist in astrophysical sources. We used a microcalorimeter for such laboratory astrophysics studies because it has a resolving power ≈1000, quantum efficiency approaching 100%, and a bandwidth that spans the X-ray energies from 0.2 keV to 10 keV. Our microcalorimeter, coupled with an X-ray optic to increase the effective solid angle, provides a significant new capability for laboratory astrophysics measurements. Broadband spectra obtained from the National Institute of Standards and Technology…