| 1. |
- Adhikary, N C, et al.
(författare)
-
Ion-beam driven dust ion-acoustic solitary waves in dusty plasmas
- 2010
-
Ingår i: Physics of Plasmas. - : American Institute of Physics (AIP). - 1070-664X .- 1089-7674. ; 17:4
-
Tidskriftsartikel (refereegranskat)abstract
- The nonlinear propagation of small but finite amplitude dust ion-acoustic waves (DIAWs) in an ion-beam driven plasma consisting of Boltzmannian electrons, positive ions, and stationary negatively charged dust grains is studied by using the standard reductive perturbation technique. It is shown that there exist two critical values (γc1) and (γc2) of ion beam to ion phase velocity ratio (γ), above and below which the beam generated solitons are not possible. The effects of the parameters, namely, γ, the ratio of the ion beam to plasma ion density (μi), the dust to ion density ratio (μd), and the ion beam to plasma ion mass ratio (μ) on both the amplitude and width of the stationary DIAWs, are analyzed numerically, and applications of the results to laboratory ion beam as well as space plasmas (e.g., auroral plasmas) are explained.
|
|
| 2. |
- Amole, C., et al.
(författare)
-
Experimental and computational study of the injection of antiprotons into a positron plasma for antihydrogen production
- 2013
-
Ingår i: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 20:4, s. 043510-
-
Tidskriftsartikel (refereegranskat)abstract
- One of the goals of synthesizing and trapping antihydrogen is to study the validity of charge-parity-time symmetry through precision spectroscopy on the anti-atoms, but the trapping yield achieved in recent experiments must be significantly improved before this can be realized. Antihydrogen atoms are commonly produced by mixing antiprotons and positrons stored in a nested Penning-Malmberg trap, which was achieved in ALPHA by an autoresonant excitation of the antiprotons, injecting them into the positron plasma. In this work, a hybrid numerical model is developed to simulate antiproton and positron dynamics during the mixing process. The simulation is benchmarked against other numerical and analytic models, as well as experimental measurements. The autoresonant injection scheme and an alternative scheme are compared numerically over a range of plasma parameters which can be reached in current and upcoming antihydrogen experiments, and the latter scheme is seen to offer significant improvement in trapping yield as the number of available antiprotons increases.
|
|
| 3. |
- Anderson, Johan, 1973, et al.
(författare)
-
A fractional Fokker-Planck model for anomalous diffusion
- 2014
-
Ingår i: Physics of Plasmas. - : AIP Publishing. - 1089-7674 .- 1070-664X. ; 21:12, s. aricle no: 122109-
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, we present a study of anomalous diffusion using a Fokker-Planck description withfractional velocity derivatives. The distribution functions are found using numerical means forvarying degree of fractionality of the stable Lévy distribution. The statistical properties of thedistribution functions are assessed by a generalized normalized expectation measure and entropyin terms of Tsallis statistical mechanics. We find that the ratio of the generalized entropy andexpectation is increasing with decreasing fractionality towards the well known so-called sub-diffusivedomain, indicating a self-organising behavior.
|
|
| 4. |
- Anderson, Johan, 1973, et al.
(författare)
-
Electron geodesic acoustic modes in electron temperature gradient mode turbulence
- 2012
-
Ingår i: Physics of Plasmas. - : AIP Publishing. - 1089-7674 .- 1070-664X. ; 19:8
-
Tidskriftsartikel (refereegranskat)abstract
- In this work, the first demonstration of an electron branch of the geodesic acoustic mode (el-GAM) driven by electron temperature gradient (ETG) modes is presented. The work is based on a fluid description of the ETG mode retaining non-adiabatic ions and the dispersion relation for el-GAMsdriven nonlinearly by ETG modes is derived. A new saturation mechanism for ETG turbulence through the interaction with el-GAMs is found, resulting in a significantly enhanced ETGturbulence saturation level compared to the mixing length estimate.
|
|
| 5. |
- Anderson, Johan, 1973, et al.
(författare)
-
Secondary instability of electromagnetic ion-temperature-gradient modes for zonal flow generation
- 2011
-
Ingår i: Physics of Plasmas. - 1089-7674 .- 1070-664X. ; 18:072306
-
Tidskriftsartikel (refereegranskat)abstract
- An analytical model for zonal flow generation by toroidal ion-temperature-gradient (ITG) modes, including finite β electromagnetic effects, is derived. The derivation is based on a fluid model for ions and electrons and takes into account both linear and nonlinear β effects. The influence of finite plasma β on the zonal flow growth rate (γ_ZF) scaling is investigated for typical tokamak plasma parameters. The results show the importance of the zonal flows close to marginal stability where γ_ZF/γ_ITG ≫ 1 is obtained. In this region the parameter γ_ZF/γ_ITG increases with β, indicating that the ITG turbulence and associated transport would decrease with β at a faster rate than expected from a purely linear or quasi-linear analysis.
|
|
| 6. |
- Anderson, Johan, 1973, et al.
(författare)
-
Signature of a universal statistical description for drift-wave plasma turbulence
- 2010
-
Ingår i: Physics of Plasmas. - : AIP Publishing. - 1089-7674 .- 1070-664X. ; 17:11
-
Tidskriftsartikel (refereegranskat)abstract
- This letter provides a theoretical interpretation of numerically generated probability densityfunctions ͑PDFs͒ of intermittent plasma transport events. Specifically, nonlinear gyrokineticsimulations of ion-temperature-gradient turbulence produce the time series of heat flux thatmanifestly exhibit non-Gaussian PDFs with enhanced tails. It is demonstrated that, after the removalof autocorrelations, the numerical PDFs can be matched with predictions from a fluid theoreticalsetup based on the instanton method. This result points to a universality in the modeling ofintermittent stochastic process offering a predictive capability.
|
|
| 7. |
- Anderson, Johan, 1973, et al.
(författare)
-
Statistical analysis and modeling of intermittent transport events in the tokamak scrape-off layer
- 2014
-
Ingår i: Physics of Plasmas. - : AIP Publishing. - 1089-7674 .- 1070-664X. ; 21:12, s. article no. 122306-
-
Tidskriftsartikel (refereegranskat)abstract
- The turbulence observed in the scrape-off-layer of a tokamak is often characterized by intermittentevents of bursty nature, a feature which raises concerns about the prediction of heat loads on thephysical boundaries of the device. It appears thus necessary to delve into the statistical propertiesof turbulent physical fields such as density, electrostatic potential, and temperature, focusing on themathematical expression of tails of the probability distribution functions. The method followedhere is to generate statistical information from time-traces of the plasma density stemming fromBraginskii-type fluid simulations and check this against a first-principles theoretical model. The analysis of the numerical simulations indicates that the probability distribution function of the intermittent process contains strong exponential tails, as predicted by the analytical theory.
|
|
| 8. |
- Badziak, J, et al.
(författare)
-
Generation of ultraintense proton beams by multi-ps circularly polarized laser pulses for fast ignition-related applications
- 2011
-
Ingår i: Physics of Plasmas. - New York : American Institute of Physics (AIP). - 1070-664X .- 1089-7674. ; 18:5
-
Tidskriftsartikel (refereegranskat)abstract
- A scheme of generation of ultraintense proton beams relevant for proton fast ignition (PFI) which employs multi-ps, circularly polarized laser pulse irradiating a thick (≥ 10 μm) H-rich target is proposed and examined using one-dimensional particle-in cell-simulations. It is shown that a 5-ps laser pulse of intensity ∼ (2–5) × 1020W/cm2 irradiating the target of the areal proton density ∼ 2 × 1020cm−2 can produce – with a high energetic efficiency – a proton beam (plasma block) of parameters (intensity, energy fluence, pulse duration, proton energy spectrum) close to those required for PFI. At a fixed total laser energy, the proton beam parameters can be controlled and fitted to the PFI requirements by changing the laser intensity (energy fluence) and/or the target thickness as well as by using a shaped (curved) target inserted into a guiding cone.
|
|
| 9. |
- Bains, AS, et al.
(författare)
-
Modulational instability of ion-acoustic wave envelopes in magnetized quantum electron-positron-ion plasmas
- 2010
-
Ingår i: Physics of Plasmas. - : American Institute of Physics (AIP). - 1070-664X .- 1089-7674. ; 17:1
-
Tidskriftsartikel (refereegranskat)abstract
- The amplitude modulation of quantum ion-acoustic waves (QIAWs) along an external magnetic field is studied in a quantum electron-positron-ion (e-p-i) magnetoplasma. Reductive perturbation technique is used to derive the three-dimensional nonlinear Schroumldinger equation which governs the slow modulation of QIAW packets. Accounting for the effects of the electron to ion number density ratio (mu), the normalized ion-cyclotron frequency (omega(c)) as well as the ratio (H) of the "plasmonic energy density" to the Fermi energy, new regimes for the modulational instability of QIAWs are obtained and analyzed. In contrast to one-dimensional unmagnetized e-p-i plasmas, the instability growth rate is shown to suppress with increasing mu or decreasing the values of H. The predicted results could be important for understanding the salient features of modulated QIAW packets in dense astrophysical plasmas as well as to the next generation intense laser solid density plasma experiments.
|
|
| 10. |
- Beurskens, M N A, et al.
(författare)
-
H-mode pedestal scaling in DIII-D, ASDEX Upgrade, and JET
- 2011
-
Ingår i: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 18:5
-
Tidskriftsartikel (refereegranskat)abstract
- Multidevice pedestal scaling experiments in the DIII-D, ASDEX Upgrade (AUG), and JET tokamaks are presented in order to test two plasma physics pedestal width models. The first model proposes a scaling of the pedestal width Delta/a proportional to rho*(1/2) to rho* based on the radial extent of the pedestal being set by the point where the linear turbulence growth rate exceeds the E x B velocity. In the multidevice experiment where rho* at the pedestal top was varied by a factor of four while other dimensionless parameters where kept fixed, it has been observed that the temperature pedestal width in real space coordinates scales with machine size, and that therefore the gyroradius scaling suggested by the model is not supported by the experiments. The density pedestal width is not invariant with rho* which after comparison with a simple neutral fuelling model may be attributed to variations in the neutral fuelling patterns. The second model, EPED1, is based on kinetic ballooning modes setting the limit of the radial extent of the pedestal region and leads to Delta(psi) proportional to beta p(1/2). All three devices show a scaling of the pedestal width in normalised poloidal flux as Delta(psi) proportional to beta p(1/2), as described by the kinetic ballooning model; however, on JET and AUG, this could not be distinguished from an interpretation where the pedestal is fixed in real space. Pedestal data from all three devices have been compared with the predictive pedestal model EPED1 and the model produces pedestal height values that match the experimental data well.
|
|
