Admissible equilibria of non-neutral plasmas in a Malmberg-Penning trap

A "parallel current constraint" is derived, that in combination with the Poisson equation allows one to select admissible equilibria of non-neutral plasmas in a Malmberg-Penning trap in the presence of a nonuniform and nonaxisymmetric magnetic field. Asymmetry-induced currents (analogous to the Pfirsch-Schluter currents in Tokamaks) appearing in a non-neutral plasma even in the absence of magnetic drifts are explicitly computed in the case of a uniformly tilted magnetic field

Equilibrium of non-neutral plasmas in a Malmberg\u2013Penning trap with a weakly tilted magnetic field

The effect of small asymmetric magnetic perturbations on the equilibrium of a non-neutral plasma confined in a Malmberg-Penning trap is analyzed. A constraint, known in the theory of tandem mirrors as the condition of current closure, is derived for non-neutral plasmas. Together with Poisson's equation, this constraint provides a set of equations for determining self-consistent asymmetric equilibria of non-neutral plasmas in Malmberg-Penning traps. As an example of this approach, the non-neutral plasma equilibrium in the presence of a weak magnetic tilt is analyzed. Analytical and semianalytical solutions for the electric potential variations inside the trap are found in a paraxial limit for various radial density profiles of the plasma, including the case of global thermal equilibrium. The numerical procedure aimed to obtain self-consistent plasma equilibria for a magnetic field with a large asymmetry is also discussed. The newly developed method can be straightforwardly applied to determine plasma equilibria under the effect of the magnetic perturbations of higher multipolarity (such as, quadrupole or octupole fields)

Multiresolution analysis of the two-dimensional free decaying turbulence in a pure electron plasma

The two-dimensional (2D) freely decaying turbulence is investigated experimentally in an electron plasma confined in a Malmberg\u2013Penning 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

Mortality and pulmonary complications in patients undergoing surgery with perioperative SARS-CoV-2 infection: an international cohort study

Background: The impact of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) on postoperative recovery needs to be understood to inform clinical decision making during and after the COVID-19 pandemic. This study reports 30-day mortality and pulmonary complication rates in patients with perioperative SARS-CoV-2 infection. Methods: This international, multicentre, cohort study at 235 hospitals in 24 countries included all patients undergoing surgery who had SARS-CoV-2 infection confirmed within 7 days before or 30 days after surgery. The primary outcome measure was 30-day postoperative mortality and was assessed in all enrolled patients. The main secondary outcome measure was pulmonary complications, defined as pneumonia, acute respiratory distress syndrome, or unexpected postoperative ventilation. Findings: This analysis includes 1128 patients who had surgery between Jan 1 and March 31, 2020, of whom 835 (74·0%) had emergency surgery and 280 (24·8%) had elective surgery. SARS-CoV-2 infection was confirmed preoperatively in 294 (26·1%) patients. 30-day mortality was 23·8% (268 of 1128). Pulmonary complications occurred in 577 (51·2%) of 1128 patients; 30-day mortality in these patients was 38·0% (219 of 577), accounting for 81·7% (219 of 268) of all deaths. In adjusted analyses, 30-day mortality was associated with male sex (odds ratio 1·75 [95% CI 1·28–2·40], p\textless0·0001), age 70 years or older versus younger than 70 years (2·30 [1·65–3·22], p\textless0·0001), American Society of Anesthesiologists grades 3–5 versus grades 1–2 (2·35 [1·57–3·53], p\textless0·0001), malignant versus benign or obstetric diagnosis (1·55 [1·01–2·39], p=0·046), emergency versus elective surgery (1·67 [1·06–2·63], p=0·026), and major versus minor surgery (1·52 [1·01–2·31], p=0·047). Interpretation: Postoperative pulmonary complications occur in half of patients with perioperative SARS-CoV-2 infection and are associated with high mortality. Thresholds for surgery during the COVID-19 pandemic should be higher than during normal practice, particularly in men aged 70 years and older. Consideration should be given for postponing non-urgent procedures and promoting non-operative treatment to delay or avoid the need for surgery. Funding: National Institute for Health Research (NIHR), Association of Coloproctology of Great Britain and Ireland, Bowel and Cancer Research, Bowel Disease Research Foundation, Association of Upper Gastrointestinal Surgeons, British Association of Surgical Oncology, British Gynaecological Cancer Society, European Society of Coloproctology, NIHR Academy, Sarcoma UK, Vascular Society for Great Britain and Ireland, and Yorkshire Cancer Research

Effect of a weakly tilted magnetic field on the equilibrium of nonneutral plasmas in a Malmberg-Penning trap

The effect of a weakly tilted magnetic field perturbations on the equilibrium of a nonneutral plasma confined in a Malmberg-Penning trap is analyzed. A constraint (\u201ccondition of current closure\u201d) is introduced, that in combination with the Poisson equation allows to select admissible plasma equilibria in the trap in the presence of a non-uniform and a non-axisymmetric magnetic field. Longitudinal plasma currents (analogous to the Pfirsch\u2013Schl\ufcter currents in Tokamaks) appearing in a nonneutral plasma even in the absence of magnetic drifts are explicitly computed in the case of a uniformly tilted magnetic field

Transport induced by symmetry breaking in a nonneutral plasma

Small asymmetries of the confining electric and magnetic fields pose an upper limit on the lifetime of nonneutral plasmas trapped in Malmberg-Penning traps. The present paper reviews the effect of magnetic and electric field errors on the equilibrium of nonneutral plasma based on a suitable parallel current constraint. Together with Poisson's equation, this constraint provides a full set of equations for determining self-consistent asymmetric equilibria of non-neutral plasmas in a Malmberg-Penning trap. Using this approach, the effect on the plasma equilibrium of weak magnetic and electric squeezes (field errors with azimuthal number m=0), tilt (m=1) and quadrupole (m=2) distortions is investigated. Analytical and semi-analytical solutions for the electric potential variation inside the trap are found in a paraxial limit for various radial density profiles of the plasma, including the case of global thermal equilibrium. A direct analog of the Pfirsch-Schl\ufcter and Stupakov currents is also derived. The presented theory of the plasma equilibrium distorted by field errors provides the basis for elaborating a self-consistent theory of the asymmetry induced transport in a Malmberg-Penning trap

Relativistic effects on the equilibrium of electron plasmas

Relativistic effects on the radial equilibrium of non-neutral plasmas confined in cylindrical traps are analyzed for rigid and sheared modes of plasma rotation, both with and without the presence of a coaxial inner charged conductor. The changes with respect to the non-relativistic results are especially pronounced for the fast rotational equilibrium solutions. In particular, relativistic effects can limit the plasma outer radius. Analytical estimates of this maximum radius are found both for a rigid plasma rotation and for the case of a uniform plasma density. It is also observed that the Brillouin density limit is modified when the shielding of the external magnetic field by the current associated with the plasma rotation becomes significant

Relativistic thermal equilibrium of nonneutral plasmas

Finite temperature effects on the relativistic radial equilibrium of a non-neutral plasma are analyzed. An equation for an effective potential governing the self-consistent radial density profile is derived in the case of global thermal equilibrium. The effect of a finite temperature turns out to be particularly strong for the fast mode of rigid plasma rotation, where the density profile can extend beyond the cold limiting radius

Equilibrium of nonneutral plasmas in a Malmberg-Penning trap with a tilted magnetic field

The effect of a weakly tilted magnetic field perturbations on the equilibrium of a nonneutral plasma confined in a Malmberg-Penning trap is analyzed. A constraint is introduced, that in combination with the Poisson equation allows to select admissible plasma equilibria in the trap in the presence of a non-uniform and a non-axisymmetric magnetic field. Longitudinal plasma currents (analogous to the Pfirsch-Schluter currents in Tokamaks) appearing in a nonneutral plasma even in the absence of magnetic drifts are explicitly computed in the case of a uniformly tilted magnetic field

MEP: a 3D PIC Code for the Simulation of the Dynamics of a Non-Neutral Plasma

The 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]