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Physical review. E

Ultracold plasma expansion in quadrupole magnetic field

Sergey Ya. Bronin, Evgenii Vladimirovich Vikhrov, Boris B. Zelener, B. V. Zelener

Published Oct 23, 2023• 7 citations
Publisher

Abstract

We present simulation results of ultracold Sr plasma expansion in a quadrupole magnetic field by means of molecular dynamics. An analysis of plasma evolution influenced by a magnetic field is given. Plasma confinement time behavior under variation of magnetic field strength is estimated. Similarity of the time dependence of the concentration and distribution of ion velocities against the parameters of the plasma and magnetic field is established. Simulation results are in agreement with the experimental ones.

DOI
10.1103/physreve.108.045209

Related papers

Comment on “Ultracold plasma expansion in quadrupole magnetic field”

Matthew Schlitters, Matthew Miller, Ben Farley +1 more

Bronin et al. [Phys. Rev. E 108, 045209 (2023)2470-004510.1103/PhysRevE.108.045209] recently reported molecular-dynamics simulations of ultracold neutral plasmas expanding in a quadrupole magnetic field. While the main results are in agreement with prior experimental measurements, we present data showing oscillations not captured in the simulations of Bronin et al. Plasmas formed using pulsed or continuous-wave ionization processes have similar confinement times.

Physical review. E•Aug 21, 2024•2 citations

Low-Frequency Ion Oscillations during the Expansion of Ultracold Plasma

Sergey Ya. Bronin, Evgenii Vladimirovich Vikhrov, B. B. Zelener +1 more

Abstract The results of calculations using the molecular dynamics method of low-frequency ion oscillations in ultracold plasma, previously observed in the experiment, are presented. Oscillations of the radial velocity of ions and changes in the direction of their flows during the expansion of ultracold plasma in a quadrupole magnetic field are detected. This is due to the influence of the magnetic field on the charge imbalance, which leads to the simultaneous existence of potential wells for both electrons and ions. Ion temperature oscillations with a frequency close to the ion plasma frequency are also detected. Satisfactory agreement with the experiment is obtained.

High Temperature•Oct 1, 2024•0 citations

Reply to “Comment on ‘Ultracold plasma expansion in quadrupole magnetic field' ”

Sergey Ya. Bronin, Evgenii Vladimirovich Vikhrov, B. B. Zelener +1 more

In this Reply, we respond to the Comment by Schlitters et al. on our recent work [Phys. Rev. E 108, 045209 (2023)10.1103/PhysRevE.108.045209], where we present simulation results of ultracold Sr plasma expansion in a quadrupole magnetic field using a molecular-dynamics method. In the Comment, Schlitters et al. present their experimental results, some of which, from their point of view, contradict our simulation results and others that confirm the experiments of Gorman et al. [Phys. Rev. Lett. 126, 085002 (2021)10.1103/PhysRevLett.126.085002] and our results. In addition, Schlitters et al. also provide results that were not described in our work. Here we show that there is not a contradiction but a misunderstanding of our results. This is due to the fact that simulations allow the use of processing methods that are difficult to obtain in experiment. We also present different simulation results related to expansion velocity variations that reflect the experimental results of Schlitters et al. and provide an explanation for the origin of these variations.

Physical review. E•Aug 21, 2024•1 citation

Simulation of ultracold plasma expansion in homogeneous magnetic field

Evgenii Vladimirovich Vikhrov, B. B. Zelener, B. B. Zelener

We present molecular dynamics simulation results for an ultracold $^{40}$Ca plasma in a constant, homogeneous magnetic field. The magnetic field induces a significant spatial separation of charges. Furthermore, a significant fraction of the electrons escapes from the region bounded by the ions, in contrast to the case of plasma expansion into a vacuum. This leads to the formation of a quasineutral plasma core containing the remaining electrons and surrounded by an outer, thick ion shell, where the ion density drops sharply. Anisotropy in the ion kinetic energy is also observed, depending on the direction of ion motion relative to the magnetic field lines. The simulation results are in agreement with experimental data on ion dynamics.

arXiv:2609.28829•Sep 23, 2026•0 citations

Ultracold Plasma Dynamics in a Magnetic Field

Xianli Zhang

Plasmas, often called the fourth state of matter and the most common one in the universe, have parameters varying by many orders of magnitude, from temperature of a few hundred kelvin in the Earth's ionosphere to 10 16 K in the magnetosphere of a pulsar. Ultracold plasmas, produced by photoionizing a sample of laser-cooled and trapped atoms near the ionization limit, have extended traditional neutral plasma parameters by many orders of magnitude, to electron temperatures below 1 K and ion temperatures in the tens of &mu K to a few Kelvin, and densities of 10 5 cm -3 to 10 10 cm -3 . These plasmas thus provide a testing ground to study basic plasma theory in a clean and simple system with or without a magnetic field. Previous studies of ultracold plasmas have primarily concentrated on temperature measurements, collective modes and expansion dynamics in the absence of magnetic fields. This thesis presents the first study of ultracold plasma dynamics in a magnetic field. The presence of a magnetic field during the expansion can initiate various phenomena, such as plasma confinement and plasma instabilities. While the electron temperatures are very low in ultracold plasmas, we need only tens of Gauss of magnetic field to observe significant effects on the expansion dynamics. To probe the ultraocold plasma dynamics in a magnetic field, we developed a new diagnostic - projection imaging, which images the ion distribution by extracting the ions with a high voltage pulse onto a position-sensitive detector. Early in the lifetime of the plasma (< 20 &mu s), the size of the image is dominated by the time-of-flight Coulomb explosion of the dense ion cloud. For later times, we measure the 2-D Gaussian width of the ion image, obtaining the transverse expansion velocity as a function of magnetic field (up to 70 G),and observe that the transverse expansion velocity scales as B &minus1/2 , explained by a nonlinear ambipolar diffusion model that involes anisotropic diffusion in two different directions. We also present the first observation of a plasma instability in an expanding ultracold plasma. We observe periodic emission of electrons from an ultracold plasma in weak, crossed magnetic and electric fields, and a strong perturbed electron density distribution in electron time-of-flight projection images. We identify this instability as a high-frequency electron drift instability due to the coupling between the electron drift wave and electron cyclotron harmonic, which has large wavenumbers corresponding to wavelengths close to the electron gyroradius.

•Jan 1, 2009•1 citation

Magnetic Confinement of an Ultracold Neutral Plasma

Grant M. Gorman, M. K. Warrens, S. J. Bradshaw +1 more

We demonstrate magnetic confinement of an ultracold neutral plasma (UCNP) created at the null of a biconic cusp, or quadrupole magnetic field. Initially, the UCNP expands due to electron thermal pressure. As the plasma encounters stronger fields, expansion slows and the density distribution molds to the field. UCNP electrons are strongly magnetized over most of the plasma, while ion magnetization is only significant at the boundaries. Observations suggest that electrons and ions are predominantly trapped by magnetic mirroring and ambipolar electric fields, respectively. Confinement times approach 0.5 ms, while unmagnetized plasmas dissipate on a timescale of a few tens of microseconds.

arXiv:2010.16355•Physical Review Letters•Feb 25, 2021•34 citations
We present simulation results of ultracold Sr plasma expansion in a quadrupole magnetic field by means of molecular dynamics. An analysis of plasma evolution influenced by a magnetic field is given. Plasma confinement time behavior under variation of magnetic field strength is estimated. Similarity of the time dependence of the concentration and distribution of ion velocities against the parameters of the plasma and magnetic field is established. Simulation results are in agreement with the experimental ones.
Abstract The results of calculations using the molecular dynamics method of low-frequency ion oscillations in ultracold plasma, previously observed in the experiment, are presented. Oscillations of the radial velocity of ions and changes in the direction of their flows during the expansion of ultracold plasma in a quadrupole magnetic field are detected. This is due to the influence of the magnetic field on the charge imbalance, which leads to the simultaneous existence of potential wells for both electrons and ions. Ion temperature oscillations with a frequency close to the ion plasma frequency are also detected. Satisfactory agreement with the experiment is obtained.
In this Reply, we respond to the Comment by Schlitters et al. on our recent work [Phys. Rev. E 108, 045209 (2023)10.1103/PhysRevE.108.045209], where we present simulation results of ultracold Sr plasma expansion in a quadrupole magnetic field using a molecular-dynamics method. In the Comment, Schlitters et al. present their experimental results, some of which, from their point of view, contradict our simulation results and others that confirm the experiments of Gorman et al. [Phys. Rev. Lett. 126, 085002 (2021)10.1103/PhysRevLett.126.085002] and our results. In addition, Schlitters et al. also provide results that were not described in our work. Here we show that there is not a contradiction but a misunderstanding of our results. This is due to the fact that simulations allow the use of processing methods that are difficult to obtain in experiment. We also present different simulation results related to expansion velocity variations that reflect the experimental results of Schlitters et al. and provide an explanation for the origin of these variations.
We present molecular dynamics simulation results for an ultracold 40^{40}40Ca plasma in a constant, homogeneous magnetic field. The magnetic field induces a significant spatial separation of charges. Furthermore, a significant fraction of the electrons escapes from the region bounded by the ions, in contrast to the case of plasma expansion into a vacuum. This leads to the formation of a quasineutral plasma core containing the remaining electrons and surrounded by an outer, thick ion shell, where the ion density drops sharply. Anisotropy in the ion kinetic energy is also observed, depending on the direction of ion motion relative to the magnetic field lines. The simulation results are in agreement with experimental data on ion dynamics.
Plasmas, often called the fourth state of matter and the most common one in the universe, have parameters varying by many orders of magnitude, from temperature of a few hundred kelvin in the Earth's ionosphere to 10 16 K in the magnetosphere of a pulsar. Ultracold plasmas, produced by photoionizing a sample of laser-cooled and trapped atoms near the ionization limit, have extended traditional neutral plasma parameters by many orders of magnitude, to electron temperatures below 1 K and ion temperatures in the tens of &mu K to a few Kelvin, and densities of 10 5 cm -3 to 10 10 cm -3 . These plasmas thus provide a testing ground to study basic plasma theory in a clean and simple system with or without a magnetic field. Previous studies of ultracold plasmas have primarily concentrated on temperature measurements, collective modes and expansion dynamics in the absence of magnetic fields. This thesis presents the first study of ultracold plasma dynamics in a magnetic field. The presence of a magnetic field during the expansion can initiate various phenomena, such as plasma confinement and plasma instabilities. While the electron temperatures are very low in ultracold plasmas, we need only tens of Gauss of magnetic field to observe significant effects on the expansion dynamics. To probe the ultraocold plasma dynamics in a magnetic field, we developed a new diagnostic - projection imaging, which images the ion distribution by extracting the ions with a high voltage pulse onto a position-sensitive detector. Early in the lifetime of the plasma (< 20 &mu s), the size of the image is dominated by the time-of-flight Coulomb explosion of the dense ion cloud. For later times, we measure the 2-D Gaussian width of the ion image, obtaining the transverse expansion velocity as a function of magnetic field (up to 70 G),and observe that the transverse expansion velocity scales as B &minus1/2 , explained by a nonlinear ambipolar diffusion model that involes anisotropic diffusion in two different directions. We also present the first observation of a plasma instability in an expanding ultracold plasma. We observe periodic emission of electrons from an ultracold plasma in weak, crossed magnetic and electric fields, and a strong perturbed electron density distribution in electron time-of-flight projection images. We identify this instability as a high-frequency electron drift instability due to the coupling between the electron drift wave and electron cyclotron harmonic, which has large wavenumbers corresponding to wavelengths close to the electron gyroradius.
We demonstrate magnetic confinement of an ultracold neutral plasma (UCNP) created at the null of a biconic cusp, or quadrupole magnetic field. Initially, the UCNP expands due to electron thermal pressure. As the plasma encounters stronger fields, expansion slows and the density distribution molds to the field. UCNP electrons are strongly magnetized over most of the plasma, while ion magnetization is only significant at the boundaries. Observations suggest that electrons and ions are predominantly trapped by magnetic mirroring and ambipolar electric fields, respectively. Confinement times approach 0.5 ms, while unmagnetized plasmas dissipate on a timescale of a few tens of microseconds.