We demonstrate the trapping of a strongly magnetized, quasineutral ultracold plasma in a nested Penning trap with a background field of 2.9 T. Electrons remain trapped in this system for several milliseconds. Early in the evolution, the dynamics are driven by a breathing-mode oscillation in the ionic charge distribution, which modulates the electron trap depth. Over longer times scales, the electronic component undergoes cooling. Trap loss resulting from E x B drift is characterized.
We demonstrate the trapping of a strongly magnetized, quasineutral ultracold plasma in a nested Penning trap with a background field of 2.9 T. Electrons remain trapped in this system for several milliseconds. Early in the evolution, the dynamics are driven by a breathing-mode oscillation in the ionic charge distribution, which modulates the electron trap depth. Over longer times scales, the electronic component undergoes cooling. Trap loss resulting from E x B drift is characterized.
Cold Rydberg atoms and ultracold plasmas have been studied in the strong-magnetization regime. In this new territory, novel atomic and plasma states---such as guiding-center drift Rydberg attains and strongly magnetized, quasi-neutral, ultracold plasmas---have been created and investigated. The evolution dynamics studies of these exotic diamagnetic forms of matter, made possible by implementing a superconducting magnetic atom trap, revealed rich dynamical features in the systems: The Landau-quantized energy structure has led to entirely different evolutions of the highly excited atoms in laser-excited or drift Rydberg states than in magnetic-field-free cases; and the presence of the strong magnetic field has drastically altered the collisional behavior and expansion dynamics of the plasmas. Furthermore, atom cooling and trapping methodology has been extended in multiple directions. Firstly, laser cooling and magnetic trapping of ground-state atoms has been demonstrated in magnetic; fields exceeding 3 Tesla, representing a 20-fold increase in the field-strength of cold-atom traps. Secondly, the trapping of Rydberg atoms with a lifetime of 80 ms has been achieved. This trapping technique exploits the quasi-free nature of Rydberg electrons, which can be adopted in other forms of Rydberg-atom trapping. Lastly; the trapping of two-component, ultracold plasmas has been demonstrated in a nested Penning-trap configuration. The confinement of quasi-neutral ultracold plasmas allowed us to observe novel effects such as the correlation between the ionic oscillation and the electron energy distribution.
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.
Ultracold neutral plasmas represent a regime of plasmas that is not entirely described by theory, but is critical to our understanding of many phenomena. Though their low temperature makes observing them more manageable, even "confined" ultracold plasmas do not remain contained for more than a few hundred microseconds. No steady state or long-term confinement of an ultracold plasma created by pulse ionization has ever been demonstrated. In this thesis, the construction of a Penning trap for calcium ultracold neutral plasma is presented. The trap consists of a uniform magnetic field to trap the electrons radially and a quadrupole electric field to trap them in the axial direction, under the hypothesis that the space charge of the electrons will trap the ions. To the best of the author's knowledge, no ion trap of this configuration has been used to confine ultracold neutral plasmas. In addition to the Penning trap, this thesis also presents work done on other projects. This includes data acquisition and analysis on freely expanding ultracold neutral plasmas with varying density gradients, research on dielectric discharge barrier plasmas, and presentations given on these subjects. Finally, a short list of skills developed over the course of this program is given.
We describe a hybrid molecular dynamics approach for the description of ultracold neutral plasmas, based on an adiabatic treatment of the electron gas and a full molecular dynamics simulation of the ions, which allows us to follow the long-time evolution of the plasma including the effect of the strongly coupled ion motion. The plasma shows a rather complex relaxation behavior, connected with temporal as well as spatial oscillations of the ion temperature. Furthermore, additional laser cooling of the ions during the plasma evolution drastically modifies the expansion dynamics, so that crystallization of the ion component can occur in this nonequilibrium system, leading to lattice-like structures or even long-range order resulting in concentric shells.
We describe a hybrid molecular dynamics approach for the description of ultracold neutral plasmas, based on an adiabatic treatment of the electron gas and a full molecular dynamics simulation of the ions, which allows us to follow the long-time evolution of the plasma including the effect of the strongly coupled ion motion. The plasma shows a rather complex relaxation behavior, connected with temporal as well as spatial oscillations of the ion temperature. Furthermore, additional laser cooling of the ions during the plasma evolution drastically modifies the expansion dynamics, so that crystallization of the ion component can occur in this nonequilibrium system, leading to lattice-like structures or even long-range order resulting in concentric shells.
We present the first large-scale simulations of an ultracold neutral plasma, produced by photoionization of laser-cooled xenon atoms, from creation to initial expansion, using classical molecular-dynamics methods with open boundary conditions. We reproduce many of the experimental findings such as the trapping efficiency of electrons with increased ion number, a minimum electron temperature achieved on approach to the photoionization threshold, and recombination into Rydberg states of an anomalously low principal quantum number. In addition, many of these effects establish themselves very early in the plasma evolution ( similar ns) before the present experimental observations begin.