Dependence of the Confinement Time of an Electron Plasma on the Magnetic Field in a Quadrupole Penning Trap

A quadrupole Penning trap is used to confine electrons in weak magnetic fields. Perturbations due to space charge and imperfections in the trap geometry, as well as collisions with the background gas molecules, lead to loss of the electrons from the trap. We present in this work the results on measurements of the electron confinement time and its dependence on the magnetic field in a quadrupolar Penning trap. We describe a method to measure the confinement time of an electron cloud under weak magnetic fields (0.01 T - 0.1 T). This time is found to scale as τ∝B1.41 in variance with the theoretically expected confinement time that scales as τ∝B2 for trapped electrons that are lost through collisions with the neutrals present in the trap. A measurement of the expansion rate of the electron plasma in the trap through controlled variation of the trap voltage, yields expansion times that depend on the energy of escaping electrons. This is found to vary in our case in the scaling range B 0.32 to B 0.43. Distorting the geometry of the trap, results in a marked change in the confinement time's dependence on the magnetic field. The results indicate that the confinement time of the electron cloud in the trap is limited by both, effects of collisions and perturbations that result in the plasma loss through expansion in the trap

Dependence of the confinement time of an electron plasma on the magnetic field in a quadrupole Penning trap

Abstract A quadrupole Penning trap is used to confine electrons in weak magnetic fields. Perturbations due to space charge and imperfections in the trap geometry, as well as collisions with the background gas molecules, lead to loss of the electrons from the trap. We present in this work the results on measurements of the electron confinement time and its dependence on the magnetic field in a quadrupolar Penning trap. We describe a method to measure the confinement time of an electron cloud under weak magnetic fields (0.01 T - 0.1 T). This time is found to scale as τ∝B1.41 in variance with the theoretically expected confinement time that scales as τ∝B2 for trapped electrons that are lost through collisions with the neutrals present in the trap. A measurement of the expansion rate of the electron plasma in the trap through controlled variation of the trap voltage, yields expansion times that depend on the energy of escaping electrons. This is found to vary in our case in the scaling range B 0.32 to B 0.43. Distorting the geometry of the trap, results in a marked change in the confinement time’s dependence on the magnetic field. The results indicate that the confinement time of the electron cloud in the trap is limited by both, effects of collisions and perturbations that result in the plasma loss through expansion in the trap

Energy distribution of electrons under axial motion in a quadrupole Penning trap

We present results of the energy distribution function of trapped electrons through a measurement on their axial oscillation in a quadrupole Penning trap. Electrons emitted from a thoriated tungsten filament with a range of energies (3-5 eV) are trapped in a low magnetic field quadrupole Penning trap. Subsequent to storage the trapped electrons are detected through monitoring their axial oscillations by an electronic tank circuit that is weakly coupled to the trap, by resonant energy transfer to the electrons. The technique developed using LabVIEW enables a direct measurement of the energy distribution function of the electrons in the trap. We obtain a normal distribution of energy, with a maximum that coincides with the potential applied on the electron filament, indicating that the energy distribution of electrons in the trap reflects the energy distribution of the thermionically emitted electrons from the filament.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author