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.

Highlights

  • An essential requirement of ion traps is to confine electrons or ions for longer periods of time under minimal perturbations, in order to carry out studies on them [1,2,3,4]

  • The confinement time is finite due to several reasons that include collisions with the surrounding neutrals, anharmonicities in the trap potential induced by deviations from the ideal geometry of the trap, and in situations involving a large number of charged particles, space charge effects in the trap [5]

  • In work examining the background pressure’s effect in addition to the applied magnetic field, B, measurements of the variation of the radial density of trapped electrons at the centre of the trap [12, 15] reveal that the confinement time varies with B and pressure, P, as τ ∝ B3/2/P

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Summary

Introduction

An essential requirement of ion traps is to confine electrons or ions for longer periods of time under minimal perturbations, in order to carry out studies on them [1,2,3,4]. Induced asymmetries have been applied to investigate plasma confinement time [10] and these lead to a different dependence on the magnetic field.

Results
Conclusion

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