Miniaturized magnet-less RF electron trap. II. Experimental verification

Abstract

Atomic microsystems have the potential of providing extremely accurate measurements of timing and acceleration. However, atomic microsystems require active maintenance of ultrahigh vacuum in order to have reasonable operating lifetimes and are particularly sensitive to magnetic fields that are used to trap electrons in traditional sputter ion pumps. This paper presents an approach to trapping electrons without the use of magnetic fields, using radio frequency (RF) fields established between two perforated electrodes. The challenges associated with this magnet-less approach, as well as the miniaturization of the structure, are addressed. These include, for example, the transfer of large voltage (100–200 V) RF power to capacitive loads presented by the structure. The electron trapping module (ETM) described here uses eight electrode elements to confine and measure electrons injected by an electron beam, within an active trap volume of 0.7 cm3. The operating RF frequency is 143.6 MHz, which is the measured series resonant frequency between the two RF electrodes. It was found experimentally that the steady state electrode potentials on electrodes near the trap became more negative after applying a range of RF power levels (up to 0.15 W through the ETM), indicating electron densities of ≈3 × 105 cm−3 near the walls of the trap. The observed results align well with predicted electron densities from analytical and numerical models. The peak electron density within the trap is estimated as ∼1000 times the electron density in the electron beam as it exits the electron gun. This successful demonstration of the RF electron trapping concept addresses critical challenges in the development of miniaturized magnet-less ion pumps.