Measurement of the longitudinal energy distribution of electrons in low energy beams using electrostatic elements

Abstract

The Transverse Energy Spread Spectrometer (TESS) was designed primarily to study the mean transverse energy spread of electrons emitted from photocathode electron sources at both room and liquid nitrogen temperatures as a function of quantum efficiency through analysis of the photoemission footprint. By reconfiguring the potentials applied to different detector elements, TESS can also be used to measure the mean longitudinal energy spread of photoemitted electrons. Initial plans were to use electrostatic wire meshes as a retarding element which prevents the detection of electrons with insufficient energy to overcome a variable potential barrier. However, this method has proved impractical and a new method has been proposed in which the photocathode bias potential is swept (effectively from a state of no electron emission to full emission) and the emitted photocurrent is then detected by using a photoemitted charge collector. In this article, we present the TESS set-up and analyze this new method to measure the longitudinal energy distribution curve. Experimental results are presented and compared to simulated results by utilising a custom designed tracking code.

Charged particle tracking through electrostatic wire meshes using the finite element method

“…In this section, a mesh with sizes given in Ref. 4 are used as a representation of a physical mesh with cell pitch, wire thickness, bend radii, and depth of 0.5 mm, 0.05 mm, 0.05 mm, and 0.035 mm, respectively.…”

“…The code was developed to study a multi-mesh system which filters electrons based on their initial energy when emitted from a photocathode. 4,5,11 In this system, two meshes are placed between a photocathode and detector with the first mesh held at a potential that will accelerate particles from the cathode source towards the mesh and the second mesh at a potential that will stop particles passing through which have insufficient energy to do so. The general potential layout of this system was shown in the inset of Fig.…”

“…Wire meshes, an orthogonal array of equispaced crossing wires, are often used in charged particle transport in particle accelerators, such as in ion sources, 1 and are also used in mass spectrometers, 2 electrostatic precipitators for cleaning air, 3 and may be used as a retardation energy filter to study the distribution of low energy electrons. 4 In the first two cases, they are used to accelerate electrons and ions in a static field. In the case of a retardation filter, the exact potential at the center of the mesh cells needs to be known to achieve better resolution of the energy of particles that can pass through the filter.…”

Energy distribution and adiabatic guiding of a solid-neon-moderated positron beam

“…Many techniques have been developed over the years to study the energy distributions of magnetically guided electron beams from various sources (e.g. [35][36][37]). Typically these beams have much higher currents (μA to mA, compared to the sub-pA currents from the typical positron beam source), and so many electron-beam analysis techniques are not possible for positron beams.…”

Development of a 3-D energy-momentum analyzer for meV-scale energy electrons

“…In the past, several techniques that minimize the sensitivity to stray fields have been developed to measure the transverse and longitudinal energy distributions of such low energy electrons. So far these techniques have been successfully implemented to either measure the 2-D transverse momentum distributions 12,13 , 2-D longitudinal and transverse energy distributions 14, 15 or the 1-D longitudinal energy distributions 16 . In this paper, we report of the development of a technique to measure the complete 3-D energy and momentum distributions of very low energy electrons using the time-of-flight approach.…”