New high luminosity “double toroidal” electron spectrometer

Abstract

In this article we describe the design and the operation of an original, high transmission, electrostatic “double toroidal” electron energy analyzer. The double toroidal analyzer allows the high resolution and high luminosity simultaneous measurement of the kinetic energy, and angular distribution of electrons, using a two-dimensional position sensitive detector. The exact shape of the electrodes is deduced from both analytical and numerical electron trajectory calculations. The electron detector is based on a charge analysis and optimized to attain a 100 kHz counting rate. The actual performances of the analyzer are illustrated with spectra obtained after resonant Auger decay of N2O excited around the nitrogen K shell (hν=401 eV), and of Kr after 3d5/2→5p excitation at hν=91.2 eV. A “étendue” of 15% of the pass energy, as well as a resolving power (Ep/δE) of 100were measured.

Design of a lens table for a double toroidal electron spectrometer

“…However, after implementing all the above trials, we found it extremely difficult to reach a unique simulation-based solution for the lens table. This could be due to two reasons: (1) With the downhill simplex method implemented in SIMION, it could happen that the numerical optimization ends before the global extremum is found, when the downhill walking step of the multidimensional algorithm is fractionally smaller than the tolerance, thus a single step fools the convergence criteria. (2) With the annealing technique used, the optimization performs efficiently when only a few neighboring points in the lens table are involved.…”

“…1. A new conical lens, with smaller aberrations and an easier alignment procedure, has been designed 2 to replace the original lens.…”

“…An original, high transmission double toroidal analyzer (DTA) with its electrostatic transfer lens have been developed by one of us. 1,2 Later, this instrument has been complemented by a delay-line position sensitive detector development, 40 while a TOF spectrometer was implemented to enable Auger electron-ion coincidence measurements. 24 Other research groups have built similar spectrometers in parallel with our development, 41 or inspired by our original design.…”

Invited Article: An improved double-toroidal spectrometer for gas phase (e,2e) studies

“…Using electrode geometries derived from this procedure and which slightly deviate from toroidal symmetry, they showed that improved focusing can be achieved, not only for particles traveling in circular trajectories along a centrally located equipotential line, but also for particles of greater or smaller energy than the mean pass energy. Miron et al 11 adopted this approach to develop a high-resolution electron analyzer based on two juxtaposed pairs of modified-toroidal-sector deflector plates possessing noncircular cross section. In the present design, however, our large c parameter value of 2.43 ͑see Sec.…”

“…8,9 More recently, third generation spectrometers have been developed whose analyzers incorporate two-dimensional positionsensitive detectors, enabling a range of emission angles and energies to be measured in parallel. [10][11][12][13][14][15][16] From the measured arrival positions of electrons at the detectors, their energies and emission angles are deduced.…”