Time-focusing time-of-flight, a new method to turn a MAC-E-filter into a quasi-differential spectrometer

Abstract

Spectrometers based on the magnetic adiabatic collimation followed by an electrostatic filter (MAC-E-filter) principle combine high angular acceptance with an excellent energy resolution. These features make MAC-E-filters very valuable for experiments where the kinetic energy of ions or electrons from rare processes has to be measured with utmost sensitivity and precision. Examples are direct neutrino mass experiments like KATRIN which investigate the energy of electrons in the endpoint region of the tritium $$\beta $$ β -spectrum. However, the MAC-E-filter is a very sharp energy high-pass filter but not a differential spectrometer. To determine a spectral shape of a charged particle source, different electric retarding potentials have to be used sequentially, reducing the statistics. In a previous work we have shown that the advantages of the standard MAC-E-filter can be combined with a measurement of the time-of-flight (TOF), allowing to determine spectral information over a certain energy range with one retarding potential only, with the corresponding gain in statistics. This TOF method requires one to know the start time of the charged particles, which is not always possible. Therefore, we propose a new method which does not require the determination of the start time and which we call “time-focusing time-of-flight” (tfTOF): by applying a time dependent acceleration and deceleration potential at a subsequent MAC-E-filter, an energy dependent post-bunching of the charged particles is achieved.

Background reduction at the KATRIN experiment by the shifted analysing plane configuration

“…Several other options of detecting or removing the remaining part of the KA-TRIN background, Rydberg background electrons, are considered, including timeof-flight spectroscopy [41], the idea of time-focusing time-of-flight measurements [42] or making use of the specific angular distribution of the Rydberg electrons to filter out background events. Should one of these methods be successful, a symmetric configuration of the fields might be considered again because of the improved filter width (e.g.…”

The design, construction, and commissioning of the KATRIN experiment

“…By measuring the time it takes for an electron emitted via UV laser pulse to its detection, we can carry out time-of-flight (ToF) measurements. The e-gun ToF mode allows for differential electron spectroscopy with a MAC-E filter [141], either for testing novel approaches for determining the neutrino mass [142][143][144], for energy loss measurements [136], or for calibration and commissioning measurements of the MS and WGTS [137]. Some applications of this mode are discussed in the following sections.…”

Wideband precision stabilization of the -18.6kV retarding voltage for the KATRIN spectrometer

“…Here, any time-dependent variation, with Δ𝑈 (𝑡) 𝑈 0 has only a small effect. To investigate the effect of different noise waveforms, time-of-flight simulations were performed, building on previous work [12,13]. In the simulation, the electrons are tracked in small steps along the 𝑧-axis inside the spectrometer.…”