Optimization of GEM-based detector readout electrode structure for SXR imaging of tokamak plasma

The paper presents an optimization of a readout structure of the GEM-based detector designed for X-ray imaging for DTT tokamak in the energy range of 2–15 keV. The readout electrode of approximately 100 cm2 surface is composed of hexagonal pixels connected in a way that allows reducing the actual number of signal pixels (electronics channels). At the same time, based on time coincidence analysis, it makes possible to unambiguously identify the position of the recorded X-ray photon. For the input spectrum, the Detective Quantum Efficiency (DQE) of the detector was calculated using the Geant4 program and the spatial distributions of electron avalanches at the readout electrode were simulated using the Garfield++ program. These were conducted for a given energy range of radiation and a statistical distribution consistent with the shape of the spectrum considering the DQE of the detector. As a result, the size of a single hexagonal pixel was proposed to capture the position of the recorded radiation quanta in an optimal and effective way.

Simple "Reactor model" of relativistic runaway electron avalanches dynamics

<p>A possible mechanism responsible for Terrestrial Gamma-ray Flashes (TGFs) is feedback in the relativistic runaway electron avalanches (RREA) dynamics. In this research, a new way of RREAs self-sustaining is suggested. This self-sustaining feedback can be described in the following way. Let the thundercloud consist of two regions with the electric field so that runaway electrons accelerated in one region move in the direction of another one and vice versa. For instance, such an electric field structure might appear with one positive charge layer situated between two negative charge layers. In this system, the following feedback mechanism occurs. An RREA developing in one region will produce bremsstrahlung gamma-rays. These gamma-rays will propagate into another region and produce RREAs within it. These RREAs will develop backward and radiate gamma-rays, which will penetrate the first region, generating secondary RREAs. In this way, the primary avalanche reproduced itself by the gamma-ray exchange between two sideways oriented areas with the electric field. In this work, it is shown that the electric field values required for TGF generation by this mechanism are lower than values required in Relativistic Feedback Discharge Model.</p>

Catalog of TGEs observed at Aragats during 2008-2020

<p>For 12 years we monitored particle fluxes on Mt. Aragats 7/24 and discovered the most<br>powerful natural electron accelerator operated in the thunderclouds. This natural electron<br>accelerator provided more than 450 Thunderstorm Ground enhancement events (TGEs). We<br>make exhausting analysis of these events and will present yearly and monthly distributions,<br>as well the day hour distributions. Also, we will present the distribution of the outside<br>temperature and precipitation occurrences which are correlated with particle fluxes. We<br>address questions about TGE evolution and atmospheric conditions supporting the<br>origination of the relativistic runaway electron avalanches and demonstrate the relativistic<br>runaway electron avalanche is possible on Aragats only in Spring-Autumn seasons.</p>

Energy spectra of electrons and gamma rays produced by the electron accelerator in thunderclouds

We measure energy spectra of electrons and gamma rays of electromagnetic avalanches developed in the electrified atmosphere as they arrive at the earth’s surface at 3200 m height where Aragats research station is located. We compare intensities and spectra shapes of 2 thunderstorm ground enhancements (TGE) observed in June and September 2020 with simulated ones. Although, the variants of electric field strength and topology assumed in the simulations are too simplified to reproduce the rather complicated and dynamic nature of the atmospheric electric field the closeness of several measured and observed parameters allows us to confirm that the relativistic runaway electron avalanches (RREA) is the origin of TGE, and to outline most probable characteristics of the atmospheric electric field for particular observed TGE events.