Obsah obrázku text, Písmo, snímek obrazovky, řada/pruh Popis byl vytvořen automaticky 2. INon-Self Sustained Electrical Discharges FB242 Gas discharges: physical mechanisms and applications A small electric current is flowing with the current densities 10-12 až 10-6 A/m2 is always flowing in a weak el. field near the ground surface due to backgroung ionization due to natural processes such as cosmic rays, radioactive decay of radioactive materials (including uranium, thorium, and radium) existing naturally in soil and rock. Ionis Non-self sutained dark Townsend discharge (a typical case) http://www.tpub.com/doeinstrument/instrumentation%20and%20control_files/image211.jpg auto0 auto0 V > V1 Electron avalanche ionization . 1 {\rm Td} = 10^{-17}\rm V\cdot cm^2 Elastic and inelasctic electron collisions in Ar (the processes rate constants vs. Electron energy in electronvolts (An electron emperature of 11 600 K corresponds to the electron kinetic energy of 1 eV.) Day1View3Mar08.dvi (berkeley.edu) l Elastic and inelastic electron collisions: cross section lIn 1912 and 1922 Ramsauer and Townsend respectively observed that or slow-moving electrons in argon, krypton, or xenon, the probability of collision between the electrons and gas atoms obtains a minimum value for electrons with a certain amount of kinetic energy (about 1 electron volts for xenon gas). This is the quantum-mechanical Ramsauer–Townsend effect. l Avalanche!!! l l l l l l l l l l l l l 1 Td (Townsend) = 10-17 V.cm-2 The townsend (symbol Td) is a physical unit of the reduced electric field (ratio E/N), where E is electric field and N is concentration of neutral particles. Townsend ionization coefficient α and electron attachment coefficient η (eta) in air η - the probability that an electron drifting through a gas under the influence of a uniform electric field will undergo electron attachment in a unit distance of drift. e + O2 + M → O2- + M three-body el. attachment e + O2 +ˇ3.6 eV→ O- + O dissociative el. attachment l smoke-detector-1 http://www.safetyissues.com/magazine/2002/4/SmokeDetector/SmokeDetector.jpg Prof. Charpak, Nobel prize 1992 „Multiwire Proportional Counters“ The discovery of the W and the Z particles was rewarded with the Nobel Prize in Physics in 1984 (Carlo Rubbia and Simon van der Meer, CERN). The particle collision in which the Z particle is created and then rapidly decays into an electron and its antiparticle, the positron, can be seen in the middle of the picture. The tracks of all the charged particles are detected in the central drift chamber. The Z particle is only created in one particle collision in a thousand million. disch6 Obrázok, na ktorom je adaptér Automaticky generovaný popis There is still a lack of high-performance terahertz (THz) modulators with wide operation bandwidth and large modulation depth due to the underlying physics limitation behind existing approaches. Meanwhile, for many applications, simple compact THz modulators working straightforward in the transmission mode are also highly desired. Here, we demonstrate a THz modulator with a maximal transmission-amplitude modulation depth of 99.9% (switching ratio of 1000) based on a commonly used silica-on-silicon structure. Different from those reported graphene or metamaterials enhanced proposals, the device we proposed works within a reversible avalanche breakdown region of silicon that has not been studied yet and has the potential to modulate/switch THz waves efficiently. Further, we proved that the modulation depth exceeds 97% in the frequency range from 0.2 to 1 THz in the experiment. The simplicity and generality of this new type of near-perfect THz modulator will undoubtedly attract lots of attention of researchers in the near future due to its potential to be engineered into integrated devices. •Photonics Research 9(2021) 370-378 http://www.aholme.co.uk/Avalanche/Avalanche.htm Rev. Sci. Instrum. 87, 054708 (2016); doi: 10.1063/1.4948727 „High-voltage pulse with leading edge about 200 ps and amplitude about 2 kV has been output by the designed circuit“.