naa a22 4500 510789927 CHVBK 20180411083316.0 cr unu---uuuuu 180411e20130901xx s 000 0 eng 10.1134/S1063773713090089 doi (NATIONALLICENCE)springer-10.1134/S1063773713090089 Sub-terahertz emission from solar flares: The plasma mechanism of chromospheric emission [Elektronische Daten] [V. Zaitsev, A. Stepanov, V. Melnikov] We consider the plasma mechanism of sub-terahertz emission from solar flares and determine the conditions for its realization in the solar atmosphere. The source is assumed to be localized at the chromospheric footpoints of coronal magnetic loops, where the electron density should reach n ≈ 1015 cm−3. This requires chromospheric heating at heights h ⩾ 500 km to coronal temperatures, which provides a high degree of ionization needed for Langmuir frequencies ν p ≈ 200-400 GHz and reduces the bremsstrahlung absorption of the sub-THz emission as it escapes from the source. The plasma wave excitation threshold for electron-ion collisions imposes a constraint on the lower density limit for energetic electrons in the source, n 1 > 4 × 109 cm−3. The generation of emission at the plasma frequency harmonic ν ≈ 2ν p rather than the fundamental tone turns out to be preferred. We show that the electron acceleration and plasma heating in the sub-THz emission source can be realized when the ballooning mode of the flute instability develops at the chromospheric footpoints of a flare loop. The flute instability leads to the penetration of external chromospheric plasma into the loop and causes the generation of an inductive electric field that efficiently accelerates the electrons and heats the chromosphere in situ. We show that the ultraviolet radiation from the heated chromosphere emerging in this case does not exceed the level observed during flares. Pleiades Publishing, Ltd., 2013 Sun nationallicence flares nationallicence sub-terahertz emission nationallicence chromosphere nationallicence particle acceleration nationallicence plasma heating nationallicence Zaitsev V. Institute of Applied Physics, Russian Academy of Sciences, ul. Ul'yanova 46, 603950, Nizhni Novgorod, Russia aut Stepanov A. Pulkovo Astronomical Observatory, Russian Academy of Sciences, 196140, Pulkovo, Russia aut Melnikov V. Pulkovo Astronomical Observatory, Russian Academy of Sciences, 196140, Pulkovo, Russia aut Astronomy Letters Springer US; http://www.springer-ny.com 39/9(2013-09-01), 650-659 1063-7737 39:9<650 2013 39 11443 https://doi.org/10.1134/S1063773713090089 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1134/S1063773713090089 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Zaitsev V. Institute of Applied Physics, Russian Academy of Sciences, ul. Ul'yanova 46, 603950, Nizhni Novgorod, Russia aut NATIONALLICENCE 700 1- Stepanov A. Pulkovo Astronomical Observatory, Russian Academy of Sciences, 196140, Pulkovo, Russia aut NATIONALLICENCE 700 1- Melnikov V. Pulkovo Astronomical Observatory, Russian Academy of Sciences, 196140, Pulkovo, Russia aut NATIONALLICENCE 773 0- Astronomy Letters Springer US; http://www.springer-ny.com 39/9(2013-09-01), 650-659 1063-7737 39:9<650 2013 39 11443 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer