Effect of electron emission processes on macroparticle charging in plasma systems with electron beam

The effect of different electron emission processes on macropraticle (MP) charging in a plasma at the presence of electron beam is investigated. A complete model of the MP charging in the beam-plasma systems, which includes possible electron emission processes from the MP surface, such as secondary...

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Дата:2020
Автори: Romashchenko, E.V., Girka, I.О., Bizyukov, A.A., Chibisov, A.D.
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Опубліковано: Національний науковий центр «Харківський фізико-технічний інститут» НАН України 2020
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Цитувати:Effect of electron emission processes on macroparticle charging in plasma systems with electron beam / E.V. Romashchenko, I.О. Girka, A.A. Bizyukov, A.D. Chibisov //Problems of atomic science and tecnology. — 2020. — № 6. — С. 150-153. — Бібліогр.: 11 назв. — англ.

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Digital Library of Periodicals of National Academy of Sciences of Ukraine
id nasplib_isofts_kiev_ua-123456789-194664
record_format dspace
spelling Romashchenko, E.V.
Girka, I.О.
Bizyukov, A.A.
Chibisov, A.D.
2023-11-28T13:42:20Z
2023-11-28T13:42:20Z
2020
Effect of electron emission processes on macroparticle charging in plasma systems with electron beam / E.V. Romashchenko, I.О. Girka, A.A. Bizyukov, A.D. Chibisov //Problems of atomic science and tecnology. — 2020. — № 6. — С. 150-153. — Бібліогр.: 11 назв. — англ.
1562-6016
PACS: 52.40.Hf
https://nasplib.isofts.kiev.ua/handle/123456789/194664
The effect of different electron emission processes on macropraticle (MP) charging in a plasma at the presence of electron beam is investigated. A complete model of the MP charging in the beam-plasma systems, which includes possible electron emission processes from the MP surface, such as secondary electron emission, the thermionic electron emission, the field electron emission and thermal-field electron emission, is presented.
Досліджено вплив різних процесів електронної емісії на зарядження макрочастинки (МЧ) у плазмі у присутності електронного пучка. Подано повну модель зарядження МЧ у пучково-плазмових системах, до складу якої входять можливі процеси електронної емісії з поверхні МЧ, такі як вторинна електронелектронна емісія, термоелектронна, автоелектронна та термоавтоелектронна емісії.
Исследовано влияние различных процессов электронной эмиссии на зарядку макрочастицы (МЧ) в плазме в присутствии электронного пучка. Представлена полная модель зарядки МЧ в пучково-плазменных системах, которая включает в себя возможные процессы электронной эмиссии с поверхности МЧ, такие как вторичная электрон-электронная эмиссия, термоэлектронная, автоэлектронная, термоавтоэлектронная эмиссии.
en
Національний науковий центр «Харківський фізико-технічний інститут» НАН України
Вопросы атомной науки и техники
Low temperature plasma and plasma technologies
Effect of electron emission processes on macroparticle charging in plasma systems with electron beam
Вплив процесів електронної емісії на зарядження макрочастинки у плазмових системах з електронним пучком
Влияние процессов електронной емиссии на зарядку макрочастицы в плазменных системах с электронным пучком
Article
published earlier
institution Digital Library of Periodicals of National Academy of Sciences of Ukraine
collection DSpace DC
title Effect of electron emission processes on macroparticle charging in plasma systems with electron beam
spellingShingle Effect of electron emission processes on macroparticle charging in plasma systems with electron beam
Romashchenko, E.V.
Girka, I.О.
Bizyukov, A.A.
Chibisov, A.D.
Low temperature plasma and plasma technologies
title_short Effect of electron emission processes on macroparticle charging in plasma systems with electron beam
title_full Effect of electron emission processes on macroparticle charging in plasma systems with electron beam
title_fullStr Effect of electron emission processes on macroparticle charging in plasma systems with electron beam
title_full_unstemmed Effect of electron emission processes on macroparticle charging in plasma systems with electron beam
title_sort effect of electron emission processes on macroparticle charging in plasma systems with electron beam
author Romashchenko, E.V.
Girka, I.О.
Bizyukov, A.A.
Chibisov, A.D.
author_facet Romashchenko, E.V.
Girka, I.О.
Bizyukov, A.A.
Chibisov, A.D.
topic Low temperature plasma and plasma technologies
topic_facet Low temperature plasma and plasma technologies
publishDate 2020
language English
container_title Вопросы атомной науки и техники
publisher Національний науковий центр «Харківський фізико-технічний інститут» НАН України
format Article
title_alt Вплив процесів електронної емісії на зарядження макрочастинки у плазмових системах з електронним пучком
Влияние процессов електронной емиссии на зарядку макрочастицы в плазменных системах с электронным пучком
description The effect of different electron emission processes on macropraticle (MP) charging in a plasma at the presence of electron beam is investigated. A complete model of the MP charging in the beam-plasma systems, which includes possible electron emission processes from the MP surface, such as secondary electron emission, the thermionic electron emission, the field electron emission and thermal-field electron emission, is presented. Досліджено вплив різних процесів електронної емісії на зарядження макрочастинки (МЧ) у плазмі у присутності електронного пучка. Подано повну модель зарядження МЧ у пучково-плазмових системах, до складу якої входять можливі процеси електронної емісії з поверхні МЧ, такі як вторинна електронелектронна емісія, термоелектронна, автоелектронна та термоавтоелектронна емісії. Исследовано влияние различных процессов электронной эмиссии на зарядку макрочастицы (МЧ) в плазме в присутствии электронного пучка. Представлена полная модель зарядки МЧ в пучково-плазменных системах, которая включает в себя возможные процессы электронной эмиссии с поверхности МЧ, такие как вторичная электрон-электронная эмиссия, термоэлектронная, автоэлектронная, термоавтоэлектронная эмиссии.
issn 1562-6016
url https://nasplib.isofts.kiev.ua/handle/123456789/194664
citation_txt Effect of electron emission processes on macroparticle charging in plasma systems with electron beam / E.V. Romashchenko, I.О. Girka, A.A. Bizyukov, A.D. Chibisov //Problems of atomic science and tecnology. — 2020. — № 6. — С. 150-153. — Бібліогр.: 11 назв. — англ.
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first_indexed 2025-11-25T08:08:43Z
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fulltext ISSN 1562-6016. ВАНТ. 2020. №6(130) 150 PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY. 2020, № 6. Series: Plasma Physics (26), p. 150-153. https://doi.org/10.46813/2020-130-150 EFFECT OF ELECTRON EMISSION PROCESSES ON MACROPARTICLE CHARGING IN PLASMA SYSTEMS WITH ELECTRON BEAM E.V. Romashchenko, I.О. Girka, A.A. Bizyukov, A.D. Chibisov V.N. Karazin Kharkiv National University, Kharkiv, Ukraine E-mail: ev.romashchenko@gmail.com The effect of different electron emission processes on macropraticle (MP) charging in a plasma at the presence of electron beam is investigated. A complete model of the MP charging in the beam-plasma systems, which includes possible electron emission processes from the MP surface, such as secondary electron emission, the thermionic elec- tron emission, the field electron emission and thermal-field electron emission, is presented. PACS: 52.40.Hf INTRODUCTION Charging of a MP in beam-plasma systems is one of the basic problems in studies of interaction between the MP and the plasma. In the presence of electron beam there are several electron emission processes from the MP surface. First, the electron beam directly causes secondary electron-electron emission from the MP sur- face. The thermionic and field electron emissions are consequences of the MP bombardment by the electron beam due to the increasing of temperature and absolute value of negative potential of the MP, respectively. MP has a negative potential in the “usual” two-component low-temperature plasma due to higher mobility of elec- trons. The MP charging due to electron beam impact and MP recharging due to electron emission are competitive processes. Moreover, under certain conditions, effect of electron emission can even be more pronounced. As a result, MP can become positively charged. In previous studies, MP charging in the electron- beam systems with account for the secondary electron emission has been investigated in the framework of the orbit motion limited (OML) approach [1] and on the basis of the discrete charging model [2]. The influence of field electron emission and secondary electron emis- sion on MP potential has been studied in [3]. The effect of thermionic electron emission and secondary electron emission on MP potential has been investigated in [4]. In the present work, the studies of MP charging are developed. A complete model of the MP charging, which includes a possible electron emission processes from the MP surface in the presence of electron beam in the plasma, is presented. Obtained results are of im- portance for better understanding of the MP charging mechanisms in the beam-plasma systems. 1. MP FLOATING POTENTIAL WITH ACCOUNT FOR EMISSION PROCESSES The steady-state potential φ, to which a MP is charged, is determined from the balance of particle fluxes which are collected by the MP surface and emitted from it:           0,    TEeeebei IIIII . (1) Неre, Ii is the ion current, Ie is the current of plasma electrons , Ib is the current of electron beam, Ie-e is the current of secondary electrons emitted from the MP surface due to bombardment of electron beam, and Ie,TE is the current of relevant electron emission (thermionic electron emission, field electron emission, thermal-field electron emission). The currents Ii , Ie, and Ib to the MP surface are cal- culated by using the OML theory [5]. The OML ap- proach is applicable for MP radius a much less than the Debye length λD=(ε0Te /n0e 2 ) 1/2 : a<< λD. In the case of negatively charged MP ,exp8 2          eВ Тееe Tk e enaI   (2)          iВ Tiii Tk e enaI   18 2 , (3)          е ebb e uenaI    12 . (4) In the case of positively charged MP ,18 2          eВ Тееe Tk e enaI   (5) ,exp8 2          iВ Тiii Tk e enaI   (6)          е ebb e uenaI    12 . (7) In (2)-(7) ne, ni, and nb are the particle density of plasma electrons, plasma ions and beam electrons, re- spectively; Te (Ti) is the electron (ion) temperature, υTe=(kBTe /me) 1/2 (υTi= (kBTi /mi) 1/2 ) is the electron (ion) thermal velocity, ue is the velocity of beam electrons, εe is the energy of beam electrons. The secondary electron current Ie-e caused by elec- tron impact is [6] ,bее II  0 . (8) The secondary electron yield δ is described by Sterng-lass’s universal curve [6]           m е m е m е      2exp4.7 , (9) ISSN 1562-6016. ВАНТ. 2020. №6(130) 151 where εem is the energy for which the secondary yield δm is maximum. In the case of positively charged MP, the vast major- ity of the secondary electrons returns to the MP surface and only the most energetic ones leave the surface. Thus, secondary electron current Ie-e is given by:                  sBsB bее Tk e Tk e II   1exp , 0 , (10) where Ts is the thermal temperature of emitted second- ary electrons, which is quite small (1...5 eV). The secondary electron emission results in the suffi- cient increasing of absolute value of MP negative poten- tial in the energy range of beam electrons, within which the secondary electron yield δ>1. Moreover, in the case of the equality of plasma and electron beam densities, the MP floating potential can even become positive [1]. Another important emission process is the thermionic electron emission. The current density of thermionic elec- tron emission is given by Richardson-Dushman equation [7]:            mpB mpРDReТEe Tk e TAjj exp2 ,, , (11) where Tmp is the MP temperature, eΦ is the work func- tion, AR is the Richardson constant. For most metals АР = (4...7)∙10 5 А/(m 2 ∙K 2 )[8]. The thermionic electron emission occurs if MP is heated to a temperature above some threshold. One can find this critical temperature by equating the plasma electron current density and current density of thermion- ic electron emission Tee jj , , (12) where current density of electrons is expressed as: 4/0 ee еnj  . (13) Here, n0 is the plasma particle density, υTe= (kBTe /me ) 1/2 is the average thermal velocity of electrons. MP critical temperature Tcr (K) еФ, еV Te =10 еV n0 =10 15 m 3 n0 =10 16 m 3 Al 4.2 2023 2218 Ti 4.3 2068 2267 Сu,W 4.5 2156 2363 The results of calculations of critical temperature Tcr for MP with different work function material such as aluminium, titanium, copper and tungsten in the plasma with electron temperature Te =10 еV and plasma density n0=10 15 ...10 16 m 3 are presented in the Table. For all the materials, except tungsten, the critical temperature is higher than the boiling temperature. The value of critical temperature of MP turns out to be higher in the plasma with density 10 16 m 3 than that in the plasma with the smaller density 10 15 m 3 . In the case of negatively charged MP, the repulsive potential accelerates thermionic electrons from the MP surface. The electric field causes the increase in the work function due to the electrostatic barrier. Richard- son-Dushman equation with Schottky correction for the work function is            mpB mpРShReТEe Tk Ebe TAjj exp2 ,, , (14) where E is the electric field. This equation is also called as Richardson-Schottky equation. The electric field on the MP surface is related to the electric potential by E=/a, (15) and Schottky correction can be rewritten as еEb а e 0 3 4   . (16) When the MP is positively charged, the electrons have to overcome the floating potential and the surface barrier. In this case, the current density of the thermion- ic emission is given by [9]                    mpBmpB MЧРТЕe Tk еe Tk е TAj exp12 ,  . (17) In the case of very strong electric field, when eΔΦ>eΦ, there is the field electron emission from MP surface. In this case the emission current density should be calculated according to Fowler-Nordheim formula [7]:               y еhE еm yth Ee j e НФe    3 )(28 exp )(8 3 2 22 , , (18) with   е Ее y 1 4 0 3  . (19) In (18), t(y) and ν(y) are the elliptical functions [7]. Field electron emission from a MP occurs when its surface electric field is about 2∙10 7 V/cm. In the follow- ing, the plasma conditions and MP size, under which MP has such electric field on its surface, are evaluated. The field emission from MP surface is absent in the case of low-temperature plasma, which consists of electrons and ions. For example, in nitrogen plasma with Te /Ti =10 normalized potential z=eφ/kBTe = 10 [8]. The corre- sponding electric field on the surface of the MP with radius 1 µm equals 3∙10 5 and 3∙10 6 V/cm for MP with radius 0.1 µm. However, the field emission from MP surface is possible in the case of plasma with electron beam. The MP can acquire the high negative charge due to bombardment of electron beam. The floating poten- tial of MP reaches -200 V for beam electron energy of the order of a few keV [1]. If electric potential of MP with radius 0.1 µm equals -200 V, the corresponding electric field on its surface is 2∙10 7 V/cm. Thus, the field emission becomes important for MP with radius of about 0.1 µm. We have emission formulas (14) and (18) for two cases: thermionic electron emission with taking into account the Schottky effect, and field electron emission, respectively. The relevant temperature and electric field ranges are determined by [10]: mpB mp e Tck TkЕe em Еe e            144 B 43 0 3 0 3   , (20) 152 ISSN 1562-6016. ВАНТ. 2020. №6(130) mpBmpB TkfTck 21  . (21) Here, )( 2 2 2 yt eE em c e    , (22) ħ is the Plank constant, and 1 2 0 2 4 1 )(2 2 1                eE еeE ym f e  . (23) The electric field-temperature curves calculated from (20) and (21) divide the diagram in the Fig. 1 into three regions: first one marked as TE, which corre- sponds to the thermionic electron emission; second one marked as FE, which corresponds to the field electron emission, and a large region TFE between them. Both temperature and electric field are high in the latter. Such a case is possible in the vacuum arc discharge. Electron emission in TFE range of temperatures and electric fields belongs to so-called thermal-field emission. The current density of thermal-field emission is given by Murphy-Good formula [7]:                     mpB mpBe GMe Tk Ebe h hTkem j exp sin2 0 0 32 2 ,     , (24) were mpBe Tk Eb em E h  41 52 4 0           . (25) Murphy-Good theory is the more general approach. The formula (24) in the limiting cases transforms to the Richardson-Schottky thermionic emission formula (14) and Fowler-Nordheim field emission formula (18):          ., ;1, , 0, , eej hj j NFe ShRe TEe  (26) Besides, the thermo-field (thermionic) emission cur- rent Ie,TE from the MP surface is limited by the space charge. The maximum current is determined by Lang- muir-Blodgett formula [11]: Fig. 1. Thermionic emission (TE), field emission (FE) and thermal-field emission (TFE) regions of temperature and electric field for 4.5 eV work function , 9 2 2 2/3 0 2/3   U m e I e  (27) where α is the tabulated function [11]. Thus, the thermal-field (thermionic) emission cur- rent Ie,TE from the MP surface is determined by the fol- lowing conditions:               ., ;, 2/3 ,, 2/3 , 2/3 ,   eTEeTEe eTEee TEe III III I (28) One can conclude that the solution of current bal- ance equation (1) requires careful choice of the appro- priate expression for emission current. At the same time, one must keep in mind that electron emission is a limit- ing process. 2. RESULTS AND DISCUSSION The current balance equation (1) is numerically solved in the two limiting cases: for MP with high tem- perature and weak surface electric field, and for MP with low temperature and strong surface electric field. The numerical calculations are carried out for a colli- sionless nitrogen plasma with the density of n0=10 16 m 3 , electron temperature of Te = 10 eV, ion temperature of Ti =1 eV, electron beam density of n0 = 10 15 m 3 , and electron beam energies of εe = 0.01...5 keV. Fig. 2. The floating potential of MP with radius 1 µm versus the electron beam energy for different MP temperatures: “cold” MP (solid line), Tmp=2363 K (dashed line); Tmp=2500 K (dotted line) To begin with, the tungsten MP with radius a = 1 μm is considered at fixed temperatures: Tmp = 2363 K (criti- cal temperature) and Tmp=2500 K in the energy range of beam electrons εe = 0.01...5 keV. This case corresponds to the thermionic electron emission. The emission current is calculated according to the Richardson-Dushman equa- tion (3) with taking into account the Schottky effect. If MP is positively charged, emission current density is cal- culated according to (9). The floating potential of MP as a function of the electron beam energy is shown in Fig. 2. The potential of “cold” MP turns out to be negative in the whole energy range of beam electrons. The secondary electron emission cannot lead to positive potential in the plasma with density larger than density of electron beam. At the temperature Tmp=2363 K, the MP potential increases, but it remains negative. At the higher temper- ature Tmp= 2500 K, the MP potential becomes positive. TE TFE FE ISSN 1562-6016. ВАНТ. 2020. №6(130) 153 The other example is shown in Fig. 3. The tungsten MP with radius 0.1 µm yields a high electric field at electron beam energy more than 2 keV. The Fig. 3 shows the comparison of MP potential without taking into account the field emission, and with it. One can see that in the first case, the MP potential φ = -400 V for the electron beam energy εe = 4 keV, and in the second case, φ = -300V. Thus, the field electron emission sufficiently decreases the absolute value of negative MP potential. Fig. 3. The floating potential of MP with radius 0.1 µm versus the electron beam energy. MP potential is calculated without taking into account the field emission (solid line). MP potential is calculated with taking into account the field emission (dashed line) CONCLUSIONS The present paper describes the mechanisms of different kind of electron emission from MP in plasma system in the presence of electron beam. Both field elec- tron emission and thermionic electron emissions result in the increasing of absolute value of MP negative potential. However, the field electron emission does not change the sign of the MP potential. This is explained by the differ- ence of the energy range of beam electrons, at which the thermionic and field electron emissions take place. REFERENCES 1. A.A. Bizyukov, E.V. Romashchenko, K.N. Sereda, and A.D. Chibisov. Electric potential of a macro- particle in beam-plasma systems // Plasma Physics Re- ports. 2009, v. 35, № 6, p. 499-501. 2. A.A. Bizyukov, E.V. Romashchenko, K.N. Sereda, and S.N. Abolmasov. Particle charging in beam-plasma systems // Problems of Atomic Science and Technology. 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Cathodic Arcs: From Fractal Spots to Energetic Condensation. New York: “Springer”, 2008. 9. G.L. Delzanno, G. Lapenta, M. Rosenberg. Attractive potential around a thermionically emitting microparticle // Phys. Rev. Letters. 2004, v. 92, № 3, p. 035002. 10. A. Modinas. Field, Thermionic and Secondary Elec- tron Emission Spectroscopy. New York: “Springer- Science+Business Media, LLC”, 1984, p. 372. 11. I. Langmuir, K.B. Blodgett. Current limited by space charge between concentric spheres // Phys. Rev. 1924, v. 24, № 1, р. 49-59. Article received 03.10.2020 ВЛИЯНИЕ ПРОЦЕССОВ ЕЛЕКТРОННОЙ ЕМИССИИ НА ЗАРЯДКУ МАКРОЧАСТИЦЫ В ПЛАЗМЕННЫХ СИСТЕМАХ С ЭЛЕКТРОННЫМ ПУЧКОМ Е.В. Ромащенко, И.А. Гирка, А.А. Бизюков, А.Д. Чибисов Исследовано влияние различных процессов электронной эмиссии на зарядку макрочастицы (МЧ) в плазме в присутствии электронного пучка. Представлена полная модель зарядки МЧ в пучково-плазменных системах, которая включает в себя возможные процессы электронной эмиссии с поверхности МЧ, такие как вторичная электрон-электронная эмиссия, термоэлектронная, автоэлектронная, термоавтоэлектронная эмис- сии. ВПЛИВ ПРОЦЕСІВ ЕЛЕКТРОННОЇ ЕМІСІЇ НА ЗАРЯДЖЕННЯ МАКРОЧАСТИНКИ У ПЛАЗМОВИХ СИСТЕМАХ З ЕЛЕКТРОННИМ ПУЧКОМ О.В. Ромащенко, I.О. Гірка, О.А. Бізюков, О.Д. Чібісов Досліджено вплив різних процесів електронної емісії на зарядження макрочастинки (МЧ) у плазмі у присутності електронного пучка. Подано повну модель зарядження МЧ у пучково-плазмових системах, до складу якої входять можливі процеси електронної емісії з поверхні МЧ, такі як вторинна електрон- електронна емісія, термоелектронна, автоелектронна та термоавтоелектронна емісії.