On the instabilities in a beam - plasma system of zonal magnetic field
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Date
1974-06
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Publisher
Turkish Atomic Energy Commission, Ankara Nuclear Research Center
Abstract
Demet plazma sistemlerinin etkileşme teorisinde, özellikle enine dielektrik tensörün tanımlanması için magnetik alanın sürekliliğini gerektiren bir koşul yoktur. Homojen bir magnetik alanın bir bölgede etkisi varsa bu yeterlidir. Öte yandan boyuna dielektrik tensör de magnetik alan şiddetine bağlı değildir.
Bu eleştirinin ışığında, bir demet-plazma sisteminde, sürekli elektrostatik fakat bölgesel magnetostatik alanların bulunması halinde de. demet-plazma etkileşmelerinin oluşabileceği söylenebilir. Homojen olmayan böyle bir sistemde plazma genellikle sıcaktır. İlâveten lineer olmayan etkiler, bu nitelikteki bir sistemde kolayca meydana gelebilir.
Bu çalışmada yukarıdaki varsayımdan hareket ederek gerçekleştirilen pratik bir demet plazma sistemi ve bu sistemden elde edilen deneysel sonuçlar verilmektedir. Bu sistem, elektrostatik çift apertür bir mercek ile bir magnetron enjeksiyonlu elektron topundan oluşmuştur. Homojen olmayan bu sistemde magnetik alan bölgeseldir.
Elektron demetinin boyuna enerjisi en çok 1.5 keV dur. Hidrojen gazı içinde (2 x 10(-4) - 8 x 10(-4) Torr) oluşturulan demet-plazma boşalmasında, 10(7) cn-3 ile 10(10) cm-3 arasında elektron yoğunlukları elde edilmiştir. Demet yoğunluğu ise, deney koşuluna bağlı kalmakla beraber, 5x10(8) cm-3 e kadar arttırılmıştır.
Deneysel olarak saptanan özellikler arasında toplam plazma frekansına yakın ω2 etkileşmesi, ωpo V ωce koşulunda ω4 etkileşmesi ve iki akışlı instabilite ile demetin tuzak- lanması gibi ilginç noktalar bulunmaktadır. Öte yandan bir Bilgisayar (Nuclear Data ND-812) yardımıyla sıcak elektron plazmasının (100 eV kadar] analizi yapılmış ve ω3 etkileşmesinde ılık iyonların (2 eV a kadar] rolü tartışılmıştır.
Deneysel sonuçlar etkileşme teorisinin ışığında irdelenmiş ve bölgesel magnetik alanlı bir demet-plazma sisteminde etkileşme kriterlerine yaklaşım koşulları saptanmıştır.
In the interaction theory of beam-plasma systems, continuity of the magnetic field is not prerequisite in the definition of especially the transversal dielectric tensor. The presence of a homogeneous magnetic field effect in one zone suffices. On the other hand, the longitudinal dielectric tensor is not dependent upon the intensity of magnetic field. By these premises, it can be said that beam-plasma interaction will occur in a beam - plasma system where constant electrostatic and regional magnetostatic fields are present. In an inhomogeneous system of this kind the plasma is generally hot. Moreover, nonlinear effects can readily occur in a system of this configuration. This paper deals with a practical beam - plasma system realized by acting on the above assumptions, and with the experimental results obtained with the system. This system consisted of a double - aperture electrostatic lens and a magnetron - injection electron gun. In this inhomogeneous system the magnetic field is zonal. The longitudinal energy component of the electron beam is 1,5 keV maximum. Electron densities of 10(7) cm- 3 to 10(10) cm-3 were obtained in the beam-plasma discharge produced in Hydrogen gas at 2x10-4 to 8x10-4 Torr. Although contingent upon experimental condition, beam density was increased up to 5x10(8) cm-3. Among the interesting observations experimentally determined were, ω2 interaction near the total plasma frequency, ω4 interaction under ωpo > ωce condition, trapping of the beam with two - stream instability, etc. An analysis of the hot electron plasma (up to 100 eV) was carried out, using a computer (Nuclear Data ND -812].; and the role of warm ions (up to 2 eV) in the interaction also pointed out The experimental results were discussed in view of the interaction theory, and conditions were determined for the approach to interaction criteria in a beam-plasma system of zonal magnetic field.
In the interaction theory of beam-plasma systems, continuity of the magnetic field is not prerequisite in the definition of especially the transversal dielectric tensor. The presence of a homogeneous magnetic field effect in one zone suffices. On the other hand, the longitudinal dielectric tensor is not dependent upon the intensity of magnetic field. By these premises, it can be said that beam-plasma interaction will occur in a beam - plasma system where constant electrostatic and regional magnetostatic fields are present. In an inhomogeneous system of this kind the plasma is generally hot. Moreover, nonlinear effects can readily occur in a system of this configuration. This paper deals with a practical beam - plasma system realized by acting on the above assumptions, and with the experimental results obtained with the system. This system consisted of a double - aperture electrostatic lens and a magnetron - injection electron gun. In this inhomogeneous system the magnetic field is zonal. The longitudinal energy component of the electron beam is 1,5 keV maximum. Electron densities of 10(7) cm- 3 to 10(10) cm-3 were obtained in the beam-plasma discharge produced in Hydrogen gas at 2x10-4 to 8x10-4 Torr. Although contingent upon experimental condition, beam density was increased up to 5x10(8) cm-3. Among the interesting observations experimentally determined were, ω2 interaction near the total plasma frequency, ω4 interaction under ωpo > ωce condition, trapping of the beam with two - stream instability, etc. An analysis of the hot electron plasma (up to 100 eV) was carried out, using a computer (Nuclear Data ND -812].; and the role of warm ions (up to 2 eV) in the interaction also pointed out The experimental results were discussed in view of the interaction theory, and conditions were determined for the approach to interaction criteria in a beam-plasma system of zonal magnetic field.
Description
Keywords
Zonal magnetic field, Bölgesel manyetik alan, Beam - plasma system, Işın - plazma sistemi, Instabilities, Kararsızlıklar
Citation
Sinman, S. ve Sinman A. (1974). On the instabilities in a beam - plasma system of zonal magnetic field. Technical Journal, 1(2), 57-88.