Feedback model of secondary electron emission in DC gas discharge plasmas

Abstract

Feedback is said to exist in any amplifier when the fraction of output power in fed back as an input. Similarly, in gaseous discharge ions that incident on the cathode act as a natural feedback element to stabilize and self sustain the discharge. The present investigation is intended to emphasize the feedback nature of ions that emits secondary electrons (SEs) from the cathode surface in DC gas discharges. The average number of SEs emitted per incident ion and non ionic species (energetic neutrals, metastables and photons) which results from ion is defined as effective secondary electron emission coefficient (ESEEC, E g). In this study, we derive an analytic expression that corroborates the relation between E g and power influx by ion to the cathode based on the feedback theory of an amplifier. In addition, experimentally, we confirmed the typical positive feedback nature of SEE from the cathode in argon DC glow discharges. The experiment is done for three different cathode material of same dimension (tungsten (W), copper (Cu) and brass) under identical discharge conditions (pressure: 0.45 mbar, cathode bias: −600 V, discharge gab: 15 cm and operating gas: argon). Further, we found that the E g value of these cathode material controls the amount of feedback power given by ions. The difference in feedback leads different final output i.e the power carried by ion at cathode (P i C ¢ |). The experimentally obtained value of P i C ¢ | is 4.28 W, 6.87 W and 9.26 W respectively for W, Cu and brass. In addition, the present investigation reveals that the amount of feedback power in a DC gas discharges not only affect the fraction of power fed back to the cathode but also the entire characteristics of the discharge.

Analysis of application range of simplified models for field to thermo-field to thermionic emission processes from the cathode

“…Electron emission plays a crucial role in the complex process of plasma-cathode interactions in gas discharges, and it serves as a fundamental component in various plasma phenomena and applications. Consequently, it is necessary to gain a profound understanding of diverse electron emission mechanisms to develop suitable mathematical models for numerical simulations [1][2][3][4][5]. Electrons inside the metal cathode are emitted through two distinct processes: electrons acquiring sufficient energy to surpass the potential barrier at the surface, called the work function, and electrons weakening the potential barrier through tunneling effects.…”

Secondary electron emission yield from vertical graphene nanosheets by helicon plasma deposition

“…The SEE is an important process in surface physics with applications in numerous fields, such as microchannel tube, [3] plasma display screen, [4] photomultiplier tube, [5] scanning electron microscope, [6] etc. The SEE can also adversely affect the applications and performance of devices, such as particle accelerator, [7] spacecraft surface, [8,9] fusion plasma, [10] RF/DC bias plasma process discharge, [11,12] Hall and spiral wave plasma thrusters, [13,14] etc. In plasma, strong SEE can significantly increase the electron heat flux from the plasma to the wall, resulting in (i) wall heating and wall evaporation, and (ii) plasma cooling and even extinction.…”

Generation scenarios of anodic structures and experimental realization of turbulence in unmagnetized plasma

“…Glow discharge is one of the earliest and most widely studied experimental plasmas representing the primitive form of many of the present-day advanced plasma facilities. The first studies reported by Irving Langmuir has helped in providing fundamental understanding of electrical discharges, ionization processes, sheath phenomena, collision-excitation-recombination and secondary emission processes, current density requirements and I-V characteristics of a discharge [1][2][3][4]. In glow discharge, though the ideal plasma condition is typically satisfied only for the homogenous electroneutral (weakly ionized non-equilibrium) region called 'positive column', interestingly from the early days itself, most of the attentions were focused on the sheath regions especially the cathode sheath since it is vital for sustaining glow discharge by maintaining a strong electric field.…”