| 1 | Generation scenarios of anodic structures and experimental realization of turbulence in unmagnetized plasma显示文摘In the present work,we report development of a DC glow discharge plasma(GDP)set-up to study controlled evolution of anodic structures having distinctive geometry,size and layers,generated in front of a positively biased electrode,submerged in unmagnetized plasma.For such an anodic structure,we have also investigated the condition under which the turbulence is triggered.Characteristic of these structures,generated in front of a positively biased electrode,depends on multiple parameters such as the ratio of anode to cathode size,electrode separation,gas pressure,biasing configuration such as anode bias,cathode bias and grounding schemes.We attempted to classify different anodic structures observed experimentally,as anode glow,fireball,anode spot,double layer and multiple double layers(MDLs)based on its physical characteristics.Among these structures the present investigation is focused on MDLs.The number of layers,observed in MDLs varied from as high as six to as low as zero,by controlling the operating discharge parameters,externally.Diagnostics were carried out using Langmuir probe.The analysis of floating potential fluctuations corresponds to a multiple anodic structure showed emergence of turbulence,at its critical stage,satisfying condition for self-organized criticality(SOC).This was identified with three slopes observed in the power spectrum,resembling the sand-pile model.Though,the GDP is completely different from that of the magnetically confined plasma,the nature of turbulence observed with SOC,is very similar to that observed in the scrape of layer of fusion devices.Therefore,the present investigation could provide new approach to study turbulence of similar nature,under an experimental condition that is free from the complexities of complicated field geometries used in confinement devices. | Prince ALEX Suraj Kumar SINHA | 2020 | Plasma Science and Technology2020，22，8： | 0 |
| 2 | Feedback model of secondary electron emission in DC gas discharge plasmas显示文摘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 electronemission coefficient(ESEEC,_Eg).In this study,we derive an analytic expression that corroborates the relation between_Eg 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 SEEfrom 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_Eg 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 and9.26 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. | Saravanan ARUMUGAM Prince ALEX Suraj Kumar SINHA | 2018 | Plasma Science and Technology2018，20，2： | 0 |
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