Spectroscopic temperature measurements of air breakdown plasma using a 110 GHz megawatt gyrotron beam

Hummelt, Jason S.; Shapiro, Michael A.; Temkin, Richard J.

doi:10.1063/1.4773037

Cited by 33 publications

(21 citation statements)

References 18 publications

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“…[13][14][15][16][17][18][19][20] Work has begun to experimentally characterize these plasma formations. 21 However, many physical aspects of these unique plasma structures have yet to be measured. In order to better understand high frequency microwave breakdown, as well as to validate the existing numerical models, it is necessary to further experimentally characterize these plasmas.…”

Section: A Backgroundmentioning

confidence: 99%

Electron density and gas density measurements in a millimeter-wave discharge

et al. 2016

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Electron density and neutral gas density have been measured in a non-equilibrium air breakdown plasma using optical emission spectroscopy and two-dimensional laser interferometry, respectively. A plasma was created with a focused high frequency microwave beam in air. Experiments were run with 110 GHz and 124.5 GHz microwaves at powers up to 1.2 MW. Microwave pulses were 3 µs long at 110 GHz and 2.2 µs long at 124.5 GHz. Electron density was measured over a pressure range of 25 to 700 Torr as the input microwave power was varied. Electron density was found to be close to the critical density over the pressure range studied and to vary weakly with input power. Neutral gas density was measured over a pressure range from 150 to 750 Torr at power levels high above the threshold for initiating breakdown. The two-dimensional structure of the neutral gas density was resolved. Intense, localized heating was found to occur hundreds of nanoseconds after visible plasma formed. This heating led to neutral gas density reductions of greater than 80% where peak plasma densities occurred. Spatial and temporal structure of gas heating at atmospheric pressure were found to agree well with numerical simulations.

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Section: A Backgroundmentioning

confidence: 99%

Electron density and gas density measurements in a millimeter-wave discharge

et al. 2016

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“…It is worth noticing that N 2 second positive system dominates the emission spectra after the nitrogen spark. This system is also preferred to measure the temperature because it is very intense compared to emission observed from other emitting plasma species in the air discharge and is observed in any discharge condition, from low to high (atmospheric) pressure . The other reason for selecting the N 2 second positive system for the measurements of rotational temperatures (and gas temperatures) in microplasmas was due to the fact that this band system could be observed in the discharge as long as there is an addition of the little amount of N 2 in the discharge gas.…”

Section: Methodsmentioning

confidence: 99%

“…The rotational temperature of N 2 molecules calculated from the second positive system of N 2 (C 3 Π u →B 3 Π g ) was assumed to be equal to the translational temperatures and considered to be the gas temperature. This should be valid while considering the short times of rotational to translational energy transfer at atmospheric pressure . Indeed at atmospheric pressure, in He/N 2 plasma, N 2 (C‐B) emission yields a good measurement of gas temperature, and even for Ar/N 2 plasma, the gas temperature was determined accurately if the

v^{'} = 3

and

v^{'} = 4

levels of the N 2 (C) state chosen for gas temperature calculation …”

Section: Methodsmentioning

confidence: 99%

“…For this reason, the gas temperature measurements in non‐equilibrium plasmas are often obtained by optical emission spectroscopy from the population distribution in rotational levels of excited states of nitrogen molecules (rotational temperature). This was adopted as well as utilized successfully by many researchers and was found to be accurate and reliable . On the other hand, in order for the discharge to be in non‐equilibrium, the energy gained in vibrational excitation should be greater than the energy lost by vibrational to translational ( V – T ) relaxation, and finally results in T vib > T trans ( T rot ), where the non‐equilibrium nature of the discharge is justified by the ratio of vibrational to rotational temperature ( T vib / T rot ) …”

Section: Introductionmentioning

confidence: 99%

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The Influence of Discharge Capillary Size, Distance, and Gas Composition on the Non-Equilibrium State of Microplasma

Majeed

Zhong

et al. 2016

Plasma Process. Polym.

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The non-equilibrium state of microplasma from the mixture of He and N 2 was studied by exploring the rotational and vibrational temperatures of molecular nitrogen under various discharge conditions. At a varying gap distance of 1-3 mm (with a step of 1 mm) from the exit of the capillary to the water surface, the average rotational temperature of N 2 was found to increase from 983 to 1250 K while the corresponding vibrational temperature of N 2 was reduced from 4875 to 3099 K. Consequently, the average vibrational to rotational temperature ratio of N 2 was decreased from 4.96 to 2.48. By widening the capillary inner diameter from 100 to 200 mm, the average rotational temperature of N 2 was elevated from 891 to 1090 K whereas the average vibrational temperature of N 2 was dropped from 4662 to 3646 K and hence, the ratio of vibrational to rotational temperature of N 2 was lessened from 5.23 to 3.34. Moreover, with the addition of more nitrogen into the flow, i.e., by increasing the flow rate of N 2 from 0 to 15 sccm (with an interval of 5 sccm), the average rotational temperature of N 2 was intensified from about 942 to 1404 K, whereas the corresponding vibrational temperature of N 2 was reduced from 5011 to 3254 K. Therefore, the corresponding ratios of vibrational to rotational temperature of N 2 were declined from 5.3 to 2.3. The results demonstrate that the surface area to volume ratio of microplasma and gas conductivity have a significant effect on the nonequilibrium nature of He-N 2 atmospheric pressure microplasma.

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“…14,15 First, the studies of overcritical millimeter-wave discharge are explained. For the experiments, [16][17][18][19][20][21][22] a 110 GHz millimeter-wave beam is focused. The plasma is ignited at its focal point.…”

Section: Introductionmentioning

confidence: 99%

Experimental investigation of ionization front propagating in a 28 GHz gyrotron beam: Observation of plasma structure and spectroscopic measurement of gas temperature

Tabata

Harada

Nakamura

et al. 2020

Journal of Applied Physics

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Atmospheric millimeter-wave discharge was investigated experimentally using a 28 GHz gyrotron. The propagation velocity of an ionization front, plasma structure, and vibrational and rotational temperatures of nitrogen molecules were measured at a beam intensity lower than 1.0 GW/m 2 , which is below the breakdown threshold. Results show that the propagation velocity of an ionization front increased monotonically with beam intensity and decreased with ambient pressure. In addition, four typical plasma structures having different space occupancies were observed. Furthermore, at any beam intensity below 0.5 GW/m 2 , the vibrational temperature was found to be saturated at about 6000 K. The corresponding electron number density is almost equal to the cut-off density. Finally, it was suggested that the propagation velocity depends on the plasma space occupancy.

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Spectroscopic temperature measurements of air breakdown plasma using a 110 GHz megawatt gyrotron beam

Cited by 33 publications

References 18 publications

Electron density and gas density measurements in a millimeter-wave discharge

Electron density and gas density measurements in a millimeter-wave discharge

The Influence of Discharge Capillary Size, Distance, and Gas Composition on the Non-Equilibrium State of Microplasma

Experimental investigation of ionization front propagating in a 28 GHz gyrotron beam: Observation of plasma structure and spectroscopic measurement of gas temperature

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