# The importance of thermal dissociation in CO2 microwave discharges investigated by power pulsing and rotational Raman scattering

Dirk C.M. van den Bekerom, Jose M. Palomares Linares, Tiny Verreycken, Eddie M. van Veldhuizen, Sander Nijdam, G. Berden, Waldo A. Bongers, M.C.M. van de Sanden, Gerard J. van Rooij (Corresponding author)

3 Citations (Scopus)

### Abstract

The input power of a CO2 microwave plasma is modulated at kHz rate in scans of duty cycle at constant average power to investigate gas heating dynamics and its relation to dissociation efficiency. Rotational temperature profiles obtained from rotational Raman scattering reveal peak temperatures of up to 3000 ${\rm{K}}$, while the edge temperature remains cold (500 ${\rm{K}}$). During the plasma 'OFF'-period, the gas cools down convectively, but remains overall too hot to allow for strong overpopulation of vibrational modes (2200 ${\rm{K}}$ in the core). Fast optical imaging monitors plasma volume variations and shows that power density scales with peak power. As dissociation scales with observed peak rotational temperature, it is concluded that thermal processes dominate. A simple 0D model is constructed which explains how higher power density favors dissociation over radial energy transport. Thermal decomposition is reviewed in relation to quenching oxygen radicals with vibrationally excited CO2, to reflect on earlier reported record efficiencies of 90%.
Language English 055015 14 Plasma Sources Science and Technology 28 5 10.1088/1361-6595/aaf519 Published - May 2019

### Keywords

• carbon dioxide
• microwave plasma
• rotational Raman
• vibrational excitation non-equilibrium
• gas conversion

### Cite this

@article{5b58923b3e4747ceb5186b68007752d9,
title = "The importance of thermal dissociation in CO2 microwave discharges investigated by power pulsing and rotational Raman scattering",
abstract = "The input power of a CO2 microwave plasma is modulated at kHz rate in scans of duty cycle at constant average power to investigate gas heating dynamics and its relation to dissociation efficiency. Rotational temperature profiles obtained from rotational Raman scattering reveal peak temperatures of up to 3000 ${\rm{K}}$, while the edge temperature remains cold (500 ${\rm{K}}$). During the plasma 'OFF'-period, the gas cools down convectively, but remains overall too hot to allow for strong overpopulation of vibrational modes (2200 ${\rm{K}}$ in the core). Fast optical imaging monitors plasma volume variations and shows that power density scales with peak power. As dissociation scales with observed peak rotational temperature, it is concluded that thermal processes dominate. A simple 0D model is constructed which explains how higher power density favors dissociation over radial energy transport. Thermal decomposition is reviewed in relation to quenching oxygen radicals with vibrationally excited CO2, to reflect on earlier reported record efficiencies of 90{\%}.",
keywords = "carbon dioxide, microwave plasma, rotational Raman, vibrational excitation non-equilibrium, gas conversion",
author = "{van den Bekerom}, {Dirk C.M.} and {Palomares Linares}, {Jose M.} and Tiny Verreycken and {van Veldhuizen}, {Eddie M.} and Sander Nijdam and G. Berden and Bongers, {Waldo A.} and {van de Sanden}, M.C.M. and {van Rooij}, {Gerard J.}",
year = "2019",
month = "5",
doi = "10.1088/1361-6595/aaf519",
language = "English",
volume = "28",
journal = "Plasma Sources Science and Technology",
issn = "0963-0252",
publisher = "Institute of Physics",
number = "5",

}

The importance of thermal dissociation in CO2 microwave discharges investigated by power pulsing and rotational Raman scattering. / van den Bekerom, Dirk C.M.; Palomares Linares, Jose M.; Verreycken, Tiny; van Veldhuizen, Eddie M.; Nijdam, Sander; Berden, G.; Bongers, Waldo A.; van de Sanden, M.C.M.; van Rooij, Gerard J. (Corresponding author).

In: Plasma Sources Science and Technology, Vol. 28, No. 5, 055015, 05.2019.

TY - JOUR

T1 - The importance of thermal dissociation in CO2 microwave discharges investigated by power pulsing and rotational Raman scattering

AU - van den Bekerom,Dirk C.M.

AU - Palomares Linares,Jose M.

AU - Verreycken,Tiny

AU - van Veldhuizen,Eddie M.

AU - Nijdam,Sander

AU - Berden,G.

AU - Bongers,Waldo A.

AU - van de Sanden,M.C.M.

AU - van Rooij,Gerard J.

PY - 2019/5

Y1 - 2019/5

N2 - The input power of a CO2 microwave plasma is modulated at kHz rate in scans of duty cycle at constant average power to investigate gas heating dynamics and its relation to dissociation efficiency. Rotational temperature profiles obtained from rotational Raman scattering reveal peak temperatures of up to 3000 ${\rm{K}}$, while the edge temperature remains cold (500 ${\rm{K}}$). During the plasma 'OFF'-period, the gas cools down convectively, but remains overall too hot to allow for strong overpopulation of vibrational modes (2200 ${\rm{K}}$ in the core). Fast optical imaging monitors plasma volume variations and shows that power density scales with peak power. As dissociation scales with observed peak rotational temperature, it is concluded that thermal processes dominate. A simple 0D model is constructed which explains how higher power density favors dissociation over radial energy transport. Thermal decomposition is reviewed in relation to quenching oxygen radicals with vibrationally excited CO2, to reflect on earlier reported record efficiencies of 90%.

AB - The input power of a CO2 microwave plasma is modulated at kHz rate in scans of duty cycle at constant average power to investigate gas heating dynamics and its relation to dissociation efficiency. Rotational temperature profiles obtained from rotational Raman scattering reveal peak temperatures of up to 3000 ${\rm{K}}$, while the edge temperature remains cold (500 ${\rm{K}}$). During the plasma 'OFF'-period, the gas cools down convectively, but remains overall too hot to allow for strong overpopulation of vibrational modes (2200 ${\rm{K}}$ in the core). Fast optical imaging monitors plasma volume variations and shows that power density scales with peak power. As dissociation scales with observed peak rotational temperature, it is concluded that thermal processes dominate. A simple 0D model is constructed which explains how higher power density favors dissociation over radial energy transport. Thermal decomposition is reviewed in relation to quenching oxygen radicals with vibrationally excited CO2, to reflect on earlier reported record efficiencies of 90%.

KW - carbon dioxide

KW - microwave plasma

KW - rotational Raman

KW - vibrational excitation non-equilibrium

KW - gas conversion

U2 - 10.1088/1361-6595/aaf519

DO - 10.1088/1361-6595/aaf519

M3 - Article

VL - 28

JO - Plasma Sources Science and Technology

T2 - Plasma Sources Science and Technology

JF - Plasma Sources Science and Technology

SN - 0963-0252

IS - 5

M1 - 055015

ER -