technological plasma workshop 2016

Technological Plasma Workshop 2016

Programme and Book of Abstracts

Ricoh Arena, Coventry 12th and 13th October 2016

TPW Background The Technological Plasma Workshop (TPW) is principally a UK‐based international forum in science and technology of plasmas and gas discharges. Delegates from all countries are very welcome to participate in this workshop.

Since the EPSRC Technological Plasma Initiative in 1997, technological plasmas have found applications in diverse fields ranging from nano‐science, energy, through biomedicine and environment, to space exploration. They offer major collaboration opportunities for academic and industrial communities and exciting career prospects for younger scientists and engineers.

To support a full realisation of these opportunities, TPW aims to foster academic‐industry collaboration and to engage young plasma scientists with a scientific programme anchored by leading plasma scientists. The workshop will comprise invited talks, contributed presentations and a poster session.

In 2011, the TPW became a conference of the Institute of Physics (IOP) Plasma Physics Group and since 2014 TPW has been held in Conjunction with the Vacuum Expo and the Vacuum Symposium. This year the event is co‐sponsored with the IOP Dielectrics and Dielectrics and Electrostatics Group.

SCIENTIFIC COMMITTEE

Professor Adrian Cross University of Strathclyde Chairman

Dr Mark Bowden The Open University

Professor Timo Gans University of York

Dr Felipe Iza Loughborough University

John Simmons RF Services, UK

ORGANISING COMMITTEE

John Simmons RF Services

Professor Adrian Cross University of Strathclyde

Dr Felipe Iza Loughborough University

Dr Nadarajah Manivannan Brunel University

Conference Schedule

Wednesday 12th of October 2016

12:30 ‐ 13:30 Registration

Session Chair: Felipe Iza, Loughborough University, UK

13:30 ‐ 13:40 Welcome, introduction and announcements TPW Organising Committee

13:45 ‐ 14:30 Plasma‐catalysis: a promising solution for gas clean‐up and fuel/chemical

synthesis (invited)

Xin Tu, University of Liverpool, UK

14:35 ‐ 14:55 EHD‐driven mass transport enhancement in surface dielectric barrier

discharges

Alex Shaw, Loughborough University, UK

15:00 ‐ 15:30 Coffee break

Session Chair: Paul May, University of Bristol, UK

15:30 ‐ 15.50 Experimental investigation of electron beam generation from a pseudospark structure

Huabi Yin, University of Strathclyde, UK

15:55 ‐ 16.15 Surface Activation of Rigid and Flexible Substrates for Thin Film Photovoltaics using Atmospheric Pressure Plasma Fabiana Lisco, Loughborough University, UK

16:15 ‐ 17:30 Posters (Vacuum Expo Exhibition Hall)

19:30 ‐ Dinner (Cosmo Restaurant, 36‐42 Corporation St, Coventry CV1 1GF)

Conference Schedule (cont’d) Thursday 13th of October 2016

Session Chair: Adrian Cross, University of Strathclyde, UK

09:30 ‐ 09:50 A 0.2 THz extended interaction oscillator driven by a pseudospark‐ sourced sheet electron beam Guoxiang Shu, University of Strathclyde, UK

09:55 ‐ 10:15 Computational methods for ion source design Jonathan Smith, Tech‐X, UK Ltd

10:15 ‐ 10:40 Coffee Break

Session Chair: Felipe Iza, Loughborough University, UK

10:45 ‐ 11:30 Non‐thermal plasma for pollution control (invited) Wamadeva Balachandran, Brunel University, UK

11:35 ‐ 11:55 Experimental results of the NOx abatement form the exhaust of a diesel engine with non‐thermal plasma and Ag/Al2O3 catalyst Nadarajah Manivannan, Brunel University, UK

12:00 ‐ 12:20 Inductively Coupled Impulse Sputtering Daniel Loch, Sheffield Hallam University, UK

12:20 ‐ 13:30 Lunch and visit to exhibitors at the vacuum symposium

Session Chair: Nadarajah Manivannan, Brunel University, UK

13:30 ‐ 14:15 Advanced Oxidation Processes for efficient water treatment (invited) Chedly Tizaoui, Swansea University, UK

14:20 ‐ 14:40 Optimisation of the mass transfer of gaseous phase plasma effluent to liquid phase and its applications Alexander Wright, Loughborough University, UK

14:45 ‐ 15:05 Gyrotron Backward Wave Oscillators using a helical waveguide for materials processing

Adrian Cross, University of Strathclyde, UK

15:05 ‐ 15:15 Closing remarks and depart TPW Organising Committee

TECHNOLOGICAL PLASMA WORKSHOPS 2016

Presentation Abstracts

Plasma-catalysis: a promising solution for gas clean-up and fuel/chemical synthesis

Xin Tu

Department of Electrical Engineering and Electronics, University of Liverpool, Liverpool, L69 3GJ, UK

E-mail: [email protected]

The rapid exhaustion of fossil fuel reserves and the adverse effects of climate change caused by

increasing global energy demands have attracted great attention and pose serious threats to humankind. The emergence of new energy technologies is very crucial and essential to reduce the negative effects of climate change and to ensure global energy security based on sustainable and renewable energy sources.

Recently, the combination of non-thermal plasma and heterogeneous catalysis (known as plasma-catalysis) has been regarded as a promising and effective solution for gas clean-up and for the conversion of greenhouse gases (e.g. CH4 and CO2) into value-added fuels and chemicals (e.g. hydrogen or syngas) at low temperatures [1-2]. The combination of plasma and catalysts has the great potential to generate a synergistic effect, which can activate catalysts at low temperatures and improve the activity and stability of the catalysts, resulting in the remarkable enhancement of reactant conversion, selectivity and yield of end-products, as well as the energy efficiency of the process [3]. The idea of plasma-catalysis has also been extended to the synthesis, preparation and modification of catalysts to improve the activity and stability of the catalyst.

We have developed different atmospheric pressure plasma sources (dielectric barrier discharge and gliding arc) for the conversion and activation of methane, carbon dioxide and biomass tar into value-added fuels and chemicals [1-7]. The integration of plasma and supported metal catalysts clearly exhibits a significant synergistic effect, showing both the conversion of reactants and the yield of target products are significantly enhanced compared to the reaction using plasma alone or catalysis alone.

Reference 1. D. H. Mei, X. B. Zhu, C. F. Wu, B. Ashford, P. T. Williams, and X. Tu, Applied Catalysis B: Environmental,

182, 525-532 (2016). 2. Y. X. Zeng, X. B. Zhu, D. H. Mei, B. Ashford, and X. Tu, Catalysis Today, 256, 80-87 (2015). 3. X. Tu and J. C. Whitehead, Applied Catalysis B: Environmental, 125, 439-448 (2012). 4. D. H. Mei, B. Ashford, Y. L. He, and X. Tu, Plasma Processes and Polymers, DOI: 10.1002/ppap.201600076

(2016) 5. S. Y. Liu, D. H. Mei, Z. Shen, and X. Tu, Journal of Physical Chemistry C, 118, 10686-10693 (2014). 6. S. Y. Liu, D. H. Mei, L. Wang, and X. Tu, Chemical Engineering Journal, DOI: 10.1016/j.cej.2016.08.005

(2016). 7. L. Wang, S. Y. Liu, C. Xu, and X. Tu, Green Chemistry, DOI: 10.1039/c6gc01604a (2016).

EHD-driven mass transport enhancement in surface dielectric barrier discharges

A Shaw1, M Taglioli2,1, A Wright1, G Neretti2, P Seri2, C A Borghi2, and F Iza1

1Wolfson School of Mechanical, Electrical and Manufacturing Engineering, Loughborough University, Loughborough, LE11 3TU, UK

2Department of Electrical, Electronic and Information Engineering, University of Bologna, Bologna, 40136, Italy


Atmospheric-pressure Surface Dielectric Barrier Discharges (S-DBDs) have been widely investigated in the past two decades for aerodynamic applications[1] due to their mechanical simplicity, electrical control capability and low power consumption. In these devices, energy transfer from charged to neutral particles results in an electrohydrodynamic (EHD) body force, a phenomenon also known as ionic wind. In its simplest implementation, the ionic wind imparts momentum to the background gas in the direction parallel to the dielectric surface.

Surface Dielectric Barrier Discharges (S-DBDs) have received renewed attention in recent years for their potential application in emerging biomedical, environmental and agricultural applications[2]. In most of these applications, the plasma is not in direct contact with the substrate being treated and the transport of reactive species from the plasma to the substrate is typically assumed to be controlled by diffusion or gas flows.

Here, we demonstrate that generally this is not the case and that electrohydrodynamic (EHD) forces can produce jets that enhance the delivery of these species, thereby influencing the efficacy of the S-DBD device. In particular, we have studied the degradation of potassium indigotrisulfonate solutions exposed to S-DBDs generated in devices with annular electrodes of diameters varying between 10mm and 50mm. All the devices were driven at constant linear power density (Watts per cm of plasma length) and although local plasma properties remained the same in all the devices, a three-fold efficacy enhancement was observed for devices of diameter ~30mm due to EHD effects.

References:

[1] Neretti G, Cristofolini A and Borghi C A 2014 Experimental investigation on a vectorized aerodynamic dielectric barrier discharge plasma actuator array J. Appl. Phys. 115 163304

[2] Shaw A, Shama G and Iza F 2015 Emerging applications of low temperature gas plasmas in the food industry. Biointerphases 10 029402

Experimental investigation of electron beam generation from a pseudospark discharge

H. Yin, J. Zhao, L. Zhang, G. Shu, W. He, and A. D. R. Phelps and A.W. Cross

Department of Physics, SUPA, University of Strathclyde, Glasgow, G4 0NG, UK


The outstanding feature of using a pseudospark discharge for electron beam production is the formation of an ion channel following the pseudospark anode, which enables the beam to propagate and eliminates the need for a guiding magnetic field [1]. When a high voltage is applied to the hollow cathode, the electric field across the anode-cathode gap penetrates a short distance into the hollow cathode region due to the small cathode aperture. A PS discharge will occur if the pressure in the system is suitably low (typically 50-500 mTorr) so that the discharge is at the left-hand side (with respect to the minimum) of the Paschen curve. In such a PS discharge condition, the gas breakdown will occur along the longest possible path, allowing a virtual anode to form, extending from the anode into the hollow cathode region. As the virtual anode reaches the cathode surface field-enhanced emission begins to occur. Electrons begin emitting from the cathode surface at an increased rate, augmented by secondary emission and are accelerated toward the aperture by the electric field. Consequentially this rapid increase in electron emission results in a rapid increase in the beam current. As the beam propagates through the anode its front edge ionizes the background gas, forming a plasma channel, while the following beam electrons expel part of the plasma electrons so that an ion-channel is formed, confining the beam and eliminating the need for any external magnetic guide field. A high current density, high brightness electron beam with a sweeping voltage can therefore be generated and propagated by ion channel focusing.

Pseudospark discharges have been explored for various important applications, especially high quality electron beam generation for microwave and millimetre-wave sources and potential terahertz devices. High frequency sources above 100 GHz are very attractive for a wide range of research and technical applications, including molecular spectroscopy, bio- imaging and security screening. As the frequencies move into the sub-terahertz and terahertz region, the size of device reduces greatly. This brings a challenge with regard to device fabrication. Therefore a compact and simplified structure is desirable, with the pseudospark- sourced electron beam an ideal choice for high power, high frequency sources. This paper presents some experimental results of the electron beam current dependence on the gap separation of a singal-gap pseudospark structure. At a certain gap seperation, the relationship between the beam current and discharge voltage was studied [2]. It is found that the electron beam only starts to occur when the charging voltage is above a certain value and increases with the increasing discharge voltage following two tendencies. Under the same discharge voltage, the configuration with the larger electrode gap separation will generate higher electron beam current. Post acceleration experiments of the hollow cathode beam will also be presented. These results bring insight for the designs of future terahertz sources.

[1] W. He.,L. Zhang, et al, “Generation of broadband terahertz radiation using a backward wave oscillator and

pseudospark‐sourced electron beam”, Appl. Phys. Lett. 107, 133501 (2015).

[2] J. Zhao, H. Yin,L. Zhang, G. Shu, W. He, et al, “Influence of the electrode gap separation on the pseudospark‐

sourced electron beam generation”, Phys. Plasmas 23(7) 073116 (2016)

Surface Activation of Rigid and Flexible Substrates for Thin Film Photovoltaics using Atmospheric Pressure Plasma

F. Lisco, A. Shaw, A. Wright, F. Iza, and J.M. Walls

Wolfson School of Mechanical, Electrical and Manufacturing Engineering, Loughborough University, Leicestershire, LE11 3TU, UK


Reducing fabrication costs is a major driving force in photovoltaic research. Atmospheric processes such as spin coating, spraying or printing are being developed to reduce the cost/Wp of CIGS, CZTS and perovskite solar technologies. For all technologies, surface cleaning and activation prior to thin film deposition is required and for this vacuum based low pressure plasma is a well-established technique. However, a vacuum based surface pre-treatment is not compatible with atmospheric deposition methods.

We show that atmospheric-pressure plasmas are highly effective in activating the surface of substrates commonly used in photovoltaic device fabrication and demonstrate its effectiveness on both rigid and flexible substrates.

The effectiveness of using atmospheric-pressure plasmas to increase surface energy is demonstrated using Water Contact Angle (WCA) measurements and chemical changes are analysed using X-ray Photoelectron Spectroscopy (XPS). Scanning Electron Microscopy (SEM) images show no alteration of the surface morphology of the substrates after the plasma treatment.

(a) (b)

Figure 1: The atmospheric pressure plasma jet used in this work (a) Schematic diagram of the experimental arrangement. (b) An image of the plasma jet used for the ATM pressure plasma treatment.

A 0.2 THz extended interaction oscillator driven by a pseudospark-sourced sheet electron beam

Guoxiang Shu, Wenlong He, Liang Zhang, Huabi Yin, Junping Zhao, Alan D.R. Phelps and Adrian W. Cross

Department of Physics, SUPA, University of Strathclyde, Glasgow, G4 0NG, U.K.


The pseudospark low-pressure discharge has long been of interest for high-speed switching applications but its production of a high current density, high brightness electron beam makes it an ideal driver for some designs of RF, microwave and millimetre-wave sources. The pseudospark discharge has the potential to be used as an electron beam source in THz devices, and one of its major advantages is that the formation of an ion channel following the pseudospark anode focuses the beam and eliminates the need for a guiding magnetic field [1- 4].

This paper present the design of a planar G-band (200GHz) extended interaction oscillator (EIO) driven by a pseudospark-sourced sheet electron beam. The use of a planar interaction circuit combined with the merits of a pseudospark-sourced sheet electron beam namely its large beam cross section and high current density enables a peak output power of 2 kW at around 0.2 THz to be obtained. The performance of a planar EIO driven by a sheet electron beam as compared to an EIO driven by a pseudospark-sourced pencil electron beam will be presented.

References: [1] Yin, H., Cross, A.W., He, W., Phelps, A.D.R., Ronald, K., Bowes, D., Robertson, C.W., 2009, “Millimeter wave generation from a pseudospark sourced electron beam” Phys. Plasmas 16(6) 063105. [2] Bowes, D., Yin, H., He, W., Ronald, K., Phelps, A.D.R., Chen, X., Li, D. and Cross, A.W., 2014, “Visualization of a Pseudospark-Sourced Electron Beam” IEEE Trans. Plasma Sci., PP(19). [3] Bowes, D., Yin, H., He, W., Zhang, L., Cross, A.W., Ronald, K., Phelps, A.D.R., Chen, D., Zhang, P., Chen, X., Li, D., 2014, “X-ray Emission as a Diagnostic from Pseudospark- Sourced Electron Beams” Nucl. Inst. Meth. B 335 pp74-77. [4] He W., Zhang L., Bowes D., Yin H., Ronald K., Phelps A.D.R. and Cross A.W., “Generation of broadband terahertz radiation using a backward wave oscillator and pseudospark-sourced electron beam”, Appl. Phys. Lett. 107, 133501 (2015); http://dx.doi.org/10.1063/1.4932099.

Computational methods for ion source design

M. Kundrapu1, S.A. Veitzer1, P.H. Stoltz1 , K.R.C. Beckwith1 and J.D.A. Smith2* 1 Tech-X Corporation, Boulder, 80303 CO, USA

2 Tech-X UK Ltd, Sci-Tech Daresbury, Warrington WA4 4FS


This presentation summarizes some common kinds of ion sources used in industry and research. Different characteristic time and length scales determine the computational methods that can efficiently address different problems within ion source design.

A summary of the difference between electrostatic and electromagnetic particle-in-cell methods is provided, and these are contrasted with fluid techniques. New techniques are shown within the VSim[1] particle-in-cell software that can add insight to Penning type sources and are applied to a current project to optimise a Versatile Arc Discharge Ion Source (VADIS[2]) at CERN. (Fig 1).

The USim[3] software for modelling of ICP type sources is introduced. Fluid routines and equations used to model the GEC ICP chamber are discussed in the context of computation of temperature and density distributions which show good agreement with probe measurements.

The model is applied to the ICP ion source used at Oak Ridge National Laboratory. (Fig 2)

[1] VSim : www.txcorp.com/vsim [2] R.Kirchner, Nucl. Instrum. and Meth. B 204 (2003) 179-190 [3] USim : www.txcorp.com/usim

Fig 1: 3D Simulated potential distribution inside the axis of the VADIS anode (a) lineout on axis (b) 2D slice. Charge density (c) lineout on axis (d) 2D slice.

Fig 2 : Plasma velocity incident on the SNS ICP ion source for (a) default experimental configuration (b) new wide leg design

(b)

(a)

(c)

(d)

Non-thermal plasma for pollution control

Wamadeva Balachandran, Nadarajah Manivannan, Maysam Abbod, Radu Beleca

Centre for Electronic Systems Research, Institute of Environment, Health and Societies, College of Engineering, Design and Physical Sciences, Brunel University London, Uxbridge,

Middlesex UB8 3PH


Air pollutants generated by ships in both gaseous and particulate forms have long term effect on the quality of the environment and cause a significant exposure risk to people living in proximities of harbours or in the neighbouring coastal areas. It has been estimated that ships produce at least 15% of the world’s NOx, ~4% of greenhouse gases, ~5% of black carbon and ~7% of global SO2 output. International shipping traffic presents a major challenge in terms of environment and human health which entails severe economic consequences. During the past decade, the use of non-thermal plasma for the abatement of NOx and SOx has been gaining momentum. Non-thermal plasma selectively transfers input electrical energy to the electrons and to not expend this in heating the entire gas stream, which generates free radicals through collisions and promotes the desired chemical changes in the marine diesel engine exhaust gas. This presentation will briefly review the different methods of producing non-thermal plasma for abatement of diesel engine exhaust gas. Out of all the different methods, non-thermal plasma generated by electron beams, corona discharges and microwave has been identified as possible techniques to be used on board ships due to advantages such as lower costs, higher removal efficiency and smaller space requirement compared to the existing water scrubbers and SCRs.

In a recently completed FP7 project DEECON, a pilot-scale non-thermal plasma reactor was developed and used in conjunction with electrically charged sea water scrubber to remove the pollutants from the exhaust gas generated by a 200 kW diesel engine [1]. The results obtained demonstrated that > 90% of NOx can be removed successfully using microwave generated non-thermal plasma [2]. Some of the practical difficulties encountered in sustaining the desired plasma volume with minimum energy will be discussed during this presentation.

References:

(1) Natale, F.D., Carotenuto, C., D’Addio, L., Lancia, A., Antes,T., Szudyga, M., Jaworek, A., Gregory, D., Jackson, M., Volpe, P., Beleca, R., Manivannan, N., Abbod, M., Balachandran, W., “New technologies for marine diesel engines emission controls”, Chemical Engineering Transaction, Vol. 32, 2013.

(2) Balachandran, W., Manivannan, N., Beleca, R., and Abbod, M., Brennen D., Alozie, N.S., and Ganippa, L.C. ‘Non-thermal Plasma System for Marine Diesel Engine Emission Control’ IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 52, NO. 3, 2016

13

Experimental results of the NOx abatement form the exhaust of a diesel engine with non-thermal plasma and Ag/Al2O3 catalyst

N Manivannan1,2, W Balachandran1,2, G Agozzino1,3, M Abbod1, D Brennen1 and M Jeyananthamoorthy4

1Centre for Electronic Systems Research

2 Institutes of Environment, Health and Societies 3Institute of Material and Manufacturing, College of Engineering, Design and Physical Sciences

Brunel University, London UB8 3PH 4Department of Chemical Engineering, Università di Napoli Federico II, Dip. di Ingegneria

Chimica, dei Materiali della Produzione Industriale, Naples, Italy

Abatement of NO from a diesel engine was experimentally demonstrated for exhaust gas

from a 2 kW diesel engine. A non-thermal plasma (NTP) followed by Ag/Al2O3 catalyst was

used to convert NOx (NO+NO2) into harmless N2. A high frequency (~ 4.5 MHz) AC corona

source with the voltage up to 30kV was used to produce the required NTP. In this set-up, the produced NTP will be a streamer plasma [1], where no arc-discharge between the high voltage and ground electrode would not be produced due to the fast switching of polarity

between plates. The 2% Ag (by weight) was uniformly impregnated onto the 3 mm Al2O3

beads and heated to 350-4000c to activate the catalytic effect. In the NTP, NO would be turned into NO2 and in the catalytic chamber, the NO2 would be turned into N2. The inherent

presence of the HC in the exhaust stream, has improved the conversion of NO2 to N2 and

addition of extra HC has demonstrate more than 90% abatement of NOx. The following table shows a typical set of results obtained. These results clearly shows the use of combination of

NTP + catalyst + HC. Though it was noted that exhaust has contains 12% of O2, CO2,CO,

H2O and other unknown gas traces, the proposed techniques has shown repeatable performance, which are superior to the bottle gas experiments reported in [2].

References

(1) Omarov, O.A. & Rukhadze, A.A. Bull. Lebedev Phys. Inst. (2009

(2) McAdams, R., Beech, P. & Shawcross, J.T. Plasma Chem Plasma Process (2008)

HC Plasma Catalyst Plasma + Catalyst

Plasma + HC

Plasma + Catalyst + HC

NO (% ) 0 45 59 61.45 91.8 100

NOx (%) 0 19.2 38.6 65.32 40 91.7

NO NO2

(%) 0 25.8 - - 51.8 -

14

Inductively Coupled Impulse Sputtering

Daniel A Loch and Arutiun P Ehiasarian

Sheffield Hallam University, HIPIMS Technology Centre, Howard Street, Sheffield, UK

Abstract not available at the time of printing

15

Advanced Oxidation Processes for efficient water treatment Chedly Tizaoui

College of Engineering, Bay Campus, Swansea University, Swansea SA1 8EN


Advanced Oxidation Processes (AOPs) are those processes that generate highly reactive species by dissipating high energy (chemical, electrical or radiation) into the water body. The most potent species produced by AOPs are hydroxyl radicals (•OH), which are extremely unstable species characterised by a one-electron deficiency. AOPs are used to destroy resistant organic contaminants even those which are difficult to degrade biologically producing water, carbon dioxide and inorganic compounds. Common AOPs include those based on ozone, UV and H2O2 (e.g. O3/UV, UV/TiO2 (Fig. 1), UV/H2O2 etc.) and new types of AOPs have also gained significant interest in recent years (e.g. non-thermal plasma (NTP), ferrate, O3/US etc.). One of the promising applications of AOPs is the removal of micropollutants in water.

The occurrence of micropollutants (Fig. 2) (also called trace contaminants) in water bodies has been a growing issue for the water industry and policy makers due to the potential negative human health effects and environmental impacts that these substances cause. For example, the intersex issue in fish due to exposure to estrogenic hormones found in wastewater effluents is well established and there is growing evidence that human exposure to pharmaceutical substances via water causes diseases such as cancer, Parkinson, and reduction in sperm count in males. Disruption of the endocrine system due to exposure to a range of compounds called Endocrine Disrupting Chemicals (EDCs) found in water has also been flagged as a significant emerging environmental issue. Examples of EDCs include steroid hormones, pharmaceutical and personal care products, polychlorinated biphenyls, surfactants, pesticides, etc. Natural and synthetic estrogens are the most potent. Wastewater effluent is one of the major sources of EDCs in the natural water; this is because conventional wastewater treatment plants were not designed to specifically remove substances that cause endocrine disruption. There is hence a call to upgrade wastewater treatment plants with efficient treatments such as AOPs and this could cost the UK industry over £30bn.

This presentation will summarise our research carried out so far on the removal of EDCs using AOPs. Particular focus will be made on the degradation rates of the studied substances and the data presented will be useful to evaluate the performance of the proposed treatment techniques as means for water sustainability and reuse.

Fig. 1: UV/TiO2 reactor

Fig. 2: Types of micropollutants

16

Optimisation of the mass transfer of gaseous phase plasma effluent to a liquid and its applications

A. Wright, A.Shaw, J.Ren, F. Iza, G. Shama, H. Bandulasena

Wolfson School of Mechanical, Electrical and Manufacturing Engineering, Loughborough,

Leicestershire, LE11 3TU, United Kingdom


A novel cold atmospheric pressure plasma reactor has been designed to maximise the mass transfer of short-lived reactive species between the plasma gas phase and the liquid phase. This process is facilitated by using a microporous metallic membrane as the ground electrode bringing the plasma to the gas-liquid interface. This ensures the maximum delivery of short lived species such as .OH and NO. . Coupled with a fluidic oscillator microbubbles are produced with a large surface area to volume ratio that maximises the mass transfer.

The plasma can be modulated to manipulate the reactive species produced with the effects characterised by measuring ozone in the liquid via absorption at 254 nm and the exhaust gases with FTIR. It was observed that a duty cycle of 45% was optimal as although less ozone was produced compared to lower duty cycles (10%) the higher levels of NOx increased the solubility of the ozone in the liquid by lowering the pH and increasing the conductivity.

So far this technology has been applied to two applications; the first is the pre-treatment of biomass where extracting ethanol from biomass is challenging due to the presence of lignin which needs to be removed to expose cellulose and hemicellulose for fermentation reactions. Lignin can be broken down effectively using oxidative species with bio-ethanol yield 4 times greater than that of no pre-treatment.

The second technology is the treatment of waste water effluent where it is well documented that bacteria are dispensed into bodies of surface water downstream of waste water treatment plants and although the full environmental impact is unclear, studies have suggested these bacteria can negatively impact the nearby eco-system as they are not currently removed with existing technologies. A study was carried out with Escherichia coli JHI2025 which is a bacterium commonly found in waste water showed a 4.5 log reduction after 20 minutes. The effect of interfering substances such as humic acid and bovine serum albumin were also studied and whilst there was a small negative effect on the inactivation rate it was minimal.

17

Gyrotron Backward Wave Oscillators using a helical waveguide for materials processing

Wenlong He, Liang Zhang, Craig Donaldson, Paul McElhinney, Kevin Ronald, Alan D.R.

Phelps, and Adrian W. Cross

Department of Physics, SUPA, University of Strathclyde, Glasgow, G4 0NG, Scotland, UK


Microwave sintering of materials has attracted much research interest because of its

significant advantages (e.g. reduced sintering temperatures and soaking times) over the conventional heating [1]. Recent progress on tuneable microwave sources such as gyrotron backward wave oscillators has opened the possibility for processing materials by using higher millimetre wave frequencies. One application is the sintering of ceramic laser host materials for high-energy laser (HEL) applications [2]. Advantages of polycrystalline, compared to single-crystal, laser host materials include lower processing temperature, higher gain from higher dopant concentration, cheaper fabrication, and larger devices. For example solid-state reactive sintering of neodymium-doped yttrium aluminum garnet (Nd:YAG) can be achieved using a high power millimeter-wave beam as the heat source. The starting powder can be a mixture of commercially available alumina, yttria, and neodymia powders.

A gyrotron backward wave oscillator (gyro-BWO) operating in the millimetre wave band will be presented. The gyro-BWO was based a thermionic cathode cusp electron gun and exploited the second harmonic coupling between the cyclotron mode of a gyrating electron beam and the radiation field in a cylindrical waveguide having a helical corrugation on its internal surface. The gyro-BWO generated a maximum output power of 12 kW when driven by a 40 kV, 1.5A, annular-shaped large- orbit electron beam and achieved a frequency tuning band of 88-102.5 GHz by adjusting the cavity magnetic field [3]. Work required to achieve continuous wave operation for materials processing will be discussed.

References

[1] I. N. Sudiana, R. Ito, S. Inagaki, K. Kuwayama, K. Sako & S. Mitsudo, “Densification of Alumina Ceramics Sintered by Using Submillimeter Wave Gyrotron”, J Infrared Milli Terahz Waves p627– 638, (2013).

[2] M. Ashraf Imam, Arne W. Fliflet, Steven H. Gold, Ralph W. Bruce, Chad Stephenson,and C. R. Feng, “Millimeter-Wave Reactive Sintering of Neodymium-Doped Yttrium Aluminum Garnett”, Materials Science Forum Online, Vols. 654-656, pp 2002-2005, Online (2010-06-30), (2010) [3] W. He, C.R. Donaldson, L. Zhang, K. Ronald, P. McElhinney and A.W. Cross , “High power wideband gyrotron backward wave oscillator towards the terahertz region”, Phys. Rev. Letts, 110, art 165101, (2013).

18

TECHNOLOGICAL PLASMA WORKSHOPS 2016

Poster Session Abstracts

19

Microbubble-enhanced plasma-driven advanced oxidation processes for wastewater treatment

J. Ren*, A. Wright, A. Shaw, H. Bandulasena, G. Shama and F. Iza

Wolfson School of Mechanical, Electrical and Manufacturing Engineering, Loughborough University, Leicestershire LE11 3TU, UK


Cold atmospheric-pressure plasma is a novel technology with great potential for wastewater treatment due to its strong oxidative capability. Microbubbles have been shown to enhance mass transfer between the gas and liquid phase. In this project a novel water treatment process has been developed in which the oxidative power of cold atmospheric pressure plasmas is combined with microbubbles for the efficient transport of reactive species from the plasma gas phase to the liquid.

The key challenge in all plasma systems is the stabilization, repeatability and control of the discharge. In our system we intend to use dielectric barrier discharges (DBD) in contact with the liquid as these have emerged as a preferred arrangement for their fair uniformity, low temperature and ability to operate in air. The DBD discharge was driven by an in house built resonant power supply operating at 33 kHz with a typical operating voltage of 9 kV.

Microbubbles were generated by combining a fluidic oscillator with two kinds of microporous membranes to study the effect of different bubble sizes: a stainless steel (SS) membrane with 35 um diameter holes and a nickel (N) membrane with 20 um diameter holes. The membranes also act as ground electrodes for the generation of the plasma. This arrangement produces plasma close to the gas-liquid interface where the bubbles form; hence facilitating the transfer of oxidative species produced in the plasma directly to the liquid phase.

Preliminary tests of the microbubble-plasma reactor show that after 15 minutes of treatment with the same plasma power and flow rate, the ozone concentrations in the liquid with Ni membranes (250 ppm) are 50 ppm higher than with SS membranes (200 ppm). Oxidative species generation was also measured by adding indigo trisulphonate to the water and measuring the degradation of the dye measured over time, this followed the same trend as the ozone absorption into the liquid.

As future work we intend to perform a complete electrical and chemical characterization of the reactor, explore the relation between efficiency and pressure (flow rate), temperature, and bubble size, and assess the viability of the technology for the inactivation of pathogenic microorganisms and persistent chemical pollutants.

20

Degradation of hydrophobic coatings deposited via atmospheric plasma jet on glass substrates

K. Isbilir1, B. Maniscalco1, F. Lisco1, A. Shaw2, A. Wright2, J.M. Walls1, F. Iza2

1CREST, Wolfson School of Engineering, EESE, Loughborough University 2Wolfson School of Engineering, EESE, Loughborough University


Surface properties of glass substrates can be changed from hydrophilic to hydrophobic and even reaching super-hydrophobic characteristics by coating them using atmospheric plasmas. Hydrophobic surfaces have low surface energy and therefore are easier to keep clean. These coatings can find application in different sectors, including ophthalmic industry, screen protectors, and also photovoltaics.

There are several techniques to deposit hydrophobic and super-hydrophobic coatings [1]. Atmospheric-pressure plasmas have the advantage of being cheap, fast and easily scalable systems. They also have the capability of creating surface modification patterns, allowing spatially discrete tuning of surface properties.

In this study, a plasma jet was used to polymerise hexamethyldisiloxane (HMDSO) into polydimethylsiloxane (PDMS) thin films. Optimisation process included gas flow, liquid precursor injection rate, and treatment duration. Voltage was kept constant for all treatments.

The films showed hydrophobicity, which was measured using water contact angle technique (WCA). Typically the WCA was increase to values above 100°. Optical characteristics, including transmittance and reflectance were also measured.

From a practical point of view, it is also important to evaluate the durability of the coating in time and under stress conditions. Hence, we exposed different coatings to damp heat, UV light and abrasion tests. For most tests the hydrophobicity of the coatings was maintained although it did decreased slightly. After 300 hours exposure to damp heat and abrasion tests, the performance of the coating decreased to WCA below a 90º threshold.

Transmittance was not deeply affected after the stress tests, maintaining an averaged value of ~92%. Although further optimization can lead to longer lifetime of the coatings, the results show the potential of coatings deposited by atmospheric plasmas for ophthalmic lenses, touch screens and photovoltaic cover glass.

[1] S.S. Latthe, A.B. Gurav, C.S. Maruti, R. S. Vhatkar, “Recent Progress in Preparation of Superhydrophobic Surfaces: A Review”, Journal of Surface Engineered Materials and Advanced Technology, Vol. 2, pp. 76-94, 2012.

21

Inactivation of bacteria in final sewage treatment work effluents

A. Wright1, B. Uprety1, M.Mach2, F. Iza2, G Shama1, H. Bandulasena1, 1Department of Chemical Engineering, Loughborough University, Loughborough,

Leicestershire, LE11 3TU, United Kingdom 2Wolfson School of Mechanical, Electrical and Manufacturing Engineering, Loughborough,

Leicestershire, LE11 3TU, United Kingdom


It is well documented that bacteria are dispensed into bodies of surface water downstream of waste water treatment plants and although the full environmental impact is unclear, studies have suggested these bacteria can negatively impact the nearby eco-system. A reactor has been developed to address this problem by inactivating bacteria before water is realised from the treatment plant. The reactor uses a dielectric barrier discharge to produce highly oxidative, but short-lived species that are encapsulated in microbubbles produced by a combination of a fluidic oscillator and a microporous nickel membrane. The design is shown in figure 1.

Three operating regimes were identified by modulating the plasma ON time. This enabled strong control over the gas plasma chemistry (O3, OH, etc) and the pH of the liquid. Operating at 45% on-time, the reactor consumes 13W and it is able to reduce the concentration of E. coli, a bacterium commonly found in waste water, by 4.5 logs in 20 min (see figure 1).

Figure 1: Left Schematic of reaction vessel where the upper electrode is the nickel membrane. Right Inactivation of E. coli at three regimes as a function of time.

‐0.3

0.2

0.7

1.2

1.7

2.2

2.7

3.2

3.7

4.2

4.7

0 5 10 15 20

Log Reduction of Cells

Time (minutes)

10%

45%

60%

Control

Gas Inlet

Reaction

Vessel

Electrodes

pH Probe

22

DBD Plasma microbubble reactor for pretreatment of lignocellulosic biomass

Alexander Wright1, Hemaka Bandulasena1, Alex Shaw2, Felipe Iza2, David Leak3

1Department of Chemical Engineering, Loughborough University, Leics LE 11 3TU, UK2Wolfson school of Mech., Elec. & Manufact. Eng., Loughborough Univ, Leics LE 11 3TU, UK

3Department of Biology and Biochemistry, University of Bath, BA2 7AY, United Kingdom

Extracting ethanol from biomass is challenging due to the presence of lignin which needs to be removed to expose cellulose and hemicellulose for fermentation reactions. Lignin can be broken down effectively using ozone, OH radicals and other highly oxidative species. However for this pretreatment method to be feasible, operating costs should be kept low. In this study, a specially designed biomass pretreatment reactor has been tested with the purpose of breaking down lignin efficiently. The novel design produces the plasma at the gas-liquid interface of the bubbles; hence facilitating the transfer of oxidative species produced by the plasma to the liquid phase immediately after production. To disperse the ozone efficiently, microbubbles were generated by the conjunction of a fluidic oscillator and a microporous nickel membrane which also acts as one of the electrodes for generating the plasma. The DBD discharge was driven by a home-built half-bridge resonant power supply operating at 19kHz and 10kVrms. To control operation temperature the plasma was modulated. The duty cycle of the modulating signal was varied between 10% and 45% by adjusting the on-time between 90 and 663ms and keeping a constant off-time of 810ms. Preliminary characterisation tests identified two operating regimes for this reactor. Due to heating effects, low duty cycles (~10%) favoured ozone production while higher duty cycles (~45%) produced more NOx. Analysis of OH radical production by observing the chemical conversion of Terephthalic acid to 2-hydroxy Terephthalic acid showed compelling evidence for the existence of hydroxyl radicals. The plasma emitted UVB and UVC when air was used as gas supply but UVA can also be produced when the reactor is operated with a 5% He-N2 admixture.

Miscanthus was chosen for the pretreatment studies as it contains high amount of lignin; and hence it is problematic for ethanol extraction. ~3L samples containing 2.5% w/w biomass were pre-treated for times ranging from 30 minutes to 4 hours at 10% and 45% duty cycle. Following the pretreatment, enzymes were used to ferment cellulose and convert to bioethanol.

Figure 1: FTIR analysis of plasma products after 90 minute treatments.

0

100

200

300

400

500

0 20 40 60

Max Ozone

Concentration (ppm)

Duty Cycle (%)

0

100

200

300

400

500

600

0 20 40 60Max conccentaton (Ppm)

Duty Cycle(%)

N2O

N2O5

HNO3

NO2

23

Characterisation of an Atm-Pressure Dielectric Barrier Discharge in Air and a Protocol for Comparing the Biocidal Properties of Plasma Devices

Alex Shaw1, Paolo Seri2, Carlo A. Borghi2, Gilbert Shama3, Felipe Iza1

1Wolfson school of Mech., Elec & Manufact. Eng., Loughborough Univ, Leics LE 11 3TU, UK 2Dept. of Electrical, Electronic and Information Engineering “Guglielmo Marconi”, University of

Bologna, Bologna, 40129, Italy 3Department of Chemical Engineering, Loughborough University, Leics LE11 3TU, UK

Low temperature atmospheric pressure dielectric barrier discharge plasmas can be used in a wide range of applications including ozone production, surface modification, sterilisation and medical treatments. They utilise the convenience of atmospheric pressure operation and their inherently low operation temperature meaning that sensitive targets can be exposed to the plasma without undergoing thermal damage. Plasma is not widely used for sterilisation or cleaning purposes as more work is needed to develop an optimised power supply and plasma device that is capable of repeatable bacterial inactivation; we also do not fully understand which components of plasma kill bacteria and how this is carried out.

Here we report both the characterisation of a plasma device by Ultraviolet (UV) & Infra-red (IR) absorption spectroscopy and also electrical characterisation by means of power, voltage and frequency measurements. UV absorption at 256 nm is used to measure the temporal evolution of ozone concentration and FTIR spectroscopy is used to measure the concentration of HNO3, N2O, N2O5 and NO2 plasmas a function of the electrical input parameters.

The plasma was driven by an in-house built half-bridge resonant power supply. The frequency during the experiments was varied between 11 and 16 kHz which affected the operating voltage of the plasma as well as the power. The duty cycle was also varied in order to control the temperature of the plasma chamber between 5 and 25% on time. Air flow in the chamber was varied during the ozone concentration measurements between 0 and 2 SLM.

The idea of quantitive antibacterial characterisation is bridged with the proposal of a biological sample preparation protocol for producing bacterial samples to test the antibacterial efficacy of a plasma device. While reviewing literature around bacterial inactivation, we noticed that different institutions report drastically different reductions in bacterial reduction after plasma treatments even with similar operating regimes.

A reference protocol for bacterial preparation is proposed in the form of gram positive Bacillus subtilis spores (ATCC 6633) deposited as a monolayer on a polycarbonate membrane. The advantages of using this particular bacterium are that it is non-pathogenic, and once produced, spores stocks can be kept for many years with only a negligible reduction in viability. Using spores from a stock obviates the need to produce micro-organisms at a particular phase of growth for each experimental trial, which reduces variability between experiments and speeds up the experimental procedures. Results from testing of the above bacterial sample preparation protocol by both plasma and UV exposure are presented along with analysis of the error in results when compared to standard sample preparation protocols.

24

Reaching beyond the surface in plasma treatments

A.H. Shaw1, G. Shama2, F. Iza1 1Wolfson School of Mechanical, Electrical and Manufacturing Engineering, Loughborough

University, Leicestershire LE 11 3TU, UK 2Chemical Engineering Department, Loughborough University


Cold atmospheric pressure plasmas have been shown to possess bactericidal potential. Many research groups are looking into developing biomedical applications for plasma; however some big questions still remain. There are several main hurdles that need to be jumped before plasma has a chance to break through into the medical treatments market, one of these is penetration. Can plasma penetrate beyond the surface and reach cells beyond those on the surface? Can we make plasma treatments to penetrate, for example, through skin?

This research looks into whether a ‘plasma injection system’ can be developed to fire droplets of water through plasma and penetrate skin. Previous research has shown that penetration of water jets (2.5-6µL of fluid) into the skin is possible. We are looking at much lower volumes of fluid to be injected in a repetitive droplet firing system as opposed to a jet. Our current system uses a piezo-electric actuator that drives a syringe plunge to fire water droplets out of an orifice with a diameter that ranges between 50µm and 200µm.

These droplets travel between two plasma electrodes that are used to generate an RF plasma. The plasma is modulated as a means to control the gas temperature of the discharge, and the injection system and the RF generator are synchronised to control that the injected water droplets transit between the electrodes when the plasma is active. At high input power, the droplets can be fully evaporated and with large droplets the discharge gets quenched. At lower input power, however, droplets can transit the plasma without evaporating and undergo reactions with the background plasma, up-taking reactive species such as H2O2.The droplet then carries on to the surface of the skin model where they have enough momentum to penetrate and reach beyond the outer surface.

Preliminary results show that penetration of the droplets into artificial skin (agar)1,2 is possible and that fired droplets of low concentrations of hydrogen peroxide can kill bacteria, such as Escherichia coli, embedded in it.

Future work entails developing a stronger firing mechanism to deliver droplets with even higher velocity, therefore being able to penetrate targets with even smaller droplets and measurements of the concentration of hydrogen peroxide in the droplets after passing through the plasma.

1. J. Li et al., J. Biomech. Eng. 132, 101005-1 (2010) 2. J Stachowiak et al., J Control. Release 135, 104 (2009)

25

Chemical fluorescent probes for the characterisation of atmospheric-pressure plasmas

A. Wright1, C. Castelló-Beltrán2, B.R. Buckley3, H. Bandulasena1, Felipe Iza2 1Department of Chemical Engineering, Loughborough University, Loughborough, Leicestershire, LE

11 3TU, United Kingdom

2Wolfson School of Mechanical, Electrical and Manufacturing Engineering, Loughborough

University, Loughborough, Leicestershire, LE 11 3TU, United Kingdom 3Department of Chemistry, Loughborough University, Loughborough, Leicestershire, LE 11 3TU,

United Kingdom

In recent years there has been a growing interest in plasmas interacting with liquids, for example in sanitization of drinking water and in medical applications where the plasma interacts with biofluids and/or culture growth media.1 The transport of reactive species at these plasma-liquid interfaces is particularly complex and quantifying the dose of species that are actually delivered to the liquid phase through gas plasma diagnostics is particularly challenging. In this context, the development of chemical fluorescent probes that report quantitatively and selectively on the actual dose of reactive species delivered to a liquid is particularly appealing.

One of the key reactive species produced in plasmas interacting with liquids is ozone (O3). Chemical probes to detect ozone have been developed for other applications and indigo carmine, a blue chemical probe that when oxidized by ozone becomes transparent, has widely been used. However, this reaction is unspecific to O3 and other species produced in the plasma such as singlet oxygen and hydroxyl radicals can also oxidize the probe, given false readings.

Recently, Pittsburgh green, a dichlorofluorescein-derived chemical probe that is specific to O3, has been developed.2,3 This probe undergoes a β-elimination in the presence of O3 to produce a fluorescent product which can then be optically detected. The reaction is quantitative and selectivity studies indicate that Pittsburgh green is selective against a number of other reactive oxygen species, including 1O2, O3, O2

-, OH, H2O2, OCl- and NOO-.

In this work we compare UV and IR absorption spectroscopy measurements of ozone in the gas phase to those of the Pittsburgh green fluorescent probe in the liquid phase and a protocol to use this novel chemical probe as a diagnostic of atmospheric-pressure plasmas systems is presented.

1 P.J. Bruggeman et al. 2016 “Plasma-Liquid Interactions: A Review and Roadmap”, J. Phys. D

(submitted) 2 A. L. Garner et al. 2009 “Specific fluorogenic probes for ozone in biological and atmospheric

samples”, Nat. Chem. 1 316 3 C. Castelló Beltrán C et al. 2015 “Virtues and limitations of Pittsburgh green for ozone detection”

Chem. Commun. 51 1579

technological plasma workshop 2016

Documents