TiPToP - TaIlored Pulse excitation for TailOred Plasma chemistries

Plasma technologies already form a key part of many of today's multi-billion pound industries such as the nanoscale fabrication of microprocessors, energy efficient lighting, production of solar cells and the deposition of advanced functional coatings. Underpinning the effectiveness of these essential technologies is the unique non-equilibrium environment created within the plasma; including a mix of reactive neutral particles, ions and energetic electrons. Many applications rely on the synergistic interaction between the mix of species created in the plasma and a sample surface; however one of the fundamental challenges in plasma science is tailoring the mixture of reactive plasma species such that they have the desired effect on a target.
In other words, detailed control of the plasma chemistry is essential for success in plasma-enabled applications, both existing and emerging.

The chemistry in these plasmas is largely controlled by the electrons; more precisely the distribution of energies that the electrons have. Different electron energy distribution functions (EEDF) drive differences in the plasma chemistry and therefore in the observed effect on a surface, making the EEDF, and especially control over the EEDF of key importance. In traditional low-pressure plasma applications, tailoring of the EEDF through e.g. multi-frequency applied voltages or magnetic fields, has proven to be a viable method for plasma chemistry control.

However, the same cannot be said in the fast emerging field of atmospheric-pressure plasma (APP) science. Where plasmas are generated at much higher pressure (in open air), meaning there are many more collisions between plasma particles, severely hindering existing low-pressure EEDF control methods. Given the reliance on plasma chemistry in many APP applications, establishing a viable technique to control the EEDF is an even more pressing challenge than in low-pressure systems. Success in this endeavour would have a profound impact across the entire application space of APPs, which includes activities such as high-value materials processing, renewable chemistry and healthcare technologies.

In this proposal, we bring together expertise from the University of York and the University of Liverpool in state-of-the-art pulsed power technology, the latest plasma diagnostic techniques and novel multiscale numerical modelling to address the challenge of plasma chemistry control for atmospheric-pressure plasmas. We aim to develop an extremely agile high-voltage pulsed power technology, in which pulse characteristics such as rise time, duration and repetition rate can be varied by the user. With this flexibility, the electrical excitation of the discharge can be used to modify the EEDF and therefore control and tailor the plasma chemistry of the APP.

Sophisticated plasma diagnostics and numerical modelling will enable us to understand the underpinning mechanisms of the observed changes in chemistry for different pulse shapes, leading to a new capability for atmospheric-pressure plasma technologies: flexible, tailored plasma chemistry. This would be an international first and deliver user-controlled tunability of well-defined plasma chemistries without changing background gas or plasma source design.

The impact of plasma technology on every day life is often underestimated. Non-equilibrium plasmas are a key technology in the manufacturing of products like computer chips, mobile phones, solar cells, high-intensity lighting and wear-resistant coatings. Furthermore, atmospheric-pressure plasma science is on the verge of maturing into mainstream technology with applications in medicine, renewable chemistry, food preservation and materials processing. Given the widespread use of non-equilibrium plasmas, it is clear that further progress in this field will have an immediate impact on the health and wealth of the nation.
Our project aims to address one of the major roadblocks faced in this field: the lack of a technique that facilitates detailed control of the plasma chemistry. We propose the development of a sub-nanosecond pulsed-power technology that will allow direct control over the electron energy distribution function, which drives the plasma chemistry in these types of plasmas.
In the short term, the impact of our project will primarily be of academic nature with anticipated major advances in the field of plasma science, and with further impacts across the fields of pulsed power technology, optical diagnostics and multiscale modelling. The combination of these activities allows us to develop not only an understanding of the plasma chemistry in non-equilibrium plasmas, but importantly, also give us methods to control the chemistry. The impact in the academic community, as outlined in the academic beneficiaries section, will be realised through dissemination activities, including publications in leading scientific journals, e.g. Physical Review Letters, Nature Communications and Applied Physics Letters, presentations at leading international conferences, e.g. Gordon Conference on Plasma Science, Gaseous Electronics Conference and European Physical Society Conference on Plasma Physics. In addition, the PIs/CoI have an extensive network of ongoing collaborations in a range of low-temperature plasma applications. Outcomes from this project will directly feed into these partnerships, creating direct impact in these fields.

In the longer term, the economic and societal impact of this project will be realised. Application of our newly developed technology opens up a range of new industrial and medical applications that so far have been hampered by a lack of plasma sources with a controllable chemistry. A primary target for societal impact of this proposal is the area of medical technology, where cold plasmas, delivering reactive oxygen and nitrogen species, are being investigated for novel medical treatments for e.g. wound healing and cancer treatment. The proposed plasma technology has the potential to allow a precisely controlled dose of plasma species to be delivered to a patient, enabling a safe and efficient use in a medical setting. Furthermore, we also anticipate impact in other plasma-based industries, especially those where plasma chemistry plays a crucial role. Primary examples include renewable chemistry, including CO2 conversion, and materials processing, e.g. surface functionalisation of heat-sensitive materials.
Finally, the project offers the PDRAs a career development that allows them to develop towards becoming leaders in the rapidly expanding field of atmospheric-pressure plasma technology; whether this is in academia, existing industry or through new start-up companies.
The ways this impact will be achieved, as detailed in the Pathways to Impact document, are to showcase our technology to relevant partners and set up dedicated proof-of-concept projects for specific applications, leading to further industrial uptake and development.

In summary, applications of our novel technology, once realised, will have significant impact in the EPSRC Prosperity Outcomes 'Health', 'Productivity' and 'Resilience'.