# A Coaxial Dielectric Barrier Discharge Reactor for Treatment of Winter Wheat Seeds
###### Abstract  
Non-thermal atmospheric pressure plasmas have been recently explored for their potential usage in agricultural applications as an interesting alternative solution for a potential increase in food production with a minor impact on the ecosystem. However, the adjustment and optimization of plasma sources for agricultural applications in general is an important study that is commonly overlooked. Thus, in the present work, a dielectric barrier discharge (DBD) reactor with coaxial geometry designed for the direct treatment of seeds is presented and investigated. To ensure reproducible and homogeneous treatment results, the reactor mechanically shakes the seeds during treatment, and ambient air is admixed while the discharge runs. The DBD, operating with argon and helium, produces two different chemically active states of the system for seed modification. The temperature evolution was monitored to guarantee a safe manipulation of seeds, whereas a physiological temperature was assured by controlling the exposure time. Both treatments led to a remarkable increase in wettability and acceleration in germination. The present study showed faster germination acceleration (60% faster after 24 h) and a lower water contact angle (WCA) (82% reduction) for winter wheat seeds by using the described argon discharge (with air impurities). Furthermore, the treatment can be easily optimized by adjusting the electrical parameters. plasma agriculture; DBD; wheat; germination acceleration; seed; cold atmospheric plasma (CAP); plasma source +
Footnote †: journal: Applied Physics Letters
an urgent topic. Among them, the use of plasma in agriculture has gained increasing attention over time [3; 4; 5; 6]. Non-thermal atmospheric pressure plasmas offer unique possibilities for the treatment of heat-sensitive targets, such as polymers and biological organisms [7; 8]. In the last decade, the number of published papers dealing with its use in agriculture has linearly risen [9]. In this field, scientists have observed that plasmas are able to sanitize food products and decontaminate plant seeds, fruits, and vegetables [5; 10; 11; 12]. Several authors have reported the efficient improvement of the germination and growth of agriculturally relevant plant species such as wheat [13; 14; 15; 16; 17; 18; 19; 20; 21; 22; 23; 24], maize [14; 25], lupine [14], soya beans [26; 27], mung beans [28], radish [29; 30; 31], pea [32; 33; 34; 35], and rice [29; 36]. It has been shown that exposure to plasma improves water uptake by the seed [34; 37], decreases the contact angle of the seed surface [23; 37], and functionalities the seed coat by attaching new chemical bonds to the surface [34; 38]. In addition to physical changes at the seed surface, physiological alterations along with effects on seedling growth and development [39; 40] and improved tolerance against various stresses [11; 41] have been observed as well. However, depending on the plasma source and treatment conditions, negative effects on germination and seedling growth are observed [39; 42]. Thus, the type of treatment (direct or indirect), reactor configuration, gas, and electrical parameters have an impact on the germination and further plant growth [42]. Moreover, the reactor geometry needs to be adapted according to the target type and application desired. Cold plasmas can be generated at atmospheric pressure using different reactor configurations [43]. Among them, plasma jets provide only a small plasma plume for surface treatment, which considerably limits the active zone [44]. Corona discharge reactors can easily be up-scaled to increase the treatment area by implementing several additional electrodes [45]. The discharge produced is quite inhomogeneous and can affect the substrate non-uniformly. Dielectric barrier discharge (DBD) reactors present great flexibility concerning the electrode's arrangement [46] due to their coplanar configuration allowing the indirect treatment of substrates until planar and coaxial configurations, producing big volumes of plasma.