# Characterization and Optimization of a Conical Corona Reactor for Seed Treatment of Rapeseed
## 1 Introduction
Artificially contaminated rapeseed seeds treated under multiple filling conditions presented a reduction in _Bacillus atrophaeus_ spores of almost 2.7 log [30]. However, the same treatment condition affected the seed's viability, and a complete loss of germination was observed. In contrast, single filling only affected seed germination to a lower degree, while reaching a decontamination efficiency of 2.6 log units [30], indicating that plasma parameters need to be defined for appropriate treatment effects. A low-pressure RF capacitive coupled plasma (CCP) reactor was used by [PERSON] et al., 2015 [31], for enhancing the germination of rapeseed under drought stress. According to the study, plasma treatment improved water uptake by the seeds and increased the accumulation of soluble sugars and proteins [31]. [PERSON] et al., 2017 [16], observed yield enhancement in field experiments of treated rapeseed using a low-pressure microwave discharge in combination with beneficial fungi spores. On the one hand, plasma technology seems promising as an environmentally friendly alternative for agriculture, because the species produced are limited in space and time and do not encompass non-natural compounds. On the other hand, the diversity of plasma sources and the complexity of generated discharges lead to diverging results (improvement or impairment of germination, water uptake, growth, and others). Therefore, the reactor and discharge parameters have to be carefully studied and adjusted for securing or enhancing seed germination. Among the many possible ways of generating NTP at atmospheric pressure, corona discharge stands out as a well-known and easy option. It occurs in strongly non-uniform electric fields and is generated using asymmetric electrodes. The most frequent configuration comprises a pin-to-plate set of electrodes. In the present work, a pin-to-plate corona discharge reactor with a horn-like nozzle was studied. The original version of this reactor was previously reported elsewhere [32]. Filamentary corona discharges are usually very inhomogeneous. [PERSON] et al., 2018 [32], reported an improvement in treatment uniformity of PET samples when changing the reactor nozzle size. The use of a conical nozzle led to a uniform treatment area underneath the reactor (up to 30 cm\({}^{2}\)) [32]. Here, this conical reactor was adapted for the treatment of seeds with small and round shapes. The funnel reactor was mounted on top of a glass Petri dish in which small seeds could be placed. Thus, the system remained closed, and the seeds were prevented from being blown away. The new reactor configuration was characterized and its suitability for seed treatment was investigated using rapeseed. The discharge power could be easily controlled by the applied voltage duty cycle, which also contributed to gas temperature regulation. For this direct treatment reactor configuration, an influence of the number of seeds on the discharge parameters was observed. The effects of plasma treatment parameters on seed surface hydrophilicity and germination kinetics were studied.