# Characterization and Optimization of a Conical Corona Reactor for Seed Treatment of Rapeseed
## 1 Introduction  
Non-thermal plasmas (NTP) are chemically active media composed of electrons, neutral particles, ionized atoms and molecules, photons, and reactive species [1]. NTPs can be generated in a reactor by means of an electrical discharge in a variety of gases (noble and molecular gases) and at different pressure ranges [2]. The possibility of producing cold plasma at atmospheric pressure cheapens the process broadening the spectrum of applications. Due to the reactive composition and low temperature, NTPs have been used and studied for application in a diversity of fields, such as material processing [3], surface cleaning [4], decontamination [5], medicine [6], and agriculture [7, 8]. Plasma agriculture is a novel plasma application that has rapidly grown in the past 20 years [7]. A large number of published articles in this field focused on the plasma application for post-harvest [9], such as the treatment of fruits and vegetables for preservation and increased shelf life [10, 11]. However, investigations on the use of cold plasmas in pre-harvest stages are gaining considerable attention. NTPs are being explored as a possible green alternative to the use of agrochemicals, given the substantial negative impact of the latter on the ecosystem [7]. Plasma has demonstrated promising effects that could lead to decreased infections by pathogens in seeds, growing plants and soil [12, 13, 14], improve crop abiotic stress tolerance [15], and increase plantation yield [16]. Effects of plasma treatment have been studied for a wide variety of plant species (such as soybean [17], wheat [18], barley [19], maize [20], tomato [21], radish [22], and pea [23]) and different plasma sources, including low pressure and atmospheric pressure devices, have been developed. Oilseed crops are grown worldwide given their economic value and relevance for the production of edible oils and renewable energy [24]. Rapeseed is an essential oilseed crop being the second most produced oil crop in the world with a harvest of 75.9 million tons in 2017/2018 [25]. However, with climate change and the ongoing COVID-19 pandemic, the global production of rapeseed is prone to decline [25], which contrasts with the rapidly increasing consumption demand. Given the impractical solution of increasing the cultivation land area, it is important to find alternatives for securing and possibly increasing crop yield. Genetic improvement of rapeseed to develop climate-adapted cultivars can help to increase production under abiotic stress [26]. Another alternative for improving resistance to abiotic stress is the use of chemical priming of the seeds [26]. As a physical method, plasma treatment is being investigated for securing yield and enhancement of biotic stress resistance and thus, can be an advantageous option for the treatment of rapeseed. Recently, diverse plasma sources have been reported in the literature for the treatment of rapeseed for different purposes. [PERSON] et al., 2018 [27], investigated the effects of a low-pressure radio frequency (RF) discharge treatment of rapeseed and observed enhancement of seed germination, plant growth, and yield. [PERSON] et al., 2019 [28], studied the treatment response of exposed rapeseed to low-pressure dielectric barrier discharge (DBD). It was concluded that plasma stimulates germination and increases amylase activity [28]. Other studies investigated the decontamination of rapeseed seed surfaces using plasma [29; 30]. [PERSON] et al., 2017 [29], used a corona discharge plasma jet for the treatment of rapeseed and reported a maximum reduction of 2.2 log of total aerobic bacteria. In this study, the corona discharge had a dual effect, promoting germination and seedling growth in addition to reducing the microbial load [29]. [PERSON] et al., 2020 [30], reported the indirect treatment of rapeseed seeds and other crop seeds using plasma-processed air produced in an atmospheric pressure microwave reactor.