Plasma treatments are currently being assessed as a seed processing technology for agricultural purposes where seeds are typically subjected to pre-sowing treatments to improve the likelihood of timely and uniform germination. The aim of this review is to summarize the hypotheses and present the evidence to date of how plasma treatments affect seeds, considering that there is difficulty in standardizing the methodology in this interdisciplinary field given the plethora of variables in the experimental setup of the plasma device and handling of biological samples. The ever increasing interest for plasma agriculture drives the need for a review dedicated to seeds, which is understandable to an interdisciplinary audience of biologists and plasma physicists. Seeds are the first step of the agricultural cycle and at this stage, the plant can be given the highest probability of establishment, despite environmental conditions, to exploit the genetic potential of the seed. Furthermore, seedlings seem to be too sensitive to the oxidation of plasma and therefore, seeds seem to be the ideal target. This review intentionally does not include seed disinfection and sterilization due to already existing reviews. Instead, a summary of the mechanisms of how plasma may be affecting the seed and its germination and developmental properties will be provided and discussed.

Designing plasma-enhanced chemical vapour deposition (PECVD) reactors to coat large-area glass plates (~1 m²) for flat panel display or solar cell manufacturing raises challenging issues in physics and chemistry as well as mechanical, thermal, and electrical engineering, and material science. In such reactive glow discharge plasma slabs, excited at RF frequency (from 13.56 MHz up to ~100 MHz), the thin-film deposition uniformity is determined by the gas flow distribution, as well as the RF voltage distribution along the electrodes, and by local plasma perturbations at the reactor boundaries. All these aspects can be approached by analytical and numerical modelling. Moreover, the film properties are largely determined by the plasma chemistry involving the neutral radicals contributing to film growth, the effect of ion bombardment, and the formation and trapping of dust triggered by homogeneous nucleation. This paper will review progress in this field, with particular emphasis on modelling developments.

In small area capacitive reactors, the rf and dc components of the plasma potential can be assumed to be uniform over all the plasma bulk because of the low plasma resistivity. In large area reactors, however, the rf plasma potential can vary over a long range across the reactor due to rf current flow and the nonzero plasma impedance. A perturbation in rf plasma potential, due to electrode edge asymmetry or the boundary of a dielectric substrate, propagates along the resistive plasma between capacitive sheaths. This is analogous to propagation along a lossy conductor in a transmission line and the damping length of the perturbation can be determined by the telegraph equation. Some consequences are the following: (i) The spatial variation in sheath rf amplitudes causes nonuniform rf power dissipation near to the reactor sidewalls. (ii) The surface charge and potential of a dielectric substrate can be negative and not only positive as for a uniform rf plasma potential. The variation of sheath dc potential across a dielectric substrate causes nonuniform ion energy bombardment. (iii) The self-bias voltage depends on the plasma parameters and on the reactor and substrate dimensions—not only on the ratio of electrode areas. (iv) The nonuniform rf plasma potential in presence of the uniform dc plasma potential leads to nonambipolar dc currents circulating along conducting surfaces and returning via the plasma. Electron current peaks can arise locally at the edge of electrodes and dielectric substrates. Perturbations to the plasma potential and currents due to the edge asymmetry of the electrodes are demonstrated by means of an analytical model and numerical simulations.

In the next generation of fusion reactors, such as DEMO, neutral beam injectors (NBIs) of high energy (0.8-1 MeV) deuterium atoms with high wall-plug efficiency (>50%) will be required to reach burning plasma conditions and to provide a significant amount of current drive. The present NBI system for DEMO assumes that 50 MW is delivered to the plasma by 3 NBIs. In the Siphore NBI concept, negative deuterium ions are extracted from a long, thin ion source 3 m high and 15 cm wide, accelerated and subsequently photo-neutralized. This requires the development of a new generation of negative ion sources. At the Swiss Plasma Center, a novel radio frequency helicon plasma source, based on a resonant network antenna source delivering up to 10 kW at 13.56 MHz, has been developed and is presently under study on the Resonant Antenna Ion Device (RAID). RAID is a linear device (1.9 m total length, 0.4 m diameter) and is equipped with an extensive set of diagnostics for full plasma characterization. In this work, the principles of operation of resonant antennas as helicon sources are introduced. We present absolute spectroscopy, Langmuir probe, and interferometry measurements on helicon plasmas. We characterize the performance of the source in terms of hydrogen/deuterium dissociation and negative ion production as a function of the input power. Furthermore, first results with the helicon birdcage antenna installed on the Cybele negative ion source at CEA-IRFM are presented, as a first step towards the validation of the Siphore concept.

Plasma treatments are currently being assessed as a seed processing technology for agricultural purposes. There is sufficient information as a proof‐of‐concept, but a lack of standardization in the methodology prevents a convincing evaluation of plasma treatment on seeds. It would be helpful to coordinate research efforts to make the entry for newcomers into this interdisciplinary field less overwhelming and to aid in transferring this technology into the industry by establishing a common protocol. This review presents the parameters used in the seed preparation, the plasma treatment of the seed, and the seed posttreatment. This summary of the plasma and biological parameters is intended to raise awareness about questions that need to be addressed to properly record protocol details and reproduce results for the plasma treatment of seeds.