## 5 Conclusions  
The main result of this work is the revelation of another important parameter significantly affecting the processes of electrodes electrical erosion and the synthesis of NPs in a pulse-periodic SD--the degree of the electrodes' asymmetry in the rod-to-rod (rod-to-thick tube) configuration. It was demonstrated that it is possible to control the size and concentration of synthesized NPs by changing the degree of the electrodes' asymmetry by setting their end faces at a certain angle. With an increase in the degree of the electrodes' asymmetry, larger NPs (with sizes greater than 40 nm) appeared in the aerosol composition and their agglomeration increased. This behavior, observed with an increase in the angle between electrodes end faces, is associated with the localization of SD channels in the region of the shortest distance between electrodes and, consequently, with a local increase in the density of the discharge current and in the density of the power released in the discharge. During the electroerosive wear of asymmetrically arranged electrodes by the ODP, a great part of the end faces of both electrodes became parallel. At the same time, parameters of the synthesized NPs approached those of the NPs synthesized on initially symmetric electrodes. This led to an asymptotic decrease in the average size of NP agglomerates to 150 nm for the case of the ODP and to 130 nm for the case of the UDP at the maximum degree of the electrodes' arrangement asymmetry. In conclusion, it is also important to note that, with the ODP, an increase in the degree of electrodes' asymmetry led to an increased mass production rate and energy efficiency of NP synthesis, and a significant part of this increase was due to the contribution of large NPs with a size of more than 40 nm. Thus, in these regimes a large mass production rate was realized with a sharp deterioration in the qualitative composition of NPs. The parallel arrangement of electrodes' end faces provided the most stable mode of continuous synthesis of NPs of small sizes (less than 40 nm), both for the ODP and UDP. It is also important that, in all the cases, a significant proportion of synthesized NPs remained inside the interelectrode gap, settling on electrodes' end faces and not contributing to the energy efficiency of the synthesis. This effect can be minimized by controlling the SDG configuration and the speed parameters of blowing the electrode ends with gas, and by increasing the width of the gap between electrodes. The effect of synthesized NP transfer to the opposite electrode with the UDP led to the occurrence of electroerosive instability. It appeared in the form of a protrusion on the anode surface, around which the SD process is localized, causing its further growth. This process led to an unstable regime of NP synthesis. As instability developed, the height of the protrusion on the surface of the anode increased, reducing the gap between electrodes. The protrusion grew due to the transfer of the cathode material by synthesized NPs to the area of its formation at the anode. Nevertheless, in the context of individual NP synthesis and the reduction of their agglomeration in the aerosol, the use of UDPs may be promising for practical applications, provided that the electroerosive instability development is prevented. Our further research will be devoted to finding conditions for preventing such instabilities. Conceptualization, K.K. and V.I. ; Methodology, K.K. ; Validation, K.K. and M.U. ; Formal Analysis, K.K. ; Investigation, K.K. and M.U. ; Resources, V.I. ; Data Curation, M.U., E.K. and A.L. ; Writing--Original Draft Preparation, K.K. ; Writing--Review & Editing, V.I. ; Visualization, K.K. and M.U. ; Supervision, A.E. and V.I. ; Project Administration, V.I. ; Funding Acquisition, V.I. and K.K. All authors have read and agreed to the published version of the manuscript.