## 1 Introduction  
The main purpose and role of the lightning protection rod is preventing indirect or direct lightning strike near the substation, facility, telecommunication line etc. Recently, cases of harm caused by lightning strike with high voltage and current flow is increasing with the increasing global average temperature due to global warming.  
The conventional Franklin rod is for the safe discharge of lightning strikes caused by thunderstorm clouds on a facility and skyscrapers, and it has been the most widely used air terminal. In other words, the basic role of the Franklin rod is inducing lightning strikes as receptors with low impedance paths, and then attracting the lightning stroke and the lightning current flow using a sharp tip to ground the system. The Franklin rod has been validated in many studies conducted around the globe over a span of many decades, from indirect and direct lightning surges. However, the Franklin rod for inducing lightning surges to specific spots is not perfect at preventing facilities from being struck by lightning strike. Even if the Franklin rod induces a high current by lightning strike from the rod tip to ground the system, the high lightning current impulse may still affect the communication facilities, computers, and weak electrical devices of the building.  
For the above reason, recently, new different kinds of lightning protection rods have been introduced. One is the charge transfer system (CTS) and another is early streamer emission (ESE). Many researchers have suggested that the CTS and ESE lightning rods will have a larger protection area than that of a Franklin lightning rod of similar dimensions [1; 2; 3].  
Recently, some studies have focused on CTS for preventing indirect and direct lightning strikes [4; 5; 6]. They suggest a new type of CTS, consisting of cylindrical CTS, many brushes, and a floating conductor. The floating conductor is located near the brushes. However, studies have only focused on the modification of the structure and shape of the CTS as well as the effectiveness of CTS according to the presence or absence of the floating electrode; the optimized air space between the floating conductor and brushes has not been suggested, in spite of the performance of CTS depending on the air space (air space is \(>\)2 mm, based on empirical study). In addition, currently the CTS is being used without quantitative data about the air space [5; 6].  
From the view point of the above reason, the scientific aim of our research work is investigating the optimized air space for performance improvement of SK-AOR380 with various previous research as a basis for the work, using the numerical analysis method. The subject of the research was to obtain an optimized air space between the ionizer conductor and current collector. To investigate the optimized air space, a simple method is adopted; the air space is reduced with decreasing \(\upmu\)m units in terms of electric field distribution and electron density, which is coupled with the charge continuity equation for a positively charged ion, negatively charged ion, and free electron, based on [PERSON]'s equation. This study extends the existing research in CTS type lightning rods, and these simulation results are expected to bring useful information to decide the optimized air space between the ionizer conductor and current collector.  
In this paper, Section 2 presents a modeling method and detailed description of the analysis approach for numerical analysis, Section 3 describes the results of simulation work, Section 4 is a discussion, indicating the limitations, practical application, and future directions of research in this field. Section 5 presents the final conclusions of the research.