## 4 Conclusions  
This paper reported the experimental characterization and comparison of the nanosecond pulsed breakdown behavior of \(SF_{6}\), \(C_{4}F_{7}N\), and \(C_{4}F_{7}N\)-based mixtures. \(C_{4}F_{7}N\) outperforms \(SF_{6}\) in high voltage pulsed hold-off conditions experiencing a 6.8 kV/ns pulse. The 20/80 mixtures of \(C_{4}F_{7}N\) with \(N_{2}\) did not match or exceed \(SF_{6}\) performance in peak pulsed electric field hold-off, as shown in the previous DC and AC results [4, 5, 6, 31, 32]. Insulating gases, such as \(SF_{6}\), in spark gaps show a wide variance in dielectric strength under pulsed electric fields [28, 29, 30]. The 50/50 mixtures of \(C_{4}F_{7}N\) with \(CO_{2}\) and \(N_{2}\) as buffer approached the performance of \(SF_{6}\). \(C_{4}F_{7}N\) consistently showed less variation in breakdown characteristics, whether in pure or mixture form, compared to \(SF_{6}\). The measured variation in breakdown performance of \(C_{4}F_{7}N\) at 253 kPa and 258 kPa can be attributed to the variance in the output pulse of the Marx generator. In future, larger datasets with a more consistent HV excitation source may be able to isolate the statistical variation in these pressure regimes. Notably, \(C_{4}F_{7}N\) has a lower vapor pressure and higher boiling point than \(SF_{6}\); 294 kPa and \(-4.7\)\({}^{\circ}\)C compared to 2108 kPa and \(-63.9\)\({}^{\circ}\)C [34, 34]. Thus, mixture and buffer gases are appealing to permit \(C_{4}F_{7}N\) to operate across large pressure and temperature regimes.  
Other works have shown that \(C_{4}F_{7}N\) has many decomposition products, such as \(CN\) and \(CF_{3}\), which occur with electron attachment or once the gas is fully ionized [3, 9, 12, 35]. \(SF_{6}\) tends to avoid these issues as long as impurities such as oxygen and water are kept low [36]. There are also long-term pulsed performance concerns of \(C_{4}F_{7}N\), and its voltage holds off over time; some systems measured a 14% reduction in the dielectric strength of \(C_{4}F_{7}N\) and \(CO_{2}\) mixtures after just 9 months [16]. \(C_{4}F_{7}N\) has a range of incompatible materials to be considered when designing HV systems [15, 16, 17, 19]. These designs may have an increase in manufacturing costs, affect operational lifetimes, and require more research and design. Future research in development, deployment, cost, and environmental impact of \(C_{4}F_{7}N\) devices is still required for large-scale industrial applications.  
Thus, \(C_{4}F_{7}N\) is not a simple drop-in replacement for \(SF_{6}\) as more design considerations must be taken into account, such as lifetime, material compatibility, operating temperature and pressure regimes, and buffer gases. Under pulsed conditions, with relatively low shot numbers, \(C_{4}F_{7}N\) may be a suitable replacement for \(SF_{6}\) but requires mixing ratios of 50% or more. Pure \(C_{4}F_{7}N\) also has a dielectric strength greater than \(SF_{6}\) under pulsed conditions, permitting the design of more compact pulsed power systems. There is an ongoing search for alternatives to \(SF_{6}\) as an insulating gas.  
Data collection and experiment construction, L.S., J.M. and L.B.; data processing, L.S.; writing, editing, data interpretation, L.S., J.S., A.N., J.D. and A.Y. All authors have read and agreed to the published version of the manuscript.  
This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07 NA27344.  
The raw data supporting the conclusions of this article will be made available by the authors upon reasonable request (the raw data must be approved for release by sponsor).  
The authors declare no conflicts of interest.The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.