material obtainable between the electrodes, slightly imbedding 

 them in it. When very high electrical energy is discharged 

 across the gap, the water is vaporized almost instantaneously 

 and the gap resistance is raised. 



In studying the literature and noting the size of the conduc- 

 tors used in some tests it is apparent that few experimenters 

 have realized the magnitude of the first surge of current. For 

 example, in discharging 3000 watt-seconds of energy across 

 the electrodes, the current has been measured in excess of 

 220, 000 amperes for brief periods. (Short, heavy leads are 

 essential for such an operation.) Very high temperatures at 

 the gap were also reported and, on one occasion, electrodes 

 made of titanium showed considerable melting. (Titanium 

 melts at 1800°C.) 



Since it is desired to have the electrical discharge appear 

 only at the exposed electrode surface, NEL underwater spark 

 gaps have all been based upon the principle of the "horn gap. " 

 The basic design of this gap is shown in figure 1 . While the 

 optimum electrode material is tungsten, it is difficult to 

 machine and, for experimental purposes, too expensive. 

 Most of the NEL electrodes were machined from either brass 

 or copper. Some of the NEL gaps have been fired thousands 

 of times. 



Figure 1. Basic design of horn gap (before encapsulating), 



