How do I make a “directed” spark gap?
The simplest way to get what you described is a set up like this sketch:


Distance &quot;a&quot; is longer than your arc can jump.
Distance &quot;b&quot; and &quot;c&quot; together are shorter than &quot;a.&quot;
Your object must be conductive.
Your arc must be able to jump the distance &quot;b&quot; + &quot;c&quot;.
Distance &quot;b&quot; + &quot;c&quot; + &quot;d&quot; can be pretty much any distance you like - but distance &quot;b&quot; + &quot;c&quot; must always be shorter than &quot;a&quot; and the arc must be able to jump the &quot;b&quot; + &quot;c&quot; distance.

The distances must always be measured between the points of closest approach