Capacitor, Cornell-Dubilier 942C20P15K-F 0.15uF, 2000V
These poly capacitors are the best you can use for Tesla coils period! They can be used for both solid state (DRSSTC) and spark gap Tesla coils. These capacitors can take an enormous beating and keep coming back for more!
Click here for the datasheet (PDF)
Note: The photo above is a generic photo for this capacitor product line.