Working an electrical effect with a cloud layer's more effective by the way

1. Make a gray scale plasma "cloud" noise layer (in GIMP, Render>Clouds>Solid Noise)

2. Have a second layer be a linear gradient, from black '0 0 0' to white '255 255 255', do it in the center at a short length

3. Make that second layer's blend mode 'difference'

4. Merge Down

5. Invert

6. Adjust brightness and contrast levels of the bolt you want, right in the middle. If you can, use curves

I just tried this technique in gimp and it works very well, thanks!