This is the method I use to paint blue plasma weapons. I like to think that the plasma will be the hottest/brightest at the bottom of the coils where they meet the rest of the gun. So I like to paint the coils brighter near the bottom and darker near the top, where the coils will be the coolest.

Coils

1. Base coat the coils using Bold Titanium White
2. Apply a few thin coats of Teclis Blue over the white
3. Being careful to avoid the recesses between the coils, paint from about halfway down the coils to the top of the coils using a thin layer of Alaitoc Blue
4. Paint the very top of the coils using a thing layer of Kantor Blue , again being careful to avoid the recesses between the coils
5. Apply a 1:1 mix of Lahmian Medium and Baharroth Blue to the very bottom of the coils. Let it pool a little and use a brush to draw it up into the coils, about halfway, in a sort of bell curve shape.
6. Repeat the previous step, this time drawing the paint about 1/4 of the way up the coils
7. Thin down a 2:1 mix of Bold Titanium White and Baharroth Blue using Lahmian Medium and apply it to the very deepest recesses at the bottom of the coils, focusing towards the center
8. Repeat the previous step, this time using only Bold Titanium White and heavily thinning it down with Lahmian Medium

Glow

1. Apply a thin coat of Alaitoc Blue around the rim surrounding the coils
2. In the corners, the center, and anywhere the light would be the brightest apply a thin coat of Teclis Blue
3. Repeat the previous step, this time being much more conservative in your application, using Baharroth Blue