Ghost image/alpha gain in Bump map?

Hi--

I'm trying to demonstrate a TIG (Heliarc) welding process. Guided by a couple of good suggestions here, I modeled the weld bead out of a poly torus, then attached a ramp to the Transparency channel of the Bead image in the color channel of the material. The idea is to animate the Position of the ramp node. Could probably be done other ways, but seems to work OK.

Anyway, the problem is this ghost image that shows up in the viewport and the render on the left side of the shot. After beating on it for a while, I discovered that I can make it disappear by lowering the Alpha gain in the Bump map node. Unfortunately, this also lowers the contrast in the completed bead to the right of the shot. These are just stills--I haven't actually animated it yet.

I'd appreciate any comments, observations or suggestions. Please see the three attached images for reference. I've included a screenshot of the shader network also.

Thanks!

--Tim

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