Reply To: Global Warming

[asymmetric_implosion]

Is the tip of the anode blocked as well? There are plenty of images of brems emission from the tip of the anode as well as the base. My working hypothesis is electrons that were once confined during the pinch escape the pinch region when the current falls below the confinement threshold. That explains why they are late in time and why they are hard. Another option is current restriking to the anode after the pinch but I’ve never observed any electrical evidence to support a current restrike near the tip of the anode. An imaging diagnostic would help verify the shield placement. I never trust detectors without images to verify what they are seeing.

I attached an image of an SS304 anode with a hydrogen pinch. The image is integrated over 100 shots at 250 kA. The image is of the >10 keV spectrum. The anode wall is too thick to see the anode base but the tip of the anode is clearly visible. The really striking feature is the lack of a pinch. Too little mass density in the pinch to produce significant brems while Fe does a fine job of converting electrons to x-rays. Put argon in instead of hydrogen and you get a nice visible pinch.

I suggest switching to a gas that does not produce neutrons to verify that your x-rays are not really gamma rays. SS304 vacuum chamber can produce (n,gamma) reactions that lead to 800 keV photons. The reaction relies on fast neutrons so it could explain the time lag in the second pulse. Neutrons are slow compared to photons. Have you considered using a stepwedge spectrometer to measure your photon spectrum? They are cheap and easy to setup. The data analysis requires a little work, but flat response films like GAF film reduce some of the problems. It is perfect for machines that can replace the films between shots. Film to digital reduction does not require developing with GAF as it visibly darkens from white to gray. A modest quality scanner is all that is required to convert from film to digital data.

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