I am modeling an electron gun that should impact and charge another surface. I’ve gotten the electron gun to work, but it is not generated any secondary electrons. Is there a way to initialize secondary electron emissions from a source other than the ambient electrons? I’m having difficulties finding a solution in the users manuals.
In case anyone else runs into a similar issue: I was initially setting up the electron gun as a thruster only emitting electrons, but SEs are turned off for thrusters to avoid non-physical SE emissions (stated in the User’s Manual). I am now modeling the electron gun as a source using the “AxisymTabulatedVelocitySurfDistrib” and just setting the energy distribution to one energy. I just followed the info from the “Controlling NUM from SPIS UI” manual to turn on SEs from a source, and all is working now.
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One of the most difficult parts was formatting the tabulated distribution for the AxisymTabulatedVelocitySurfDistrib" because I couldn’t find any examples. I wanted to do a 1 keV beam with a half angle of 2 degrees, and this formatting ended up working (figured it out with the help of Chat GPT-5):
0.000000000000e+00 1.000000000000e-09 1000.000000 0.100000
3.490658503989e-03 1.000100529830e-02 1000.000000 0.100000
6.981317007977e-03 4.000389933427e-02 1000.000000 0.100000
1.047197551197e-02 9.000831653181e-02 1000.000000 0.100000
1.396263401595e-02 1.600136476031e-01 1000.000000 0.100000
1.745329251994e-02 2.500190395553e-01 1000.000000 0.100000
2.094395102393e-02 3.600233957011e-01 1000.000000 0.100000
2.443460952792e-02 4.900253756721e-01 1000.000000 0.100000
2.792526803191e-02 6.400233954351e-01 1000.000000 0.100000
3.141592653590e-02 8.100156273116e-01 1000.000000 0.100000
3.490658503989e-02 1.000000000000e+00 1000.000000 0.100000
The columns from left to right are: angle in radian, cumulative flux as a function of angle, energy in eV, energy distribution
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Hi Kaylee, you’re not the only one having difficulties finding a solution in the manuals! But your approach is a good one. Just understanding the “electronSecondaryEmission” parameter is a chore. If source1 is the only population that would generate secondaries, I suspect “192” is the correct choice? bit 2 (i.e. secondaries from secondaries) in the triplet usually triggers some stability issues for me
The model for secondary emission is due for an update that we hope to release in November this year.
Hi Fredrik, thanks for your response! I’ve been using “455” to simulate secondaries from the ambient environment, source1, and secondaries from secondaries which seems to be giving me reasonable results
If it works, it works! The current model of secondaries were designed after two experimental papers that showed quite high yields (≈1) when the primary electron impacted with ≤ 10 eV energy (e.g. a 30 eV electron on a -20 V surface). This is not agreement with improved measurement campaigns though, so it was likely an instrumental artefact and so the new model will rectify that, amongst other things. Coincidentally, many SPIS simulation setups would trigger secondaries from secondaries within this energy span, and is why I never believed in my sim results with this flag on. But this may not be a large effect in your simulations!
Thanks for sharing your solution as well