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Meeting Location: 8.1-001
IPP-HGW Zoom Raum 2 (ID: 948-1054-7070 / PW: 021741)
1. Neutralize Plasma Particles
When particles recombine and neutralize on the surface, they are either released as a molecule in a cosine distribution or reflected as an atom. The reflection coefficient can be looked up in the TRIM database. We discussed the assumptions on the incidence angle of the particle used for the TRIM database. Dieter volunteered to find this out.
Regarding the wetted area, it was noted that if an island is intersected with multiple targets, a shadow region can appear if they are not placed equidistant from the stagnation points in between.
2. Collect Neutral Particles
On the topic of indirect collection to build up neutral pressure, the interplay of ionization mean free path, and neutral-neutral collision mean free path was discussed.
3. Remove Neutral Particles
The sub-divertor volume does not play a role on the sub-divertor pressure, once steady state conditions are reached. However, a smaller volume will reach these conditions faster.
For particle removal we discussed TMP and Cryo pumps. To pump Helium, cryo pumps can be transiently operationally frosted with Argon, or by design covered with activated carbon.
We discussed Non evaporable getters (NEG), i.e. through liquid mercury. https://www.leybold.com/en-us/products/vacuum-pumps/ultra-high-vacuum-pumps
Further, different flow regime dependent options to minimize losses from the sub-divertor through the pump gap have been discussed. Noticeably the TESLA valve: https://en.wikipedia.org/wiki/Tesla_valve
4. Plug Neutral Particles
The ionization length could be plotted over T_e and n_e, over just plotting the ionization rate coefficient over T_e. This should be plotted for expected impurities.
5. Screen Impurity Particles
Impurities can be screened in the Divertor, Plasma SOL, or Edge. Neutral screening can be maximized by minimizing the ionization mean free path and maximizing the length particles have to travel.
Impurities have been categorized into:
Intrinsic: H (D+T), He
Seeded: Ne, Ar, N, Xe
PFC: W, W alloy (3.5Ni1.5Fe), EUROFER97, O, C While carbon is more relevant for confinement experiements and not for FPP’s it was noted that trace amounts of O and C are present in W, W alloy, or EUROFER97 which come to the surface. For EUROFER97 we only have ADAS data for 3 sigma of the composition. There is no ADAS data for V, Ta, Mn which in total amount to 0.76% of EUROFER97.
Are there other steels specifically designed for the high neutron fluxes of FPP’s?