Hello! SPIS user!
I’m interested in plume analysis.
So I would like to know if it is possible to simulate other reactions (elastic collision, dissociation reaction, excitation) through SPIS other than CEX reaction.
Looking forward to your positive response.
Thanks!
This is how my SPIS-documentation-trained AI answered your response =) . Please note that photoionization needs a bugfix that is in the pipeline:
Yes, it is possible to simulate volume reactions other than Charge Exchange (CEX) in SPIS. While older versions were primarily limited to CEX, more recent versions (specifically starting with SPIS 6.0 and the integration of the Generic Volume Interactor) allow for a wide range of physico-chemical interactions.
1. The Generic Volume Interactor
The GenericVolInteraction (available in the Erosion & Contamination package) allows you to define custom reactions between different plasma species. To use this, you set the global parameter volInteractTypeX to GenericVolInteraction.
2. Supported and Exemplified Reactions
The sources explicitly list and provide examples for several types of reactions beyond CEX:
Elastic Collisions: These are explicitly supported and provided as a syntax example: {Thruster0_Xe+}+{Xe}>{Thruster0_Xe+}+{Xe}.
Ionisation: This includes both ionization by electron impact (e.g., {Xe}+{electron}>{Xe+}+2{electron}) and photo-ionization (e.g., {Xe}+{hv}>{Xe+}+{electron}).
Recombination: An example provided is {Xe+}+{electron}>{Xe}.
Custom Reactions (Dissociation/Excitation): While “dissociation” and “excitation” are not listed as predefined keywords, the interactor uses a generic reaction syntax that allows you to define any reaction of the form: Name : N1{reactant1}+ N2{reactant2}> M1{product1}+...+{MMproductM}. This means if you define the reactants (e.g., a molecule) and the products (e.g., dissociated fragments) and provide the corresponding cross-section, you can simulate these processes.
3. Setting Cross-Sections for New Reactions
For any custom reaction like dissociation or excitation, you must define the reaction rate using a cross-section. The parameter crossSectionVolInteractX can be defined in three ways:
Constant: A single float value in m2.
Tabulated (Series): A table of cross-sections versus the impinging particle energy in eV.
External File: A dedicated ASCII file containing the energy and cross-section columns.
4. Recognized Predefined Types
If you use recognized names in your reaction definition, SPIS can automatically pull cross-sections from its material datasets if they are defined there. Recognized names include:
CEX: Charge exchange (cross-sections in the CCEX material parameter).
Ionized: Ionisation by electron impact (cross-sections in the CION material parameter).
Photo: Photo-ionisation (cross-sections in the CPHO material parameter).
Important Considerations
Trajectory-Based Calculation: Interactions can now be computed along the particle trajectory (in each mesh cell crossed), which improves accuracy for these complex reactions.
Population Requirements: For reactants to be valid, they must generally correspond to existing populations in your simulation, defined either by their chemical formula or their population name (e.g., ions1, elec1).