1. Kinetic Modeling of the Sheath Scale in the Lunar Plasma Environment Tech-X Corporation 5621 Arapahoe Ave., Boulder, CO 80303 http://www.txcorp.com Peter Messmer*, Keegan Amyx, Peter Stoltz, Andrew Poppe, Mihay Horanyi, Scott Robertson, Zoltan Sternovsky messmer@txcorp.com CCLDAS All Hands Meeting, Boulder, CO, July 10, 2009

2. VORPAL - A Plasma Modeling Framework Original target applications: Laser Wakefield Acceleration PIC, Fluid, Hybird Electrostatic, EM Multi-Dimensional (N=1,2,3) Fully parallel Scaling for > 32,000 PEs Flexible domain decomposition Broad range of physics features : -Complex geometries -Ionization, recombination, CEX physics -Field ionization http://www.txcorp.com/products/VORPAL

3. Code/setup Validation with 1D Photoelectron Sheath R. Garad & J Tunaley, JGR 76(10), 2498, 1971 A. Poppe & M. Horanyi, WPDP, 2009 2D ES simulation, Y periodic, 200 x 10 cells   dx = 10 50 particles per cell nominal Simulation Garad&Tunaley Monoenergetic Maxwellian

4. 2D Monoenergetic Sheath 2D ES simulation, left wall = 0V 200 x 100 cells Electrons, Protons Monoenergetic,V 0 = 200 eV (!) electrons protons  

5. Scenario with Surface Charging Surface-Charging No surface charging (just for comparison)

6. 2D Thermal Sheath with Surface Charging 2D ES simulation, left wall = 0V 200 x 100 cells Electrons Heavy Protons, Heavy electrons (m/m 0 = 5000) Vsig = 3eV, V therm = 3 eV Electron impact creates “heavy electrons” Electrons get absorbed

7. Electric field mainly due to positive charge of emitting region Charging Non Charging

8. “Heavy Electrons” follow the electric field lines 2D ES simulation, left wall = 0V 200 x 100 cells Electrons Heavy Protons, Heavy electrons (m/m 0 = 5000) Vsig = 3eV, V therm = 3 eV

9. Initial 3D simulations 3D ES simulation, bottom wall = 0V 10 x 100 x 100 cells Electrons Protons, Heavy electrons (m/m 0 = 5000) Vsig = 3eV, V therm = 3 eV Charging of surface No charging of surface

10. Summary / Conclusions / Future work  Presented VORPAL simulations of plasma sheath  Validated with kinetic theory for 1D sheath  Presented 2D simulation with/without surface charging  “heavy electrons” move in electrostatic field, follow (curved) field lines Future work:  Convergence studies, more realistic parameters  Inclusion of solar wind  Time dependent problems, angular dependency of photo-currents  Complex geometries (crater, habitat, instrument)  3D Work supported by CCLDAS and Tech-X Corp.