1. Diversion of Plasma in Beam Port with a Vertical Magnetic Field: 3-D Simulations D. V. Rose, D. R. Welch, and S. S. Yu Presented at the ARIES Project Meeting July 1-2, 2002 Research supported by the DOE through PPPL and the HIF VNL

2. Review: A plasma can be blown off the chamber wall and expand into the beam port We expect the plasma to be of order 10 14 cm -3 density and 10 eV Neutral fraction may be quite small for these conditions Plasma can be diverted to port wall with a vertical or dipole magnetic field B Plasma from chamber Beam Port

3. 2-D Simulations Showed Confinement of Drifting, Low-  Plasmas Case 1: 10-eV, 10 14 cm -3 plasma,  = 8  nkT/B 2 = 0.04, B y = 1 kG, v drift = 3 – 9 cm/  s, mean ion cyclotron radius  c = m i v i c/eB ~ 3 mm (protons) Case 2: 100 eV, 10 14 cm -3 plasma,  = 0.4, v drift = 9 cm/  s

4. Review: 100-eV plasma with v = 9 cm/  s; 2-D results show plasma ion stagnation at ~15.5 cm

5. Long wavelength, low-  plasma penetration model 1 1) W. Peter, A. Ron, and N. Rostoker, Phys. Fluids 26, 2276 (1983) 2) L. Lindberg, Astrophys. Space Sci. 55, 203 (1978). Initial plasma penetration distance is found to be: But instability of boundary layer allows further penetration (flute- type instability). Growth rate is relatively fast [O(10 ns)], with “finger” sizes 2 < r Li /4 ~ 0.25 cm. plasmavacuum dE x x z ByBy + + + + + + - - - - - - - - Boundary interface wavelengths and “finger” widths not adequately resolved in initial simulations.

6. 3-D Simulation of 10 14 cm -3, 100 eV, v drift = 9cm/  s case: 3-D simulations use same EM implicit field solver as 2-D case. Initial simulations use smaller beam port radius (2.5 cm) for computational efficiency Same plasma parameters as 2-D case. Plasma 30 cm 15 cm; B y0 =1 kG 5 cm 10 cm vdvd 15 cm; B y0 =0 ByBy ByBy ByBy ByBy ByBy

7. Test Case: Ion expansion without applied B y -field… 0 ns 50 ns 100 ns 150 ns 200 ns 250 ns

8. Greater ion expansion into applied B-field is observed in 3D case. 0 ns 50 ns 1 kG applied B y field V drift = 9 cm/  s T e =T i = 100 eV Plasma B y0 = 0 Vacuum B y0 = 1 kG 200 ns 100 ns 150 ns

9. Plasma penetration is different for 2-D and 3-D cases: 3-D 2-D 25 ns 50 ns 100 and 250 ns At (x,y) = (0,0)

10. Conclusions 2D and 3D calculations predict expected plasmas diverted by a moderate strength magnetic field (1 kG) [worst case?] 2D results suggested that B-field region need extend no further than a few cm (beam deflection is small of order 10 -5 radian), but 3D results suggest that this region needs to be at least twice as long. 3D results illustrate possibility of deeper penetration by a “few” particles – larger-scale, higher fidelity simulations are required to address this. Laboratory testing/benchmarking of diverter plasma would be “relatively” easy – i.e. cable gun plasmas of a few eV and controllable densities could be injected into a dipole B-field inside a pipe…