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

Review: A plasma can be blown off the chamber wall and expand into the beam port We expect the plasma to be of order 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

2-D Simulations Showed Confinement of Drifting, Low-  Plasmas Case 1: 10-eV, 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, cm -3 plasma,  = 0.4, v drift = 9 cm/  s

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

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.

3-D Simulation of 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

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

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

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)

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 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…