Gas and Electron Effects on Intense, Space Charge Dominated Ion Beams in Magnetic Quadrupoles: Comparison Of Experiments and Simulations*

Accelerators for inertial fusion energy, high-energy density physics and other high intensity applications have an economic incentive to minimize the clearance between the beam edge and the aperture wall. This increases the risk from electron clouds and gas desorbed from walls. Using the High Current Experiment at LBNL, we have measured the beam (0.18 A, 1 MeV K$^{+})$ distribution upstream and downstream of a short lattice of magnetic quadrupoles where the 2rms beam size is $\ge $50{\%} of the quadrupole aperture, and the generalized perveance is $\approx $10$^{-3}$. Between magnets, the transverse beam distribution is also imaged. The beam potential is 1-2 kV, large enough to trap electrons produced by, for example, K$^{+}$ - gas collisions. The measurements are compared to WARP PIC simulations that include the self-consistent tracking of electrons and ions.