Recent developments in the 3D, electromagnetic, particle-in-cell code, QUICKSILVER

Abstract

The recently developed 3-D particle-in-cell (PIC) code QUICKSILVER1 is being used for full 3-D simulations of an applied-B ion diode. A barrel diode geometry is used; ions are accelerated radially inward from a cylindrical anode at r -R to a concentric cathode at r -Rd, while electron flow to the anode is inhibited by an externally applied magnetic field. Two major simplifications of the geometry are made for the simulations. First, since barrel diodes typically have small aspect ratios d/R << 1, we use Cartesian coordinates, with x representing the radial coordinate (diode gap), y the azimuthal coordinate, and z the diode height. Secondly, we use a uniform applied magnetic field B,. the simulations is to investigate how inhomogeneities in the y-direction (corresponding to azimuthal variations in the cylindrical system) affect the stability of the diode, since linear analysis has indicated that instabilities are possible .2The principal goal of Preliminary simulations have demonstrated a violent instability which rapidly saturates in only a few ion transit times. include 3-D particle plots, contour maps of field quantities in selected planes, and time histories of field components at various points in the diode. Near saturation of the instability, we observe the onset of several phenomena. First, we see the growth of large variations of the ion current in the y-direction. Secondly, the energy spectrum of the beam passing through the gas cell foil broadens, and the beam divergence in the y-direction also grows. Finally, we see electron loss to the anode, resulting in a diode efficiency of 85 -90%. This is very different from 2-D PIC simulations of the cross section of the diode in the x-z plane (which assume invariance in the y-direction), which run at 100% efficiency. Results of these simulations will be presented.1.

<title>Some models and codes in imaging and high-current electron optics</title>

“…We can represent a mesh design procedure as a sequence of the next steps, those are provided in iterations for every block 1. Using the grid obtained in a previous iteration to solve the equation 912(1,1) = cos jl yu(i, l)922(i, 1), i, / = 0,1; gii(,)(x + y) = 922(, )(x + y), , = (6) for the parameters a, b, c, a, , 8. Let (7) Then = a + 2a01 + 7012, = 6a + 26a1 + 7l2, 9?2 = b0 -a0i -/3/ -70i1, = b-&i-6/3l-S7il, 92 = co+2floi+70i2, 62 = 5c+ 28i+à7i2.…”

“…A good review of 2-D and 3-D applied code package have been made by Drobot [6] as well as descriptions of particular PlC codes, the QN3D [7] and the QUICKSILVER codes [8]. We mention also the object oriented code OOPIC [9], that is developping in Berkeley.…”