Comparative simulations of conceptual ion extractors for use in asymmetric inertial electrostatic confinement

Many deep space propulsion missions currently use ballistic trajectories to reach their destinations. To reduce the times of flight, electric or plasma based propulsion systems are used. While Hall Effect thrusters are the general standard for plasma propulsion, new technologies can enable shorter travel times. The Helicon Injected Inertial Plasma Electrostatic Rocket (HIIPER) is an attempt to create a new type of robust plasma propulsion solution and is the predecessor to a propulsion and power plant hybrid device, integrating two systems on a vessel to one. Using an asymmetric Inertial Electrostatic Confinement (IEC) device as the plasma accelerator stage of HIIPER, plasma must escape the IEC in order to generate thrust or collect power by means of direct energy conversion. To that end, a simulation was designed and run developing the first step of a series of simulations to characterize and rapidly develop HIIPER. This simulation is built in COMSOL Multiphysics and investigates different methods of extracting ions from an IEC using a variety of electrostatic fields at the asymmetry of the IEC to characterize which types of fields result in the highest momentum transfer. The IEC is set to an 8 kV bias with the charged elements of extractors set to 6 kV. The outer shell and exit sampling domain is set to ground potential. Ions are introduced into the IEC perpendicular to the exit channel, reflecting similar conditions in the actual HIIPER experiment. Ions are introduced at 2 eV to characterize the IEC’s performance. Seven cases are studied using conceptual and actual ion extraction and focusing devices and it is discovered that using a quadruple helix extractor, two ground helices opposite each other perpendicular to two charged helices opposite each other, produces the highest relative momentum of all the cases at 2.36 times the momentum achieved by using an asymmetric IEC without any plasma extraction device. The focusing qualities of each device and the exit velocities of the ions are also computed. With this solution, further studies in the experimental phase are possible, as well as being the first step for developing ion-electron interaction simulations, which will be used to compare and verify plasma finite element simulations also in work using COMSOL with the goal of developing simulation tools that can be used to more rapidly iterate the design and progress of HIIPER. It may also be possible to use these results in other electrostatic plasma systems where magnetic fields may be undesirable as a means of focusing and extracting plasmas