Nascap-2k Self-Consistent Simulations of a VLF Plasma Antenna
We simulate the plasma response through tens of cycles of the Demonstration and Science Experiments (DSX) kilovolt near-square-wave very low frequency (VLF) (0.1-50 kHz) antenna in Medium Earth Orbit plasma with Nascap-2k. DSX is an Air Force Research Laboratory experiment that will explore the physics of electromagnetic wave injection from space transmitters, wave propagation, and wave-particle interactions in the magnetosphere. DSX will transmit and receive VLF waves and quantify their effect on the trapped electron populations in the magnetosphere. In these preflight calculations, the plasma is modeled with a hybrid particle-in-cell (PIC) approach with PIC ions and fluid barometric electron densities. The plasma response, collected ion currents, and chassis floating potential are computed self-consistently with a near-square-wave bias applied to the antennas. Particle injection and splitting are used to replenish the plasma depleted at the boundary, represent the thermal distribution, and maintain appropriately sized macroparticles. Therefore, limitation of current due to the thermal distribution of ions and the resulting angular momentum barrier is included. Above the ion plasma frequency, the plasma current lags the voltage by about 10, while below the ion plasma frequency, the current leads the voltage by about 7 . The volume ion current shows periodic launch of blocks of energetic ions radially outward.
Nascap-2k Spacecraft Charging Code Overview
Nascap-2k is a modern spacecraft charging code, replacing the older codes NASA Charging Analyzer Program for GEosynchronous Orbit (NASCAP/GEO), NASA Charging Analyzer Program for Low-Earth Orbit (NASCAP/LEO), Potentials Of Large objects in the Auroral Region (POLAR), and Dynamic Plasma Analysis Code (DynaPAC). The code builds on the physical principles, mathematical algorithms, and user experience developed over three decades of spacecraft charging research. Capabilities include surface charging in geosynchronous and interplanetary orbits, sheath, and wake structure, and current collection in low-Earth orbits, and auroral charging. External potential structure and particle trajectories are computed using a finite element method on a nested grid structure and may be visualized within the Nascap-2k interface. Space charge can be treated either analytically, self-consistently with particle trajectories, or consistent with imported plume densities. Particle-in-cell (PIC) capabilities are available to study dynamic plasma effects. Auxiliary programs to Nascap-2k include Object Toolkit (for developing spacecraft surface models) and GridTool (for constructing nested grid structures around spacecraft models). The capabilities of the code are illustrated by way of four examples: charging of a geostationary satellite, self-consistent potentials for a negative probe in a low-Earth orbit spacecraft wake, potentials associated with thruster plumes, and PIC calculations of plasma effects on a very low frequency (about 1 to 20 kHz) antenna
The REX-ISOLDE project
The Radioactive Beam Experiment REX-ISOLDE [1–3] is a pilot experiment at ISOLDE (CERN) testing the new concept of post acceleration of radioactive ion beams by using charge breeding of the ions in a high charge state ion source and the efficient acceleration of the highly charged ions in a short LINAC using modern ion accelerator structures. In order to prepare the ions for the experiments singly charged radioactive ions from the on-line mass separator ISOLDE will be cooled and bunched in a Penning trap, charge bred in an electron beam ion source (EBIS) and finally accelerated in the LINAC. The LINAC consists of a radiofrequency quadrupole (RFQ) accelerator, which accelerates the ions up to 0.3 MeV/u, an interdigital H-type (IH) structure with a final energy between 1.1 and 1.2 MeV/u and three seven gap resonators, which allow the variation of the final energy. With an energy of the radioactive beams between 0.8 MeV/u and 2.2 MeV/u a wide range of experiments in the field of nuclear spectroscopy, astrophysics and solid state physics will be addressed by REX-ISOLDE.