Self-consistent simulations of heavy-ion beams interacting with electron-clouds

Abstract

Electron-clouds and rising desorbed gas pressure limit the performance of many existing accelerators and, potentially, that of future accelerators including heavy-ion warm-dense matter and fusion drivers. For the latter, self-consistent simulation of the interaction of the heavy-ion beam(s) with the electron-cloud is necessary. To this end, we have merged the two codes WARP (HIF accelerator code) and POSINST (high-energy e-cloud build-up code), and added modules for neutral gas molecule generation, gas ionization, and electron tracking algorithms in magnetic fields with large time steps. The new tool is being benchmarked against the High-Current Experiment (HCX) and good agreement has been achieved. The simulations have also aided diagnostic interpretation and have identified unanticipated physical processes. We present the "roadmap" describing the different modules and their interconnections, along with detailed comparisons with HCX experimental results, as well as a preliminary application to the modeling of electron clouds in the Large Hadron Collider.

Overview of theory and simulations in the Heavy Ion Fusion Science Virtual National Laboratory

“…Experiments in the VNL have targeted this area as a major element of a campaign to understand the highbrightness transport of beams [22,23]. Much recent effort has been devoted to making the simulation tools more capable of supporting these efforts.…”

“…Multi-species interaction models: A comprehensive set of models governing the interaction of positively-charged beams with stray particles was developed and implemented in WARP [22,23,26,27]. Secondary electron emission induced by ions, neutral emission, and other processes are included.…”

“…These capabilities have been applied to experiments on HCX [22,23,30], wherein the ion beam is directed onto a plate at the end of the system, generating copious primary electrons, which then generate secondaries. A set of control electrodes set to potentials that are varied from shot to shot offers a variety of operating conditions.…”

Critical issues for high-brightness heavy-ion beams --prioritized

“…Multiple developments that increase code operating speeds by several orders of magnitude, making it feasible to perform 3-D simulations with the added effects above. Speed enhancements include parallel operation, adaptive mesh refinement [12], particle timestep subcycling [13], and a drift-Lorentz electron mover tracking charged particles in magnetic fields using large time steps [14,15]. For relativistic interactions of beams, a further few orders of magnitude reduction in computational time is possible, using our recent discovery of a preferred frame of reference [16].…”

“…The generation and transport of all species (beam particles, ions, electrons, and gas molecules) is performed in a self-consistent manner (the electron, ion and gas distributions can also be prescribed -if needed-for special study or convenience). The code runs in parallel and benefits from adaptive mesh refinement [12], particle timestep sub-cycling [13], a new "drift-Lorentz" particle mover for tracking charged particles in magnetic fields using large time steps [14,15], and for relativistic beams, the recent discovery of a preferred frame of reference [16] that reduces computation time by a factor of 2γ 2 where γ = (1-v 2 /c 2 ) -0.5 . These advanced numerical techniques allow for significant speed-up in computing time (orders of magnitude) relative to brute-force integration techniques, allowing for self-consistent simulations of electron-cloud effects and beam dynamics, which were out of reach with previously available tools.…”