Quantitative experiments with electrons in a positively charged beam

Abstract

Intense ion beams are an extreme example of, and difficult to maintain as, a non-neutral plasma. Experiments and simulations are used to study the complex interactions between beam ions and (unwanted) electrons. Such "electron clouds" limit the performance of many accelerators. To characterize electron clouds, a number of parameters are measured including: total and local electron production and loss for each of three major sources, beam potential versus time, electron line-charge density, and gas pressure within the beam. Electron control methods include surface treatments to reduce electron and gas emission, and techniques to remove, or block, electrons from the beam. Detailed, selfconsistent simulations include beam-transport fields, and electron and gas generation and transport, to compute unexpectedly rich behavior, much of which is confirmed experimentally. For example, in a quadrupole magnetic field, ion and dense electron plasmas interact to produce multi-kV oscillations in the electron plasma and distortions of the beam velocity space distribution, without becoming homogenous or locally neutral.[159 words, ~150 allowed] 2

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

“…We have only a short experiment in which to measure electron cloud effects, so it is essential to benchmark simulations with these results, so as to validate the simulations that can then examine the effects in longer accelerators. We have shown that, with sufficient electron density, significant effects can be observed and accurately simulated with only four quadrupole magnets [6].…”

“…Observed and simulated an oscillation involving bunching of electrons in a quadrupole magnet. Obtained good agreement on the frequency, wavelength, and amplitude of the oscillations [6]. 6.…”

“…Obtained good agreement on the frequency, wavelength, and amplitude of the oscillations [6]. 6. Transported a 1 MeV, 0.18 A K+ beam through 10 electrostatic quadrupoles with little or no beam loss or degradation, even for the beam filling 60% and 80% of the electrode radius [7].…”

Heavy ion fusion science research for high energy density physics and fusion applications

“…Experiments were performed to study the matching and transport of a space-charge dominated ion beam in the solenoid transport channel shown in Figure 1, including the effects of gas and electrons on the beam. These experiments provide a basis for comparison of solenoid transport with magnetic quadrupole transport in accelerators, for application to warm-dense matter and heavy-ion fusion [10]. The beam energy and current was the same as indicated in Section 2.…”

Self-consistent 3D modeling of electron cloud dynamics and beam response

“…Copious electrons are generated by slamming the beam onto the end plate. We study electron effects in the magnetic section, which is heavily instrumented with diagnostic devices and suppressor electrodes dedicated to the various measurements of electron flux, electron energy spectrum, and gas analysis [26][27][28][29][30][31][32]. The primary electrons created at the end plate propagate upstream, entering only two quadrants of the fourth (last) magnet because of the sign of E × B.…”