UMD, College Park, Maryland, USA
The University of Maryland Electron Ring (UMER) is a low-energy scaled facility for the study of intense beam dynamics, relevant to higher energy, high intensity accelerators. Many parameters crucial to understanding space charge dominated beam evolution, such as transverse emittance and longitudinal temperature, require the use of turn-by-turn interceptive diagnostics. To meet this need, we plan to implement an extraction section with a fast-pulsed electric-field kicker. This paper presents a suite of simulations used to guide the design process and predict extraction performance, using the WARP Particle-in-cell (PIC) code. Simulations in a transverse slice geometry predict beam trajectory and monitor beam evolution through extraction. After isolating a design based on centroid tracking, extraction acceptance is probed and an analysis proposed to estimate the error tolerances of the new ring elements.
UMD, College Park, Maryland, USA
Linear perturbation analysis of the RMS envelope equations predicts a frequency splitting of the transverse envelope resonances with the onset of space charge. These resonances are a potential source of beam degradation for space-charge-dominated particle accelerators and storage rings. We use WARP for both envelope code integration and particle-in-cell (PIC) simulations to predict the behavior of these resonances for an existing alternating gradient lattice storage ring. The focus of these simulations is tailored toward examining physics that is scalable to future high-intensity accelerators. This paper provides detailed simulation results and a design for an experimental demonstration at the University of Maryland Electron Ring (UMER), a high intensity 10 keV electron storage ring.
UMD, College Park, Maryland, USA
Longitudinal perturbations in intense beams can lead to instabilities or degradation of beam quality, ultimately affecting the performance of accelerators, especially near the source where space charge is important. In this experimental study, conducted on the University of Maryland Electron Ring (UMER), large-amplitude perturbations are purposefully generated and their propagation observed over a long transport length. It is found that narrow, large-amplitude perturbations on a long-pulse beam develop into Korteweg-deVries (KdV) type soliton wave trains. Each peak in the wave train has a constant width and amplitude over a long propagation distance, with the amplitude inversely proportional to the square of the width. Furthermore, two such pulses are seen to interact with each other and emerge from the collision unchanged. The experimental data is compared with the KdV model and particle-in-cell simulations with good agreement. We induce perturbations using two methods: using photoemission to perturb the density at the cathode, or using an induction cell to directly perturb particle velocities.
UMD, College Park, Maryland, USA
We have observed evidence of a multi-stream instability in a long non-relativistic space-charge dominated beam evolving with an initial non-linear distribution and zero external longitudinal containment. This type of instability can be detrimental to intense accelerators that propagate rectangular distributions, such as in a ring with single or multi-bunch injection. The longitudinal forces in these intense bunches causes the beam to expand axially; in the case of the University of Maryland Electron Ring (UMER), the initial long bunch is injected to fill a fraction of the ring, coasting beyond the point where the head and tail overlap. Adjacent filaments at that point are separated in velocity space by 2cs and approach a separation of cs. The onset of the instability has been observed to depend on the injected beam current, bunch length, and other experimental factors. Comparisons with simple analytical calculations and PIC simulations have shown good agreement in the time to onset.
