Electron dynamics for high-intensity hollow electron beams

Abstract

Hollow Electron Lenses (HEL) will be installed at the High Luminosity Large Hadron Collider to provide a continuous and controlled depletion of beam halo particles by interaction with a superimposed hollow electron beam, of intensity as high as 5 A, and radii 1.1–2.2 mm for 7 TeV LHC operations. In this paper, issues related to the propagation of high intensity hollow electron beams are discussed and the simulations of the electron beam dynamics with feedback to the HEL design are presented. The main results are the rise of the electron beam accelerating voltage from 10 kV, as in the initial proposal, to 15 kV and the validation of the 5 T magnetic field at the main solenoids as being sufficient to guarantee a stable electron beam.

Hollow electron lenses for beam collimation at the High-Luminosity Large Hadron Collider (HL-LHC)

“…It is designed to sustain, without damage and with limited temperature increase, a continuous operation of the electron beam at 15 kV in DC mode, for a total power of 75 kW. This criterion is very pessimistic, as electron beam simulations [39] indicate that at maximum current, the electron beam energy is not expected to exceed 12 keV, for a maximum of 60 kW. Furthermore, it is planned to bias the electrodes at the entrance of the collector, to reduce the energy deposited to the collector, the secondary electron emission (therefore maximizing the electron efficiency) and the gas induced desorption (to guarantee best vacuum performance).…”

“…The initially estimated residual kick in the centre of the hollow electron beam is about 5 nrad and below 0.1 nrad in the vertical and horizontal planes, respectively [56], with the current HL-LHC HEL design. This is prior to a final optimization of the magnetic system design [39]. Hence, only the vertical residual kick was simulated, being the dominant contribution.…”

Nonuniform electron distributions in a solenoidal ioniser

“…The diocotron instability growth rate can be minimised by using an electron beam that extends across the entire liner, rather than using a hollow loop for the filament. The hollow electron beam had previously been selected to allow atomic and molecular beams to pass directly into the ioniser, however the use of an off-axis electron source has been demonstrated and would avoid any obstructions [36].…”