Collimation with Hollow Electron Beams

A novel concept of controlled halo removal for intense high-energy beams in storage rings and colliders is presented. It is based on the interaction of the circulating beam with a 5-keV, magnetically confined, pulsed hollow electron beam in a 2-m-long section of the ring. The electrons enclose the circulating beam, kicking halo particles transversely and leaving the beam core unperturbed. By acting as a tunable diffusion enhancer and not as a hard aperture limitation, the hollow electron beam collimator extends conventional collimation systems beyond the intensity limits imposed by tolerable losses. The concept was tested experimentally at the Fermilab Tevatron proton-antiproton collider. The first results on the collimation of 980-GeV antiprotons are presented.

Figure 1

Layout of the beams in the Tevatron.

Figure 2

Hollow electron gun: (a) top view; (b) side view; (c) measured current density profile; (d) measured charge density $\rho$ and calculated radial electric field $E_r$.

Figure 3

Relative intensity and luminosity of the affected bunch train, for different transverse sizes of the electron beam. The light gray trace is the electron beam current (right axis).

Figure 4

Emittance evolution of the affected bunch train. The light gray trace is the electron beam current (same experiment as Fig. 3).

Figure 5

Results of a collimator scan: (top) relative intensity $n$ of the affected bunch train and collimator distance from the beam axis vs time; (bottom) relative steady-state decay rate $\dot{n}$ of the affected bunch train vs collimator position, for each data set (letters $A$ through $J$).