A high quality electron and pion beam for NAL

Abstract

A design for a secondary electron beam suitable for electron scattering experiments at the National Accelerator Laboratory is presented. Using standard NAL beam transport magnets it will operate at up to 300 GeV/ c with the following properties: acceptance 9.5 μsr% Δp/ p(fw), momentum bite ±2%, momentum resolution of momentum hodoscope Δp/ p=±0.30% (hw at base), final spot size ≤±3.0mm×±5.5mm(hw at base). Hodoscopes are also included for measuring the angles at which electrons pass through the experimental target with resolutions in both planes of better than ±0.1 mr. These properties are achieved by a periodic beam structure which includes correction of 2nd order aberrations by means of sextupoles. The yield of electrons is estimated to be ∽10 8/10 13 incident protons when the energy of the electrons is about one half the energy of the protons. It is emphasized that synchrotron radiation by electrons in the beam transport magnets is very significant in reducing pion contamination of the final beam spot. It is shown that superconducting magnets to enhance this effect are superfluos. Pion impurity is ≤0.01% at every energy and may be made essentially zero at energies greater than 160 GeV. The beam is designed with four focussing stages, the first two of which provide a beam spot of sufficient quality for tagged photon experiments.