Beam Emittance Measurements for the Low-Energy Demonstration Accelerator Radio-Frequency Quadrupole

TL;DR

This paper reports on measurements of beam emittance in the LEDA RFQ, a continuous-wave proton accelerator, using wire scanners and quadrupole gradient variation to analyze beam properties at different currents.

Contribution

It introduces a method for inferring beam emittance by measuring beam profiles at a single location while varying quadrupole gradients in the HEBT.

Findings

Emittance measurements across 25-100 mA currents.

Beam profile changes with quadrupole gradient.

Identification of transverse waist in beam profile.

Abstract

The Low-Energy Demonstration Accelerator (LEDA) radio-frequency quadrupole (RFQ) is a 100% duty factor (CW) linac that delivers >100 mA of H+ beam at 6.7 MeV. The 8-m-long, 350-MHz RFQ structure accelerates a dc, 75-keV, 110-mA H+ beam from the LEDA injector with >90% transmission. LEDA [1,2] consists of a 75-keV proton injector, 6.7-MeV, 350-MHz CW RFQ with associated high-power and low-level rf systems, a short high-energy beam transport (HEBT) and high-power (670-kW CW) beam stop. The beam emittance is inferred from wire scanner measurements of the beam profile at a single location in the HEBT. The beam profile is measured as a function of the magnetic field gradient in one of the HEBT quadrupoles. As the gradient is changed the spot size passes through a transverse waist. Measurements are presented for peak currents between 25 and 100 mA.