Abstract
The longitudinal acceptance of the Spallation Neutron Source superconducting linac is computed with a longitudinal model. A beam current monitor and beam loss monitors are utilized in a new beam acceptance measurement technique, and the measured results show close agreement with the model. Based on the simulations and on the measurements of the superconducting linac acceptance, we developed a novel method to measure beam bunch shape, beam energy profile, and the longitudinal emittance at the entrance of the linac. The experimental measurements reveal that a large longitudinal beam halo exists in the injected beam to the superconducting linac, and the longitudinal rms emittance is approximately twice that of the nominal design. The simple measurement method is applicable to other superconducting linacs.
Highlights
The Spallation Neutron Source (SNS) is a short-pulse neutron scattering facility at Oak Ridge National Laboratory
The beam acceptance measured with the beam current monitor (BCM) and beam loss monitors (BLMs) is close to the model prediction
The SNS beam loss monitor (BLM) is a modified version of the well-known FNAL ion chamber, and there are 74 BLMs installed in the Superconducting Linac (SCL)
Summary
The Spallation Neutron Source (SNS) is a short-pulse neutron scattering facility at Oak Ridge National Laboratory. The accelerator complex consists of a 2.5 MeV HÀ injector, a 1 GeV linear accelerator, an accumulator ring, and associated beam transport lines. Most of the beam energy comes from a Superconducting Linac (SCL) of approximately 160 meters long—from 186 MeV to 1 GeV. Beam is accumulated in the ring over 1060 turns reaching an intensity of 1:5 Â 1014 protons per pulse, extracted and transported to a liquid-mercury target for neutron production [1]. Because of the rf superconductivity technology and the high intensity beams, conventional beam interception diagnostic devices could contaminate the cavity delicate surfaces, and are not acceptable in the SCL. The SCL acceptance is measured using beam transmission determined by nonintercepting devices—a beam current monitor (BCM) and the beam loss monitors (BLMs), in conjunction with phase and energy scanning techniques. The beam acceptance measured with the BCM and BLMs is close to the model prediction
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