Speaker
Description
Introduction
A fourth-generation synchrotron light source: NanoTerasu consists of a 3-GeV linear accelerator (linac) and a storage ring equipped with insertion devices. Since the stored beam current in the storage ring decays due to beam lifetime effects caused by residual gas scattering and Touschek scattering, electrons are continuously injected from the linac in top-up mode to maintain the stored current at 400 mA. In the linac, a certain fraction of the electron beam is continuously lost, generating secondary radiation such as neutrons and bremsstrahlung inside the accelerator tunnel. To improve the beam transport efficiency of the linac and characterize the secondary radiation source, we measured the secondary neutron dose distribution in the linac tunnel using passive dosimeters and assessed the longitudinal beam-loss profile.
Methods
To measure the neutron dose distribution in the linac tunnel, passive dosimeters (Nagase Luminescence Badges) were installed at 3-m intervals on the inner wall of the tunnel at beamline height for more than one month of beam operation. The beam-loss distribution along the beam direction was evaluated by fitting the measured dose distribution at each section with a line-source model.
Results
The measured neutron dose distribution can be reproduced by modeling multiple line sources distributed along the linac. The relative beam-loss magnitude at each section of the linac was determined.
Conclusions
The longitudinal beam-loss distribution was evaluated by fitting the neutron dose distribution measured with passive dosimeters to a multi-line-source model. The beam-loss profile derived using this approach will contribute to improving the beam transport efficiency of the linac.