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Development of Control Technology for High-Intensity Proton Beams at J-PARC
—Contributing to Safer Facility Operation for Target Damage Mitigation with a Beam Shaping Method using Non-Linear Optics—

At the neutron source facility of J-PARC, the production target's steel vessel is exposed to high-intensity proton beams leading to damage. To suppress the damage, it is necessary to reduce the current density of the proton beam. It was, however, difficult to reduce the density because the Gaussian beam shape being similar to the bell shape cannot be changed with conventional beam tuning technology based on linear optics.

It has long been known that an octupole electromagnet can be used to shape the beam into a flat shape and reduce the current density. However, it was difficult to apply this shaping method to practical use for control of the high-intensity beam because the adjusting parameters such as the magnetic field were complicated.

With detailed analysis of the beam shaping based on non-linear optics, it was clarified that only two parameters characterize the beam shape, and beam shaping has become easier. With the present beam shaping method, the beam shape was found to be controlled as expected and reduced the current density of the beam by 30%.

With the development of this beam shaping technology, J-PARC's neutron source facility has become able to perform more stable and high-intensity beam operations. This result is an important technology for controlling target damage in future high-intensity accelerator facilities.

Comparison of the beam shapes (beam profiles) calculated (line) and observed (dot) results right before the neutron production target
(a) Conventional beam shaping method (conventional linear optics)
(b) New beam shaping method (non-linear optics)
The beam profiles in the horizontal and vertical planes are shown at the top and bottom, respectively.

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