  The power of the proton beam of a high-power spallation neutron source
generally ranges from 100 kW to several MW. The distribution of the power
density of the beam on the target is critical for the stable operation of the
high-power spallation target. This study proposes a beam monitoring method that
involves restoring the image of a high-power proton beam spot on a target based
on the principle of pinhole imaging by using the back-streaming of secondary
neutrons from the spallation target. Fast and indirect imaging of the beam spot
can be achieved at a distance of tens of meters from the target. The proposed
method of beam monitoring can flexibly adjust the size of the pinhole and the
measurement distance to control the intensity of flux of the secondary neutrons
according to the demands of the detection system, which is far from the
high-radiation target area. The results of simulations showed that the proposed
method can be used to restore the beam spot of the incident proton by using the
point response function and images of the secondary neutrons. Based on the
target and the Back-n beamline in the CSNS, the effectiveness of this method
has also been confirmed.
