Performance of the correlated painting based on the mechanical structure of the anticorrelated painting scheme

The China Spallation Neutron Source (CSNS) accelerator consists of an 80 MeV $H^{-}$ Linac and a 1.6-GeV rapid cycling synchrotron (RCS). The painting scheme is one of the most important factors for the control of low beam loss at high beam power. In the painting injection of the CSNS/RCS, position scanning is used in both horizontal and vertical planes, and the anticorrelated painting is the design scheme. By using the anticorrelated painting, the beam power has successfully reached 50 kW. However, some problems have been found in the higher power beam commissioning, for instance, too large beam size after painting, nonuniform beam distribution, large transverse coupling effect, and so on, resulting in additional beam loss and making it difficult to satisfy the requirements of a high-power user mode. In order to solve these problems, flexibility in the CSNS design has been exploited to implement the correlated painting by using the rising current curve of the pulse power supply. The effectiveness of the new method has been verified in the simulation and beam commissioning, which can well control the full beam emittance and improve the beam distribution. By using the new method, the beam power on the target has successfully risen from 50 kW to the design value of 100 kW. Under the mechanical structure of the anticorrelated painting scheme where the position scanning is used in both horizontal and vertical planes, the correlated painting has been successfully achieved by using the rising current curve.

Figure 1

The schematic diagram of the injection system.

Figure 2

Schematic drawing of the position variation of the circulating beam emittance ellipse in the anticorrelated painting process.

Figure 3

Simulation results of the circulating beam distribution at the magnet BH3 in the initial stage of injection for the anticorrelated painting.

Figure 4

Schematic drawing of the position variation of the circulating beam emittance ellipse in the correlated painting process.

Figure 5

Distance changing between the circulating beam and vacuum chamber for different vertical painting curves. Since the vertical painting bump is in the negative direction, the pulse current and bump position differ by a negative sign. Therefore, the $Y$-axis is rotated 180° to avoid misunderstanding.

Figure 6

BH and BV pulse current curves for the anticorrelated painting (a) and correlated painting (b).

Figure 7

Comparison of the input and output pulse current curves for the correlated painting method.

Figure 8

Comparison of the transverse beam distributions for the correlated and anticorrelated painting in the simulation under the same conditions. Subgraph (a): horizontal beam distributions; subgraph (b): vertical beam distributions.

Figure 9

Comparison of the beam loss during the 200 turns injection and 2000 turns acceleration processes for the two painting methods in the simulation under the same conditions.

Figure 10

Comparison of the simulation results of the transverse coupling effects for the correlated and anticorrelated painting. Subgraphs (a), (b), (e), and (f): the horizontal painting range was changed with the vertical painting range fixed to 17.5 mm; subgraphs (c), (d), (g), and (h): the vertical painting range was changed with the horizontal painting range fixed to 27 mm.

Figure 11

Comparison of the transverse beam distributions for the correlated and anticorrelated painting in the beam commissioning. Subgraph (a): horizontal beam distributions; subgraph (b): vertical beam distributions.

Figure 12

The measured beam loss for the correlated and anticorrelated painting during the injection.

Figure 13

The transverse coupling effects for the correlated and anticorrelated painting measured in the beam commissioning. Subgraphs (a), (b), (e), and (f): the horizontal painting range was changed with the vertical painting range fixed to 17.5 mm; subgraphs (c), (d), (g), and (h): the vertical painting range was changed with the horizontal painting range fixed to 27 mm.