Beam dynamics simulation of a double pass proton linear accelerator

A recirculating superconducting linear accelerator with the advantage of both straight and circular accelerator has been demonstrated with relativistic electron beams. The acceleration concept of a recirculating proton beam was recently proposed [J. Qiang, Nucl. Instrum. Methods Phys. Res., Sect. A 795, 77 (2015)] and is currently under study. In order to further support the concept, the beam dynamics study on a recirculating proton linear accelerator has to be carried out. In this paper, we study the feasibility of a two-pass recirculating proton linear accelerator through the direct numerical beam dynamics design optimization and the start-to-end simulation. This study shows that the two-pass simultaneous focusing without particle losses is attainable including fully 3D space-charge effects through the entire accelerator system.

Figure 1

Layout of the double-pass scheme.

Figure 2

Energy gain along the LINAC. Blue is the first pass and red is the second pass.

Figure 3

Separation length from a cavity entrance to the next cavity entrance.

Figure 4

rms beam envelope for the first pass using 6D waterbag initial distribution with 20 mA bunch current. Radio-frequency cavities are represented by “x” patterned boxes, and the $\mathrm{F}/\mathrm{D}$ quadrupoles are represented by up/down rods. The blue/red curves corresponds to horizontal/vertical. The dashed curve represents $\mathrm{\Delta }\epsilon /\epsilon$.

Figure 5

rms beam envelope for the second pass using 6D waterbag initial distribution with 20 mA bunch current.

Figure 6

rms beam envelope for the first pass using 6D Gaussian initial distribution with 20 mA bunch current.

Figure 7

rms beam envelope for the second pass using 6D Gaussian initial distribution with 20 mA bunch current.

Figure 8

rms beam envelope for the first pass using 6D waterbag initial distribution with 40 mA bunch current.

Figure 9

rms beam envelope for the second pass using 6D waterbag initial distribution with 40 mA bunch current.

Figure 10

rms beam envelope for the first pass using 6D Gaussian initial distribution with 40 mA bunch current.

Figure 11

rms beam envelope for the second pass using 6D Gaussian initial distribution with 40 mA bunch current.

Figure 12

rms beam envelope through the first arc with waterbag initial distribution and 20 mA bunch current. The circle patterned boxes represent the bending magnets.

Figure 13

rms beam envelope through the second arc with waterbag initial distribution and 20 mA bunch current. The downward circle patterned box represent the bending magnet of negative bending angle.

Figure 14

rms beam envelope through the first arc with waterbag initial distribution and 40 mA bunch current.

Figure 15

rms beam envelope through the second arc with waterbag initial distribution and 40 mA bunch current.

Figure 16

Field profile of rf cavity. Orange line represents the 5 cell rf cavity used for Project-X. Blue dashed line represents the single cell bunching cavity.

Figure 17

rms beam statistics from the first-pass LINAC entrance to the second-pass LINAC exit with 20 mA bunch current and a waterbag initial distribution.

Figure 18

rms beam statistics from the first-pass LINAC entrance to the second-pass LINAC exit with 20 mA bunch current and a Gaussian initial distribution.

Figure 19

rms beam statistics from the first-pass LINAC entrance to the second-pass LINAC exit for 40 mA bunch current and waterbag initial distribution.

Figure 20

rms beam statistics from the first-pass LINAC entrance to the second-pass LINAC exit for 40 mA bunch current and Gaussian initial distribution.

Figure 21

Maximum transverse radius (blue) and longitudinal (red) phase for 20 mA case with waterbag (top) and Gaussian (bottom) initial distribution.

Figure 22

Maximum transverse radius (blue) and longitudinal (red) phase for 40 mA case with waterbag (top) and Gaussian (bottom) initial distribution.