Koji Takata

Simulation of Phase Modulation for Longitudinal Emittance Blow-Up in J-PARC MR

The J-PARC MR provides a coasting proton beam for nuclear physics experiments by slow extraction. The longitudinal emittance should be enlarged until the MR flat top to mitigate the microwave instability. We have investigated a Phase Modulation (PM) method[1,2,3,4] by using a High Frequency Cavity (HFC) to increase the emittance. We have performed extensive simulation studies to find the appropriate parameters of the PM through the particle tracking simulation. We found that the effective HFC frequency has linear dependence with the PM frequency as shown in Fig. 1, where the emittance is smoothly enlarged. Furthermore, we found that the required HFC voltage is inverse proportional to the square root of the duration time of the PM as shown in Fig. 2. These PM properties will be used for the design of the HFC. We describe the particle tracking simulation results of controlled emittance blow-up by the PM.

Simulation of Debunching for Slow Extraction in J-PARC MR

The J-PARC MR delivers a proton beam for nuclear physics experiments with slow extraction. The beam is debunched at flat top to obtain a coasting beam by turning off the rf voltage. The beam loading effect can disturb the uniformity of the debunching at the flat top. We describe the results of the particle tracking simulation including the beam loading effect.

Extension of napoly integral for transverse wake potentials to general axisymmetric structure

The Napoly integral for the wake potential calculations in the axisymmetric structure is a very useful method because the integration of Ez field can be confined in a finite length instead of the infinite length by deforming the integration path, which reduces CPU time for the accurate calculations. However, his original method could not be applied to the transverse wake potentials in a structure where the two beam tubes on both sides have unequal radii. In this case, the integration path needs to be a straight line and the integration stretches out to an infinite in principle. We generalize the Napoly integrals so that integrals are always confined in a finite length even when the two beam tubes have unequal radii, for both longitudinal and transverse wake potential calculations. The extended method has been successfully implemented to ABCI code.

ABCI progresses and plans: Parallel computing and transverse Shobuda-Napoly integral

In this paper, we report the recent progresses of ABCI. First, ABCI now supports parallel processing in OpenMP for a shared memory system, such as a PC with multiple CPUs or a CPU with multiple cores. Tests with a Core2Duo (two cores) show that the new ABCI is about 1.7 times faster than the non-parallelized ABCI. The new ABCI also supports the dynamic memory allocation for nearly all arrays for field calculations so that the amount of memory needed for a run is determined dynamically during runtime. A user can use any number of mesh points as far as the total allocated memory is within a physical memory of his PC. As a new and important progress of the features, the transverse extension of Napoly integral (derived by Shobuda) has been implemented: it permits calculations of wake potentials in structures extending to the inside of the beam tube radius or having unequal tube radii at the two sides not only for longitudinal but also for transverse cases, while the integration path can be confined to a finite length by having the integration contour beginning and ending on the beam tubes. The future upgrade plans will be also discussed. The new ABCI is available as a Windows stand-alone executable module so that no installation of the program is necessary.