research news

accelerator physics

Accurate Simulation of Beam–Beam Interactions

J. Qiang, M. A. Furman, and R. D. Ryne, “A parallel particle-in-cell model for beam–beam interaction in high energy ring colliders,” J. Comp. Phys. 198, 278 (2004). HEP, SciDAC

Accurate simulations of the electromagnetic interaction between two beams are needed to help optimize the luminosity in high energy accelerators. While beam–beam interactions have been studied for many years, the extreme computational cost has caused most previous studies to use simplified models. Qiang et al. have developed the first fully self-consistent model of colliding beams that can simultaneously handle all of the physical processes accurately. They tested the performance of the model on several architectures and applied it to studying the flip-flop instability in an electron–positron collider.

X-Band Linear Collider R&D

Z. Li, N. T. Folwell, L. Ge, A. Guetz, V. Ivanov, M. Kowalski, L.-Q. Lee, C.-K. Ng, G. Schussman, R. Uplenchwar, M. Wolf, and K. Ko, “X-band linear collider R&D in accelerating structures through advanced computing,” Proceedings of the 9th European Particle Accelerator Conference (2004). HEP, SciDAC

A major computational effort is addressing key design issues in the high gradient accelerating structures for the proposed X-band linear collider, GLC/NLC (Global Linear Collider/Next Linear Collider). A new suite of parallel tools based on unstructured grids has been applied successfully to the design of complex cavities with high accuracy, and to realize end-to-end simulation of accelerator systems. The new simulation tools have played an important role in the R&D of X-band accelerating structures, in cell design, wakefield analysis, and dark current studies (Figure 1).

Figure 1. Evolution to steady state of surface emissions in NLC square waveguide bend at high power. The wave travels from left to right. Primary particles are red and secondaries are green.

A Multibunch Plasma Afterburner

R. Maeda, T. Katsouleas, P. Muggli, C. Joshi, W. B. Mori, and W. Quillinan, “Possibility of a multibunch plasma afterburner for linear colliders,” Phys. Rev. STAB 7, 111301 (2004). HEP, SciDAC, NSF

Recently a plasma wakefield afterburner concept was proposed for doubling the energy of a linear collider, in which single electron and positron bunches collide at the interaction point of the collider. Maeda et al. considered the possibility of extending the afterburner concept using multiple bunches. Simulation results indicated that an energy-of-collision/energy-of-linac ratio of 2.8 could be obtained with 4% energy spread and 0.29 relative luminosity by utilizing five drive bunches per accelerated bunch.

Proton Shock Acceleration

L. O. Silva, M. Marti, J. R. Davies, R. A. Fonseca, C. Ren, F. S. Tsung, and W. B. Mori, “Proton shock acceleration in laser–plasma interactions,” Phys. Rev. Lett. 92, 015002 (2004). HEP, NSF, FCT

Recent experimental results show that ultra-intense laser–solid interactions can produce proton beams, with potential applications in proton imaging and proton therapy, but there is still debate about where the protons originate and about the acceleration mechanisms. Using 1D and 2D simulations, Silva et al. have identified two acceleration mechanisms: (1) proton acceleration due to the ambipolar fields arising in the free expansion of the strongly heated electrons at the front and rear of the target, and (2) proton acceleration in a collisionless, electrostatic shock formed at the front of the target.