Accelerator Physics
Optimizing luminosity in high-energy colliders
The beam-beam interaction puts a strong limit on the performance of most high-energy colliders. The electromagnetic fields generated by one beam focus or defocus the beam moving in the opposite direction, reducing luminosity and sometimes causing beam blowup. Qiang et al. performed the first-ever million-particle, million-turn, “strong-strong” (i.e., self-consistent) simulation of colliding beams (in the Large Hadron Collider). Instead of a conventional particle-mesh code, they used a method in which the computational mesh covers only the largest of the two colliding beams, allowing them to study long-range parasitic collisions accurately and efficiently.
J. Qiang, M. Furman, and R. Ryne, “Strong-strong beam-beam simulation using a Green function approach,” Phys. Rev. ST AB 5, 104402 (2002). HEP, SciDAC
Electron clouds and particle accelerator performance
Electron clouds have been shown to be associated with limitations in particle-accelerator performance in several of the world’s largest circular proton and positron machines. Rumolo et al. have studied the interaction between a low-density electron cloud in a circular particle accelerator with a circulating charged particle beam. The particle beam’s space charge attracts the cloud, enhancing the cloud density near the beam axis (Figure 1). This enhanced charge and the image charges associated with the cloud charge and the conducting wall of the accelerator may have important consequences for the dynamics of the beam propagation.
G. Rumolo, A. Z. Ghalam, T. Katsouleas, C. K. Huang, V. K. Decyk, C. Ren, W. B. Mori, F. Zimmermann, and F. Ruggiero, “Electron cloud effects on beam evolution in a circular accelerator,” Phys. Rev. ST AB 6, 081002 (2003). HEP, SciDAC, NSF
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Figure 1 |
Developing future plasma-based accelerators
High-gradient acceleration of both positrons and electrons is a prerequisite condition to the successful development of a plasma-based linear collider. Blue et al. provided simulation support for the E-162 Plasma Wakefield Accelerator experiment at the Stanford Linear Accelerator Center. This work was successful at demonstrating the high-gradient acceleration of positrons in a meter-scale plasma for the first time. Excellent agreement was found between the experimental results and those from 3D particle-in-cell simulations for both energy gain and loss.
B. E. Blue, C. E. Clayton, C. L. O'Connell, F.-J. Decker, M. J. Hogan, C. Huang, R. Iverson, C. Joshi, T. C. Katsouleas, W. Lu, K. A. Marsh, W. B. Mori, P. Muggli, R. Siemann, and D. Walz, “Plasma-wakefield acceleration of an intense positron beam,” Phys. Rev. Lett. 90, 214801 (2003). HEP, SciDAC, NSF
Electron cloud development in proton storage rings
Pivi and Furman have simulated electron cloud development in the Proton Storage Ring (PSR) at Los Alamos National Laboratory and the Spallation Neutron Source (SNS) under construction at Oak Ridge National Laboratory. Their simulation provides a detailed description of the secondary electron emission process, including a refined model for the emitted energy spectrum and for the three main components of the secondary yield, namely, the true secondary, rediffused, and backscattered components.
M. T. F. Pivi and M. A. Furman, “Electron cloud development
in the Proton Storage Ring and in the Spallation Neutron Source,” Phys.
Rev. ST AB 6, 034201 (2003). HEP, SNS