• D. Wang, M. Farkhondeh, C. Tschalaer, F. Wang, A. Zolfaghari, T. Zwart, J. van der Laan
  MIT, Middleton, Massachusetts
• M. Blaskiewicz, Y. Luo, L. Wang
  BNL, Upton, Long Island, New York

The eRHIC is a new generation lepton-hadron collider undergoing design studies by a collaboration of BNL, MIT, DESY and BINP. The collider complex will consist of a hadron machine that is mainly the existing RHIC with necessary upgrades, and a new lepton machine that can provide intense, highly polarized electron and positron beams at energy of 5-10 GeV. The ring-ring option of eRHIC is to build a 5-10 GeV electron ring with a injector chain. In this paper the beam lifetime of lepton beams is calculated.

• Y.Y. Lee, G.J. Mahler, W. Meng, D. Raparia, L. Wang, J. Wei
  BNL, Upton, Long Island, New York

This paper describes the simulation studies on the motions of stripped electrons generated in the injection section of the Spallation Neutron Source (SNS) accumulator ring and the effective collection mechanism. Such studies are important for high intensity machines, in order to reduce beam loss and protect other components in the vicinity. The magnetic field is applied to guide electrons to a collector, which is located at the bottom of the beam chamber. Part of the study results with and without considering the interactions between electrons and materials are presented and discussed. The final engineering design of the electron collector (catcher) is also presented and described.

• J. Wei, M. Bai, M. Blaskiewicz, P. Cameron, R. Connolly, A. Della Penna, W. Fischer, H. Huang, U. Iriso, R.C. Lee, R.J. Michnoff, V. Ptitsyn, T. Roser, T. Satogata, S. Tepikian, L. Wang, S.Y. Zhang
  BNL, Upton, Long Island, New York

Electron cloud is found to be a serious obstacle on the upgrade path of the Relativistic Heavy Ion Collider (RHIC). At twice the design number of bunches, electron-ion interactions cause significant instability, emittance growth, and beam loss along with vacuum pressure rises when the beam is accelerated across the transition.

• S.Y. Zhang, J.G. Alessi, M. Bai, M. Blaskiewicz, P. Cameron, K.A. Drees, W. Fischer, J. Gullotta, P. He, H.-C. Hseuh, H. Huang, U. Iriso, R.C. Lee, V. Litvinenko, W.W. MacKay, T. Nicoletti, B. Oerter, S. Peggs, F.C. Pilat, V. Ptitsyn, T. Roser, T. Satogata, L. Smart, L. Snydstrup, P. Thieberger, D. Trbojevic, L. Wang, J. Wei, K. Zeno
  BNL, Upton, Long Island, New York

Work performed under the auspices of the US Department of Energy.

• C.-F. Wu, S. Dong, S. Hongbing, D. Jia, H. Lin, L. Wang
  USTC/NSRL, Hefei, Anhui

Mafia code has been used to calculate the RF properties versus the geometric parameters and dielectric permittivity for the X-band (f=9.37GHz) hybrid dielectric-iris-loaded traveling accelerating structure. The simulation results show that when the range of the permittivity is about 5-9, the new structure may have lower ratio (about 1) of peak surface electric field at the iris to axial accelerating electric field by optimizing the geometric parameters, while r, Q, r/Q of the new structure being comparable to iris-loaded accelerating structure. The experimental investigations of the permittivity of the ceramics have been made at the X-band by using the cavity perturbation technique. The measured results are in good agreement with the simulation results of Microwave Studio. Furthermore, the stability of the ceramics is examined. A number of experimental results show that the certain ceramic with permittivity of 5.78 is applied to the design of the new accelerating structure.

• H. Xu, H. He, W. Li, G. Liu, L. Liu, S. Shang, B. Sun, L. Wang
  USTC/NSRL, Hefei, Anhui

• H. Zhang, L. Wang
  USTC/NSRL, Hefei, Anhui
• Y.L. Li
  DESY, Hamburg

• L. Wang, J. Wei
  BNL, Upton, Long Island, New York

Electron cloud due to beam induced multipacting is one of the main concerns for the high intensity rings because the electron multipacting becomes stronger with the increment of beam intensity. Electrons generated and accumulated inside the beam pipe form an "electron cloud" that interacts with the circulating charged particle beam. With sizeable amount of electrons, this interaction can cause beam instability, beam loss and emittance growth. At the same time, the vacuum pressure will rise due to electron desorption. This talk intends to provide an overview of the dynamics of the typical electron multipacting in various magnetic fields and mitigation measures in both long bunch and short bunch rings.

• H.-C. Hseuh, M. Blaskiewicz, P. He, Y.Y. Lee, C. Pai, D. Raparia, R.J. Todd, L. Wang, J. Wei, D. Weiss
  BNL, Upton, Long Island, New York
• S. Henderson
  ORNL, Oak Ridge, Tennessee

The inner surfaces of the 248 m SNS accumulator ring vacuum chambers are coated with ~100 nm of titanium nitride (TiN) to reduce the secondary electron yield (SEY) of the chamber walls. All the ring inner surfaces are made of stainless or inconel, except those of the injection and extraction kickers. Ceramic vacuum chambers are used for the 8 injection kickers to avoid shielding of a fast-changing kicker field and to reduce eddy current heating. The internal diameter was coated with Cu to reduce the beam coupling impedance and provide passage for beam image current, and a TiN overlayer to reduce SEY. The ferrite surfaces of the 14 extraction kicker modules were coated with TiN to reduce SEY. Customized masks were used to produce coating strips of 1 cm x 5 cm with 1 to 1.5 mm separation among the strips. The masks maximized the coated area to more than 80%, while minimizing the eddy current effect to the kicker rise time. The coating method, as well as the physical and electromagnetic properties of the coatings for both types of kickers will be summarized, with emphasis on the effect to the beam and the electron cloud buildup.

†Corresponding author email: hseuh@bnl.gov.

• H. Fukuma
  KEK, Ibaraki
• L. Wang
  BNL, Upton, Long Island, New York

• L. Wang, H.-C. Hseuh, Y.Y. Lee, D. Raparia, J. Wei
  BNL, Upton, Long Island, New York
• S.M. Cousineau, S. Henderson
  ORNL, Oak Ridge, Tennessee

The beam loss along the Spallation Neutron Source’s (SNS’s) accumulator ring is mainly located at the collimator region. From the ORBIT simulation, the peak power deposition at the three collimators is about 500, 350 and 240 W/m, respectively. Therefore, a sizeable number of electrons may be accumulated at this region due to the great beam loss. This paper simulated the electron cloud at the collimator region and the possible remedy.

• L. Wang, T.L. Houck, G.A. Westenskow
  LLNL, Livermore, California

An anode stalk support insulator in a magnetically insulated transmission line was designed and modeled. One of the important design criteria is that within space constraints, the electric field along the insulator surface has to be minimized in order to prevent a surface flashover. In order to further reduce the field on the insulator surface, metal rings between insulator layers were also specially shaped. To facilitate the design process, electric field simulations were performed to determine the maximum field stress on the insulator surfaces and the transmission line chamber.

• S. Sampayan, G.J. Caporaso, Y.-J. Chen, S.A. Hawkins, L. Holmes, J.F. McCarrick, S.D. Nelson, C. Nunnally, B.R. Poole, A. Rhodes, M. Sanders, S. Sullivan, L. Wang, J.A. Watson
  LLNL, Livermore, California

We are developing of a compact accelerator system primarily intended for pulsed radiography. Design characteristics are an 8 MeV endpoint energy, 2 kA beam current and a cell gradient of approximately 3 MV/m. Overall length of the device is below 3 m. Such compact designs have been made possible with the development of high specific energy dielectrics (> 10 J/cc), specialized transmission line designs and multi-gap laser-triggered low jitter (<1 ns) gas switches. In this geometry, the pulse forming lines, switches and insulator/beam pipe are fully integrated within each cell to form a compact stand-alone stackable unit. We detail our research and modeling to date, recent high voltage test results, and the integration concept of the cells into a radiographic system.

• L. Wang, G. Feng, W. Li, H. Xu, H. Zhang
  USTC/NSRL, Hefei, Anhui