• S. Doebert, C. Adolphsen, G.B. Bowden, D.L. Burke, J. Chan, V.A. Dolgashev, J.C. Frisch, R.K. Jobe, R.M. Jones, R.E. Kirby, J.R. Lewandowski, Z. Li, D.J. McCormick, R.H. Miller, C.D. Nantista, J. Nelson, C. Pearson, M.C. Ross, D.C. Schultz, T.J. Smith, S.G. Tantawi, J.W. Wang
  SLAC, Menlo Park, California
• T.T. Arkan, C. Boffo, H. Carter, I.G. Gonin, T.K. Khabiboulline, S.C. Mishra, G. Romanov, N. Solyak
  Fermilab, Batavia, Illinois
• Y. Funahashi, H. Hayano, N. Higashi, Y. Higashi, T. Higo, H. Kawamata, T. Kume, Y. Morozumi, K. Takata, T. T. Takatomi, N. Toge, K. Ueno, Y. Watanabe
  KEK, Ibaraki

During the past five years, there has been an concerted effort at FNAL, KEK and SLAC to develop accelerator structures that meet the high gradient performance requirements for the Next Linear Collider (NLC) and Global Linear Collider (GLC) initiatives. The structure that resulted is a 60-cm-long, traveling-wave design with low group velocity (< 4% c) and a 150 degree phase advance per cell. It has an average iris size that produces an acceptable short-range wakefield in the linacs, and dipole mode damping and detuning that adequately suppresses the long-range wakefield. More than eight such structures have operated over 1000 hours at a 60 Hz pulse rate at the design gradient (65 MV/m) and pulse length (400 ns), and have reached breakdown rate levels below the limit for the linear collider. Moreover, the structures are robust in that the breakdown rates continue to decrease over time, and if the structures are briefly exposed to air, the rates recover to their low values within a few days. This paper presents a final summary of the results from this program, which effectively ended last August with the selection of ‘cold’ technology for a next generation linear collider.

• N. Barov, J.S. Kim, A.W. Weidemann
  Far-Tech, Inc., San Diego, California
• R.H. Miller, C.D. Nantista
  SLAC, Menlo Park, California

Linear colliders and FEL facilities need fast, nondestructive beam position and profile monitors to facilitate machine tune-up, and for use with feedback control. FAR-TECH, Inc. is developing a resonant cavity diagnostic to simultaneously measure the dipole, quadrupole and sextupole moments of the beam distribution. Measurements of dipole and quadrupole moments at multiple locations yield information about beam orbit and emittance. The sextupole moment can reveal information about beam asymmetry which is useful in diagnosing beam tail deflections caused by short range dipole wakefields. In addition to the resonance enhancement of a single-cell cavity, use of a multi-cell standign-wave structure further enhances signal strength and improves the resolution of the device. An estimated rms beam size resolution is sub micro-meters and beam position is sub nano-meter.

• R.M. Jones, R.H. Miller
  SLAC, Menlo Park, California

The progress of multiple bunches of charged particles down the main L-band linacs of the ILC (International Linear Collider) can be disrupted by wakefields. These wakefields correspond to the electromagnetic fields excited in the accelerating cavities and have both long-range and short-range components. Here we investigate the impact of the long-range wakefields on the trailing bunches caused by the leading bunches. In general, the dipole mode degeneracy will be removed both because of manufacturing errors and because the higher order mode couplers are dipole asymmetric and lie neither in the horizontal nor vertical plane. This creates 2 dipole eigenmodes which are rotated with respect to the horizontal and vertical axes and which may have slightly different frequencies. These eigenmodes can couple the horizontal and vertical dipole excitations. We simulate the progress of the ILC beam down the collider under the influence of these wakefields. In particular, we investigate the consequences on the final emittance dilution of the beam of coupling of the horizontal to the vertical motion of the beam.

• J.W. Wang, C. Adolphsen, V. Bharadwaj, G.B. Bowden, V.A. Dolgashev, R.M. Jones, E.N. Jongewaard, J.R. Lewandowski, Z. Li, R.H. Miller
  SLAC, Menlo Park, California

There are many challenges in the design of the normal-conducting portion of ILC positron injector system such as achieving adequate cooling with the high rf and particle loss heating, and sustaining high accelerator gradients during millisecond-long pulses in a strong magnetic field. The proposed design for the positron injector contains both standing-wave and traveling-wave L-band accelerator structures for high RF efficiency, low cost and ease of fabrication. This paper presents results from studies of particle energy deposition for both undulator based and conventional positron sources, cooling system design, accelerator structure optimization, RF pulse heating, cavity frequency stabilization, and RF feed system design.