• L. Laurent, V.A. Dolgashev, C.D. Nantista, S.G. Tantawi
  SLAC, Menlo Park, California
• M. Aicheler, S.T. Heikkinen, W. Wuensch
  CERN, Geneva
• Y. Higashi
  KEK, Ibaraki

Cavity pulsed heating experiments have been conducted at SLAC National Accelerator Laboratory in collaboration with CERN and KEK. These experiments were designed to gain a better understanding on the impact of high power pulsed magnetic fields on copper and copper alloys. The cavity is a one port hemispherical cavity that operates in the TE013-like mode at 11.424 GHz. The test samples are mounted onto the endcap of the cavity. By using the TE013 mode, pulsed heating information can be analyzed that is based only on the impact of the peak magnetic field which is much bigger in value on the test sample than on any other place in the cavity. This work has shown that pulsed heating surface damage on copper and copper alloys is dependent on processing time, pulsed heating temperature, material hardness, and crystallographic orientation and that initial stresses occur along grain boundaries which can be followed by pitting or by transgranular microfractures that propagate and terminate on grain boundaries. The level of pulsed heating surface damage was found to be less on the smaller grain samples. This is likely due to grain boundaries limiting the propagation of fatigue cracks.

• J. Neilson, V.A. Dolgashev, S.G. Tantawi
  SLAC, Menlo Park, California

Typical surface damage in travelling wave accelerator structures occurs on the high field region of the iris. As the damage accumulates the coupling between cavities is affected resulting in changes in the phase shift between cells. This issue can be reduced by use of SW cells that are fed in parallel. RF breakdown is contained to the cell where it originates and the available electromagnetic energy for a given gradient is minimized by the parallel feed. Several schemes[1] have been proposed for parallel fed SW structures. Some of the proposed designs fed several cells from each arm, which reduces the advantage of localizing a RF breakdown to an individual cavity. In addition they use a standing wave in the feed arms which allows coupling between cells. We are proposing a somewhat more complex approach using a directional coupler on each cell and serpentine waveguide connection between couplers. This design approach isolates the cells and gives an individual rf feed to each cell resulting in the maximum increase in the operational robustness of the accelerator structure.

1. O. N. Brezhnev, P. V. Logatchev, V. M. Pavlov, O. V. Pirogov, S. V. Shiyankov,' Parallel-Coupled Accelerating Structures', Proceedings of LINAC 2002, Gyeongju, Korea, pg 215-217

• F.V. Hartemann, F. Albert, S.G. Anderson, C.P.J. Barty, A.J. Bayramian, R.E. Bonnanno, T.S. Chu, R.R. Cross, C.A. Ebbers, D.J. Gibson, T.L. Houck, R.A. Marsh, D.P. McNabb, M. J. Messerly, R.D. Scarpetti, M. Shverdin, C. Siders, S.S.Q. Wu
  LLNL, Livermore, California
• C. Adolphsen, A.E. Candel, E.N. Jongewaard, Z. Li, C. Limborg-Deprey, T.O. Raubenheimer, S.G. Tantawi, A.E. Vlieks, F. Wang, J.W. Wang, F. Zhou
  SLAC, Menlo Park, California
• V.A. Semenov
  UCB, Berkeley, California

Continued progress in accelerator physics and laser technology have enabled the development of a new class of tunable x-ray and gamma-ray light sources based on Compton scattering between a high-brightness, relativistic electron beam and a high intensity laser pulse produced via chirped-pulse amplification (CPA). A precision, tunable, monochromatic (< 0.4% rms spectral width) source driven by a compact, high-gradient X-band linac designed in collaboration with SLAC is under construction at LLNL. High-brightness (250 pC, 3.5 ps, 0.4 mm.mrad), relativistic electron bunches will interact with a Joule-class, 10 ps, diode-pumped CPA laser pulse to generate tunable γ-rays in the 0.5-2.5 MeV photon energy range. This gamma-ray source will be used to excite nuclear resonance fluorescence in various isotopes. Fields of endeavor include homeland security, stockpile science and surveillance, nuclear fuel assay, and waste imaging and assay. The source design, key parameters, and current status will be discussed, along with important applications, including nuclear resonance fluorescence and high precision medical imaging.

• T. Tajima, L. Civale, T. Doi, G.V. Eremeev, N.F. Haberkorn, M. Hawley, A. Matsumoto, R.K. Schulze, A.T. Zocco
  LANL, Los Alamos, New Mexico
• V.A. Dolgashev, J. Guo, D.W. Martin, S.G. Tantawi, C. Yoneda
  SLAC, Menlo Park, California
• B. Moeckly
  STI, Santa Barbara, California

In order to overcome the theoretical limit of ~200 mT peak surface magnetic field for niobium SRF cavities, an idea of coating multi-layer thin film superconductors separated with thin dielectric layers has been suggested. We are testing MgB2, NbN and NbC as candidates for the realization of this idea. The results of surface characterization, Auger depth profile, DC magnetization measurements with SQUID, low- and high-field measurements with a TE013-like mode copper cavity coupled with a 11.4 GHz short-pulse Klystron will be presented.