• P.K. Ambattu, G. Burt, M.I. Tahir
  Cockcroft Institute, Lancaster University, Lancaster
• P.A. Corlett, P.A. McIntosh, A.J. Moss
  STFC/DL/ASTeC, Daresbury, Warrington, Cheshire

Compact X-ray sources are integral parts of systems used in medical, industrial and security applications. The X-ray dose rate for a particular application mainly depends on the energy and current of the beam used to hit the target, usually made of tungsten. In applications that need higher penetration (100s of mm in steel), the beam energy needed is in the range of 1-5 MeV which can only be obtained using an RF linear accelerator. In order to reduce the size of the linac, higher RF frequencies (X-band) should be used while in order to reduce the overall bulk, RF focusing is employed instead of solenoidal focusing. Thus the main attraction of an X-band linac compared to a lower frequency version is the amount of lead required for shielding the system, and hence its weight. For capturing and bunching the low energy dc beam, a bunching section is needed in front of the main linac. The bunching cavity can either be a part of the main linac cavity or an independently powered section which can be used for certain specific applications as a shorter 1 MeV linac. In this paper, the design and simulations of an X-band buncher to be suitable for compact X-ray sources is presented.

• K. Yokoyama, S. Fukuda, Y. Higashi, T. Higo, S. Matsumoto
  KEK, Ibaraki
• S. Calatroni, R. Santiago Kern, W. Wuensch
  CERN, Geneva
• C. Pasquino
  Politecnico/Milano, Milano

To investigate the breakdown characteristic related to the differences in purity and hardness, four types of oxygen-free copper (OFC) materials, usual class 1 OFC with/without diamond finish, 7-nine large-grain copper and 6-nine hot-isotropic-pressed copper, were tested with the DC spark test system at CERN. Measurements of beta, breakdown fields and breakdown probability are discussed followed by the surface inspection mostly with SEM on the tested materials.

• T. Sakai, M. Ikeda, S. Ohsawa, N. Sakabe, T. Sugimura
  KEK, Ibaraki

A new type of rotating anticathode X-ray generator has been developed, in which the electron beam up to 120keV irradiates the inner surface of a U-shaped Cu anticathode. A high-flux electron beam is obtained by optimizing the geometry of the combined function bending magnet. In order to minimize the sizes of the X-ray source, the electron beam is focused in a short distance by the combined function bending magnet, of which geometrical shape was determined by simulation with the codes of Opera-3D, General Particle Tracer (GPT) and CST STUDIO. The result of simulation clearly shows that the role of combined function in the bending magnet and the steering magnet is important to focus the beam in small sizes. FWHM sizes of the beam were predicted by simulation to be 0.45mm (horizontal) and 0.05mm (vertical) for a beam of 120keV and 75mA of which effective brilliance is about 500kW/mm2 with the supposition of a two-dimensional Gaussian distribution. The beam focus sizes on the target will be verified in the experiments by using the high-voltage power supply for the X-ray generator improved from 60kV to 120kV and 75mA.

• X. Yin, S. Fu, K.Y. Gong, L. Liu, J. Peng, H. Song, Y.C. Xiao
  IHEP Beijing, Beijing

The CSNS is a spallation neutron research facility being built at Dongguan in Guangdong Province [1]. The 324MHz Alvarez-type Drift Tube Linac (DTL) will be used to accelerate the H^- ion beam from 3 to 80.0 MeV with peak current 15mA. The R&D of a prototype structure at the low energy section of DTL is taking place at IHEP. The first unit tank 2.8m in length for the energy range from 3 to 8.88 MeV and 28 drift tubes containing electromagnetic quadrupoles are developed. This paper introduces the R&D status of the tank and 28 drift tubes. The measurement results of the focusing quadrupoles are also presented.

• X. Yin, S. Fu, K.Y. Gong, A.H. Li, H.C. Liu, J. Peng, Z.R. Sun, Y.C. Xiao
  IHEP Beijing, Beijing

In the China Spallation Neutron Source project [1], the 324HMz Alvarez-type DTL will be used to accelerate the H^- ion beam from 3 to 80.0MeV. The DTL linac has been designed as four tanks and the electromagnetic quadrupoles will be used for the transverse focusing inside the drift tubes. The geometries of the DTL cells were optimized by using SUPERFISH and the beam dynamics simulation was performed with PARMILA code. In this paper both the physical design and the engineering designs are presented.

• S. Ramberger, P. Bourquin, Y. Cuvet, A. Dallocchio, G. De Michele, F. Gerigk, J.-M. Giguet, J.-B. Lallement, A.M. Lombardi, E. Sargsyan, M. Vretenar
  CERN, Geneva

The design of the Drift Tube Linac (DTL) for the new linear accelerator Linac4 at CERN has been made ready for production: H–ion beams of up to 40 mA average pulse current are to be accelerated from 3 to 50 MeV by three RF tanks operating at 352.2 MHz and at duty cycles of up to 10%. In order to provide a margin for longitudinal matching from the chopper line, the longitudinal acceptance has been increased. The synchronous phase starts at -35° in tank1 and ramps linearly to -24° over the tank while it went from -30° to -20° in the previous design. The accelerating gradient has been lowered to 3.1 MV/m in Tank1 and increased to 3.3 MV/m in Tank2 and Tank3 for a better distribution of RF power between tanks that is compatible with a mechanical design. To make the transverse acceptance less sensitive to alignment and gradient errors, the focusing scheme has been changed to FFDD over all 3 tanks. Design features that were demonstrated in earlier reports have been improved for series production. Results of high power RF tests of the DTL prototype equipped with PMQs are reported that test the voltage holding in the first gaps in presence of magnetic fields.

• T. Ito
  JAEA/LINAC, Ibaraki-ken
• C. Kubota, F. Naito, K. Nanmo
  KEK, Ibaraki

The operation of the DTL and the Separated type DTL (SDTL) of the J-PARC started in November 2006. The DTL and SDTL are currently running stable and accelerating the beam. For stable operation of the DTL/SDTL, We have done maintenance of the equipments, like an RF coupler, and improved the troubles. In this paper, we will present the operation experiences of the DTL and the SDTL.

• I. Terechkine, J. DiMarco, W. Schappert, D.A. Sergatskov, M.A. Tartaglia
  Fermilab, Batavia

Development of solenoid-based focusing lenses for transport channel of an R&D linac front end at FNAL is in its final stage. Lenses for the room temperature section of the linac are assembled in individual cryovessels and certified using a devoted stand. During this certification process, for each lens, position of its optical axis relative to the cryovessel is found in the warm and cold state. Lenses for the superconducting sections are ready for production, and development of a cryomodule to house multiple superconducting lenses and RF cavities is in progress. Studies were also conducted to measure fringe magnetic field of a lens in a cryomodule, to investigate a laser-based method of alignment, and to evaluate the extent of beam quality degradation due to imperfections in lens construction and alignment. This report presents some results of these studies.

• N. Solyak
  Fermilab, Batavia

Project X is a proposed high-intensity H^- accelerator complex that could provide beam for a variety of physics projects: neutrino-, kaon- and muon-based precision experiments. Other applications are under investigation. In the current proposal CW 3MW linac would contains few types of superconducting cavities and focising elements to accelerate beam from 2.5 MeV up to 3 GeV. The paper presents the status of the 3GeV x 1mA CW linac, including design and testing of the linac components, beam physics studies and future plans.

• G. Bellodi, M. Eshraqi, M.G. Garcia Tudela, L.M. Hein, J.-B. Lallement, A.M. Lombardi, P.A. Posocco, E. Sargsyan
  CERN, Geneva
• J. Stovall
  TechSource, Santa Fe, New Mexico

Linac4 is a new 160 MeV, 40 mA average beam current H^- accelerator which will be the source of particles for all proton accelerators at CERN as from 2015. Construction started in October 2008, and beam commissioning of the 3MeV frontend is scheduled for early next year. A baseline design of the linac beam dynamics was completed 2 years ago and validated by a systematic campaign of transverse and longitudinal error studies to assess tolerance limits and machine activation levels. Recent studies have been mainly focused on optimising this design to achieve both a smoother performance for nominal beam conditions and to gain operational flexibility for non-nominal scenarios. These include a review of the chopper beam dynamics design, a re-definition of the DTL and CCDTL inter-tank regions and a study of operational schemes for reduced beam currents (either permanent or in pulse-to-pulse mode). These studies have been carried out in parallel to first specifications for a beam commissioning strategy of the linac and its low-energy front-end.

• C. Compton, J. Bierwagen, S. Bricker, J. DeLauter, K. Elliott, W. Hartung, M. Hodek, J.P. Holzbauer, M.J. Johnson, O.K. Kester, F. Marti, D. R. Miller, S.J. Miller, D. Norton, J. Popielarski, L. Popielarski, N. Verhanovitz, K. Witgen, J. Wlodarczak, R.C. York
  NSCL, East Lansing, Michigan

Superconducting quarter-wave resonators, half-wave resonators, and cryomodules are being prototyped and fabricated at Michigan State University (MSU) for two ion linac projects. The 3 MeV per nucleon reaccelerator project (ReA3) is under construction as an upgrade to MSU's nuclear physics research program. ReA3 requires 15 production resonators, housed in three cryostats, with commissioning to begin in 2010. In parallel, MSU is engaged in a future laboratory upgrade, the Facility for Rare Isotope Beams (FRIB). FRIB requires a 200 MeV per nucleon driver linac, which includes 344 resonators (four different betas) housed in 52 cryomodules. FRIB development work is underway, with the prototyping of a FRIB cryomodule planned for early 2011. In addition, the acquisition strategy for FRIB resonators and cryomodules is being finalized, and the technology transfer program is being initiated. The status of the resonator and cryomodule production effort will be presented in this paper, including an overview of the acquisition strategy for FRIB.

• Y.K. Batygin
  LANL, Los Alamos, New Mexico

Particle-core interaction is the well-developed model of halo formation in high-intensity beams. In present paper an analytical solution for averaged single particle dynamics around uniformly charged beam core is obtained. The problem is analyzed through sequence of canonical transformations of Hamiltonian describing nonlinear particle oscillations. An analytical expression for maximum particle deviation from the axis is obtained. Results of the study are in good agreement with numerical simulations and with previously achieved data.

• V.A. Lebedev, J.-F. Ostiguy, N. Solyak
  Fermilab, Batavia
• A.V. Aleksandrov, A.P. Shishlo
  ORNL, Oak Ridge, Tennessee

A beam loss in the superconducting part of the SNS linac has been observed during its commissioning and operation. Although this loss does not prevent the SNS high power operation it results in an almost uniform irradiation of linac components and increased radiation levels in the tunnel. A multi-particle tracking could not explain the beam loss and its dependence on the machine parameters. It was recently found that the loss is related to the intrabeam particle collisions resulting in a stripping of one of two H^- ions. The paper describes experimental observations and corresponding calculations of the intrabeam stripping.

• Y.-J. Chen, D.T. Blackfield, G.J. Caporaso, S.A. Hawkins, S.D. Nelson, B. R. Poole
  LLNL, Livermore, California

Compact dielectric wall (DWA) accelerator technology is being developed at the Lawrence Livermore National Laboratory [1]. The DWA accelerator's beam tube is a stack of high gradient insulators, consisting of alternating layers of insulators and conductors. Characteristically, insulators' surface breakdown thresholds go up as the applied voltages' pulse width goes down. To attain the highest accelerating gradient in the DWA accelerator, the accelerating voltage pulses should have the shortest possible duration. This can be done by appropriately timing the switches in the transmission lines, which feed the continuous HGI tube. The accelerating voltage pulses arrive at the accelerator axis along the beam tube at different times so as to appear to the charged particle bunch as a traveling accelerating voltage wave. We have studied the beam transport in a baseline DWA configuration by performing PIC simulations using the 3-D, EM PIC code, LSP [2]. Sensitivity of the output beam parameters to the switch timing will be presented. In addition to the baseline configuration, various alternative focusing schemes will be discussed.

[1] G. J. Caporaso, Y-J Chen and S. E. Sampayan, "The Dielectric Wall Accelerator", Rev. of Accel. Sci. and Tech., vol. 2, p. 253 (2009).
[2] Alliant Techsystems Inc., http://www.lspsuite.com/.