• C. Chu, V.V. Danilov, D.-O. Jeon, M.A. Plum
  ORNL, Oak Ridge, Tennessee

An automated transverse beam matching application has been developed for the Spallation Neutron Source (SNS) beam transport lines. The application is written within the XAL Java framework and the matching algorithm is based on the simplex optimization method. Other functionalities, such as emittance calculated from profile monitor measurements (adopted from a LANL Fortran code), profile monitor display, and XAL on-line model calculation, are also provided by the application. Test results obtained during the SNS warm linac commissioning will be reported. A comparison between the emittances obtained from this application and an independent Trace-3D routine will also be shown.

• D.-O. Jeon
  ORNL, Oak Ridge, Tennessee

It is important to bring the cavity field amplitude and phase to the design values for a high intensity linac such as the Spallation Neutron Source (SNS)linac. A few techniques are available, such as the longitudinal acceptance scan and phase scan. During SNS linac commissioning, tuning of cavities was conducted using the acceptance scan and phase scan technique based on multiparticle simulations. The two techniques are compared.

• I.E. Campisi, S. Assadi, F. Casagrande, M. Champion, C. Chu, S.M. Cousineau, M.T. Crofford, C. Deibele, J. Galambos, P.A. Gurd, D.R. Hatfield, M.P. Howell, D.-O. Jeon, Y.W. Kang, K.-U. Kasemir, Z. Kursun, H. Ma, M.F. Piller, D. Stout, W.H. Strong, A.V. Vassioutchenko, Y. Zhang
  ORNL, Oak Ridge, Tennessee

The Spallation Neutron Source being built at the Oak Ridge National Laboratory employs eighty one 805 MHz superconducting cavities operated at 2.1 K for the H^- beam to gain energy in the main linac from 187 MeV to about 1 GeV. The superconducting cavities and cryomodules with two different values of beta .61 and .81 have been designed and constructed at Jefferson Lab for operation at 2.1 K with unloaded Q’s in excess of 5x109. To gain experience in testing cryomodules in the SNS tunnel before the final commissioning of the 2.1 K Central Helium Liquefier, integration tests were conducted on a medium beta (.61) cryomodule at 4.2 K. This is the first time that a superconducting cavity system specifically designed for 2.1 K operation has been extensively tested at 4.2 K without superfluid helium. Even at 4.2 K it was possible to test all of the functional properties of the cryomodule and of the cavities. In particular, at a nominal BCS Qo˜7x108, simultaneous pulse operation of all three cavities in the cryomodule was achieved at accelerating gradients in excess of 12 MV/m. These conditions were maintained for several hours at a repetition rate of 30 pps. Details of the tests will be presented and discussed.

• S. Henderson, A.V. Aleksandrov, D.A. Bartkoski, C. Chu, S.M. Cousineau, V.V. Danilov, G.W. Dodson, J. Galambos, D.-O. Jeon, M.A. Plum, M.P. Stockli
  ORNL, Oak Ridge, Tennessee

The Spallation Neutron Source accelerator systems will provide a 1.0 GeV, 1.4 MW proton beam to a liquid mercury target for neutron production. The accelerator complex consists of an H^- injector capable of producing 38 mA peak current, a 1 GeV linear accelerator, an accumulator ring and associated transport lines. The linear accelerator consists of a Drift Tube Linac, a Coupled-Cavity Linac and a Superconducting Linac which provide 1.5 mA average current to the accumulator ring. The staged beam commissioning of the accelerator complex is proceeding as component installation progresses. Recently, the normal-conducting linear accelerator was beam commissioned. A number of beam dynamics and beam quality measurements will be reported, including the measurement of transverse emittances in the H^- injector, and the evolution of halo and emittance along the linac.

• S. Henderson, I.E. Campisi, J. Galambos, D.-O. Jeon, Y. Zhang
  ORNL, Oak Ridge, Tennessee

We describe the techniques which will be employed for establishing RF and quadrupole setpoints in the SNS superconducting linac. The longitudinal tuneup will be accomplished using phase-scan methods, as well as a technique that makes use of the beam induced field in the unpowered cavity.* The scheme for managing the RF and quadrupole setpoints to achieve a given energy profile will be described.

*L. Young, Proc. PAC 2001, p. 572.

• D.-O. Jeon, C. Chu, V.V. Danilov
  ORNL, Oak Ridge, Tennessee

It is crucial to minimize beam loss and machine activation by obtaining optimal transverse matching for a high-intensity linear accelerator such as the Spallation Neutron Source linac. For matching the Drift Tube Linac (DTL) to Coupled Cavity Linac (CCL), there are four wire-scanners installed in series in CCL module 1 as proposed by the author.* A series of measurements was conducted to minimize envelope breathing and the results are presented here. As an independent approach, Chu et al is developing an application based on another technique by estimating rms emittance using the wire scanner profile data.** For matching the Medium Energy Beam Transport Line to the DTL, a technique of minimizing rms emittance was used and emittance data show that tail is minimized as well.

*D. Jeon et al., "A technique to transversely match high intensity linac using only rms beam size from wire-scanners," Proceedings of LINAC2002 Conference, p. 88. **C. Chu et al., "Transverse beam matching application for SNS," in this conference proceedings.