• S.M. Cousineau
  ORNL, Oak Ridge, Tennessee

Space charge effects are a major contributor to beam halo and emittance growth leading to beam loss in high intensity, low energy accelerators. As future accelerators strive towards unprecedented levels of beam intensity and beam loss control, a more comprehensive understanding of space charge effects is required. A wealth of simulation tools have been developed for modeling beams in linacs and rings, and with the growing availability of high-speed computing systems, computationally expensive problems that were inconceivable a decade ago are now being handled with relative ease. This has opened the field for realistic simulations of space charge effects, including detailed benchmarks with experimental data. A great deal of effort is being focused in this direction, and several recent benchmark studies have produced remarkably successful results. This paper reviews the achievements in space charge benchmarking in the last few years, and discusses the challenges that remain.

• G.P. Jackson
  Hbar Technologies, LLC, West Chicago, Illinois

• K.-U. Kasemir, M. Champion, M.T. Crofford, H. Ma
  ORNL, Oak Ridge, Tennessee

When initial beam studies at the Spallation Neutron Source (SNS) indicated a need for better compensation of the effects of beam loading, a succession of rapid-prototyping and experimentation lead to the development of a simple yet successful adaptive feed forward technique within a few weeks. We describe the process and first results.

• C. Pai, H. Hahn, H.-C. Hseuh, Y.Y. Lee, W. Meng, J.-L. Mi, D. Raparia, J. Sandberg, R.J. Todd, N. Tsoupas, J.E. Tuozzolo, D.S. Warburton, J. Wei, D. Weiss, W. Zhang
  BNL, Upton, Long Island, New York

Two extraction kicker magnet assemblies that contain seven individual pulsed magnet modules each will kick the proton beam vertically out of the SNS accumulator ring into the aperture of the extraction lambertson septum magnet. The proton beam then travels to the 1.4 MW SNS target assembly. The 14 kicker magnets and major components of the kicker assembly have been fabricated in BNL. The inner surfaces of the kicker magnets were coated with TiN to reduce the secondary electron yield. All 14 PFN power supplies have been built, tested and delivered to ORNL. Before final installation, a partial assembly of the kicker system with three kicker magnets was assembled to test the functions of each critical component in the system. In this paper we report the progress of the construction of the kicker components, the TiN coating of the magnets, the installation procedure of the magnets and the full power test of the kicker with the PFN power supply.

• J.-G. Wang
  ORNL, Oak Ridge, Tennessee
• N. Tsoupas
  BNL, Upton, Long Island, New York
• M. Venturini
  LBNL, Berkeley, California

The accumulator ring of the Spallation Neutron Source (SNS) at ORNL employs in its straight sections closely packed quadrupole doublet magnets with large aperture of R=15.1 cm and relatively short iron-to-iron distance of 51.4 cm.* The magnetic interference among the magnets in the doublet assemblies is not avoidable due to the fringe fields. Though each magnet in the assemblies has been individually mapped to high accuracy of delta(B)/B~1x10-4, the experimental data including the magnet interference effect in the assemblies will not be available. We have performed 3D computer simulations on a quadrupole doublet model in order to assess the degree of the interference and to obtain relevant data which should be very useful for the SNS commissioning and operation. This paper reports our simulation results.

*N. Tsoupas et al. "A Large-aperture Narrow Quadrupole for the SNS Accumulator Ring," Proc. EPAC 2002, p.1106, Paris, June 3-7, 2002.

• J.-G. Wang
  ORNL, Oak Ridge, Tennessee

3D computing simulations have been performed to study the magnetic field distribution of the injection chicane dipoles in the SNS ring.* The simulation studies have yielded the performance characteristics of the magnets and generated the magnetic field data in three dimensional grids, which can be used for detailed investigation of beam dynamics. Based on the simulation data, a 3D multipole expansion of the chicane dipole field, consisting of generalized gradients and their derivatives, has been made. The harmonic and pseudo-harmonic components in the expansion give much insight into the magnet physics. The expansion is quasi-analytical by fitting numeric data into a few interpolation functions. A 5th-order representation of the field is generated, and the effects of even higher order terms on the field representation are discussed.

*The injection chicane dipoles were designed at BNL by Y.Y. Lee, W. Meng, et al. See "Injection into the SNS Accumulator Ring: Minimizing Uncontrolled Losses and Dumping Stripped Electrons," D.T. Abell, Y.Y. Lee, W. Meng, EPAC 2000.

• R.F. Welton, S.N. Murray, M.P. Stockli
  ORNL, Oak Ridge, Tennessee
• R. Keller
  LBNL, Berkeley, California

The ion source developed for the Spallation Neutron Source* (SNS) is a radio frequency, multi-cusp source designed to produce ~ 40 mA of H^- with a normalized rms emittance of less than 0.2 pi mm mrad. To date the source has been utilized in the commissioning of the SNS accelerator, delivering beams of 10^-50 mA with duty-factors of typically ~0.1% for operational periods of several weeks and availabilities now ~99%. Ultimately the SNS facility will require beam duty-factors of 6% (1 ms pulse length, 60 Hz repetition rate, 21 day run-period). Over the last year, several experiments were performed in which the ion source was continuously operated at full duty-factor and maximum beam current on a dedicated test stand. Recently, a breakthrough in our understanding of the Cs release process has led to the development of a new source conditioning technique which resulted in a dramatic increase in beam persistence with time. Average H^- beam attenuation rates have been improved from ~5 mA/day to ~0.4 mA/day, allowing beams in excess of 30 mA to be delivered continuously at full duty factor for periods of ~20 days. Prior to this development, full duty factor beams could only be sustained for periods of several hours.

• T. Hunter, SH. Heimsoth, DL. Lebon, RM. McBrien, J.-G. Wang
  ORNL, Oak Ridge, Tennessee

The Spallation Neutron Source (SNS) contains more than 600 magnets. Among them, about 400 magnets for the Linac and transfer lines are being measured on site at Oak Ridge National Laboratory. These magnets include Permanent Magnet Quadrupoles, Electro-magnetic Quadrupoles, Dipoles and Correctors. The Permanent Magnet Quadrupoles are installed in the Drift Tube Linac (DTL) and are the only Permanent Magnets in the machine. These measurements are for magnets installed in the DTL, Coupled Cavity Linac (CCL), Superconducting Linac (SCL), High Energy Beam Transport (HEBT), and the Ring to Target Beam Transport (RTBT) line. All magnets have met specifications. Approximately three fourths of the magnets have so far been measured and installed. This presentation outlines the magnet measurements for SNS at ORNL and overviews the activities and accomplishments to date.

• 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.

• J.A. Holmes, S.M. Cousineau, V.V. Danilov
  ORNL, Oak Ridge, Tennessee

We define self-consistent beam distributions to have the following properties: 1) time-independence or periodicity, 2) linear space charge forces, and 3) maintainance of their defining shape and density under all linear transformations. The periodic condition guarantees zero space-charge-induced halo growth and beam loss during injection. Some self-consistent distributions can be manipulated into flat, or even point-like, beams, which makes them interesting to colliders and to heavy-ion fusion. This paper presents methods for painting 2D and 3D self-consistent distributions and for their manipulation to produce flat and point-like beams.

• J.A. Holmes, V.V. Danilov
  ORNL, Oak Ridge, Tennessee
• L.K. Jain
  UW/Physics, Waterloo, Ontario

Detailed studies of the transverse stability of the SNS ring have been carried out for realistic injection scenarios. For coasting beam models and single harmonic impedances, analytic and computational results including phase slip, chromaticity, and space charge are in excellent agreement. For the dominant extraction kicker impedance and bunched beams resulting from injection, computationally determined stability thresholds are significantly higher than for coasting beams. At this time, we have no analytic model to treat the bunched beam case, but we present a formulation that provides an approach to this problem.

• D. Raparia, Y.Y. Lee, J. Wei
  BNL, Upton, Long Island, New York

• R. Keller, P.A. Luft, M. T. Monroy, A. Ratti, M.J. Regis, D. L. Syversrud, J.G. Wallig
  LBNL, Berkeley, California
• D.E. Anderson, R.F. Welton
  ORNL, Oak Ridge, Tennessee

A novel concept for creating intense beams of negative hydrogen ion beams is presented. In this approach, an ECR ion source operating at 2.45 GHz frequency is utilized as a primary plasma generator and coupled to an SNS-type multi-cusp H^- ion source. The secondary source is driven by chopped dc power avoiding the use of filaments or of an internal rf antenna. The development of the new ion source is aimed at the future beam-power goal of 3 MW for the Spallation Neutron Source (SNS) that will be pursued after the start of SNS operations, but application to other proton driver accelerators that include an accumulator ring is feasible as well. The first two phases of this development effort have been successfully completed: assembly of a test stand and verification of the performance of an rf-driven SNS ion-source prototype; and extraction of electrons with more than 350 mA current from a 2.45-GHz ECR ion source obtained on loan from Argonne National Laboratory. The next goal is the demonstration of actual H^- ion production by this novel, hybrid ion source. This paper describes the source principle and design in detail and reports on the current status of the development work.

• Y.W. Kang, A.V. Aleksandrov, D.E. Anderson, M.M. Champion, M. Champion, M.T. Crofford, C. Deibele, G.W. Dodson, R.E. Fuja, P.E. Gibson, P.A. Gurd, T.W. Hardek, G.A. Johnson, P. Ladd, H. Ma, M.P. McCarthy, M.F. Piller, J.Y. Tang, A.V. Vassioutchenko, D.C. Williams
  ORNL, Oak Ridge, Tennessee
• J.A. Billen, J.T. Bradley, D. Rees, W. Roybal, J. Stovall, K.A. Young, L.M. Young
  LANL, Los Alamos, New Mexico

SNS is managed by UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. Department of Energy. SNS is a partnership of six national laboratories: Argonne, Brookhaven, Jefferson, Lawrence Berkeley, Los Alamos, and Oak Ridge.

• Q.S. Shu, G. Cheng, J. T. Susta
  AMAC, Newport News, Virginia
• S.J. Einarson
  CPI/BMD, Beverley, Massachusetts
• T. Garvey
  LAL, Orsay
• W.-D. Müller, D. Proch
  DESY, Hamburg
• T.A. Treado
  CPI, Beverley, Massachusetts

More and more accelerators are built with superconducting cavities operating at cryogenic temperatures, and the probability of a ceramic window failure presents increasing problems because of the resulting contamination of the cavities surfaces and the resulting accelerating electric field degradation. A cost effective design and fabrication method for the TESLA cavities has been developed in the framework of a DOE STTR grant. This new design replaces the present TESLA cylindrical ceramic windows with two planar disc windows separated by a vacuum space and is optimized for RF input power, vacuum characteristics, and thermal properties. This novel coupler will reduce the costs of fabrication and improve the RF performance of the coupler, the vacuum between the two windows, and the cleaning procedure. Two couplers with this design have been fabricated and are presently being conditioned for testing at DESY, Germany, and LAL, France, on the RF high power testing stand and on a test cryomodule.

• E. Daly, G.K. Davis, W.R. Hicks
  Jefferson Lab, Newport News, Virginia

The new tuner design for the 12 GeV Upgrade SRF cavities consists of a coarse mechanical tuner and a fine piezoelectric tuner. The mechanism provides a 30:1 mechanical advantage, is pre-loaded at room temperature and tunes the cavities in tension only. All of the components are located in the insulating vacuum space and attached to the helium vessel, including the motor, harmonic drive and piezoelectric actuators. The requirements and detailed design are presented. Measurements of range and resolution of the coarse tuner are presented and discussed.

• P. Kneisel, G. Ciovati, G. Myneni
  Jefferson Lab, Newport News, Virginia
• T. Carneiro
  Reference Metals, Bridgeville, Pennsylvania
• D. Proch, W. Singer, X. Singer
  DESY, Hamburg

In a previous paper* we have reported about initial tests of single cell 1500 MHz cavities made from high purity niobium with three different Ta contents of 160 ppm, ~600 ppm and ~1400 ppm. These cavities had been treated by buffered chemical polishing several times and 100 mm, 200 mm and 300 mm of material had been removed from the surfaces. This contribution reports about subsequent tests following post purification heat treatments with Ti and “in situ” baking. As a result, all cavities exhibited increased quench fields due to the improved thermal conductivity after the heat treatment. After the "in situ" baking at 120C for ~40 hrs the always present Q-drop at high fields disappeared and further improvements in accelerating gradient could be realized. Gradients as high as Eacc = 35 MV/m were achieved and there were no clear indications that the cavity performance was influenced by the Ta content in the material. A multi-cell cavity from the high Ta content material is being fabricated and results will be presented at this conference.

*P. Kneisel et al., Linac 2004.

• P. Kneisel, G. Ciovati, G. Myneni
  Jefferson Lab, Newport News, Virginia
• T. Carneiro
  Reference Metals, Bridgeville, Pennsylvania
• J.S. Sekutowicz
  DESY, Hamburg

We have fabricated and tested several single cell cavities using material from very large grain niobium ingots. In one case the central grain exceeded 7" in diameter and this was used for a 2 GHz cavity. This activity had a dual purpose: to investigate the influence of grain boundaries on the often observed Q-drop at gradients Eacc > 20 MV/m in the absence of field emission, and to study the possibility of using ingot material for cavity fabrication without going through the expensive process of sheet fabrication. The sheets for these cavities were cut from the ingot by wire electro-discharge machining (EDM) and subsequently formed into half–cells by deep drawing. The following fabrication steps were standard: machining of weld recesses, electron beam welding of beam pipes onto the half cells and final equator weld to join both half cell/beam pipe subunits.The cavities showed heavy Q–disease caused by the EDM; after hydrogen degassing at 800C for 3 hrs in UHV the cavities showed promising results, however, a Q-drop above Eacc ~ 20 MV/m was still present. Testing of the cavities is still ongoing – so far accelerating gradients of 30 MV/m have been achieved.

• P. Kneisel, G. Ciovati, G. Myneni, G. Wu
  Jefferson Lab, Newport News, Virginia
• J.S. Sekutowicz
  DESY, Hamburg

Coaxial higher order mode (HOM) couplers were developed initially for PETRA cavitiesand subsequently for TESLA cavities. They were adopted later for SNS and Jlab upgrade cavities. The principle of operation is the rejection of the fundamental mode by the tunable filter configuration of the coupler and the transmission of the HOMs. It has been recognized recently that, in high average power applications, the pick-up probe of the HOM coupler must be superconducting in order to avoid substantial heat dissipation by the fundamental mode fields and deterioration of the cavity Q. In addition, the thermal conduction of existing rf feedthrough designs is only marginally sufficient to keep even the niobium probe tip superconducting in cw operation. We have equipped a single-cell niobium cavity with different HOM coupler configurations and tested the different designs by measuring Q vs Eacc behavior at 2 K for different feedthroughs and probe tipmaterials

• J.P. Ozelis, J.R. Delayen, J. Mammosser
  Jefferson Lab, Newport News, Virginia

As part of its efforts for the SNS construction project, Jefferson Lab has produced 23 cryomodules for the superconducting linac. These modules contained 81 industrially produced multicell Nb accelerating cavities. Each of these cavities was individually tested before assembly into a cryomodule to verify that they achieved the required performance. This ensemble of cavities represents the 3rd largest set of production superconducting cavities fabricated and tested to date. The timely qualification testing of such a collection of cavities offers both challenges and opportunities. Their performance can be characterized by achieved gradient at the required Qo, achieved peak surface field, onset of field emission, and observations of multipacting. Possible correlations between cavity performance and process parameters, only really meaningful in the framework of a large scale production effort, will also be presented. In light of the potential adoption of these cavities for projects such as the Rare Isotope Accelerator or Fermilab Proton Driver, such an analysis is crucial to their success.

• C.E. Reece, E. Daly, T. Elliott, J.P. Ozelis, H.L. Phillips, T.M. Rothgeb, K. Wilson, G. Wu
  Jefferson Lab, Newport News, Virginia

The use of higher-order-mode (HOM) pickup probes in the presence of significant fundamental rf fields can present a thermal challenge for cw or high average power SRF cavity applications. The electric field probes on the HOM-damping couplers on the JLab "High Gradient" and "Low Loss" seven-cell cavities for the CEBAF upgrade are exposed to approximately 10% of the peak magnetic field in the cavity. To avoid significant dissipative losses, these probes must remain superconducting during operation. Typical cryogenic rf feedthroughs provide a poor thermal conduction path for the probes, and provide inadequate stabilization. We have developed solutions that meet the requirements, providing a direct thermal path from the niobium probe, thorough single-crystal sapphire, to bulk copper which can be thermally stationed (or heat sunk). Designs, electromagnetic and thermal analyses, and performance data will be presented.

• M. Stirbet, G.K. Davis, M. A. Drury, C. Grenoble, J. Henry, G. Myneni, T. Powers, K. Wilson, M. Wiseman
  Jefferson Lab, Newport News, Virginia
• I.E. Campisi, Y.W. Kang, D. Stout
  ORNL, Oak Ridge, Tennessee

The Spallation Neutron Source (SNS) makes use of 33 medium beta (0.61) and 48 high beta (0.81) superconducting cavities. Each cavity is equipped with a fundamental power coupler, which should withstand the full klystron power of 550 kW in full reflection for the duration of an RF pulse of 1.3 msec at 60 Hz repetition rate. Before assembly to a superconducting cavity, the vacuum components of the coupler are submitted to acceptance procedures consisting of preliminary quality assessments, cleaning and clean room assembly, vacuum leak checks and baking under vacuum, followed by conditioning and RF high power testing. Similar acceptance procedures (except clean room assembly and baking) were applied for the airside components of the coupler. All 81 fundamental power couplers for SNS superconducting cavity production have been RF power tested at JLAB Newport News and, beginning in April 2004 at SNS Oak Ridge. This paper gives details of coupler processing and RF high power-assessed performances.

• F. Casagrande, I.E. Campisi, P.A. Gurd, D.R. Hatfield, M.P. Howell, D. Stout, W.H. Strong
  ORNL, Oak Ridge, Tennessee
• D. Arenius, J.C. Creel, K. Dixon, V. Ganni, P.K. Knudsen
  Jefferson Lab, Newport News, Virginia

The Spallation Neutron Source (SNS) is under construction at Oak Ridge National Laboratory. The cold section of the Linac consists of 81 superconducting radio frequency cavities cooled to 2.1K by a 2400 Watt cryogenic refrigeration system. The major cryogenic system components include warm helium compressors with associated oil removal and gas management, 4.5K cold box, 7000L liquid helium dewar, 2.1K cold box (consisting of 4 stages of cold compressors), gaseous helium storage, helium purification and gas impurity monitoring system, liquid nitrogen storage and the cryogenic distribution transfer line system. The overall system commissioning strategy and status will be presented.

• 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.J. Error, D.R. Bruce, J.J. Fazekas, S.A. Helus, J.R. Maines
  ORNL, Oak Ridge, Tennessee

The SNS Project is a 1.4 MW accelerator-based neutron source located at Oak Ridge National Laboratory in Oak Ridge, Tennessee. For shielding purposes, a 17 foot berm of native soil has been constructed on top of the accelerator tunnel system. This backfill has caused ongoing settlement of the tunnels. The settlement has been monitored by the SNS Survey and Alignment Group at regular intervals, in order to discover the patterns of deformation, and to determine when the tunnels will be stable enough for precise alignment of beam line components. The latest monitoring results indicate that the settlement rate has significantly decreased. This paper discusses the techniques and instrumentation of the monitoring surveys, and provides an analysis of the results.

• P.E. Gibson, A.V. Aleksandrov, M.M. Champion, G.W. Dodson, J.P. Schubert, J.Y. Tang
  ORNL, Oak Ridge, Tennessee

The Spallation Neutron Source (SNS) is an accelerator-based neutron source being built at Oak Ridge National Laboratory. The warm linac portion, designed by Los Alamos, has been installed and commissioned. The warm linac is comprised of six Drift Tube Linac (DTL) tanks and four Coupled Cavity Linac (CCL) modules. For commissioning purposes the accelerating systems have been operated at less than the design 6% duty factor. During lower power operation there is less RF cavity heating. This decrease in heat load causes operational stability issues for the associated Resonance Control Cooling Systems (RCCSs) which were designed for full duty factor operation. To understand this effect operational results have been analyzed and tests have been performed. External system factors have been explored and the resulting impacts defined. Dynamic modeling of the systems has been done via a collaboration with the Institute for Nuclear Research (INR), Moscow, Russia. New RCCS operation code has been implemented. Increases in system performance achieved and solutions employed will be presented.

• S.A. Helus, D.R. Bruce, J.J. Error, J.J. Fazekas, J.R. Maines
  ORNL, Oak Ridge, Tennessee

Optical tooling has been a mainstay of the accelerator alignment community for decades. Even now in the age of electronic survey equipment, optical tooling remains a viable alternative, and at times the only alternative. At SNS, we combine traditional optical tooling alignment methods, instrumentation, and techniques, with the more modern electronic techniques. This paper deals with the integration of optical tooling into the electronic survey world.

• 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.

• R.T. Roseberry, S. Assadi, G.R. Murdoch
  ORNL, Oak Ridge, Tennessee

The Spallation Neutron Source Project (SNS) is an accelerator-based neutron source currently under construction at Oak Ridge National Laboratory (ORNL). The availability of space along completed portions of the accelerator for the addition of beam diagnostic is limited. A new platform for mounting a variety of instruments has been created by replacing part of the Medium Energy Beam Transport (MEBT) section of the accelerator developed by Lawrence Berkeley National Laboratory. The design and current capabilities of this instrument platform will be presented along with plans for future enhancements.

• G.W. Dodson, M. Giannella, A.T. Ruffin, T.L. Williams
  ORNL, Oak Ridge, Tennessee

The SNS Front End, Drift Tube Linac and most of the Coupled Cavity Linac have been operated during commissioning. Beam loss data were taken with differential Beam Current Monitors, and Beam loss Monitors during commissioning. Residual activation data were taken at various times during and after the run. An analysis of beam loss trending, beam loss monitor data and residual activation will be shown.

• K.R. Rust, W.E. Barnett, R.I. Cutler, J. T. Weaver
  ORNL, Oak Ridge, Tennessee
• S. Dewan, R. Holmes, S. Wong
  IE Power Inc., Mississauga, Ontario
• R.F. Lambiase, J. Sandberg
  BNL, Upton, Long Island, New York
• J. Zeng
  Digital Predictive Systems Inc., Toronto

This paper describes the types and quantities of magnet power supplies required for the SNS Linear Accelerator, High-Energy Beam Transport (HEBT), Ring and the Ring-Target Beam Transport (RTBT). There are over 600 magnets and more than 550 magnet power supplies. These magnet power supplies range in size from the bipolar-corrector supplies rated at 35 volts, 20 amps to the main-ring dipole supply that is rated at 440 volts, 6000 amps. The Linac power supplies have a ripple/stability specification of 1000 parts per million while the ring supplies have a specification of 100 parts per million. There are also pulsed power supplies for beam injection and beam extraction. The paper will show acceptance test results from the manufacturers as well as test results performed by the SNS magnet power supply group.

• S. Lenci, E.L. Eisen
  CPI, Palo Alto, California

• D. Rees, G. Bolme, S.I. Kwon, J.T.M. Lyles, M.T. Lynch, M. Prokop, W. Reass, P.J. Tallerico
  LANL, Los Alamos, New Mexico

• K.A. Young, J.T. Bradley, T.W. Hardek, M.T. Lynch, D. Rees, W. Roybal, P.J. Tallerico, P.A. Torrez
  LANL, Los Alamos, New Mexico

The RF system for the 805 MHz normal conducting linac of the Spallation Nuetron Source (SNS) accelerator was designed, procured and tested at Los Alamos National Laboratory(LANL) and then installed and commissioned at Oak Ridge National Laboratory (ORNL). The RF power for this room temperature coupled cavity linac (CCL) of SNS accelerator is generated by four pulsed 5 MW peak power klystrons operating with a pulse width of 1.25 mSec and a 60 Hz repetition frequency. The RF power from each klystron is divided and delivered to the CCL through two separate RF windows. The 5 MW RF system advanced the state of the art for simultaneous peak and average power. This paper summarizes the problems encountered, lessons learned and results of the high power testing at LANL of the 5 MW klystrons, 5 MW circulators, 5 MW loads, and 2.5 MW windows.*

*Tom Hardek is now at ORNL.

• D.E. Anderson, J. Hicks, D. E. Hurst, E.R. Tapp, M. Wezensky
  ORNL, Oak Ridge, Tennessee
• D. Baca, W. Reass
  LANL, Los Alamos, New Mexico
• V.V. Peplov
  RAS/INR, Moscow

The first-generation high frequency switching megawatt-class high voltage converter modulators (HVCM) developed by Los Alamos National Laboratory for the Spallation Neutron Source at Oak Ridge National Laboratory have been installed and are now operational. Each unit is capable of delivering pulses up to 11 MW peak, 1 MW average power at voltages up to 140 kV to drive klystron(s) rated up to 5 MW. To date, three variations of the basic design have been installed, each optimized to deliver power to a specific klystron load configuration. Design improvements, with the primary intention of improving system reliability and availability, have been under development since the initial installation of the HVCM units. This paper will examine HVCM reliability studies, reliability operational data, and modifications and improvements performed to increase the overall system availability. We will also discuss system enhancements aimed at improving the ease of operation and providing for additional equipment protection features.

• M. Champion, M.T. Crofford, K.-U. Kasemir, H. Ma, M.F. Piller
  ORNL, Oak Ridge, Tennessee
• L.R. Doolittle, A. Ratti
  LBNL, Berkeley, California

The design and production of the Spallation Neutron Source Linac Low-Level RF control system is complete, and installation will be finished in Spring 2005. The warm linac beam commissioning run in Fall 2004 was the most extensive test to date of the LLRF control system, with fourteen (of an eventual 96) systems operating simultaneously. In this paper we present an overview of the LLRF control system, the experience in designing, building and installing the system, and operational results.

• M.T. Crofford, M. Champion, K.-U. Kasemir, H. Ma, M.F. Piller
  ORNL, Oak Ridge, Tennessee

• Y.W. Kang, D.E. Anderson, I.E. Campisi, M. Champion, M.T. Crofford, R.E. Fuja, P.A. Gurd, S. Hasan, K.-U. Kasemir, M.P. McCarthy, D. Stout, J.Y. Tang, A.V. Vassioutchenko, M. Wezensky
  ORNL, Oak Ridge, Tennessee
• G.K. Davis, M. A. Drury, T. Powers, M. Stirbet
  Jefferson Lab, Newport News, Virginia

SNS is managed by UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. Department of Energy. SNS is a partnership of six national laboratories: Argonne, Brookhaven, Jefferson, Lawrence Berkeley, Los Alamos, and Oak Ridge.

• H. Ma, M. Champion, M.T. Crofford, K.-U. Kasemir, M.F. Piller
  ORNL, Oak Ridge, Tennessee
• L.R. Doolittle, A. Ratti
  LBNL, Berkeley, California

A full digital Low-Level RF controller has been developed for SNS LINAC. Its design is a good example of a modern digital implementation of the classic control theory. The digital hardware for all the control and DSP functionalities, including the final vector modulation, is implemented on a single high-density FPGA. Two models for the digital hardware have been written in VHDL and Verilog respectively, based on a very low latency control algorithm, and both have been being used for supporting the testing and commissioning the LINAC to the date. During the commissioning, the flexibility and ability for precise controls that only digital design on a larger FPGA can offer has proved to be a necessity for meeting the great challenge of a high-power pulsed SCL.

• M.P. McCarthy, D.E. Anderson, R.E. Fuja, P.A. Gurd, T.W. Hardek, Y.W. Kang
  ORNL, Oak Ridge, Tennessee
• J.T. Bradley, D. Rees, W. Roybal, K.A. Young
  LANL, Los Alamos, New Mexico

The Spallation Neutron Source (SNS) linac will provide a 1 GeV proton beam for injection into the accumulator ring. In the normal conducting (NC) section of this linac, the Radio Frequency Quadupole (RFQ) and six drift tube linac (DTL) tanks are powered by seven 2.5 MW, 402.5 MHz klystrons and the four coupled cavity linac (CCL) cavities are powered by four 5.0 MW, 805 MHz klystrons. Eighty-one 550 kW, 805 MHz klystrons each drive a single cavity in the superconducting (SC) section of the linac. The high power radio frequency (HPRF) equipment was specified and procured by LANL and tested before delivery to ensure a smooth transition from installation to commissioning. Installation of RF equipment to support klystron operation in the 350-meter long klystron gallery started in June 2002. The final klystron was set in place in September 2004. Presently, all RF stations have been installed and high power testing has been completed. This paper reviews the progression of the installation and testing of the HPRF Systems.

• M.F. Piller, M. Champion, M.T. Crofford, H. Ma
  ORNL, Oak Ridge, Tennessee
• L.R. Doolittle
  LBNL, Berkeley, California

• A. Webster, C. Deibele, J. Pogge
  ORNL, Oak Ridge, Tennessee
• J.F. Power
  LANL, Los Alamos, New Mexico

The Spallation Neutron Source (SNS) is an accelerator-based neutron source being built at Oak Ridge National Laboratory. The BPMs (Beam Position Monitors) requires RF reference signals to measure the phase of the beam with respect to the RF. In the MEBT (Medium Energy Beam Transport) Line and in the DTLs (Drift Tube Linac Cavities) are cavities that accelerate and bunch the beam at 402.5 MHz. In the CCLs (Coupled Cavity Linac) and SCLs (Superconducting Linac) accelerate the beam at 805 MHz. To mitigate effects of RF leakage into the BPM electrodes it is required to measure the phase in the MEBT and DTLs at 805 MHz and in the CCL and SCL at 402.5 MHz. We are directly connected to the RF group MO (master oscillator) and send these signals along the entire linac using fiber optic technology. Schematics, measurements, and installation update are discussed.

• 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. An
  ORNL, Oak Ridge, Tennessee

Frequency and electromagnetic field distribution sensitivity of a superconducting RF (SRF) cavity due to cavity’s small deformation are the fundamental phyical paramethers in cavity and tuner design. At low temperature, the frequency sensitivity can be obtained by measuring prototype cavity, but it is not easy to test the filed distribution sensitivity. This paper presents and describes a simulation method combining ANSYS and SUPERFISH to calculate the cavity frequency and field distribution variation due to cavity’s small deformation caused by mechanical force, radiation force, thermal expansion etc.. As an example, the simulation results of the frequency and field flatness sensitivity on the SNS cavities were confirmed by their test results.

sun_ancn@yahoo.com

• S. Henderson, P. Chu, S.M. Cousineau, V.V. Danilov, J.A. Holmes, T.A. Pelaia, M.A. Plum
  ORNL, Oak Ridge, Tennessee

The Spallation Neutron Source (SNS) Accumulator Ring will reach peak intensities of 1.5x10¹⁴ protons/pulse through multi-turn charge-exchange injection. Accumulation of these unprecedented beam intensities must be accomplished while maintaining extremely low losses (less than 1 W/m). It is anticipated that the control of the ring optics will be important for achieving these low loss rates. We describe our plans for measuring and correcting the optical functions of the accumulator ring lattice.

• I.E. Campisi
  ORNL, Oak Ridge, Tennessee

The superconducting linac for the Spallation Neutron Source is in the process of being commissioned. Eighty-one cavities resonating at 805 MHz are installed in the SNS tunnel in 11 medium beta (.61) cryomodules each containing 3 cavities and 12 high beta (.81) cryomodules each with 4 cavities. The niobium cavities and cryomodules were designed and assembled at Jefferson Lab and installed in the SNS tunnel at Oak Ridge and are operating at 2.1 K. A preliminary test of one medium beta cryomodule was performed at 4.2 K in September 2004. All functional parameters of the cryomodule were proven to meet specifications at that temperature. The Central Helium Liquefier is being commissioned for 2.1 K operation and all cavities will be tested by late Spring 2005. The testing will include all of the functional parameters necessary for beam operation, to be carried out in summer 2005. The focus of the testing is to characterize the cavities’ maximum gradients and that sustained simultaneous operation can be achieved for all the cavities in preparation of beam commissioning. The results of cryomodule and cavity testing in the superconducting linac will be presented.

• C.D. Long
  Innovative Design, Knoxville, Tennessee
• W. Blokland, D.J. Murphy, J. Pogge, J.D. Purcell
  ORNL, Oak Ridge, Tennessee
• M. Sundaram
  University of Tennessee, Knoxville, Tennessee

The Spallation Neutron Source (SNS) accelerator systems will deliver a 1.0 GeV, 1.4 MW proton beam to a liquid mercury target for neutron scattering research. The accelerator complex consists of a 1 GeV linear accelerator, an accumulator ring and associated transport lines. The SNS diagnostics platform is PC-based running Windows XP Embedded for its OS and LabVIEW as its programming language. Coordinating timing among the various diagnostics instruments with the generation of the beam pulse is a challenging task that we have chosen to divide into three phases. First, timing was derived from VME based systems. In the second phase, described in this paper, timing pulses are generated by an in house designed PCI timing card installed in ten diagnostics PCs. Using fan-out modules, enough triggers were generated for all instruments. This paper describes how the Timing NAD (Network Attached Device) was rapidly developed using our NAD template, LabVIEW’s PCI driver wizard, and LabVIEW Channel Access library. The NAD was successfully commissioned and has reliably provided triggers to the instruments. This work supports the coming third phase where every NAD will have its own timing card.

• I.H. Yu, D.T. Kim, S.-C. Kim, I.-S. Park, S.J. Park
  PAL, Pohang, Kyungbuk
• Y.-S. Cho
  KAERI, Daejon

The PEFP (Proton Engineering Frontier Project) at the KAERI (Korea Atomic Energy Research Institute) is building a high-power proton linear accelerator aiming to generate 100-MeV proton beams with 20-mA peak current (pulse width and max. repetition rate of 1 ms and 120 Hz respectively). We are developing a prototype digital BPPM (Beam Position and Phase Monitor) for the PEFP linac utilizing the digital technology with field programmable gate array (FPGA). The RF input signals are down converted to 10 MHz and sampled at 40 MHz with 14-bit ADC to produce I and Q data streams. The system is designed to provide a position and phase resolution of 0.1% and 0.1? RMS respectively. The fast digital processing is networked to the EPICS-based control system with an embedded processor (Blackfin). In this paper, the detailed description of the prototype digital beam position and phase monitor will be described with the performance test results.

• A.V. Aleksandrov, S. Assadi, S.M. Cousineau, V.V. Danilov, S. Henderson, M.A. Plum
  ORNL, Oak Ridge, Tennessee
• P.V. Logatchev, A.A. Starostenko
  BINP SB RAS, Novosibirsk

The design goal for the SNS ring is to accumulate 2·10¹⁴ protons per 1ms pulse at a 60Hz repetition rate. Achieving the design beam intensity with acceptable losses is a challenging task, which could be tackled more easily if reliable measurements of the beam profile in the ring are available. The high power density of the beam precludes the use of conventional wire scanners or harps and therefore non-interceptive types of profiles measurements are required. The electron beam probe method was suggested for measuring profiles in high power beams. In this method, deflection of a low energy electron beam by the collective field of the high intensity beam is measured. The charge density in the high intensity beam can be restored under certain conditions or estimated by various mathematical techniques. We studied the feasibility of using the electron beam probe for the SNS accumulator ring using computer simulations of the diagnostic setup. A realistic electron gun model and realistic proton beam distributions were used in the simulations. Several profile calculation techniques were explored and the results are reported in this paper.

• C. Deibele
  ORNL, Oak Ridge, Tennessee
• S.S. Kurennoy
  LANL, Los Alamos, New Mexico

The Spallation Neutron Source (SNS) is an accelerator-based neutron source being built at Oak Ridge National Laboratory. The 805-MHz coupled-cavity linac (CCL) accelerates an H^- beam from 86 to 186 MeV, while the 805 MHz superconducting-cavity linac (SCL) accelerates the beam to its final energy of 1 GeV. The SNS beam position monitors (BPMs) which are used to measure both position and phase of the beam relative to the master oscillator, have the dual-planed design with four one-end-shorted stripline electrodes. We argue that the BPMs are optimally broadband matched to the cabling and electronics when the geometrical mean of the sum-mode and quadrupole-mode impedances is equal to the external-line impedance, 50 Ohms. The analytical results, MAFIA and HFSS simulations, wire measurements, and beam measurements that support this statement are presented.

• M.P. Stockli, R.F. Welton
  ORNL, Oak Ridge, Tennessee

Ion beam emittances are normally measured as two-dimensional distributions of the beam current fraction within a window dx centered at position coordinate x and a window dx’ centered at trajectory angle x’. Unthresholded rms emittances evaluated from experimental data are very sensitive to noise, bias, and other undesired signals. Undesired signals occur when particles from outside the measured window dx*dx’ contribute to the signal from the particles within the measured window. Increasing the window size increases the desired signal while most undesired contributions remain unchanged. However, the decreasing resolution causes an error in the emittance results, especially in the rms emittance. Using theoretical distributions we will present the tradeoff between resolution and accuracy.

• S.D. Claudet
  CERN, Geneva

• G.R. Murdoch
  ORNL, Oak Ridge, Tennessee

SNS is managed by UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. Department of Energy. SNS is a partnership of six national laboratories: Argonne, Brookhaven, Jefferson, Lawrence Berkeley, Los Alamos, and Oak Ridge.

• 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.

• P.S. Holik
  ORNL, Oak Ridge, Tennessee

The SNS Project has 45MW of installed power. A design description under the Construction Design and Maintenance (CDM) with regard to regulations (OSHA, NFPA, NEC), reliability issues and maintenance of the AC power distribution system are herewith presented. The SNS Project has 45MW of installed power. The Accelerator Systems are Front End (FE)and LINAC KLYSTRON Building (LK), Central Helium Liquefier (CHL), High Energy Beam Transport (HEBT), Accumulator Ring and Ring to Target Beam Transport (RTBT) Support Buildings have 30MW installed power. FELK has 16MW installed, majority of which is klystron and magnet power supply system. CHL, supporting the super conducting portion of the accelerator has 7MW installed power and the RING Systems (HEBT, RING and RTBT) have also 7MW installed power.*

*SNS SRD. KJ Basis of Design. IEEE Red Book. IEEE Gold Book. IEEE Green Book. NEC NFPA.

• P.S. Holik
  ORNL, Oak Ridge, Tennessee

Description of site general grounding network. RF grounding network enhancement underneath the klystron gallery building. Grounding network of the Ring Systems with ground breaks in the Ring Tunnel. Grounding and Bonding of R&D accelerator equipment. SNS Building lightning protection.

*SNS SRD *IEEE GREEN BOOK *IEEE EMERALD BOOK

• C. Sibley III, D.J. Armstrong, A. Jones, T.A. Justice, D.H. Thompson
  ORNL, Oak Ridge, Tennessee

Work supported by the U.S. Department of Energy under contract DE-AC05-00OR22725.

• R.W. Shaw, V.A. Davis, R.N. Potter, L.L. Wilson
  ORNL, Oak Ridge, Tennessee
• C.S. Feigerle, M.E. Peretich
  University of Tennessee, Knoxville, Tennessee
• C.J. Liaw
  BNL, Upton, Long Island, New York

We have prepared and tested corrugated, thin diamond foils for use in stripping the SNS H^- Linac beam. Diamond has shown promise for providing ca. 10X increased lifetime over traditional carbon foils. The preferred foil geometry is 10.5 by 20 mm at 350 microgram/cm2, mechanically supported on preferably one, but no more than two, edges. The foils are prepared by chemical vapor deposition (CVD) on a patterned silicon substrate, followed by chemical removal of the silicon. This yields a foil with trapezoidal corrugations to enhance mechanical strength and foil flatness. Both micro- and nano-crystalline diamond foils have been grown. Microwave plasma CVD methods that incorporate high argon gas content were used to produce the latter. Sixteen foils of a variety of characteristics have been tested using the BNL 750 keV RFQ H^- beam to simulate the energy deposition in the SNS foil. Long foil lifetimes, up to more than 130 hours, have been demonstrated. Characterization of the foils after beam testing indicates creation of sp2 defects within the ion beam spot. Current efforts are centered on development of corrugation patterns that will enhance flatness of single-edge supported foils.

• M. Holding, C.M. Hammons, B.R. Lang, G.R. Murdoch, K.G. Potter, R.T. Roseberry
  ORNL, Oak Ridge, Tennessee

• 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.

• R.J. Todd, P. He, H.-C. Hseuh, D. Weiss
  BNL, Upton, Long Island, New York

The inner surfaces of the 248 m Spallation Neutron Source (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. There are approximately 100 chambers and kicker modules, some up to 5 m in length and 36 cm in diameter, coated with TiN. The coating is deposited by means of reactive DC magnetron sputtering using a cylindrical magnetron with internal permanent magnets. This cathode configuration generates a deposition rate sufficient to meet the required production schedule and produces stoichiometric films with good adhesion, low SEY and acceptable outgassing. Moreover, the cathode magnet configuration allows for simple changes in length and has been adapted to coat the wide variety of chambers and components contained within the arc, injection, extraction, collimation and RF regions. Chamber types, quantities and the cathode configurations used to coat them are presented herein. A brief summary of the salient coating properties is given including the interdependence of SEY as a function of surface roughness and its effect on outgassing. Limitations of this coating method are also discussed.

• M. A. Drury, E. Daly, G.K. Davis, J.R. Delayen, C. Grenoble, W.R. Hicks, K. King, T. Plawski, T. Powers, J.P. Preble, H. Wang, M. Wiseman
  Jefferson Lab, Newport News, Virginia

Thomas Jefferson National Accelerating Facility (Jefferson Lab) has completed production of 24 Superconducting Radio Frequency (SRF) cryomodules for the Spallation Neutron Source (SNS) superconducting linac. This includes one medium-beta (0.61) prototype, eleven medium-beta and twelve high-beta (0.81) production cryomodules. Ten medium-beta cryomodules as well as two high beta cryomodules have undergone complete operational performance testing in the Cryomodule Test Facility at Jefferson Lab. The set of tests includes measurements of maximum gradient, unloaded Q (Q0), microphonics, and response to Lorentz forces. The Qext’s of the various couplers are measured and the behavior of the higher order mode couplers is examined. The mechanical and piezo tuners are also characterized. The results of these performance tests will be discussed in this paper.

• J. Hogan, T.C. Cannella, E. Daly, M. A. Drury, J.F. Fischer, T. Hiatt, P. Kneisel, J. Mammosser, J.P. Preble, T.E. Whitlatch, K. Wilson, M. Wiseman
  Jefferson Lab, Newport News, Virginia

• J.P. Ozelis, V. Bookwalter, B.D. Madre, C.E. Reece
  Jefferson Lab, Newport News, Virginia

Jefferson Lab has extensively used a proprietary web-based system (Pansophy) that integrates commercial database, data analysis, document archiving and retrieval, and user interface software, as a coherent knowledge management product during the construction of the cryomodules for the SNS Superconducting Linac, providing elements of process and procedure control, data capture and review, and data mining and analysis. With near real-time and potentially global access to production data, process monitoring and performance analyses could be pursued in a timely manner, providing crucial feedback. The extensibility, portability, and accessibility of Pansophy via universally available software components provide the essential features needed in any information and project management system capable of meeting the needs of future accelerator construction efforts, requiring an unprecedented level of regional and international coordination and collaboration, to which Pansophy is well suited.

• R.A. Rimmer, E. Daly, J. Henry, W.R. Hicks, J.P. Preble, M. Stirbet, H. Wang, K. Wilson, G. Wu
  Jefferson Lab, Newport News, Virginia

We describe the concepts and developments underway at JLab as part of the program to develop a new CW cryomodule capable of transporting ampere-level beam currents in a compact FEL. Requirements include real-estate gradient of at least 10 MV/m and very strong HOM damping to push BBU thresholds up by two or more orders of magnitude compared to existing designs. Cavity shape, HOM damping, power couplers, tuners etc. are being designed and optimized for this application. Cavity considerations include a large iris for beam halo, low-RF losses, HOM frequencies and Q’s, low peak surface fields, field flatness and microphonics. Module considerations include high packing factor, low static heat leak, image current heating of beam-line components, cost and maintainability. This module is being developed for the next generation ERL based high power FELs but may be useful for other applications such as electron cooling, electron-ion colliders, industrial processing etc.

• J. Rathke, A. Ambrosio, H. Bluem, M.D. Cole, E. Peterson, T. Schultheiss, A.M.M. Todd
  AES, Medford, NY
• I.E. Campisi, E. Daly, J. Hogan, J. Mammosser, G. Neil, J.P. Preble, R.A. Rimmer, C.H. Rode, T.E. Whitlatch, M. Wiseman
  Jefferson Lab, Newport News, Virginia
• J.S. Sekutowicz
  DESY, Hamburg

Advanced Energy Systems has recently completed the design of a four cavity cryomodule for use as an FEL injector accelerator on the JLAB Injector Test Stand. Fabrication is nearing completion. Four 748.5 MHz single cell superconducting cavities have been completed and are currently at Jefferson Lab for final processing and test prior to integration in the module. This paper will review the design and fabrication of the cavities and cryomodule.

• M.P. Hechler, R.I. Cutler, J.J. Error
  ORNL, Oak Ridge, Tennessee
• W.J. McGahern
  BNL, Upton, Long Island, New York

SNS is managed by UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. Department of Energy. SNS is a partnership of six national laboratories: Argonne, Brookhaven, Jefferson, Lawrence Berkeley, Los Alamos and Oak Ridge.

• R. Kersevan, D.P. Briggs, I.E. Campisi, J.A. Crandall, D.L. Douglas, T. Hunter, P. Ladd, C. Luck, R.C. Morton, K.S. Russell, D. Stout
  ORNL, Oak Ridge, Tennessee

The SNS superconducting linac (SCL) consists of 23 cryomodules (CMs), with possibly 9 additional CMs being added for future energy upgrade from 1 GeV to 1.3 GeV. A total of 32 warm sections separate the comparatively short CMs, and this allows a CM exchange within 48 hours, in order to meet demanding beam availability specifications. The 32 warm section chambers are installed between each pair of CMs, with each section containing a quadrupole doublet, beam diagnostics, and pumping. The chambers are approximately 1.6 m long, have one bellow installed at each end for alignment, and are pumped by one ion-pump. The preparation and installation of these chambers must be made under stringent clean and particulate-free conditions, in order to ensure that the performance of the SCL CMs is not compromised. This paper will discuss the development of the cleaning, preparation, and installation procedures that have been adopted for the warm sections, and the vacuum performance of this system.

• D. Stout, I.E. Campisi, F. Casagrande, R.I. Cutler, D.R. Hatfield, M.P. Howell, T. Hunter, R. Kersevan, P. Ladd, W.H. Strong
  ORNL, Oak Ridge, Tennessee

The Spallation Neutron Source (SNS) cold linac consists of 11 medium beta (0.61) and 12 high beta (0.81) superconducting RF cryomodules, 32 intersegment quadrupole magnet/diagnostics stations, 9 spool beampipes for future upgrade cryomodules, and two differential pumping stations on either side of the linac. The cryomodules and spool beampipes were designed and manufactured by Jefferson Laboratory, and the quadrupole magnets and beam position monitors were designed and furnished by Los Alamos National Laboratory. The remaining items were designed by ORNL. At present we are installing and testing the cold linac. Experience gained during installation will be presented. The performance in terms of mechanical and cryogenic systems will be described.

• J. Galambos, C. Chu, S.M. Cousineau, V.V. Danilov, J.G. Patton, T.A. Pelaia, A.P. Shishlo
  ORNL, Oak Ridge, Tennessee
• C.K. Allen
  LANL, Los Alamos, New Mexico

XAL is an application programming framework used at the Spallation Neutron Source (SNS) project in Oak Ridge. It is written in Java, and provides users with a hierarchal view of the accelerator. Features include database configuration of the accelerator structure, an online envelope model that is configurable from design or live machine values, an application framework for quick-start GUI development, a scripting interface for algorithm development, and a common toolkit for shared resources. To date, about 25 applications have been written, many of which are used extensively in the SNS beam commissioning activities. The XAL framework and example applications will be discussed.

• A.V. Aleksandrov
  ORNL, Oak Ridge, Tennessee

The Spallation Neutron Source accelerator systems will deliver a 1.0 GeV, 1.4 MW proton beam to a liquid mercury target for neutron scattering research. The accelerator complex consists of an H^- injector, capable of producing one-ms-long pulses at 60Hz repetition rate with 38 mA peak current, a 1 GeV linear accelerator, an accumulator ring and associated transport lines. The 2.5MeV beam from the Front End is accelerated to 86 MeV in the Drift Tube Linac, then to 185 MeV in a Coupled-Cavity Linac and finally to 1 GeV in the Superconducting Linac. The staged beam commissioning of the accelerator complex is proceeding as component installation progresses. The Front End, Drift Tube Linac and three of the four Coupled-Cavity Linac modules have been commissioned with beam at ORNL. Results and status of the beam commissioning program will be presented.

• W. Chou, A.I. Drozhdin, C. Hill, M.A. Kostin, J.-F. Ostiguy, Z. Tang
  Fermilab, Batavia, Illinois
• H.C. Bryant
  UNM, Albuquerque, New Mexico
• R.J. Macek
  LANL, Los Alamos, New Mexico
• G. Rees
  CCLRC/RAL/ASTeC, Chilton, Didcot, Oxon
• P.S. Yoon
  Rochester University, Rochester, New York

Fermilab is working on the design of an 8 GeV superconducting RF H^- linac called the Proton Driver. The energy of the H^- beam is an order of magnitude higher than any existing H^- beams. This brings up a number of new challenges to the transport, stripping and injection into the next machine (the Main Injector), such as blackbody radiation stripping, magnetic field and residual gas stripping, Stark states of hydrogen atoms, foil stripping efficiency, single and multiple Coulomb scattering, energy deposition, foil heating and stress, radiation activation, collimation, jitter correction, etc. This paper will give a summary of these studies.*

*For details the reader is referred to FERMILAB-TM-2285-AD-T.

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

(J. Wei for the Spallation Neutron Source Collaboration) After six years, the construction of the Spallation Neutron Source (SNS) accumulator ring [1] and the transport lines is completed in March 2005. Designed to deliver 1.5 MW beam power (1.5 x 10¹⁴ protons of 1 GeV kinetic energy at a repetition rate of 60 Hz), stringent measures have been implemented in the fabrication, test, and assembly to ensure the quality of the accelerator systems. This paper summarizes the construction of the ring and transport systems with emphasis on the challenging technical issues and their solutions [2].

[1] J. Wei, et al, Phys. Rev. ST-AB, Vol. 3, 080101 (2000). [2] J. Wei, "Synchrotrons and Accumulators for High-Intensity Proton Beams", Rev. Mod. Phys., Vol. 75, 1383 – 1432 (2003).

• G.W. Dodson, T.L. Williams
  ORNL, Oak Ridge, Tennessee

The SNS Front End, Drift Tube Linac and most of the Coupled Cavity Linac have been operated during commissioning. Operating statistics were taken and used by system owners to target developments to improve accelerator availability. This progression will be shown along with the overall availability goals of the SNS and a RAM calculation showing the system and subsystem availability required to meet these goals.

• A. Feschenko, S. Bragin, Y. Kiselev, L.V. Kravchuk, O. Volodkevich
  RAS/INR, Moscow
• A.V. Aleksandrov, J. Galambos, S. Henderson, A.P. Shishlo
  ORNL, Oak Ridge, Tennessee

The ?t procedure is a time of flight technique for setting the phases and amplitudes of accelerating fields in a multi-cavity linac. It was initially proposed and developed for the LAMPF linac in the early seventies and since then has been used in several accelerators. The SNS linac includes four CCL modules (Side Coupled Structure) operating at 805 MHz for the energy range from 86.8 MeV up to 185.6 MeV. The ?t procedure has been implemented for the SNS CCL linac and was used for its initial beam commissioning. Brief theory of the procedure, the results of the design parameter calculations and the experimental results of phase and amplitude setpoints are presented and discussed.

• D. Raparia, J.G. Alessi, A. Ruggiero, W.-T. Weng
  BNL, Upton, Long Island, New York

BNL plans to upgrade the AGS proton beam from the current 0.14 MW to higher than 1.0 MW and beyond for such a neutrino facility. We have examined possible upgrades to the AGS complex that would meet the requirements of the proton beam for a 1.0 MW neutrino superbeam facility. We are proposing to replace part of the existing 200 MeV linac with coupled cavity structure from 116 MeV to 400 MeV and then add additional 1.1 GeV superconducting linac to reach a final energy of 1.5 GeV for direct H^- injection into the AGS. We will present possible choices for the upgrade and our choice and its design.

• 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.

• M.A. Plum, M. Holding, T. McManamy
  ORNL, Oak Ridge, Tennessee

The spallation neutron production target at the SNS facility is designed for 1.4 MW beam power. Both beam position and profile must be carefully controlled within narrow margins to avoid damage to the target. The position must be within 2 mm of the target center, and 90% of the beam must be within the nominal 70 mm x 200 mm spot size, without exceeding 0.18 A/m² peak beam current density. This is a challenging problem, since most of the diagnostics are 9 m upstream of the target, and because the high beam power limits the lifetime of intercepting diagnostics. Our design includes a thermocouple halo monitor approximately 2 m upstream of the target face, and a beam position monitor, an insertable harp profile monitor, and a beam shape monitor approximately 9 m upstream. In this paper we will discuss our strategy to commission the beam delivery system and to meet target requirements during nominal operation.

• 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.

• W. Blokland, D.J. Murphy, J.D. Purcell
  ORNL, Oak Ridge, Tennessee
• A.V. Liyu
  RAS/INR, Moscow
• C.D. Long
  Innovative Design, Knoxville, Tennessee
• M. Sundaram
  University of Tennessee, Knoxville, Tennessee

The Spallation Neutron Source (SNS) accelerator systems will deliver a 1.0 GeV, 1.4 MW proton beam to a liquid mercury target for neutron scattering research. The accelerator complex consists of a 1 GeV linear accelerator, an accumulator ring and associated transport lines. The SNS diagnostics platform is PC-based running Embedded Windows XP and LabVIEW. The diagnostics instruments communicate with the control system using the Channel Access (CA) protocol of the Experimental Physics and Industrial Control System (EPICS). This paper describes the Diagnostics Group’s approach to collecting data from the instruments, processing it, and presenting live in a summarized way over the web. Effectively, adding a supervisory level to the diagnostics instruments. One application of this data mining is the "Diagnostics Status Page" that summarizes the insert-able devices, transport efficiencies, and the mode of the accelerator in a compact webpage. The displays on the webpage change automatically to show the latest and/or most interesting instruments in use.

• C. Chu, T.A. Pelaia
  ORNL, Oak Ridge, Tennessee

Automated beam trajectory correction with dipole correctors is developed and tested during the Spallation Neutron Source warm linac commissioning periods. The application is based on the XAL Java framework with newly developed optimization tools. Also, dipole corrector polarities and strengths, and beam position monitor (BPM) polarities were checked by an orbit difference program. The on-line model is used in both the trajectory correction and the orbit difference applications. Experimental data for both applications will be presented.

• J. Galambos, A.V. Aleksandrov, C. Deibele, S. Henderson
  ORNL, Oak Ridge, Tennessee

To assist the beam commissioning in the Spallation Neutron Source (SNS) linac, a general purpose RF tuning application has been written to help set RF phase and amplitude. It follows the signature matching procedure described in Ref.* The method involves varying an upstream Rf cavity amplitude and phase settings and comparing the measured downstream beam phase responses to model predictions. The model input for cavity phase and amplitude calibration and for the beam energy are varied to best match observations. This scheme has advantages over other RF tuning techniques of not requiring intercepting devices (e.g. Faraday Cups), and not being restricted to a small linear response regime near the design values. The application developed here is general and can be applied to different RF structure types in the SNS linac. Example applications in the SNS Drift Tube Linac (DTL) and Coupled Cavity Linac (CCL) structures will be shown.

*T.L. Owens, M.B. Popovic, E.S. McCrory, C.W. Schmidt, L. J. Allen, "Phase Scan Signature Matching for Linac Tuning," Particle Accelerators, 1994 Vol 98, p. 169.

• M. Sundaram
  University of Tennessee, Knoxville, Tennessee
• W. Blokland
  ORNL, Oak Ridge, Tennessee
• C.D. Long
  Innovative Design, Knoxville, Tennessee

The Spallation Neutron Source (SNS) accelerator systems will deliver a 1.0 GeV, 1.4 MW proton beam to a liquid mercury target for neutron scattering research. The accelerator complex consists of a 1.0 GeV linear accelerator, an accumulator ring and associated transport lines. The SNS diagnostics platform is PC-based and will run Windows for its OS and LabVIEW as its programming language. The diagnostics platform as well as other control systems and operator consoles use the Channel Access (CA) protocol of the Experimental Physics and Industrial Control System (EPICS) to communicate. This paper describes the tools created to evaluate the diagnostic instrument using our standard programming environment, LabVIEW. The tools are based on the LabVIEW Channel Access library and can run on Windows, Linux, and Mac OS X. The data-acquisition tool uses drop and drag to select process variables organized by instrument, accelerator component, or beam parameters. The data can be viewed on-line and logged to disk for later use. A drag and drop display creation tool supports the quick creation of graphical displays to visualize the data produced by the instruments without the need for programming.

• A.V. Liyu
  RAS/INR, Moscow
• W. Blokland, D.H. Thompson
  ORNL, Oak Ridge, Tennessee

The Spallation Neutron Source (SNS) accelerator systems will deliver a 1.0 GeV, 1.4 MW proton beam to a liquid mercury target for neutron scattering research. The accelerator complex consists of a 1 GeV linear accelerator, an accumulator ring and associated transport lines. The SNS diagnostics platform is PC-based and will run Windows for its OS and LabVIEW as its programming language. Data acquisition hardware will be based on PCI cards. There will be about 300 rack-mounted computers. The Channel Access (CA) protocol of the Experimental Physics and Industrial Control System (EPICS) is the SNS control system communication standard. This paper describes the approaches, implementation, and features of LabVIEW library to CA for Windows, Linux, and Mac OS X. We also discuss how the library implements the asynchronous CA monitor routine using LabVIEW’s occurrence mechanism instead of a callback function (which is not available in LabVIEW). The library is used to acquire accelerator data and applications have been built on this library for console display and data-logging.

• S. Peng
  ORNL, Oak Ridge, Tennessee
• L.T. Hoff, K. Smith
  BNL, Upton, Long Island, New York

The low-level RF control system for the SNS Ring differs considerably from that for the Linac. To accommodate requirements for higher data throughput and improved performance the system is based on a PCI Digital Signal Processor (DSP). In accordance with SNS standards, a VME-based PowerPC© is used, but advantage is taken of the on-board PMC slot which houses a Bittware© Hammerhead© PMC card with four AD-21162 DSPs.The EPICS system handles system configuration and data traffic while the DSP performs the low-level RF controls. Protocol and software to support both the PowerPC and the DSP have been developed. This paper presents the system design and initial testing experience.

• J.Y. Tang, J.A. Crandall, P. Ladd, D.C. Williams
  ORNL, Oak Ridge, Tennessee

SNS is managed by UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. Department of Energy.

• J.Y. Tang, A.V. Aleksandrov, M.M. Champion, P.E. Gibson, J.P. Schubert
  ORNL, Oak Ridge, Tennessee
• A. Feschenko, Y. Kiselev, A.S. Kovalishin, L.V. Kravchuk, A.I. Kvasha
  RAS/INR, Moscow

The Resonance Control Cooling System (RCCS) for the warm linac of the Spallation Neutron Source was designed by Los Alamos National Laboratory. The primary design focus was on water cooling of individual component contributions. The sizing the RCCS water skid was accomplished by means of a specially created SINDA/FLUINT model tailored to these system requirements. A new model was developed in Matlab Simulink and incorporates actual operational values and control valve interactions. Included is the dependence of RF input power on system operation, cavity detuning values during transients, time delays that result from water flows through the heat exchanger, the dynamic process of water warm-up in the cooling system due to dissipated RF power on the cavity surface, differing contributions on the cavity detuning due to drift tube and wall heating, and a dynamic model of the heat exchanger with characteristics in close agreement to the real unit. Because of the Matlab Simulink model, investigation of a wide range of operating issues during both transient and steady state operation is now possible. Results of the DTL RCCS modeling are presented

• W.R. DeVan, S.E. Hicks, G.S. Lawson, W.H. Wagner, D.M. Wantland, E. Williams
  ORNL, Oak Ridge, Tennessee

Work supported by the U.S. Department of Energy under Contract DE-AC05-00OR22725.