[en] This paper describes a procedure to set the phase and amplitude of the RF fields in the Spallation Neutron Source (SNS) linac's superconducting cavities. The linac uses superconducting cavities to accelerate the H^- ion beam from the normal conducting linac at 185 MeV to a final energy of ∼1 GeV. There are two types of cavities in the linac, 33 cavities with a geometric beta of 0.61 and 48 cavities with a geometric beta of 0.81. The correct phase setting of any single superconducting cavity depends on the RF phase and amplitude of all the preceding superconducting cavities. For the beam to be properly accelerated it must arrive at each cavity with a relative phase (φ_s), called the synchronous phase, of about -20 degrees. That is, it must arrive early with respect to the phase at which it would gain the maximum energy by 20 degrees. This timing provides the longitudinal focusing. Beam particles arriving slightly later gain more energy and move faster relative to the synchronous beam particle. The problem is to set the phase and amplitude of each cavity in the linac so that the synchronous particle arrives at each cavity with the correct phase. The amplitude of each superconducting cavity will be adjusted as high as possible constrained only by the available RF power and the breakdown field of the cavity

[en] The low-energy-beam transport (LEBT) system for the Low-Energy Demonstration Accelerator (LEDA) transports the beam from the ion-source plasma surface to the LEDA RFQ entrance. The code PARMELA performed these simulations of the beam transport through the LEBT. This code can simultaneously transport three particle types of different charge-to-mass ratio. Electrostatic fields, magnetic fields, and space charge influence the beam particles in this simulation. The electrostatic fields exist in the ion-source extractor. The magnetic field exists in the ion source and in the solenoid lenses. The e^- particles, introduced into the beam of H⁺ and H₂⁺, simulate the space charge neutralization by the residual gas in the LEBT. The H⁺ and H₂⁺ ions leaving the source emerge from a longitudinal magnetic field, which causes the beam to rotate

No abstract available

[en] The codes PARMTEQM and RFQTRAK simulate the beam transport through the radio-frequency-quadrupole (RFQ) accelerator for the low-energy-demonstration accelerator (LEDA). They predict 95% transmission for a matched 110-mA proton beam with a normalized-rms emittance of 0.02 mm mrad. RFQTRAK simulates the effects of arbitrary vane-tip misalignments. This RFQ includes some new features in its design. It consists of four resonantly coupled 2-m-long segments that make up its 8-m length. It has higher vane-gap voltages at the high-energy end than the low-energy end. The entrance end of the RFQ has lower transverse focusing strength to facilitate beam matching. The exit of the RFQ has a transition cell and a radial-matching section. The exit radial-matching section matches the beam into the following accelerator

[en] The radio frequency quadrupole (RFQ) accelerator began as 'The ion linear accelerator with space-uniform strong focusing' conceived by I. M. Kapchinskii and V. A. Teplyakove. In 1979, R. H. Stokes, K. R. Crandall, J. E. Stovall and D. A. Swenson gave this concept the name RFQ. And by 1983, at least 15 laboratories throughout the world were working on various FWQ designs. In the early years, there were many types of geometry considered for the RFQ, but only a few types have survived. The two cavity geometries now used in almost all RFQs are the 4-vane and 4-rod structures. The 4-vane structure is the most popular because its operating frequency range (80 to -500 MHz) is suitable for light ions. Heavy ions require low frequencies (below 200 MHz). Because the 4-rod structure has smaller transverse dimensions than a 4-vane RFQ at the same frequency, the 4-rod RFQ is often preferred for these applications. This paper will describe how the RFQ accelerates and focuses the beam. The paper also discusses some of the important technical advances in designing and building RFQs.

[en] The code PARMILA simulates the beam transmission through the Accelerator for the Production of Tritium (APT) linac. The beam is equipartitioned when the longitudinal and transverse temperatures are equal. This paper explores the consequence of equipartitioning in the APT linac. The simulations begin with a beam that starts at the ion-source plasma surface. PARMILA tracks the particles from the RFQ exit through the 1.7-GeV linac. This paper compares two focusing schemes. One scheme uses mostly equal strength quadrupoles. The equipartitioning scheme uses weaker focusing in the high-energy portion of the linac. The RMS beam size with the equipartitioning scheme is larger, but the relative size of the halo is less than in the equal-strength design

[en] A 2.7-m side-coupled linac has been built as part of the 5-MeV injector for the cw room-temperature racetrack microtron (RTM) being constructed in collaboration with the National Bureau of Standards (NBS). The linac is designed to accelerate the electron beam from 1 to 5 MeV with an accelerating gradient of 1.5 MeV/m. Fabrication of the structure started October 4, 1982 and was completed February 28, 1983, when it was tested with a cw power level of 82 kW. The structure has an effective shunt impedance (ZT₂) of 82 5 ohm/m. No change in field distribution was detected at any power level. The operating frequency is 2380 MHz

[en] A resonance-control technique is described that has been successfully applied to several cw accelerating structures built by the Los Alamos National Laboratory for the National Bureau of Standards and for the University of Illinois. The technique involves sensing the rf fields in an accelerating structure as well as the rf power feeding into the cavity and, then, using the measurement to control the resonant frequency of the structure by altering the temperature of the structure. The temperature of the structure is altered by adjusting the temperature of the circulating cooling water. The technique has been applied to continuous wave (cw) side-coupled cavities only but should have applications with most high-average-power accelerator structures. Some additional effort would be required for pulsed systems

[en] This paper presents the results of tuning the 8 meter long Radio Frequency Quadrupole (RFQ) built for the Low Energy Demonstration Accelerator (LEDA). This 350-MHz RFQ is split into four 2-meter-long-RFQs. Then they are joined with resonant coupling to form an 8-meter-long RFQ. This improves both the longitudinal stability and the transverse stability of this long RFQ. The frequencies of the modes near the RFQ mode are measured. The authors show the effect on the RF fields of an error in the temperature of each one of the 2-meter-long-RFQs. Slug tuners distributed along the outer walls tune the RFQ. The program RFQTUNE is used to determine the length of the tuners. The tuners are machined to length when the final tuning is complete

[en] The rf power system and its closed-loop feedback control for the racetrack microtron (RTM) chopper/buncher system are described. Measurements made on the response of the feedback system to external perturbations will also be reported