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A new Allison-type emittance scanner has been built to characterize the ion sources and low energy beam transport systems at Spallation Neutron Source. In this work, the emittance characteristics of the H- beam produced with the external-antenna rf-driven ion source and transported through the two-lens electrostatic low energy beam transport are studied. The beam emittance dependence on beam intensity, extraction parameters, and the evolution of the emittance and twiss parameters over beam pulse duration are presented. [ABSTRACT FROM AUTHOR]

This paper describes the ramp up of the beam power for the Spallation Neutron Source by ramping up the pulse length, the repetition rate, and the beam current emerging from the H- source. Starting out with low repetition rates (≤10 Hz) and short pulse lengths (≤0.2 ms), the H- source and low-energy beam transport delivered from Lawrence Berkeley National Laboratory exceeded the requirements with almost perfect availability. This paper discusses the modifications that were required to exceed 0.2 ms pulse length and 0.2% duty factor with acceptable availability and performance. Currently, the source is supporting neutron production at 1 MW with 38 mA linac beam current at 60 Hz and 0.9 ms pulse length. The pulse length will be increased to ∼1.1 ms to meet the requirements for neutron production with a power between 1 and 1.4 MW. A medium-energy beam transport (MEBT) beam current of 46 mA with a 5.4% duty factor has been demonstrated for 32 h. A 56 mA MEBT beam current with a 4.1% duty factor has been demonstrated for 20 min at the conclusion of a 12-day production run. This is close to the 59 mA needed for 3 MW neutron productions. Also notable is the Cs2CrO4 cesium system, which dispenses ∼10 mg of Cs during the startup of the ion source, sufficient for producing the required 38 mA for 4 weeks without significant degradation. [ABSTRACT FROM AUTHOR]

The U.S. Spallation Neutron Source (SNS) will require substantially higher average and pulse H- beam currents than can be produced from conventional ion sources such as the base line SNS source. H- currents of 40–50 mA (SNS operations) and 70–100 mA (power upgrade project) with a rms emittance of 0.20–0.35π mm mrad and a ∼7% duty factor will be needed. We are therefore investigating several advanced ion source concepts based on rf plasma excitation. First, the performance characteristics of an external antenna source based on an Al2O3 plasma chamber combined with an external multicusp magnetic configuration, an elemental Cs system, and plasma gun will be discussed. Second, the first plasma measurements of a helicon-driven H- ion source will also be presented. [ABSTRACT FROM AUTHOR]

The Spallation Neutron Source (SNS), a large scale neutron production facility, routinely operates with 30^0 mA peak current in the linac. Recent measurements have shown that our RF-driven internal antenna, Cs-enhanced, multi-cusp ion sources injects ~55 mA of H- beam current (~1ms, 60 Hz) at 65-kV into a Radio Frequency Quadrupole (RFQ) accelerator through a closely coupled electro-static Low-Energy Beam Transport system. Over the last several years a decrease in RFQ transmission and issues with internal antennas has stimulated source development at the SNS both for the internal and external antenna ion sources. This report discusses progress in improving internal antenna reliability, H- yield improvements which resulted from modifications to the outlet aperture assembly (applicable to both internal and external antenna sources) and studies made of the long standing problem of beam persistence with the external antenna source. The current status of the external antenna ion source will also be presented. [ABSTRACT FROM AUTHOR]

Spallation Neutron Source is currently in progress of a multiyear plan to ramp ion beam power to the initial design power of 1.4 MW. Key to reaching this goal is understanding and improving the operation of the H- ion source. An Allison scanner was installed on the ion source in the test facility to support this improvement. This paper will discuss the hardware and the software control system of the installed Allison scanner. The hardware for the system consists of several parts. The heart of the system is the scanner head, complete with associated bias plates, slits, and signal detector. There are two analog controlled high voltage power supplies to bias the plates in the head, and a motor with associated controller to position the head in the beam. A multifunction data acquisition card reads the signals from the signal detector, as well as supplies the analog voltage control for the power supplies. To synchronize data acquisition with the source, the same timing signal that is used to trigger the source itself is used to trigger data acquisition. Finally, there is an industrial personal computer to control the rest of the hardware. Control software was developed using National Instruments LABVIEW, and consists of two parts: a data acquisition program to control the hardware and a stand alone application for offline user data analysis. [ABSTRACT FROM AUTHOR]

The ion source for the spallation neutron source (SNS) is a radio-frequency, multicusp source designed to deliver 45 mA of H- to the SNS accelerator with a pulse length of 1 ms and repetition rate of 60 Hz. A total of three ion sources have been fabricated and commissioned at Lawrence Berkeley National Laboratory and subsequently delivered to the SNS at the Oak Ridge National Laboratory. The ion sources are currently being rotated between operation on the SNS accelerator, where they are involved in ongoing efforts to commission the SNS LINAC, and the hot spare stand (HSS), where high-current tests are in progress. Commissioning work involves operating the source in a low duty-factor mode (pulse width ∼200 μs and repetition rate ∼5 Hz) for extended periods of time while the high-current tests involve source operation at full duty-factor of 6% (1 ms/60 Hz). This report discusses routine performance of the source employed in the commissioning role as well as the initial results of high-current tests performed on the HSS. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]