Low Energy Beam Transport System Research Articles

Proton injector operational results on a high-power continuous-wave radio-frequency quadrupole accelerator

A 50 keV proton injector utilizing a dc microwave source has been used to operate a 1.25 MeV continuous wave (cw) radio-frequency quadrupole (RFQ) accelerator. RFQ injection places stringent requirements on beam properties including centroid control, emittance, and phase-space matching. The ion source chosen for these applications is based on a microwave discharge operating at 2.45 GHz with an on-axis magnetic field near 875 G. The injector employs a space-charge-neutralized, two-solenoid-lens, low-energy beam transport (LEBT) system. Proton injector development with a 1.25 MeV RFQ has resulted in meeting the RFQ 75 mA design current specification in cw mode. Details of the ion source and LEBT operation are presented, and simulations for ion beam extraction and transport are compared with the injector measurements. The proton injector has been converted to 75 keV beam operation for injecting into a 6.7 MeV cw RFQ.

2D simulation and optimization of the volume H− ion source extraction system for the spallation neutron source accelerator

Abstract The low-energy beam transport system (LEBT) for the Spallation Neutron Source (SNS) is required to transport 35 mA of a 65 keV H − ion beam from the ion source to the RFQ accelerator entrance with a normalized rms emittance of less than 0.15 π mm mrad. A radio frequency driven, magnetically filtered multicusp ion source is under development at LBNL. The H − beam extraction from this ion source is being simulated utilizing the 2D-computer code IGUN [Rev. Sci. Instr. 63 (1992) 2756]. An H − ion extraction model is discussed. Computational results are presented for the H − ion beam emittance of a single aperture two electrode extraction system and for the tuning range of the low-energy beam transport system.

Simulation of the low energy H− injector into the National Spallation Neutron Source radio frequency quadrupole accelerator

The low energy beam transport system (LEBT) for the National Spallation Neutron Source is required to transport 35 mA of a 65 keV H− ion beam from the ion source to the radio frequency quadrupole accelerator (RFQ) entrance with a normalized root-mean-square emittance < 0.15 pi mm mrad. At a later time, it is anticipated that this beam current will be increased to 70 mA. For this purpose a radio-frequency driven, magnetically filtered multicusp ion source is under development at LBNL. The H− beam extraction from the ion source is being simulated utilizing the three-dimensional (3D) computer code ARGUS. H− ion beam extraction from the ion source requires proper simulation of the extraction of both plasma electrons and the desired H− ions. The goal is to optimize the LEBT system so that the electrons are completely deflected between the first two electrodes and the desired H− beam is properly matched into the RFQ accelerator. The magnetic field in the extraction region is being optimized by using the 3D magnetic code OPERA3D. The performance of the all electrostatic LEBT for the transport of higher currents (>70 mA) is discussed.

Status report on a dc 130 mA, 75 keV proton injector (invited)

A 110 mA, 75 keV dc proton injector is being developed at Los Alamos. A microwave proton source is coupled to a two solenoid, space-charge neutralized, low-energy beam transport (LEBT) system. The ion source produces 110 mA proton current at 75 keV using 600–800 W of 2.45 GHz discharge power. Typical proton fraction is 85%–90% of the total extracted ion current, and the rms normalized beam emittance after transport through a prototype 2.1 m LEBT is 0.20 (πmm mrad). Beam space-charge neutralization is measured to be >98% which enables the solenoid magnetic transport to successfully match the injector beam into a radio-frequency quadrupole. Beam simulations indicate small emittance growth in the proposed 2.8 m low-energy demonstration accelerator LEBT. The LEBT also contains beam diagnostics, steering, and a beam deflector for variable duty factor and accelerator fast protect functions. The injector beam availability status is also discussed.

Spallation neutron source symposium held in Washington

An important step towards the construction of a new neutron source for the Unitedstates tookplaceonMarch3 and 4,1998. About 250 attendees representing all of the major US neutron scattering facilities joined forces to present a convincing case for the importance of neutron scattering research for science, education and industry. The $1.3 billion Spallation Neutron Source (SNS) project will be built by a consortium of Department of Energy (DOE) laboratories, Oak Ridge National Laboratory (ORNL), Brookhaven National Laboratory (BNL), Argonne National Laboratory (ANL). Los Alamos National Laboratory (LANL) and Lawrence Berkeley National Laboratory (LBNL). LBNL will be responsible for designing and building the SNS's front-end system, which includes an ion source, beam formation and control hardware, and low-energy beam transport and acceleration systems. LANL will be responsible for the linac, which accelerates the H-beam from 2.5 to 1000 million electron volts. ANL and ORNL will be responsible for developing the neutron scattering instrumentation and moderator designs. BNL will be responsible for the accumulator ring structure, which bunches and intensities the ion beam for delivery onto the mercury target to produce the pulsed neutron beams. ORNL will be responsible for the coordination, installation and operation of the new source, project management, conventional construction, and design and construction of the liquid mercury target.

Instrumentation for ion sources and low energy beam transport systems (invited) (abstract)a)

In this article we describe computer-based instrumentation to control and optimize the operation of an ion source, and schemes to measure beam properties in low energy beam transport lines. Emphasis is given to the methods used at the accelerator complex of the Paul Scherrer Institute.

An electrostatic LEBT for a low-emittance injector: transport and focusing of a high-brightness H − beam from a magnetron ion source

In the context of developing an efficient low-energy beam transport (LEBT) system for a low-emittance injector the problem of transport and matching of a 30 mA, 35 kV H − beam from a magnetron-type ion source is studied; the analysis is done incorporating important experimental constraints. A 30 cm-long LEBT, consisting of six electrostatic quadrupole lenses and a short einzel lens, is designed. Its control parameters are optimized to achieve a solution which matches with the acceptance of a small-aperture radio-frequency quadrupole (RFQ) accelerator. The results of beam dynamics calculations are discussed, and the key issues for emittance growth and its control are acknowledged.

Electrostatic low-energy beam transport systems for the SSC linaca)

This paper provides arguments to choose electrostatic low-energy beam transport (LEBT) over the magnetic LEBT for the SSC linac. We will outline the rules to design the electrostatic LEBTs with examples of SSC LEBTs.

Efficient low-energy beam transport for intense, high-brightness H− beams in high energy accelerators: Perspectives and a solution using ESQ lenses (abstract)a)

The characteristics of a 30 mA, 35 kV H− beam from a volume source have been determined using emittance measurements. A low energy-beam transport (LEBT) system consisting of six electrostatic quadrupole lenses and a short (about 5 cm long) single-stage einzel lens is designed with the aim of transporting the beam over a distance of about 30 cm and focusing a clean, matched beam into a radio-frequency quadrupole accelerator of the Superconducting Super Collider. The system parameters are chosen on the basis of simulation of beam dynamics. The emittance growth in the LEBT section is within a factor of about 1.5 and this satisfies the requirement of the emittance budget. The LEBT system is designed to be mechanically rugged.

Efficient low-energy beam transport for intense, high-brightness H− beams in high energy accelerators: Perspectives and a solution using ESQ lensesa)

The characteristics of a 30 mA, 35 kV H− beam from a volume source have been determined using emittance measurements. A low energy-beam transport (LEBT) system consisting of six electrostatic quadrupole lenses and a short (about 5 cm long) single-stage einzel lens is designed with the aim of transporting the beam over a distance of about 30 cm and focusing a clean, matched beam into a radio-frequency quadrupole accelerator of the Superconducting Super Collider. The system parameters are chosen on the basis of simulation of beam dynamics. The emittance growth in the LEBT section is within a factor of about 1.5 and this satisfies the requirement of the emittance budget. The LEBT system is designed to be mechanically rugged.

The calculations of low-energy beam transport

After the ion beams are extracted from ion sources, it is necessary to transport the beams to the experimental areas or to the accelerating installations. Low-energy beam transport systems usually consist of some axially symmetrical electrostatic focusing and accelerating lenses as well as quadrupoles and dipoles. Here, we discuss the calculation methods for the beam transport in electrostatic lens systems and describe a computer program for this use.

H − ion source and LEBT activities at SSCL

The Superconducting Super Collider (SSC) ion source and low energy beam transport (LEBT) system will provide a matched 35 kV, 30 mAH − beam with normalized rms emittance of less than 0.2 π mm mrad into the SSC radio frequency quadropole (RFQ). The ion source candidates are rf-driven volume source and magnetron source. Electrostatic LEBTs, more specifically HESQ and einzel lens, are the candidate LEBTs for SSC. An extensive experimental program is under way to characterize the SSC ion sources and LEBT concepts to identify the best ion source and LEBT configuration for SSC. The available experimental results pertinent to the performance of the SSC ion sources and LEBTs will be discussed.

Low-energy injector design for SSC

An injector is being designed for SSC that will deliver 30 mA of H− at 35 keV, matched to the RFQ input. The H− ions are produced by a new rf-driven multicusp source that uses no cesium. The ions are extracted by a high-perveance accelerator designed to handle the large electron content of this type of source. The low-energy beam transport system (LEBT) uses electrostatic focusing; gas-neutralized magnetic focusing is ruled out because pulse lengths (7–35 μs) are shorter than plasma buildup times and because pulse intervals are longer than plasma decay times. Plasma buildup is prevented by the LEBT electric fields, so the system is noise free and stable. The advantages of electrostatic LEBTs were demonstrated by a previous design tested at LBL, which showed negligible emittance growth, confirming the results of computer modeling. The object of our new LEBT design is to preserve the emittance of the rf-driven source, which is less than 0.01 π mrad cm (normalized rms), and thereby produce a beam well within the SSC RFQ acceptance of 0.018 π mrad cm.

Injection of high brightness H − beams into RFQ accelerators

The state of the art in low-energy beam transport (LEBT) of high brightness H − beams from the source to the RFQ accelerator using gas focusing and solenoid or quadrupole magnets is reviewed. Proposed advanced LEBT schemes with electric focusing elements presently under investigation avoid charge neutralization and hence the beam loss and emittance degradation inherent in gas focusing systems. Results of conceptual design studies for LEBT systems with electrostatic quadrupoles (ESQ) and einzel lenses are discussed.

Computer modeling of negative ion beam formation

Sources of root-mean-square (RMS) emittance growth are described for negative ion extractors in both volume and surface negative ion sources and plasma low-energy beam transport systems. For surface negative ion sources of the Lawrence Berkeley Laboratory or Los Alamos National Laboratory [on Los Alamos Meson Particle Facility (LAMPF)], attention is paid to the nonlinear transverse emittance growth mechanism of the beam/warm plasma interaction. In some cases this is a large effect. In addition, non-normal sheath fields at a convertor are examined as a source of emittance growth. For volume sources, attention is paid to aberration production due to field penetration from the extractor, RMS emittance growth enhancement by a negatively biased plasma extraction electrode, and emittance growth caused by transverse extraction across a magnetic field. For both volume and surface sources, RMS emittance growth due to nonlinear aberration at the plasma extraction electrode is analyzed. Time-dependent contributions to emittance growth are also examined. Nonlinear saturation of ion acoustic waves caused by ion extraction from a warm plasma and beam transversal through a plasma are studied.

Accelerator mass spectrometry at Toronto

Progress in accelerator mass spectrometry at the IsoTrace Laboratory is outlined. Results from calculations on quantum mechanical effects in the sputter source which influence isotope fractionation are presented with examples from radiocarbon analysis. Advantages accruing from the installation of an electric analyser in the low energy beam transport system are discussed with examples from chlorine and carbon analysis.

The oxford folded tandem

The large vertical Van de Graaff in the Nuclear Physics Laboratory at Oxford University has been converted to a folded tandem with a rated terminal voltage of 10 MV. The new parts were designed and largely manufactured within the Laboratory and included the terminal, two negative ion sources, low energy and high energy beam transport and vacuum systems and a new control system. The conversion began in July 1977 and progressed so that experiments with the folded tandem began in January 1979. Excluding the value of manufacture and installation by Laboratory staff, the total cost of the conversion was £100 000, the major items of outside manufacture being the 180° magnet, the accelerator tubes and the serial data links. The main design features of the new accelerator are discussed as well as its performance during the first 18 months of operation.

Design of the Low-Energy Beam Transport System of the Brookhaven 200-MeV Injector Linac

Design of the Low-Energy Beam Transport System of the Brookhaven 200-MeV Injector Linac