Beam Transport Components Research Articles

Upgrade of the medium energy dump geometry for the SPIRAL2 single bunch selector

The medium energy beam transport of the SPIRAL2 superconducting linac contains a single bunch selection system equipped with a 7.5 kW beam dump. This device, originally designed with a long flat slope to decrease the power density so that the maximum operating temperature was 170 °C, was impacted by Coulomb scattering generating two side effects: heating of the downstream beam transport components and degrading of the beam current measurement uncertainty. The paper relates the way these two problems were solved.

The SNS Moderator Demonstration Facility

We describe a moderator demonstration facility at the Spallation Neutron Source (SNS). We will use the Beam Test Facility (BTF) at SNS to provide a moderator neutronics test stand with which we will verify the performance gains expected from the innovative moderator concepts central to the SNS Second Target Station. These concepts include large-volume para-hydrogen moderators and high-brightness moderators, as well as new moderator materials. The BTF provides a test facility for the new Radio-Frequency Quadrupole accelerator (RFQ) to be installed at SNS and produce a pulsed H− beam of 2.5 MeV energy. We will add to the BTF a beam chopper similar to that already used in the SNS at the RFQ exit, various beam transport components, a neutron-producing target, a cryogenic moderator test stand, a reflector-shielding assembly, and a performance assessment neutron beamline.

Accelerator mass spectrometry of the heaviest long-lived radionuclides with a 3-MV tandem accelerator

A 3-MV pelletron tandem accelerator is the heart of the Vienna environmental research accelerator (VERA). The original design of the beam transport components allows the transport of ions of all elements, from the lightest to the heaviest. For light ions the suppression of neighboring masses was sufficient to measure isotopic ratios of 14C/12C and 26Al/27Al as low as 10−15 and 10Be/9Be down to 10−13. To suppress neighboring masses for the heaviest radionuclides in the energy range of 10–20 MeV, the resolution of VERA was increased both by improving the ion optics of existing elements at the injection side and by installing a new high-resolution electrostatic separator at the high-energy side. Interfering ions which pass all beam filters are identified with a Bragg-type ionization detector and a high-resolution time-of-flight system. Two ultra-thin diamond-like carbon (DLC) foils are used in the start and stop detector, which substantially reduces losses due to beam straggling. This improved set up enables us to measure even the heaviest long-lived radionuclides, where stable isobaric interferences are absent (e.g. 236U and 244Pu), down to environmental levels. Moreover, the advantage of a ‘small’ and well manageable machine like VERA lies in its higher stability and reliability which allows to measure these heavy radionuclides more accurately, and also a large number of samples.

A fast bouncing system for the high-energy end of AMS

Drifts in the accelerator stability as well as those in beam transport components are the main limitations in achieving high precision in accelerator mass spectrometry (AMS). In order to achieve the high precision required for isotopic geology and geochronology applications, the sequence of isotopes of interest should be counted for as short an interval as possible. While fast isotope switching can be achieved readily at the low-energy end, it has hitherto not been possible to do so at the high-energy end. For a narrow range of transmission typical for most analysing magnets, fast switching (<1 ms) of the field is not possible if steady state is also desired. We have devised a novel electric means to modulate the beam trajectory in a static magnetic field for the AUSTRALIS (AMS for ultra sensitive trace element and isotopic studies) system, recently developed at the HIAF laboratory. The system is based on a pair of deflector plate sets, deflecting in the orbit plane, at the entrance and exit of the high-energy analysing magnet. Originally designed as energy modulator, the principle readily adapts as an isotope switcher. With switching time <10 ms/isotope, better than 1 permil has been achieved in Pb isotope ratio measurements.

Phase space acceptance and emittance in beam transport with application to tandem accelerators

Phase space acceptance and emittance ellipse areas for a region bounded by beam-limiting apertures of half widths r 1 and r 2 are shown to be πr 1 r 2/| a 12| and πr 1 r 2 D/| a 12|, respectively, for linear beam transport in which D is the determinant of the basic 2×2 portion of the standard beam transport matrix and a 12 is the matrix element which transforms initial divergence into final displacement. A technique of analysis using these and related results is demonstrated for typical beam transport components. Examples are given for analyzing and optimizing beam transport through tandem electrostatic accelerators.

Production of Radioactivity by Particle Accelerators

At all accelerators with energies greater than some tens of MeV, induced radioactivity results whenever beams interact with accelerator or beam transport components. Typically these interactions occur at injection and extraction points and beam splitting stations. Losses at these points are not desirable, and great efforts are often required to reduce them. Beam losses also occur at collimators, scrapers, target areas and beam dumps; these losses are deliberate and cannot be reduced. Consequently, these are usually the most radioactive areas of the accelerator, and work near them is the largest source of radiation exposure at all laboratories. It is therefore necessary to be able to anticipate the magnitude of the problems involved in such work, in order to minimize those problems in the design of a new facility. While these loss points are common to all accelerators, the magnitude of the resulting problems depends on many factors unique to each accelerator: the type of particle accelerated, the particle energy, and the geometry and composition of the items being struck. These considerations are discussed, and a general introduction is given for those not actively involved in this area.

Beam transport system for a 4 MeV dynamitron accelerator

A beam transport system was constucted for a 4 MeV Dynamitron † † From RDI, Westbury, U.S.A. accelerator which permits safe and dependable handling of ion beams up to 2 mA or electron beams up to 5 mA. In order to meet these high requirements, beam transport components such as slit shutters, apertures, Faraday cups, profile monitors and quick-closing valves were specially developed and built. As far as possible the parts of the system were made of stainless steel with metal seals, applying throughout the newest findings in ultrahigh vacuum technology. The entire installation is pumped with an oil-free pumping system.

A Precision Actuator and Shaft Encoder for a High Radiation Environment and Other Beam Component Developments at SLAC

A precision actuator and shaft encoder combination for remote handling in a high radiation and corrosive environment is described. The package allows accurate positioning of beam transport components in areas where liquid lubrication is not possible. The use of hexagonal lattice metals prevents galling or seizing of the rolling surfaces. The actuator translates rotary motion and torque supplied by a commercial radiation-resistant stepping motor into linear motion and force. Two actuators are in operation with a 7.5 cm output travel. Reproducibility is to ±1 step or 0.0015 cm. The shaft encoder resolves the turns of the motor in 1024 increments with cams and microswitches. The estimated dose rate of 1012 to 1013 ergs/g/yr in the vicinity of a SLAC high-power slit should present no problems. The second part of the paper describes a new quick-disconnect injected indium vacuum seal. Indium is extruded into a gasket groove of a flange through tapped holes by means of bolts. Finally, a blowout fuse employed in the beam stoppers of the SLAC personnel protection system is described. The fuse responds to thermal radiation from the surface of a beam stopper by melting a low-temperature eutectic diaphragm thus letting the vacuum system up to air.

1086. Sensitivity variations in the Bayard-Alpert ionization gauge. Part one: Experimental measurements with a molecular beam probe and in a randomized gas

A beam transport system was constucted for a 4 MeV Dynamitron† accelerator which permits safe and dependable handling of ion beams up to 2 mA or electron beams up to 5 mA. In order to meet these high requirements, beam transport components such as slit shutters, apertures, Faraday cups, profile monitors and quick-closing valves were specially developed and built.As far as possible the parts of the system were made of stainless steel with metal seals, applying throughout the newest findings in ultrahigh vacuum technology. The entire installation is pumped with an oil-free pumping system.

1085. Production of vacuum equipment

A beam transport system was constucted for a 4 MeV Dynamitron† accelerator which permits safe and dependable handling of ion beams up to 2 mA or electron beams up to 5 mA. In order to meet these high requirements, beam transport components such as slit shutters, apertures, Faraday cups, profile monitors and quick-closing valves were specially developed and built.As far as possible the parts of the system were made of stainless steel with metal seals, applying throughout the newest findings in ultrahigh vacuum technology. The entire installation is pumped with an oil-free pumping system.