The spallation neutron source (SNS) at Oak Ridge National Laboratory is an accelerator-based, neutron-scattering facility. SNS uses a large-scale, high-energy superconducting linac (SCL) to provide high beam power utilizing hydrogen ion (H − ) beams. For the diagnostics of high-brightness H − beams in the SCL, nonintrusive methods are preferred. This paper describes design, implementation, theoretical analysis, and experimental demonstration of a nonintrusive profile monitor system based on photodetachment, also known as laser wire, installed in the SNS SCL. The SNS laser wire system is the world's largest of its kind with a capability of measuring horizontal and vertical profiles of an operational H − beam at each of the 23 cryomodule stations along the SCL beam line by employing a single light source. Presently 9 laser wire stations have been commissioned that measure profiles of the H − beam at energy levels from 200 MeV to 1 GeV. The laser wire diagnostics has no moving parts inside the beam pipe, causes no contamination on the superconducting cavity, and can be run parasitically on an operational neutron production H − beam.

Laser wire beam profile monitor in the spallation neutron source (SNS) superconducting linac

The emittance is an important characteristic of propagating charged particle beams, because it allows the prediction of focus size and beam losses After introducing the concept and various definitions of the emittance and Twiss parameters, useful applications of this representation will be explored for the transverse emittances of charged particle beams This is followed by a presentation of different measuring methods, together with their advantages and disadvantages The second part discusses the analysis of emittance data, and possible mitigations for effects introduced by noise, bias, and other artifacts

/pdf/measuring-and-analyzing-the-transverse-emittance-of-charged-3aq3g0to7n.pdf

Measuring and Analyzing the Transverse Emittance of Charged Particle Beams

The Linac4, now being developed at CERN, will provide 160-MeV H - beams of high intensity N = 2 × 10 14 ions s - 1 . Before this beam can be injected into the CERN Proton Synchrotron Booster or future Superconducting Proton Linac for further acceleration, some sequences of 500-ps-long micro-bunches must be removed from it, using a beam chopper. These bunches, if left in the beam, would fall outside the longitudinal acceptance of the accelerators and make them radioactive. We developed a monitor to measure the time structure and spatial profile of this chopped beam, with respective resolutions Δ t ∼ 1 ns and Δ x ∼ 2 mm . Its large active area 40 mm × 40 mm and dynamic range also allows investigations of beam halos. The ion beam first struck a carbon foil, and secondary electrons emerging from the foil were accelerated by a series of parallel grid electrodes. These electrons struck a phosphor screen, and the resulting image of the scintillation light was guided to a thermoelectrically cooled, charge-coupled device camera. The time resolution was attained by applying high-voltage pulses of sub-nanosecond rise and fall times to the grids. The monitor has been tested with 700-ps-long UV laser pulses, and a 3-MeV proton beam. Its response over a wide range of beam intensities between N e ∼ 5 and 4 × 10 8 electrons emitted from the foil per pulse was studied. The monitor can also be used to measure the profiles of antiproton beams in the future facilities of Facility for Low-energy Antiproton Ion Research (FLAIR) or Extra Low Energy Antiproton Ring (ELENA).

Spatial and temporal beam profile monitor with nanosecond resolution for CERN's Linac4 and Superconducting Proton Linac

The focus of this tutorial will be on interceptive beam diagnostics such as wire scanners, screens, and harps. We will start with an overview of the various ways beams interact with materials to create signals useful for beam diagnostics systems. We will then discuss the errors in a harp or wire scanner profile measurement caused by errors in wire position, number of samples, and signal errors. Finally we will apply our results to two design examples‐the SNS wire scanner system and the SNS target harp.

Interceptive Beam Diagnostics—Signal Creation and Materials Interactions

High performance TeV energy electron/positron colliders (LC) are the first machines to require online, non-invasive beam size monitors for micron and submicron for beam phase space optimization. Typical beam densities in the LC are well beyond the threshold density for single pulse melting and vaporization of any material, making conventional wire scanners ineffective. Using a finely focused, diffraction limited high power laser, it is possible to devise a sampling profile monitor that, in operation, resembles a wire scanner. Very high resolution laser-based profile monitors have been developed and tested, first at FFTB (SLAG) and later at SLC and ATF. The monitor has broad applicability and we review here the technology, application and status of ongoing research programs.

/pdf/laser-based-profile-monitor-for-electron-beams-h6cg96lisq.pdf

Laser-based profile monitor for electron beams

After a successful demonstration of a nonintercepting beam profile monitor for the H/sup -/ beams at the 750 KeV and the 200 MeV LINAC at Brookhaven National Laboratory, the SNS project approved using a Nd:YAG laser rather than the traditional carbon wire for transverse profile monitors in the SNS superconducting LINAC. Experiments have also been performed on SNS 2.5 MeV medium energy beam transport line at LBNL. The design and the implementation of a multistation profile monitoring system using a single laser will be presented. The laser beam is scanned across the H/sup -/ beam to photoneutralize narrow slices. The liberated electrons are collected to provide a measurement of the transverse beam profile. The prototype system has been tested; the measurement and performance results will be presented.

https://epaper.kek.jp/p03/papers/wppg054.pdf

The SNS laser profile monitor design and implementation

The Spallation Neutron Source accelerator systems will provide a 1 GeV, 1.44 MW proton beam to a liquid mercury target for neutron production. Beam tuning dumps are provided at the end of the linac (the Linac Dump) and in the Ring-to-Target transport line (the Extraction Dump). Thin windows are required to separate the accelerator vacuum from the poor vacuum upstream of the beam dump. There are several challenging engineering issues that have been addressed in the window design. Namely, handling of the high local power density deposited by the stripped electrons from the H-beam accelerated in the linac, and the need for low-exposure removal and replacement of an activated window. The thermal design of the linac dump window is presented, as is the design of a vacuum clamp and mechanism that allows remote removal and replacement of the window.

/pdf/beam-dump-window-design-for-the-spallation-neutron-source-55ajpfm92t.pdf

Beam dump window design for the Spallation Neutron Source

The Spallation Neutron Source accelerator will provide a 1 GeV, 1.44 MW proton beam to a liquid mercury target for neutron production. The expected highest doses to components are in the collimation regions. This paper presents the mechanical engineering design of a typical collimator highlighting the features incorporated to assist with collimator removal once it is activated. These features include modular shielding, integrated crane mounting, remote water fittings and vacuum clamps. Also presented is the design work in progress at present to validate the remote vacuum clamp design. This includes a test rig that mimics an active handling scenario where vacuum bellows can be compressed and clamps removed/replaced from a safe distance.

Handling High Activity Components on the SNS (Collimators and Linac Passive Dump Window)

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Papers

The SNS laser profile monitor design and implementation

Beam dump window design for the Spallation Neutron Source

Handling High Activity Components on the SNS (Collimators and Linac Passive Dump Window)