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

Analysis, Prototyping, and Design of an Ionization Profile Monitor for the Spallation Neutron Source Accumulator Ring

Beam diagnostics and instrumentation are an essential part of any kind of accelerator. There is a large variety of parameters to be measured for observation of particle beams with the precision required to tune, operate, and improve the machine. In the first part, the basic mechanisms of information transfer from the beam particles to the detector are described in order to derive suitable performance characteristics for the beam properties. However, depending on the type of accelerator, for the same parameter, the working principle of a monitor may strongly differ, and related to it also the requirements for accuracy. Therefore, in the second part, selected types of accelerators are described in order to illustrate specific diagnostics needs which must be taken into account before designing a related instrument.

Beam Diagnostic Requirements: an Overview

It is proposed to use an array of metallic posts as a beam position monitor (BPM). The structure consists of a set of NN metallic vertical posts bounded from above and below by two horizontal metallic plates. The beam position offset from the symmetry axis is determined by measuring the backward radiation emitted by the beam as it traverses the array. The suggested BPM's position resolution is dominated by the thermal noise level and the shot noise level of the detectors measuring the radiation whereas the time resolution is dominated by their operation frequencies. In the optical regime and for ultra-relativistic beams the time resolution is of order of 10 ps i.e. at least two orders of magnitude higher than the common time resolution in stripline BPM. Utilizing the state of the art optical detectors the position resolution of such a BPM may reach the level of a few nanometers which is one order of magnitude better than the common position resolution of existing systems. r 2005 Elsevier B.V. All rights reserved.

/pdf/wake-field-in-an-array-of-metallic-posts-possible-3v8877b7ge.pdf

Wake-field in an array of metallic posts: Possible application for beam position monitoring

The 402.5- and 805-MHz beam position and phase monitors for the Spallation Neutron Source linac are based on standard PC technology. The SNS beam is to be injected into a storage ring with a 1-MHz circulation frequency requiring 650-ns-long minipulses. The injection cycle takes 1 ms and the machine can run at rates up to a 60 Hz. The RF input signals are down converted to 50 MHz and sampled at 40 MHz with 14-bit ADCs to produce I and Q data streams. A custom PCI module has been designed to accept modular digital front end (DFE) and analog front end (AFE) circuit cards. This hardware is installed in a standard rack-mounted 1U computer chassis running Windows 2000, Lab VIEW and custom DLL software. The system continuously self-calibrates by generating 300-ns long RF pulses which are switched between the AFE inputs and the cables going to the BPM pickups. This provides a TDR-like calibration of the entire system. The system is designed to provide a position and phase resolution of 0.1% of the beam pipe aperture and 0.1 degrees RMS respectively over a 50 /spl mu/s period. The design of the system is described as well as the initial performance measuring beam during the commissioning of the SNS MEBT.

Beam position monitor systems for the SNS linac

The linac wire scanner system for the Spallation Neutron Source (SNS) at Oak Ridge, TN, calls for 5 units in the medium energy beam transport (MEET), 5 in the drift tube linac (DTL), 8 in the coupled cavity linac (CCL), and 13 in the high energy beam transport (HEBT). The actuators are a custom design fabricated by Huntington Mechanical Laboratories. Four different strokes are required to cover the above areas. The electronics are designed and fabricated by Los Alamos National Laboratory (LANL). In this paper we will discuss the design of the actuators and the electronics, positioning accuracy tests of the actuators, and also show results from beam measurements taken during the MEET commissioning at Oak Ridge National Laboratory.

The SNS linac wire scanner system

Brookhaven is providing the Ring and Transfer Lines Beam Diagnostics for the Spallation Neutron Source (SNS), to be installed at Oak Ridge National Laboratory. The customary diagnostics that will be present include beam position monitors (BPM), ionization profile monitors (IPM), beam loss monitors (BLM), beam current monitors (BCM), coherent tune measurement, and wire scanners. An overview of these systems is presented, along with brief discussions of SNS-specific problems that must be addressed, including unprecedented beam power, large dynamic range, a stringent loss budget, space charge, beam halo, and electron cloud. We also present an overview of systems more specifically tailored to address these problems, including Beam-in-Gap measurement and cleaning, two types of incoherent tune measurement, halo monitor, and video monitors for stripping foils and the electron catcher.

Spallation Neutron Source ring diagnostics

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Beam position monitor systems for the SNS linac

The SNS linac wire scanner system

Spallation Neutron Source ring diagnostics