Wire Scanner Research Articles

Emittance Measurement for Beamline Extension at the PET Cyclotron

Particle-induced X-ray emission is used for determining the elemental composition of materials. This method uses low-energy protons (of several MeV), which can be obtained from high-energy (of tens MeV) accelerators. Instead of manufacturing an accelerator for generating the MeV protons, the use of a PET cyclotron has been suggested for designing the beamline for multipurpose applications, especially for the PIXE experiment, which has a dedicated high-energy (of tens MeV) accelerator. The beam properties of the cyclotron were determined at this experimental facility by using an external beamline before transferring the ion beam to the experimental chamber. We measured the beam profile and calculated the emittance using the pepper-pot method. The beam profile was measured as the beam current using a wire scanner, and the emittance was measured as the beam distribution at the beam dump using a radiochromic film. We analyzed the measurement results and are planning to use the results obtained in the simulations of external beamline and aligned beamline components. We will consider energy degradation after computing the beamline simulation. The experimental study focused on measuring the emittance from the cyclotron, and the results of this study are presented in this paper.

Beam experiments with a non-intercepting beam induced fluorescence profile monitor for the ADS LINAC

An accelerator-driven subcritical system (ADS) project was launched in China in 2011, aiming to design and build an ADS demonstration facility with the capability of more than 1000 MW thermal power. The driver linac is defined to be a 10 mA current of high energy protons at 1.5 GeV in continuous wave operation mode. To meet the extremely high power and intense beam accelerator requirements, non-interceptive monitors for the beam transverse profile are required for this proton linac. Taking advantage of the residual gas as active material, the Beam Induced Fluorescence (BIF) monitor exploits gas-excited fluorescence in the visible spectrum region for transverse profile measurements. The advantages of this non-intercepting method are that nothing is installed in the vacuum pipe, component design is compact and there is no need for expensive signal processing electronics. Beam experiments have been performed under constant beam conditions. The helium spectrum has been verified with different optical filters, showing that a proper optical band-pass filter covering 400–500 nm is necessary for fluorescence experiments with helium. By changing gas pressure, it is shown that gas pressure is proportional to the signal amplitude but has no influence on detected profile width. Finally, a comparison experiment between the BIF monitor and a wire scanner shows that the detected profile width results of both methods agree well.

Vibration measurements of a wire scanner – Experimental setup and models

In the next years the luminosity of the LHC will be significantly increased. This will require a much higher accuracy of beam profile measurement than actually achievable by the current wire scanner. The new performance demands a wire travelling speed up to 20ms−1 and a position measurement accuracy of the order of 1μm. The vibrations of the mechanical parts of the system and particularly the vibrations of the thin carbon wire have been identified as the major error sources of wire position uncertainty. Therefore the understanding of the wire vibrations has been given high priority for the design and operation of the new device. This article presents a new strategy to measure the wire vibrations based on the piezoresistive effect of the wire itself. An electronic readout system based on a Wheatstone bridge is used to measure the variation of the carbon wire resistance, which is directly proportional to the wire elongation caused by the oscillations.

Secondary particle acquisition system for the CERN beam wire scanners upgrade

The increasing requirements of CERN experiments make essential the upgrade of beam instrumentation in general, and high accuracy beam profile monitors in particular. The CERN Beam Instrumentation Group has been working during the last years on the Wire Scanners upgrade. These systems cross a thin wire through a circulating beam, the resulting secondary particles produced from beam/wire interaction are detected to reconstruct the beam profile. For the new secondary shower acquisition system, it is necessary to perform very low noise measurements with high dynamic range coverage. The aim is to design a system without tuneable parameters and compatible for any beam wire scanner location at the CERN complex. Polycrystalline chemical vapour deposition diamond detectors (pCVD) are proposed as new detectors for this application because of their radiation hardness, fast response and linearity over a high dynamic range. For the detector readout, the acquisition electronics must be designed to exploit the detector capabilities and perform bunch by bunch measurements at 40MHz. This paper describes the design challenges of such a system, analysing different acquisition possibilities from the signal integrity point of view. The proposed system architecture is shown in detail and the development status presented.

The control system of the multi-strip ionization chamber for the HIMM

Heavy Ion Medical Machine (HIMM) is a carbon ion cancer treatment facility which is being built by the Institute of Modern Physics (IMP) in China. In this facility, transverse profile and intensity of the beam at the treatment terminals will be measured by the multi-strip ionization chamber. In order to fulfill the requirement of the beam position feedback to accomplish the beam automatic commissioning, less than 1ms reaction time of the Data Acquisition (DAQ) of this detector must be achieved. Therefore, the control system and software framework for DAQ have been redesigned and developed with National Instruments Compact Reconfigurable Input/Output (CompactRIO) instead of PXI 6133. The software is Labview-based and developed following the producer–consumer pattern with message mechanism and queue technology. The newly designed control system has been tested with carbon beam at the Heavy Ion Research Facility at Lanzhou-Cooler Storage Ring (HIRFL-CSR) and it has provided one single beam profile measurement in less than 1ms with 1mm beam position resolution. The fast reaction time and high precision data processing during the beam test have verified the usability and maintainability of the software framework. Furthermore, such software architecture is easy-fitting to applications with different detectors such as wire scanner detector.

Thermal analysis for wire scanners in the CSNS Linac

3MeV H− beam from the Radio Frequency Quadrupole (RFQ) will be accelerated to 80MeV in the CSNS (China Spallation Neutron Source) linear accelerator (Linac). The wire scanner is used to measure the transverse beam profile and the emittance, and the carbon or tungsten wire is considered to use. Thermal analysis of the wire scanners in the Linac is presented in this paper. The maximum temperature (Tm) of the wire decreases as the beam energy increases, and we also calculate the influence of all possible parameters on Tm. Tm of carbon wire is significantly lower than tungsten wire if both the beam parameters and wire geometric parameters are set to the same, which can be attributed to its higher heat capacity and radiant emissivity. In addition, we present the results of sublimation rate of the wire, which show that tungsten wire has a much lower evaporation rate than carbon wire in the same temperature, which can be attributed to the different vapor pressures of the two materials. To limit the thermionic emission, the maximum beam frequency approximately has an exponential relationship with beam rms size at a certain beam pulse width.

Fast wire scanner for intense electron beams

We have developed a cost-effective, fast rotating wire scanner for use in accelerators where high beam currents would otherwise melt even carbon wires. This new design uses a simple planetary gear setup to rotate a carbon wire, fixed at one end, through the beam at speeds in excess of $20\text{ }\text{ }\mathrm{m}/\mathrm{s}$. We present results from bench tests, as well as transverse beam profile measurements taken at Cornell's high-brightness energy recovery linac photoinjector, for beam currents up to 35 mA.

In situmicro-focused X-ray beam characterization with a lensless camera using a hybrid pixel detector

Results of studies on micro-focused X-ray beam diagnostics using an X-ray beam imaging (XBI) instrument based on the idea of recording radiation scattered from a thin foil of a low-Z material with a lensless camera are reported. The XBI instrument captures magnified images of the scattering region within the foil as illuminated by the incident beam. These images contain information about beam size, beam position and beam intensity that is extracted during dedicated signal processing steps. In this work the use of the device with beams for which the beam size is significantly smaller than that of a single detector pixel is explored. The performance of the XBI device equipped with a state-of-the-art hybrid pixel X-ray imaging sensor is analysed. Compared with traditional methods such as slit edge or wire scanners, the XBI micro-focused beam characterization is significantly faster and does not interfere with on-going experiments. The challenges associated with measuring micrometre-sized beams are described and ways of optimizing the resolution of beam position and size measurements of the XBI instrument are discussed.

Feasibility studies of a vibration wire monitor and a halo scraper in the J-PARC L3BT

In the Japan Proton Accelerator Research Complex (J-PARC) 3-GeV rapid cycle synchrotron (RCS), transverse beam halo diagnostics and scraping are required to increase the output beam power. Wire scanners and halo scrapers were used to measure the projected beam distributions to determine the extent of beam halo formation at the linac 3-GeV beam transport line (L3BT). In order to determine more details of halo formation, we installed a vibration wire monitor (VWM) in the L3BT for the beam halo measurement. The high sensitivity of the VWM makes it a prospective tool for investigating the beam halo and weak beam scanning. Also, we developed a new vertical scraper system with a thin carbon foil to collimate the beam halo in the L3BT. In this paper, we will report a preliminary result for the beam-halo measurement by using a VWM and a halo scraper at the L3BT, and we will discuss the potential of the VWM for beam-halo diagnostics.

Evidence of a halo formation mechanism in the Spallation Neutron Source linac

A new halo formation mechanism and its mitigation scheme [D. Jeon, J. Stovall, A. Aleksandrov, J. Wei, J. Staples, R. Keller, L. Young, H. Takeda, and S. Nath, Phys. Rev. ST Accel. Beams 5, 094201 (2002)] are verified experimentally through a series of emittance measurements performed during the drift tube linac tank 1 commissioning of the Spallation Neutron Source. This is a rare experiment evidence of a halo formation mechanism. As the simulation predicts, the emittance measurements clearly show a visible halo reduction as well as a significant rms emittance reduction when the proposed round beam optics is employed. The emittance measurement results are consistent with multiparticle simulations and also consistent with wire scanner results. These measurements serve as a valuable code benchmarking for a beam under an intense space charge effect.

Use of a wire scanner for monitoring residual gas ionization in Soreq Applied Research Accelerator Facility 20 keV/u proton/deuteron low energy beam transport beam line

The ion source end of the Soreq Applied Research Accelerator Facility accelerator consists of a proton∕deuteron ECR ion source and a low energy beam transport (LEBT) beam line. An observed reduction of the radio frequency quadrupole transmission with increase of the LEBT current prompted additional study of the LEBT beam properties. Numerous measurements have been made with the LEBT bream profiler wire biased by a variable voltage. Current-voltage characteristics in presence of the proton beam were measured even when the wire was far out of the beam. The current-voltage characteristic in this case strongly resembles an asymmetric diodelike characteristic, which is typical of Langmuir probes monitoring plasma. The measurement of biased wire currents, outside the beam, enables us to estimate the effective charge density in vacuum.

Multi-OTR System for ATF2

Abstract In this paper we describe the first measurements performed during fall of 2010 and the beginning of 2011. We discuss software development, realistic simulations and new hardware improvements of a Multi-Optical Transition Radiation System installed in the beam diagnostics section of the Extraction (EXT) line of ATF2, close to the Multi Wire Scanner System. 2D emittance measurements have been successfully demonstrated and the system is being routinely used for coupling correction. Realistic beam simulations have been made and compared with measurements. A 4D emittance procedure is being prepared and some preliminary measurements have been performed. An improved optical system including a demagnifier lens to improve the beam finding procedure is being designed and will be installed during the autumn 2011 operations period. A systematic measurement campaign will take place after recovery of ATF operations (post the 2011 Tohoku Earthquake), then a comparison with wire scanners can be done. This will be a definitive test of the OTR as a beam emittance diagnostic device, which will provide fast beam emittance measurements with high statistics, giving a low error and a good understanding of emittance jitter and sources.

Yerevan synchrotron injector electron beam transversal scan with vibrating wire scanner

We have developed extended-aperture (20 mm) vibrating wire scanner (VWS) for transversal scanning of electron beams with large transversal size. Test experiments were performed in open atmosphere on the 40 MeV electron beam of the Yerevan synchrotron injector with the 4–10 μA at outlet. A construction of VWS is elaborated for scanning beams with larger transversal size. This elaboration is a new precision tool for diagnostics of beams in accelerators, which may be successfully employed, because of universality of the used operation principle, for profiling of as well large-aperture proton and ion beams.

BEPC II wire scanner system

To monitor the beam profile at the end of the linac non-destructively, a wire scanner as a new diagnostic instrument was designed, manufactured and installed in 2007. Since then, several measurements have been carried out using this device. This paper describes the whole system of the wire scanner and the testing results.

Design and simulation of a wire scanner for the CSNS linac

In this paper, we report the design and simulation of a wire scanner for the linac of the CSNS (China Spallation Neutron Source). The wire scanner is used to measure the transverse beam profile and the emittance. The effect of beam energy change upon the mechanical design of the wire scanner must be considered. The simulation results of heat on the two specified wires, tungsten and carbon, by using the finite element method software, ANSYS, are presented. In addition, the effect of wire deformation on the beam profile measurement is qualitatively analyzed, and the signal level of the wire scanner is discussed.

Suppression of Beam Loss at the First Arc Section in the J-PARC Linac

J-PARC (Japan Proton Accelerator Research Complex) linac has recently started its continuous operation to provide a 181-MeV H <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> beam to the downstream 3-GeV synchrotron and a neutron target. Immediately after the commencement of the continuous operation, significant residual radiation and beam loss were observed at the first bending magnet in the first arc section. The measured radiation and beam loss were localized in the side opposite to the deflection of the H <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> beam. A possible beam loss source is the H <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> produced by double electron-stripping of H <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> in a residual gas scattering at the front end part of the linac. To confirm this supposition, an H <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> signal was measured with a wire scanner monitor at the beam energy of 3 MeV by separating H <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> from the H <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> beam with horizontal dipole magnets. Then the separated H <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> is successfully removed by a beam scraper originally for beam chopping. With this H <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> suppression, the beam loss at the first bend was suppressed by factor of 24-31 without sacrificing the beam chopping performance. Consequently, the residual radiations were reduced to a comfortable level for the continuous operation.

The injection efficiency measurement and analysis for central region model cyclotron

At the China Institute of Atomic Energy, a central region model cyclotron has been constructed, which is dedicated for various experimental verifications to study beam properties. The design features of the ion source and injection line have already been described in other papers. We shall report here the results of the initial beam tests. A wire scanner is employed in the injection line to measure beam transverse sizes and these data can be used to fit the phase plane parameters after the ion source. Based on the beam tests results, the ion source built in 2003 has been improved recently. The improvement is mainly due to the repair of the multicusp field. From the ion source to the exit of the inflector, a transmission efficiency of 93% has been obtained for a continuous and low current input beam. It is also described here the experimental arrangement and the results.

Thermal emittance and response time measurements of a GaN photocathode

We present the measurements of thermal emittance and response time for a GaN photocathode illuminated with 5 ps pulses at 260 nm wavelength. The thermal emittance was measured downstream of a 100 kV dc gun using a solenoid scan with a wire scanner and a beam viewscreen and was found to be 1.35±0.11 mm mrad normalized rms emittance per 1 mm rms of illuminated spot size. The response time of the photoemitted electrons was evaluated using a deflecting mode rf cavity synchronized to the laser pulses and was found to be prompt within the time resolution capability of our setup.

A method for probing machine optics by constructing transverse real space beam distributions using Beam Position Monitors

At the Spallation Neutron Source (SNS) in Oak Ridge, we sought to measure the transverse tilt and profile of the beam at several locations in our Ring to Target Beam Transport (RTBT) line where we did not have wire scanners. A new method was proposed and used to construct the transverse real space beam distributions from Beam Position Monitor (BPM) signals to probe the machine optics. In this paper, we outline this method and present an experiment demonstrating this technique, and we qualitatively compare the results with profiles taken using wire scanners.

Design and simulation of the wire scanner for the injector linac of BEPCII

BEPCII, the upgrade project of Beijing Electron Positron Collider (BEPC), is an accelerator with large beam current and high luminosity, so an efficient and stable injector is required. Several beam diagnostic and monitoring instruments are used. A new diagnostic instrument — wire scanner, has been designed and will be used to measure the profile of the linac beam of BEPCII. This paper describes the prototype of this system and the cause of heat generating of the wire. Some simulation results of the heat and force by using finite element method software—ANSYS®ANSYS software is proprietary product of ANSYS, INC. are presented and discussed.