GeV Electron Accelerator Research Articles

Shielding calculations for the design of new beamlines at ALBA synchrotron

ALBA is a Spanish synchrotron facility generating intense beams of synchrotron radiation from a 3 GeV electron accelerator. At ALBA Synchrotron, electrons are first accelerated in a 110 MeV linear accelerator and then injected in Booster ring which increases the energy up to 3 GeV. Finally, the electron beam is stored in a synchrotron Storage Ring with a current up to 400 mA emitting intense beam of synchrotron radiation. Both the Booster and the Storage Ring are located inside the same concrete building, the Tunnel, while the LINAC is located in a separated concrete building, the Bunker. Outside the Tunnel, and tangentially to the Storage Ring, are located the experimental research laboratories, the Beamlines, where scientists receive synchrotron light for a wide variety of experiments. At present ALBA has 8 Beamlines installed, 3 Beamline under construction, and 1 Beamlines in the design stage.This paper details the design of the shielding elements of the new Beamlines under construction called LOREA, NOTOS and XAIRA. The first one is a soft X-ray and the other two are hard X-ray Beamlines. Shielding calculations are performed using FLUKA Monte Carlo code and aim at quantifying the total dose rate produced by the different sources of radiation at the Beamlines in operation. In particular, it details the dose generated by the gas bremsstrahlung radiation resulting from the interaction of the 3 GeV electron beam with the residual gas of the storage ring vacuum chamber and compares it to the dose rate generated by the insertion device radiation flux. The objective of the FLUKA simulations performed in this work is to establish the requirements for all the Beamline shielding elements to ensure a public dose (dose rate lower than 0.5 μSv/h) outside the shielding during Beamline operation. Results from the simulations set the general requirements for all the Beamline shielding elements, from a radiation protection point of view.

Calibration of neutron dosimeters for radiation protection use at the ALBA synchrotron experimental hall

Bright beams of synchrotron radiation are produced from a 3 GeV electron accelerator at the Spanish synchrotron facility ALBA. The electron acceleration and storage mechanisms lead to complex secondary radiation fields. These fields include electrons, photons and neutrons of a wide energy range, and have an important pulsed behaviour and very significant spatial variations. In order to perform correct dose assessments for radiation protection purposes, it is necessary to measure separately electrons, photons and neutrons. In the case of neutron dosimetry, given the strong dependence with energy of the radiation weighting factor and of the fluence to ambient dose equivalent conversion coefficient, it is necessary to have some spectrometric information to correctly assess dose. Neutron dosimeters designed at UAB, based on PADC (Poly Allyl Diglycol Carbonate) track detectors, were exposed in different places of the ALBA experimental hall and tunnel. As to date, no calibration facility provides neutron fields similar to those found at ALBA, ambient dose equivalent was originally evaluated with calibration coefficients obtained from calibration at an Am-Be neutron source. A procedure for calibrating the dosimeters based on the knowledge, either by simulation or experimental determination, of the neutron unit fluence distribution ϕE(E) at every specific point of measurement and of the dosimeter response function in terms of fluence Rφ(E) is stablished in this work. Specific values of the calibration coefficient Si, that allows determining the ambient dose equivalent value from trak density measurements, were calculated at different points of interest in ALBA and are in the range 35.8–258 cm-2mSv-1.

The eRHIC spin rotator and the beam optics of the 400 MeV transfer line to RCS

The 400 MeV LINAC1 of the proposed eRHIC collider1 is the first acceleration stage of the 18 GeV electron accelerator. The second acceleration stage of the electron accelerator is the Rapid Cycling Synchrotron (RCS), which can increase the energy of the electron bunches to 18 GeV and subsequently extract transfer and inject the 18 GeV electron bunches into the 18 GeV electron Storage Ring (SR) to collide with the hadron bunches of the existing (Relativistic Heavy Ion Collider (RHIC)) accelerator. This paper describes the beam optics of the transfer line between the 400 MeV LINAC and the RCS accelerator (LtRCS). The function of the LtRCS line is twofold, first to transfer the electron beam from the exit of the 400 MeV LINAC to the injection point of the RCS1 and second to rotate the stable spin direction of the polarized electrons from the longitudinal direction to the vertical. A detailed description of the constraints to be satisfied by the LtRCS transfer line will be given. A section will also be devoted to discuss the spin rotator2.

Generation of GeV Electron Beam From a Laser-Plasma Accelerator and Its Prospect as a Desktop Source of Energetic Positrons and Gamma Rays For Applications

Laser wakefield acceleration (LWFA) is a plasma-based electron beam accelerator technology that can deliver electron beams with energies up to several GeVs, depending mainly on the power of the used laser system and the electron injection scheme. Here, we present the results from a GeV electron accelerator with a high reproducibility and a charge up to 30 pC using 110–120-TW laser pulses and by employing the well-established self-truncated ionization injection (STII) mechanism. These electron beams can be further used via bremsstrahlung in high-Z solid materials for the generation of gamma-rays and positron beams, therefore, composing a compact radiation source for various applications. Here, we use the Monte Carlo simulation code “Geant4” for studying the properties of those radiations. As expected, the characteristics of the generated gamma-rays and positron beams showed a strong dependence on the incident electron beam, target material, and thickness. The trend of positrons and gamma-rays energies and yield is shown for different high-Z to low-Z targets with the same areal mass density. Thicknesses of the target material in terms of its radiation length have been varied periodically in order to find the optimal thickness for obtaining the maximum energy and yield of the radiations. A trend can be seen in terms of energy spectra of the gamma-rays and positrons while increasing the thickness of the targets. The amount of radiation yields is also crucial to the choice of appropriate thickness of the target. In addition, this paper provides a brief description of the electrodynamics processes such as bremsstrahlung and electron–positron pair production initiated by LWFA electron beams.

New estimation method of neutron skyshine for a high-energy particle accelerator

A skyshine is the dominant component of the prompt radiation at off-site. Several experimental studies have been done to estimate the neutron skyshine at a few accelerator facilities. In this work, the neutron transports from a source place to off-site location were simulated using the Monte Carlo codes, FLUKA and PHITS. The transport paths were classified as skyshine, direct (transport), groundshine and multiple-shine to understand the contribution of each path and to develop a general evaluation method. The effect of each path was estimated in the view of the dose at far locations. The neutron dose was calculated using the neutron energy spectra obtained from each detector placed up to a maximum of 1 km from the accelerator. The highest altitude of the sky region in this simulation was set as 2 km from the floor of the accelerator facility. The initial model of this study was the 10 GeV electron accelerator, PAL-XFEL. Different compositions and densities of air, soil and ordinary concrete were applied in this calculation, and their dependences were reviewed. The estimation method used in this study was compared with the well-known methods suggested by Rindi, Stevenson and Stepleton, and also with the simple code, SHINE3. The results obtained using this method agreed well with those using Rindi’s formula.

A comparative study of plasma channels for a 100 GeV electron accelerator using a multi-petawatt laser

Acceleration of electrons to the 100 GeV range in laser wakefield accelerators using multi-petawatt lasers is numerically modelled. It is demonstrated that an externally injected electron bunch with an initial energy of 50 MeV can achieve an energy gain of 100 GeV in the weakly non-linear regime of laser wakefield acceleration. The guiding of the laser is achieved by a plasma channel having a parabolic radial density profile. A comparative study of plasma channels (matched and unmatched) is performed to investigate the sensitivity of electron acceleration to the matching condition in this regime. It is found that unmatched channels restrict energy gain to ∼60 GeV and lead to radial loss of injected charge due to the oscillation of the spot size of the laser inside the channels.

Research with real photons at the MAMI 1.6 GeV electron accelerator

The A2-CB Collaboration at Mainz is studying the structure of hadrons by meson photoproduction using unpolarised, linearly polarised and circularly polarised photons with energies up to 1.6 GeV. Photons are energy-tagged using the Glasgow-Mainz tagged photon spectrometer and a new high-energy end-point tagger which allows η’ reactions to be studied. Reaction products are detected in a ~4π detector consisting of the Crystal Ball detector and TAPS forward wall. Transverse or longitudinally polarised proton targets are available and new techniques have been developed to measure the polarisation of recoiling protons. These facilities have allowed an extensive programme of double-polarisation meson-photoproduction experiments to be carried out to search for so-called “missing baryon resonances” on proton and deuteron targets. Searches have also been carried out to investigate narrow resonances in the η-photoproduction channel at invariant masses around 1680 MeV. Coherent π 0 production measurements have been used to estimate the neutron skin thickness in 208 Pb. This paper presents selected highlights from the A2-CB collaboration research programme at MAMI.

MEASUREMENTS OF THE RELATIVE OSCILLATOR STRENGTHS OF THE PRINCIPAL SERIES OF COPPER

New measurements of the relative oscillator strengths of copper for the 3 d 104 s 2 S 1/2→3 d 10n p 2 P 1/2, (7 ≤ n ≤ 13), and 2 P 3/2(7 ≤ n ≤ 23) series are reported. The data were acquired using the magneto-optical rotation spectroscopic technique, utilizing the linearly polarized light emitted by the 2.5 GeV electron accelerator, a 7 Tesla superconducting magnet, and a 3-meter high dispersion spectrograph with photographic detection. A quantum defect plot of the density of oscillator strengths of the discrete transitions is also presented.

Radiation damage of Nd 2Fe 14B permanent magnets at 2.5 GeV electron accelerator

Radiation-induced demagnetization of permanent magnets is one of the most important issues of synchrotron radiation facilities, especially the next-generation light sources. In this paper, the radiation damage of the permanent magnet is investigated. The relative reduction of the magnetic field intensity of Nd 2Fe 14B magnet and its spatial distribution is derived with the radiation damage experiments carried out at a 2.5 GeV electron beam. The radiation field as well as the radiation quantities related to the radiation damage, mainly including the absorbed dose and 1 MeV equivalent neutron fluence are studied with Monte Carlo simulation. The radiation-induced demagnetization is analyzed based on the above results and fitted formulas are proposed to estimate the relative reduction of magnetic field intensity. Good agreement is found between the experiment data and fitted data. The variation of hysteresis loops before and after irradiation show that the remanence could not be restored to its original value by the remagnetization.

High resolution measurement and MQDT analysis of the 5d9 6s2 np, nf (J = 1) autoionizing resonances of mercury

We report new high resolution photoabsorption measurements of the 5d-subshell excitation spectra of mercury using a 3-meter normal incidence spectrograph equipped with a 6000 line/mm holographic grating and synchrotron radiation emitted by the Bonn 2.5 GeV electron accelerator as the background source of continuum. The observed spectra reveal autoionizing resonances attached to the 5d9(2D5/2)6s2 and 5d9(2D3/2)6s2 parent ion levels of mercury. We have analysed the line shapes of the lower members of the 5d96s2 np and nf J = 1 autoionizing resonances using the phase shifted formulation of the MQDT and extracted the interaction parameters.

Induced radioactivity in rare-earth permanent magnets at 2.5 GeV electron accelerator

Rare-earth permanent magnets such as Nd 2Fe 14B and Sm 2Co 17 are the main components of the insertion devices of synchrotron radiation facilities and are used at other particle accelerators. Due to radiation safety concern the induced radioactivity in permanent magnets at a 2.5 GeV electron accelerator were studied with Monte Carlo simulations and experiments. The saturated activity of each radioactive isotope was estimated with FLUKA code (2005 version) and compared with measurement results. Three models of NEOMAX Nd 2Fe 14B magnets and one trivial Sm 2Co 17 magnet were chosen as the test magnets. The remnant dose rate at 1 m from the magnet and its cooling time dependence are calculated with the induced activities from the view of radiation protection. These are investigated under unique radiation environments due to different target conditions. The transverse distributions of induced radioactivities of several representative isotopes, which were measured at different target conditions, agree well with the electromagnetic shower characteristics at different target conditions as well as the spatial distributions of photon and neutron fluences.

Proposed scheme for compact GeV laser plasma accelerator

The design of a two-stage compact GeV electron accelerator is presented. The accelerator is as follows: (1) an ultra-short electron bunch is produced in a state-of-the-art laser-plasma accelerator (injector stage), (2) it is injected into an accelerating stage consisting of a centimeter length low density plasma interacting with a petawatt laser pulse. The parameters for the injector are taken from recent experimental results showing that high quality, ultra-short, and quasi-monoenergetic electron beams are now being produced in laser-plasma accelerators. Simulations performed with WAKE show that this method can lead to the production of high quality, monoenergetic, and sub-50 fs electron bunches at the GeV energy level.

Sensing characteristics of epitaxially-grown tin oxide gas sensor on sapphire substrate

Epitaxial SnO 2 film was grown on a sapphire substrate using a reactive rf magnetron sputter. The microstructure of the thin film was investigated using the 3C 2 beam line from a Pohang Light Source (PLS) consisting of a 2 GeV electron accelerator, four circle X-ray diffractometer, atomic force microscopy (AFM), and transmission electron microscopy (TEM) comparing with the SnO 2 film on the polished alumina. It was confirmed that the thin film grew epitaxially on the sapphire substrate with a variant crystal structure [Development of microstructure controlled and ultrathin SnO 2 gas sensing film, in: Proceedings of the 5th International Meeting on Chemical Sensors, Rome, Italy, 1994]. No grain boundary was exhibited on the surface of the epitaxial thin film. A large portion of the sorption sites in SnO 2 films appears to react easily with the gas. An epitaxial SnO 2 gas sensor, with a Pt heater and electrodes, exhibited a high sensitivity to combustible gases and a particular sensitivity of 95% to alcohol at 2000 ppm and 350°C. The sensor also showed a good stability with small baseline drift and fast reaction and recovery times of about 5 and 30 s, respectively. This experiment confirms the good gas-sensing characteristics of an epitaxially-grown SnO 2 gas sensor.

Acceleration of polarized electrons in ELSA

At the 3.5 GeV electron accelerator ELSA of Bonn University, polarized electrons have been accelerated up to 2.0 GeV, crossing several depolarizing resonances without significant depolarization. The polarized electrons were produced by photoemission from an AlGaAs–GaAs superlattice crystal using circularly polarized laser light. A harmonic correction scheme was successfully applied to the third imperfection resonance ( γa=3) and the polarization required for the planned experiments was conserved up to 2.0 GeV.

Electrodisintegration of the deuteron in the Δ-resonance region

A study of deuteron electrodisintegration has been performed as the first experiment at the new Bonn 3.5 GeV electron strecher and accelerator ELSA. This process was measured at an average four-momentum transfer Q 2 = 0.122 (GeV/ c) 2 in the invariant hadron mass range of 2.02 – 2.30 GeV. The outgoing proton was detected in coincidence with the scattered electron at three different adjustments of the spectrometer ( θ p lab = 44°, 56°, 68°). The measured differential cross sections show the influence of the excitation of the Δ(1232) resonance in the deuteron. The experimental results are compared to theoretical calculations which include meson exchange currents, final-state interactions and isobar currents.

Compact synchrotron radiation depth lithography facility

X-ray depth lithography allows the fabrication of plastic microstructures with heights of up to 1 mm but with the smallest possible lateral dimensions of about 1 μm. A resist is irradiated with ‘‘white’’ synchrotron radiation through a mask that is partially covered with x-ray absorbing microstructures. The plastic microstructure is then obtained by a subsequent chemical development of the irradiated resist. In order to irradiate a reasonably large resist area, the mask and the resist have to be ‘‘scanned’’ across the vertically thin beam of the synchrotron radiation. A flexible, nonexpensive and compact scanner apparatus has been built for x-ray depth lithography at the beamline BN1 at ELSA (the 3.5 GeV Electron Stretcher and Accelerator at the Physikalisches Institut of Bonn University). Measurements with an electronic water level showed that the apparatus limits the scanner-induced structure precision to not more than 0.02 μm. The whole apparatus is installed in a vacuum chamber thus allowing lithography under different process gases and pressures.

A new energy dispersive x-ray monochromator for soft x-ray applications

Energy dispersive x-ray monochromators allow time-resolved XANES and EXAFS measurements in the millisecond time scale. With this technique it is possible to study changes, during chemical reactions and phase transitions, in the structure of chemical substances within the environment of the absorbing atom. The instruments used up to now are not built for use under vacuum and are thus restricted to experiments above 4 keV. An energy dispersive monochromator is described which is currently being built at the Bonn 3.5 GeV electron stretcher and accelerator (ELSA). The purpose of this monochromator is to be able to measure downwards in energy at least to the sulfur K edge at 2.4 keV. The problems which had to be solved are (i) the construction of a windowless vacuum chamber for the Bragg crystal, the sample, and the detector, (ii) the short distance between the crystal and the sample, and (iii) the small radius of curvature of the Bragg crystal. Furthermore, the monochromator has to be rapidly tuned with ease to different energies.

Study of multi-hadron reactions with multi gev electron accelerator

The field covered in this paper will be restricted to fixed-target reac- tions, the probe being real or virtual photons. Multi GeV will mean here photon energy below 10 GeV, because above the effect of the Lorentz boost will confirm all the particles in the forward direction and hadrons win develop hadronic showers in matter. This win imply a completely different design of a detector. Finaly multihadron win start at 2 particles. After some considerations on the physical motivation, I will discuss the main characteristics of the detectors, then I will give some examples of the detection set-up presently under development around electron accelerators and propose some concluding remarks.

Identification of neutrons from the cooling water of a GeV electron accelerator

Measurements were made on delayed neutrons emitted by the cooling water of a beam dump for GeV electrons produced by the accelerator at the Stanford Linear Accelerator Center. A 3He spectrometer was used to measure the energy spectrum and a BF 3 counter was used to measure the half-life of the neutron activity. The spectrum showed neutron groups at 383, 1170 and 1700 keV and the possibility of another group at 2070 keV. The three lower groups, in combination with the measured half-life of 4.4±0.2 s, indicate that most of the delayed neutrons were emitted by 17N produced by the 18O(gg, p) 17N reaction.

An Energy Independent Electron Spin Precessor

The delivery on target of a polarized electron beam from a linear accelerator is straightforward. With circular accelerators this delivery becomes understandably more difficult. In order to maintain the polarization of an electron beam in a circular machine such as a synchrotron or pulse stretcher ring the electron spins must be oriented vertically so as to be parallel to the dominant guide fields. Extraction from these machines occurs in the horizontal plane so the extracted beam retains the vertical polarization. It is generally desirable to have not vertical but longitudinal polarization of the beam at the target; this requires a reorientation of the spins. The straightforward solution to this problem is to put a solenoid in the beam line to precess the spin into the horizontal plane followed by a horizontally deflecting dipole to precess the spin into the momentum direction. The angle of spin precession is energy dependent. What is needed is a method of varying the effective bend angle. One method used with polarized protons from the ZGS at Argonne involved a movable beam line. An alternative method is to utilize the noncommutativity of rotations in three dimensions. To do this requires two or more solenoids and twomore » or more dipoles. This paper discusses the theory and implementation of this method and describes a solenoid-dipole-solenoid-dipole configuration beam line suitable for the 4 GeV electron accelerator proposed by the Southeastern Universities Research Association.« less