High-energy Sections Research Articles

Beam physics of the 8-GeV [formula omitted] linac

Fermilab is developing the concept and design of an 8-GeV superconducting H- linac with the primary mission of increasing the intensity of the Main Injector for the production of neutrino superbeams. The front-end of the linac up to 420MeV operates at 325MHz and accelerates the beam from the ion source using a room temperature radio-frequency quadrupole followed by short CH type resonators and superconducting spoke resonators. In the high-energy section, the acceleration is provided by superconducting elliptical 1.3GHz cavities similar to the ones developed for the International Linear Collider (ILC). The beam physics for the linac is presented in this paper using two beam dynamics codes: TRACK and ASTRA.

Geometrical track parameters in the pallasite olivine: Identification of the cosmic ray heavy nuclei

The geometry characteristics of chemically etched tracks in the not annealed olivine crystals from pallasite meteorites are investigated with the search and identification goal of fossil tracks of galactic cosmic ray heavy and superheavy nuclei. The chosen methodology is based on precise measurements of the nucleus track parameters in the course of chemical etching of the olivine crystals. Geometric parameters of individual tracks are traced and measured in course of their step-by-step chemical etching by using a modern high-precision, completely automated facility PAVICOM designed at the Lebedev Physical Institute of Russian Academy of Sciences. A method of the layer-by-layer removal of olivine material is employed, which allows the tracks to be studied over the whole crystal volume under study. It is planned to measure the next main parameters: the cone length and diameters of etched track within the initial, high-energy section of its formation; the total residual range and diameters, corresponding to saturation zone of the primary ionization; and the etching rate along the different parts of tracks, the starting inter-volume olivine crystal point for which were fixed. The preliminary experimental results obtained for 42 tracks, detected and analyzed in the Marjalahti pallasite olivine crystals, are presented.

Physics design of the 8 GeV H-minus linac

The proposed 8 GeV proton driver (PD) linac at FNAL is based on 436 independently phased superconducting (SC) resonators (Foster and MacLachlan 2002 Proc. LINAC-2002 p 826). The linac includes a front end up to ∼420 MeV and a high energy section operating at 325 and 1300 MHz respectively. A room temperature (RT) radio frequency quadrupole (RFQ) and short H-type resonators are proposed for the initial acceleration of the H-minus or proton beam up to 10 MeV. From 10 to ∼420 MeV the voltage gain is provided by SC spoke-loaded cavities. In the high-energy section, the acceleration is provided by the International Linear Collider (ILC)-style SC elliptical cell cavities. The beam physics and the lattice design for the FNAL 8 GeV linac are discussed in this paper.

Development of a beta 0.12, 88 MHz, quarter-wave resonator and its cryomodule for the SPIRAL2 project

SPIRAL2 is a radioactive beams facility, composed of a superconducting linac driver, delivering deuterons with an energy of up to 40 MeV (5 mA) and heavy ions with an energy of 14.5 MeV/u (1 mA). This facility is now fully approved by the French government. The first prototype of beta 0.12 quarter-wave resonator has been recently fabricated by Zanon company and tested at IPN Orsay. The details on its fabrication and the results of the RF and mechanical tests at 4 K will be presented. Then, we will show the design of the cryomodule-B, dedicated to the high energy section of the linac, which is now ready to be ordered. Finally, the last studies of the R&D program, such as the last optimizations of the geometry, the new developments of the tuning system and the design of the helium vessel, are described.

Beam loss studies in high-intensity heavy-ion linacs

The proposed Rare Isotope Accelerator (RIA) Facility, an innovative exotic-beam facility for the production of high-quality beams of short-lived isotopes, consists of a fully superconducting 1.4 GV driver linac and a 140 MV postaccelerator. To produce sufficient intensities of secondary beams the driver linac will provide 400 kW primary beams of any ion from hydrogen to uranium. Because of the high intensity of the primary beams the beam losses must be minimized to avoid radioactivation of the accelerator equipment. To keep the power deposited by the particles lost on the accelerator structures below $1\text{ }\mathrm{W}/\mathrm{m}$, the relative beam losses per unit length should be less than ${10}^{\ensuremath{-}5}$, especially along the high-energy section of the linac. A new beam dynamics simulation code TRACK has been developed and used for beam loss studies in the RIA driver linac. In the TRACK code, ions are tracked through the three-dimensional electromagnetic fields of every element of the linac starting from the electron cyclotron resonance (ECR) ion source to the production target. The simulation starts with a multicomponent dc ion beam extracted from the ECR. The space charge forces are included in the simulations. They are especially important in the front end of the driver linac. Beam losses are studied by tracking a large number of particles (up to ${10}^{6}$) through the whole linac considering all sources of error such us element misalignments, rf field errors, and stripper thickness fluctuations. For each configuration of the linac, multiple sets of error values have been randomly generated and used in the calculations. The results are then combined to calculate important beam parameters, estimate beam losses, and characterize the corresponding linac configuration. To track a large number of particles for a comprehensive number of error sets (up to 500), the code TRACK was parallelized and run on the Jazz computer cluster at ANL.

Spurious ionic charge states in a tandem accelerator

Spurious projectiles appearing in a tandem accelerator when tuning highly ionized 35Cl were quantitatively analyzed in an attempt to understand their origin. Most of these ions can be explained in terms of multiple electron-capture and electron-loss reactions of the accelerating particle in the high-energy section of the accelerator. The fair agreement between the experimental yields of different spurious beams and the predictions of a theoretical model lends support to the hypothesis that such atomic collisions take place with molecules from the residual gas in the accelerator.

Spurious ionic charge states in a tandem accelerator

Spurious projectiles appearing in a tandem accelerator when tuning highly ionized 35 Cl were quantitatively analyzed in an attempt to understand their origin. Most of these ions can be explained in terms of multiple electron-capture and electron-loss reactions of the accelerating particle in the high-energy section of the accelerator. The fair agreement between the experimental yields of different spurious beams and the predictions of a theoretical model lends support to the hypothesis that such atomic collisions take place with molecules from the residual gas in the accelerator.

High-energy ion linacs based on superconducting spoke cavities

The applicability of superconducting TEM-class spoke cavities to high-energy ion linacs is discussed, and detailed designs for two TEM-class, triple-spoke-loaded superconducting niobium resonant cavities are presented. The 345 MHz cavities have a velocity range of $0.4<\ensuremath{\beta}<0.75$ and a beam aperture of 4 cm. Spoke-loaded cavities offer several advantages compared with the higher-frequency elliptical-cell cavities that are currently being developed for this range of particle velocities. The proposed triple-spoke cavities can provide broader velocity acceptance, more accelerating voltage per cavity, reduced heat-load operation at 4.2 K, and increased longitudinal acceptance through the high-energy section. Application to the proposed U.S. rare-isotope accelerator driver linac is discussed in detail.

Status of the HIIF RF linac study based on H-mode cavities

The H-mode structure family was extended recently to gain access to velocity profiles ranging from β∼0.002 to 0.6. This means that the (Heavy-Ion Inertial Fusion) (HIIF) relevant energy range is well included ( β≤0.3). RF power tests show the capability of IH-cavities to withstand about 10 MV/m effective voltage gain. A linac lattice at 30 MeV/u and based on the (Kombinierte Null Grad Struktur) (KONUS) beam dynamics is investigated at beam intensities of up to 1 A. The use of multibeam cavities along the low energy linac sections is suggested. As the RF frequency along the H-type linac is changed from around 10 MHz up to around 400 MHz, typically 32 channels could be funneled into the single aperture high-energy linac section. This principle should open the possibility to get linac beam intensities as high as 2 A within norm, transverse emittances around 1π mm mrad and a final energy spread ΔW/W∼±2×10 −4. At the low-energy end beam intensities around 500 mA along each multi aperture cavity are feasible. Higher linac beam intensities give short RF pulse lengths. This will allow to develop RF power sources with significantly higher peak power levels. Additionally, the whole system will benefit from the time-averaged wall loss reduction.

Static Debye-Waller factor analysis of hydrogen precipitates in silicon

Abstract The hydrogen-induced defects in single crystals of silicon grown by the floating-zone method in a hydrogen atmosphere, have been measured by high-energy synchrotron radiation section topography. The static Debye-Waller factor (SDWF) produced by hydrogen precipitates, which were formed in silicon under isochronal annealing, has been calculated on the basis of a statistical dynamical diffraction theory. Within a H2 molecule cluster model which we proposed for a precipitate, the size and density of hydrogen precipitates have been determined using the SDWF method and the results of infrared absorption spectrum. The character of the early stage of hydrogen precipitation indicates that hydrogen in p-type silicon is mobile and less stable, compared with that in n-type silicon.

Quadrupole field geometries for intense electron beam acceleration

High-intensity electron beams could be focused in low-frequency RF accelerators and induction linear accelerators by adding transverse components to the accelerating electric field. Calculations with a 3D code show that quasielectrostatic focusing is sufficient to transport kiloampere electron beams in RF accelerators and the high-energy sections of induction accelerators. The elimination of conventional magnetic focusing systems could lead to reductions in the volume and weight of high-current electron accelerators. Two novel quadrupole geometries are investigated: a periodic array of spherical electrodes with alternating displacements and a set of plate electrodes with elliptical apertures.

Autoneutralization of space charge dominated beams for heavy ion fusion

Several heavy ion beams, each with current in the kiloampere range and particle energy in the gigaelectronvolt range, must be focused onto a millimetre size spot to provide the power required for ignition of high gain, radiation driven targets for inertial confinement fusion. It is difficult to achieve this condition for three reasons: (a) The repulsive space charge forces within individual beams and the mutual space charge repulsion among the beams, which are strongest near the focal spot, prevent multiple beams from focusing onto a small spot. (b) Beam current increases from beam head to tail, so the beam-beam repulsion is time dependent. This prevents multiple beams from being focused onto a small spot throughout the entire pulse. (c) Radiation from the beam heated target photoionizes some beam ions into higher charge states, and these ions are expelled from the beam by the space charge force. To minimize these three effects, it is proposed to place a metallic cylinder in front of the focal spot and to cover the cylinder, at the beam entrance end, with a plastic film of submicron thickness. As the beams pass through the film, the beam space charge force draws electrons from the film to co-move with the beam, `autoneutralizing' the ion beams inside the cylinder. Although the film strips beam ions into higher charge states, particle-in-cell simulations show that autoneutralization is so effective that the residual radial electric field in the neutralized beam is considerably less than that in the unneutralized beam. The application of this scheme thereby results in a great improvement in focusing quality. Beams with higher charge state or lower mass ions, which have the advantages of reducing both the length of the high energy section of induction linacs and the strengths of the final-focusing magnets, can therefore be used

Life improvement in high temperature components for advanced power engineering

Advanced power engineering rely on technological solutions allowing the design, construction and operation of power plants according to the state of the art, extending the limits of available materials for higher cycle efficiencies, for improved reliability and availability of the systems, and assuring in the meanwhile longer service lives. Elevated temperature components, high pressure and high energy sections might be considered relevant with respect to time behaviour of the plant, since load-bearing structural materials are mainly subjected to metallurgical ageing, creep processes due to temperature exposure, thermomechanical and low cycle fatigue induced by load histories, as well as crack initiation and growth. Life improvement objective has to be fully considered and assumes a twofold application: i) at the design and construction stage, with the introduction of new materials and/or adopting better reference data and validated extrapolation procedures; ii) for existing plants, managing proper life extension methodologies integrated with plant rejuvenation, refurbishment or repowering decisions. In the following, attention will be devoted to still open questions which are susceptible to contribute to the goal of safe and reliable, high efficiency thermal power plants, as residual life evaluation in components under multiaxial stress state, on-line plant monitoring, non destructive techniques and expert systems for residual life assessment and in situ repair/treatment techniques.

A 500 MeV Low Operating Cost Electron Linac

A 500 MeV linac has been constructed and operated since Dec. 1980 at ETL in Tsukuba for the generation of high intensity photons and pions and for the electron injection to a 600 MeV storage ring and a 150 MeV beam stretcher. The linac consists of an injector with a triode type electron gun and an inflector and three kinds of twenty linearly tapered iris type accelerating sections, of which four sections are 2.3 m long and sixteen sections 3 m long. Rf power at a frequency of 2856 MHz is provided by seven 25 MW klystrons with an improved efficiency of about 50 % to save the power consumption to about 70 % of that of the ordinary linac. The maximum beam duty cycle is 0.24 %. To avoid the cumulative beam blow-up, special attention has been paid to the design of the linearly tapered iris type accelerating section and the configuration of twenty sections and eleven quadrupole doublets and a triplet. For the economical beam sharing, the beams with three different energies from low, medium and high energy sections are simultaneously provided to four experimental arears by means of the combination of three pulsed coils and four beam transport systems.

Glauber cross sections for arbitrary excitation of ground-state hydrogen by electron and proton impact

The Glauber scattering amplitude for $1s\ensuremath{-}nlm$ excitations of hydrogen by charged particle impact is reduced to a form numerically computable for arbitrary values of $n$, $l$, and $m$. The increasing number of repeated parametric differentiations appearing in earlier methods with the increase of $n$ is replaced in our method by a single contour integration, which is especially useful for large-$n$ states. In addition, whereas the available closed-form expressions would involve the calculation of a large number of hypergeometric functions as $l$ and $m$ increase for a given $n$, the present integral form involves only one hypergeometric function for any $n$, $l$, and $m$. The asymptotic form of the $1s\ensuremath{-}nlm$ amplitude as $n\ensuremath{\rightarrow}\ensuremath{\infty}$ is also presented. The procedure is applied for studying the $1s\ensuremath{\rightarrow}\mathrm{ns}(n=3, 4, 10, \mathrm{and} \ensuremath{\infty})$ and $1s\ensuremath{\rightarrow}\mathrm{np}(n=3, 4, \mathrm{and} \ensuremath{\infty})$ excitations of hydrogen by electron and proton impact. Tabular results of the cross sections are presented for differential and integrated cross sections in ${e}^{\ensuremath{-}}$-H collisions and for integrated cross sections in ${\mathrm{H}}^{+}$-H collisions. The qualitative features observed earlier for low $\mathrm{ns}$ and $\mathrm{np}$ excitations are found to exist also for $n\ensuremath{\ge}3$ excitations. The $1s\ensuremath{\rightarrow}\mathrm{ns}$ and $1s\ensuremath{\rightarrow}\mathrm{np}$ cross sections obey an ${n}^{\ensuremath{-}3}$ law asymptotically as ${n}^{\ensuremath{-}2}\ensuremath{\rightarrow}0$, which is in conformity with the analytical results obtained quite generally for $1s\ensuremath{\rightarrow}\mathrm{nlm}$ excitations. For proton impact $1s\ensuremath{\rightarrow}3p$ excitations, the Glauber results are in excellent agreement with a recent 34-state calculation. A unified graphical representation of various normalized cross sections above some specific energy is presented, whence a knowledge of the high-energy Born cross sections for any $1s\ensuremath{\rightarrow}\mathrm{ns}$ or $1s\ensuremath{\rightarrow}\mathrm{np}$ excitation suffices to determine the absolute Glauber cross sections for the process.

Performance Characteristics of a 425-MHz RFQ Linac

A radio-frequency quadrupole (RFQ) focused proton linac has been developed and successfully tested at the Los Alamos Scientific Laboratory (LASL) for the purpose of evaluating its performance and applicability as a low-beta accelerator. The geometry of the structure was designed to accept a 100-keV beam, focus, bunch, and accelerate it to 640 keV in 1.1 m with a high-capture efficiency and minimum emittance growth. The accelerator test facility includes an injector, low-energy transport section for transverse matching, and a high-energy transport section for analysis of the beam properties. The accelerator cavity is exited through a manifold powered by a 425-MHz klystron. Diagnostic instrumentation was prepared to facilitate operation of the accelerator and to analyze its performance. Measurements of the beam properties are presented and compared with the expected properties resulting from numerical calculations of the beam dynamics.