Accelerated Proton Beams Research Articles

Charm, beauty and charmonium production at HERA-B

is a fixed target experiment working on the 920 GeV proton beam of the HERA accelerator at the DESY laboratory in Hamburg. During the last data taking period (2002-2003), about 150 million dilepton triggers, 220 million minimum bias events and 35 million hard photon triggers were acquired. These large statistics allow detailed studies on the production of charmonium states in proton-nucleus p-A collisions, which extend for the first time into the negative Feynman-x () region. Measurements of the inclusive , $\Upsilon$ and open charm cross sections are also ongoing. After a brief discussion of the detector and of the data samples, we report on preliminary results obtained on these physics topics.

Dynamical mechanical analysis of proton beam irradiated polyimide

The excellent mechanical properties, the outstanding thermal stability, and the lightweight of polyimide have a particular relevance to space missions. In order to assess the lifetime of polyimide subjected to ionizing radiation and extreme temperatures, a dynamic mechanical analysis of the effect of accelerated proton beams on polyimide films is reported. The temperature dependence of the loss factor proved the presence of two relaxations; a β2 relaxation located around 100°C and a glass relaxation located around 400°C. It is concluded that degradation of polyimide subjected to proton irradiation is controlled by chain scission reactions. The observed small shift of the glass transition temperatures due to proton irradiation encourages the use of polyimide in environments that combines radiation with extreme temperatures. Additional electron spin resonance data confirmed the generation of free radicals in proton-irradiated polyimide.

長尺ケーブルを用いたコンベクトロン真空計を使った圧力測定

A Pirani gauge is usually operated in an accelerator for monitoring the pressure in the beginning of the pump down process. In the high-intensity proton beam accelerator, the gauge controller/power supply, including some semiconductor electronic devices, is often failed due to high levels of radiation, when being installed near the accelerator. In order to install the power supply far out of the tunnel, performance of the Convectron gauge was examined by using longer cables than catalog-specified cable. The gauge was tested with cables of 3 to 500 m long. An inaccurate value in the pressure reading was indicated at the pressure above 1000 Pa, when the cable length was 200 m long, or more. The voltage offset generated by cable resistance exceeds an acceptable input range of the amplifier. Remodeling the controller, a long cable of 500 m long was able to be adopted.

Melanocytomas of the optic disk

To evaluate the various forms of clinical presentation, the potential of growth, the risk of functional loss and the possibility of malignant transformation of optic disk melanocytomas in European patients. Retrospective observational case control study. Evaluation of 37 cases of optic disk melanocytomas identified in the computer files of the ocular oncology unit of Jules Gonin Hospital to determine the clinical presentation of these tumors and the risk of complications. The tumor was asymptomatic in 28 cases. Visual acuity was normal in 26 cases, subnormal in 10 cases, and in one case it was reduced to 0.1. Visual field defects were observed in 19 cases; the size and extent of the tumor and the degree of papilledema appeared to influence the severity of the visual field defect. Tumor growth was demonstrated in 6 of the 9 cases in which follow-up was for at least six years. In two cases there was presumed malignant transformation that was treated by accelerated proton beam radiotherapy. Melanocytomas in white Europeans and those of European derivation are rarely symptomatic, have only a moderate effect on visual function and show a low rate of progression over long observation. The risk of tumor progression, although sometimes occurring as much as several years after the initial diagnosis, justifies a cautious approach with long-term regular surveillance of these patients.

Progress on plasma accelerators: from the energy frontier to tabletops

This paper reviews the concepts, recent progress and current challenges for realizing the tremendous electric fields in relativistic plasma waves for applications ranging from tabletop particle accelerators to high-energy physics. Experiments in the 1990s on laser-driven plasma wakefield accelerators at several laboratories around the world demonstrated the potential for plasma wakefields to accelerate intense bunches of self-trapped particles at rates as high as 100 GeV m−1 in millimetre-scale gas jets. These early experiments have been followed in the current decade by experiments that are advancing on several fronts—increasing the accelerated charge (to the several nanocoulomb level), producing higher transverse beam quality (to the mm mrad normalized emittance level) and accessing new physics regimes at higher laser power. Several groups are engaged in pursuing two key challenges for laser wakefield accelerators—producing beams with small energy spread and extending the interaction length from millimetres to centimetres and beyond. Major breakthroughs on both fronts have occurred in the past year. In parallel with the progress in laser-driven wakefields, particle-beam driven wakefield accelerators are making large strides. A series of experiments using the 30 GeV beam of the Stanford Linear Accelerator has demonstrated high-gradient acceleration of electrons and positrons in metre-scale plasmas as well as key scaling laws for a ‘plasma afterburner’, a concept for doubling the energy of a high-energy collider in a few tens of metres of plasma. In addition to wakefield acceleration, these and other experiments have demonstrated the rich physics bounty to be reaped from relativistic beam–plasma interactions. This includes plasma lenses capable of focusing particle beams to the highest energy density ever produced, collective radiation mechanisms capable of generating high-brightness x-ray beams, collective refraction of particles at a plasma interface and acceleration of intense proton beams from laser-irradiated foils.

Spectral and angular characterization of laser-produced proton beams from dosimetric measurements

In this paper, we report the first results of dosimetric analysis of broad-spectrum, multi-MeV laser accelerated proton beams obtained during experiments at the Rutherford Appleton Laboratory using the Chirped Pulse beam of the Vulcan laser. The spectra are retrieved by a numerical analysis that allows the reconstruction of the energetic profile of the proton beam from data obtained using radiochromic film.

Optimum ions for a nuclear reactor with neutron illumination

The main advantage of fission reactors with neutron illumination is that, owing to the neutron illumination, they operate in the subcritical mode and, hence, are safe. Neutrons required for the illumination are generated during nuclear fragmentation in a target irradiated by 1–2 GeV protons. A substantial disadvantage of this method for energy generation is the severe restriction imposed on the power of a plant. This restriction is due to the restriction imposed on the intensity of an accelerated-proton beam by the tolerances for the activation of accelerator structural elements. The substitution of heavier nuclei (from carbon to argon) for protons is shown to substantially increase the intensity of an accelerated-ion beam and to provide a commercially reasonable thermal power of ∼4–6 GW.

Materials and processing of vacuum components for the high-intensity proton beam accelerator, J-PARC

The Japan Proton Accelerator Research Complex (J-PARC) project of the proton beam accelerator, involving a 400-MeV linac, a 3-GeV rapid-cycling synchrotron and a 50-GeV synchrotron, started in 2002. Materials used as vacuum components, such as electroformed copper, titanium, stainless steel and alumina ceramics, were examined from the point of view outgassing and electrical breakdown. The mechanical characteristics of a hydro-formed titanium bellows and a quick-disconnect flange system were also investigated.

Generation and Propagation of High Quality Proton Beams Produced by Laser Plasma Interactions

The acceleration of proton beams during the interaction of an ultra short and ultra intense laser pulse with matter is possibly the most important application of compact laser systems with multi-terawatt and petawatt power. High quality beams with a small energy spread are required for applications where spatially accurate energy deposition is important. For some specific applications the target may be located far from the acceleration region, in which case space charge effects and the interaction with an ambient plasma may deteriorate the beam quality during its propagation.Here, first we review a recently proposed method for producing high quality proton beams using short laser pulses and a target made of a layer of heavy ions followed by a thin proton layer with a transverse size smaller than the pulse waist. Subsequently, we investigate the effects of the beam propagation through a plasma slab in a simplified one-dimensional model.

Controlling Halo-Chaos via Variable Structure Method

We propose a variable structure control method which is anotherinnovative technique for suppressing beam halo-chaos in the periodicfocusing channels of high-current proton beam accelerator, which belongsto a high-tech field. The analysis and numerical results show that themethod is effective for controlling beam halo-chaos. Physicalimplementation of such a kind of control strategy remains an importantand open issue for further applications.

A Quasi-Potential Approach for Describing pp-Scattering at High Energies

Research into elastic scattering is one of the main methods for studying the structure and interaction between highenergy particles. Among the processes of elastic scattering of hadrons, the proton-proton scattering has a special place, since the presence of primary proton beams in accelerators allows the proton interaction to be studied at the highest energy values available. Theoretical models of elastic pp-scattering give very close predictions concerning the positions of differential cross-section minima, that is, all of them are largely constructed similarly to optical diffraction. The problems inherent in comparison of the well-known models with experiment have stimulated the active search of the ways to construct an adequate description of experimental features of elastic scattering at high energies. A quasi-potential approach to describing elastic proton-proton scattering is considered here on the basis of an eikonal approximation. A variable parameter is used in this approximation instead of an impact parameter.

First results from the HERA — B experiment

HERA — B is a fixed target experiment working at the 920 GeV proton beam of the HERA accelerator at the DESY laboratory in Hamburg. In the year 2000 the detector was almost completely installed and started the commissioning phase. We report here on the first physics results obtained on charmonium production, b-quark cross section and K s 0 , Λ and Λ ¯ production. We discuss also the detecttor status and the physics prospects for the coming running period.

Subclinical Experimental Optic Neuropathy after Accelerated Proton Beam Irradiation

Background: Accelerated proton beam irradiation has been used for several years to treat intraocular tumors. The pathophysiology of proton-beam-induced retinopathy and neuropathy has not been characterized to date. The present study investigates the early effects of irradiation with an accelerated proton beam on the optic nerve of the rabbit. Materials and Methods: The optic nerve head of Albino New Zealand rabbits (n = 14) was irradiated with a narrow beam of accelerated protons using the total dose of 60 and 43 Gy, respectively. This dose was split up into 4 equal sessions taking place on 4 consecutive days. Ophthalmoscopic examination was performed regularly, and the rabbits were sacrificed at 1, 3 and 8 months after irradiation. The eyes were enucleated and processed for light and electron microscopy. Results: Despite the absence of ophthalmoscopically detectable optic neuropathy in all 14 rabbits irrespective of the dose of irradiation, light and electron microscopy of the optic nerve showed a glial and fibrotic perivascular scar made up predominantly of altered astrocytes. This scar formation was seen as early as 1 month after irradiation and was at times accompanied by infiltration with inflammatory cells perivascularly both outside and within the optic nerve. In contrast to the astrocytes, oligodendrocytes did not show degenerative cellular alterations. During the 8-month follow-up, no signs of vascular occlusion were found. Conclusions: The observed lesions in the glial tissues with consecutive fibrosis appear to stem from a direct effect of irradiation. This may represent the initial mechanism of early subclinical irradiation-induced damage to the optic nerve before vascular occlusions may occur at a later stage, which may lead to more severe damage.

Emergency Decay Heat Removal by Reactor Vessel Auxiliary Cooling System from an Accelerator-Driven System

The passive emergency decay heat removal during severe cooling accidents in Pb/Bi-cooled 80- and 250-MW(thermal) accelerator-driven system (ADS) designs was investigated with the computational fluid dynamics code STAR-CD. For the 80-MW(thermal) design, the calculations show that no structural problems occur as long as the accelerator proton beam is switched off immediately after accident initiation. A highly unlikely delay of beam stop by 30 min after a combined loss-of-heat-sink and loss-of-flow accident would lead to increased reactor vessel temperatures, which do not cause creep failure. By using a melt-rupture disk on the vacuum pipe of the accelerator proton beam to interrupt the beam at elevated temperatures in a passive manner, the grace time before beam stop is necessary is increased from 30 min to 6 h. An emergency decay heat removal design, which would prevent radioactive release to the atmosphere even more reliably than the Power Reactor Inherently Safe Module (PRISM) design, was also investigated. For an ADS of 250-MW(thermal) power with the same vessel as the 80-MW(thermal) ADS examined, the maximum wall temperature reaches 745 K after an immediate beam stop. This does not cause any structural problems either. The grace time until a beam stop becomes necessary for the 250-MW(thermal) system was found to be ~12 min. To reduce elevated vessel temperatures more rapidly after a beam stop, alternative cooling methods were investigated, for example, filling the gap between the reactor and the guard vessel with liquid metal and the simultaneous use of water spray cooling on the outside of the guard vessel. This decreases the coolant temperatures already within minutes after switching off the proton beam. The use of chimneys on the reactor vessel auxiliary cooling system, which increase the airflow rate lowers the maximum reactor vessel wall temperature only by ~20 K. It can be concluded that the critical parameter for the emergency cooling of an ADS is the time delay in switching off the accelerator after accident initiation.

Burn-up characteristics of ADS system utilizing the fuel composition from MOX PWRs spent fuel

Burn-up characteristics of accelerator-driven system, ADS has been evaluated utilizing the fuel composition from MOX PWRs spent fuel. The system consists of a high intensity proton beam accelerator, spallation target, and sub-critical reactor core. The liquid lead–bismuth, Pb–Bi, as spallation target, was put in the center of the core region. The general approach was conducted throughout the nitride fuel that allows the utilities to choose the strategy for destroying or minimizing the most dangerous high level wastes in a fast neutron spectrum. The fuel introduced surrounding the target region was the same with the composition of MOX from 33 GWd/t PWRs spent-fuel with 5 year cooling and has been compared with the fuel composition from 45 and 60 GWd/t PWRs spent-fuel with the same cooling time. The basic characteristics of the system such as burn-up reactivity swing, power density, neutron fluxes distribution, and nuclides densities were obtained from the results of the neutronics and burn-up analyses using ATRAS computer code of the Japan Atomic Energy research Institute, JAERI.

The Multipoles Factory: an element of the LHC control

The measurements performed at CERN on prototypes and first pre-series main dipole magnets confirm the need of an active control of the Large Hadron Collider to compensate the dynamic field changes during the proton beam injection and acceleration. This control requires in turn an accurate forecast of the magnetic field in the accelerator. We plan to predict the field on the basis of two elements: theoretical field models tailored through the accumulated knowledge of the main magnets during series tests, and an on-line measurement system running on few reference magnets tracking the LHC current cycle. Data coming from this Multipoles Factory will result from the fusion of the two sources. Based on this system we foresee to deliver calibration information for pre-defined accelerator cycles as well as real time information for the active control. In this paper we report the conceptual design of the system, and we discuss the features and performance of the models that we have developed for the field forecast.

About some principal possibilities for improvement of electronuclear system's characteristics

During the last few years in the leading Russian nuclear centers conceptual research of various versions of Accelerator Driven System (ADS) were conducted. This study stimulated an occurrence of a number of original new ideas, directed on the improvement of characteristics of ADS with the primary purpose of, effective destruction of long-lived radioactive waste (LLRW). The general idea relates to sectionalized blanket with compound neutron valve. The sectionalized blankets permits a two times decrease in the proton beam of accelerator. The compound neutron valve with Np layer allows an increase in the level of nuclear safety of blanket. The different versions of sectionalized blanket are considered.

Status of the U-70 Accelerator at the Institute of High-Energy Physics

A brief history of the development and the present status of the accelerator complex at the Institute of High-Energy Physics are presented. The problems facing this complex, which mainly involve increasing the intensity of the accelerated proton beams, decreasing particle losses, and producing an efficient extraction system for high-intensity beams, are expounded. The possibility of accelerating beams of light nuclei, which are a promising tool for performing fundamental and applied research, is discussed. Attention is focused on the upgrading and reconstruction of the systems in the accelerator complex which are being performed for solving these problems.

Iridescent Art Nouveau glass – IBA and XPS for the characterisation of thin iridescent layers

The external proton beam of the Tandem accelerator of the Research Centre in Rossendorf/Germany was used to carry out non-destructive particle-induced X-ray emission (PIXE) particle-induced gamma-ray emission (PIGE) and Rutherford backscattering (RBS) measurements simultaneously on Art Nouveau artifacts produced around 1900 by Tiffany/USA and Loetz/Austria. These studies should proof the technology of producing an iridescent layer on a glass surface. By means of the yield ratio Y(Si-K)/ Y(Si-γ) of both characteristic X-radiation (Si-K) and γ-radiation (Si-γ) of the element silicon it could be shown that a thin top layer is present on the glass surface due to the treatment of the heated artifacts (about 500°C) with an alcoholic solution of SnCl 2 [1]. Combined evaluation of the PIXE and RBS spectra resulted in a thickness of 20–300 nm for this top layer. In addition, a transition region between the iridescent layer and the bulk glass was obtained by RUMP simulations. Approximately 80% of the total amount of the Sn were found to be present in this transition layer and only 10–20% in the outermost surface region. XPS studies showed that the outermost layer consists of SnO 2. The formation of other Sn compounds in the outermost near-surface region based on Sn–Si–O during the manufacturing process can be excluded.

Marcus Laurence Elwin ‘Mark’ Oliphant

Marcus Laurence Elwin ‘Mark’ Oliphant