High-energy Particle Accelerators Research Articles

The bubble regime of laser–plasma acceleration: monoenergetic electrons and the scalability

The bubble regime of electron acceleration in ultra-relativistic laser plasma is considered. It has been shown that the bubble can produce ultra-short dense bunches of electrons with quasi-monoenergetic energy spectra. The first experiment in this regime done at LOA has confirmed the peaked electron spectrum (Faure J et al 2004 Nature at press). The generated electron bunch may have density an order of magnitude higher than that of the background plasma. The bubble is able to guide the laser pulse over many Rayleigh lengths, thus no preformed plasma channel is needed for high-energy particle acceleration in the bubble regime. In this work we discuss a simple analytical model for the bubble fields as well as the scaling laws.

High-energy particle acceleration in the shell of a supernova remnant

A significant fraction of the energy density of the interstellar medium is in the form of high-energy charged particles (cosmic rays). The origin of these particles remains uncertain. Although it is generally accepted that the only sources capable of supplying the energy required to accelerate the bulk of Galactic cosmic rays are supernova explosions, and even though the mechanism of particle acceleration in expanding supernova remnant (SNR) shocks is thought to be well understood theoretically, unequivocal evidence for the production of high-energy particles in supernova shells has proven remarkably hard to find. Here we report on observations of the SNR RX J1713.7 - 3946 (G347.3 - 0.5), which was discovered by ROSAT in the X-ray spectrum and later claimed as a source of high-energy gamma-rays of TeV energies (1 TeV = 10(12) eV). We present a TeV gamma-ray image of the SNR: the spatially resolved remnant has a shell morphology similar to that seen in X-rays, which demonstrates that very-high-energy particles are accelerated there. The energy spectrum indicates efficient acceleration of charged particles to energies beyond 100 TeV, consistent with current ideas of particle acceleration in young SNR shocks.

A new solar flare scenario: - High-beta plasma disruption -

The solar corona is believed to be generally low beta. In a low-beta plasma, energy is mainly stored as magnetic energy or current. To dissipate the stored magnetic energy in the highly conductive corona, anomalous resistivity is needed. Activities of outer layers of X-ray loops in solar flares have been interpreted as the result of reconnection of magnetic field due to anomalous resistivity in a current sheet located above the flaring loop.However, recent high-cadence EUV observations show many flares without opening up of magnetic field. This means that existence of current sheets above flaring loops is not a necessary element for flares. It is also found for many flares that low temperature prominence plasma are heated in the very early phase of lifting. These observational facts require a new solar flare scenario different from reconnection.Recent multi-wavelength high-spatial and -temporal resolution observations show that flares originate in the lower atmosphere. We can expect high beta plasma and small curvature magnetic loops in the lower atmosphere. It is also observed high-velocity flows along magnetic loops associated with flares. Bounded motions of charged particles (both thermal motion and flow) along the magnetic lines of force create the centrifugal force. They exceed gravity force under certain conditions (small curvature and high velocity). They can even exceed magnetic tension force depending on beta values of the plasma in the loop.In the case of the upward acceleration (centrifugal - gravity ) plasma in a loop, whose ends are anchored at the photosphere, is unstable against the localized interchange (BALLOONING) mode. It can develop into non-linear phase and explosive phenomena are expected. This is called HIGH-BETA DISRUPTION. The high-beta disruption has many common characteristics to solar flares. Various phenomena related to solar flares such as, high-energy particle acceleration, plasma turbulence, plasma ejections, plasma heating, are interpred as the result of high-beta disruption. High spatial and temporal resolution observations of flares at various wavelengths are used to see the actual instability process. Shibasaki (2001)To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Radiological Assessment of Target Materials for Accelerator Transmutation of Waste Applications

This paper provides the radiation absorbed dose rates (rad-h-1) to a tissue-equivalent torus ring at 1 meter from radioactive spallation products in Ta, W, Pb, Bi, and LBE target materials used in Accelerator Transmutation of Waste (ATW) applications. No previous works have provided an estimate of the absorbed dose rates (rad-h-1) to tissue from activated targets for ATW applications. In addition, this paper provides the characterization of target materials of high-energy particle accelerators for the parameters of (a) spallation neutron yield (neutrons/proton), (b) spallation products yield (nuclides/proton), (c) energy-dependent spallation neutron fluence distribution (n-cm-2 MeV-1), and (d) identification of the optimal target dimensions to yield the maximum radial spallation neutron leakage from the target. A beneficial characteristic of these target materials (Ta, W, Pb, Bi, and LBE) is they do not produce radioactive transuranic isotopes, which have very long half-lives and require special handling and disposition controls. In addition, these activated, spent targets are not considered high-level radioactive waste for disposal purposes such as spent fuel from a nuclear power reactor.

Calorimetry for particle physics

Calorimetry has become a well-understood, powerful, and versatile measurement method. Besides perfecting this technique to match increasingly demanding operation at high-energy particle accelerators, physicists are developing low-temperature calorimeters to extend detection down to ever lower energies, and atmospheric and deep-sea calorimeters to scrutinize the universe up to the highest energies. The authors summarize the state of the art, with emphasis on the physics of the detectors and innovative technologies.

Anthony Leonid Turkevich

Anthony Leonid Turkevich

Properties of the electron cloud in a high-energy positron and electron storage ring

Low-energy, background electrons are ubiquitous in high-energy particle accelerators. Under certain conditions, interactions between this electron cloud and the high-energy beam can give rise to numerous effects that can seriously degrade the accelerator performance. These effects range from vacuum degradation to collective beam instabilities and emittance blowup. Although electron-cloud effects were first observed two decades ago in a few proton storage rings, they have in recent years been widely observed and intensely studied in positron and proton rings. Electron-cloud diagnostics developed at the Advanced Photon Source enabled for the first time detailed, direct characterization of the electron-cloud properties in a positron and electron storage ring. From in situ measurements of the electron flux and energy distribution at the vacuum chamber wall, electron-cloud production mechanisms and details of the beam-cloud interaction can be inferred. A significant longitudinal variation of the electron cloud is also observed, due primarily to geometrical details of the vacuum chamber. Such experimental data can be used to provide realistic limits on key input parameters in modeling efforts, leading ultimately to greater confidence in predicting electron-cloud effects in future accelerators.

A passive radon dosemeter suitable for workplaces.

The results obtained in different international intercomparisons on passive radon monitors have been analysed with the aim of identifying a suitable radon monitoring device for workplaces. From this analysis, the passive radon device, first developed for personal dosimetry in mines by the National Radiation Protection Board, UK (NRPB), has shown the most suitable set of characteristics. This radon monitor consists of a diffusion chamber, made of conductive plastic with less than 2 cm height, containing a CR-39 film (Columbia Resin 1939), as track detector. Radon detectors in workplaces may be exposed only during the working hours, thus requiring the storage of the detectors in low-radon zones when not exposed. This paper describes how this problem can be solved. Since track detectors are also efficient neutron dosemeters, care should be taken when radon monitors are used in workplaces, where they may he exposed to neutrons, such as on high altitude mountains, in the surroundings of high energy X ray facilities (where neutrons are produced by (gamma, n) reactions) or around high energy particle accelerators. To this end, the response of these passive radon monitors to high energy neutron fields has been investigated.

Monte-Carlo Calculation of the Response Functions for Two Prototype Cosmic Neutron Metrology Instruments

The response functions for two cosmic neutron detection systems have been calculated using Monte-Cario computational methods. The detection systems that form the focus of this research are modified Leake detector designs in which a central thermal neutron detector is surrounded by a sphere of high-density polyethylene. In this arrangement, the surrounding polyethylene moderates the incident fast neutrons that are then detected by the central detector; in this case a 3He-filled proportional counter. In order to extend the response of these detector systems to cater for cosmic neutron environments, a shell of high-Z material has been included in each to promote (n, xn) reactions in the polyethylene moderator. We have used shells of lead and copper for this purpose to bring the high-energy component of the cosmic field, extending up to several GeV, within the capability of the detector systems. In particular, copper has been used in comparison with lead since the former is easier and safer to machine and handle. The overall diameter of the instruments studied in this work is 208 mm.Calculations of the neutron response have been performed with MCNP4C, for the thermal - 20 MeV energy range, and with MCNPX 2.1.5 / LA150N neutron libraries for the higher-energy cosmic region of the spectrum beyond 20 MeV. The results of these calculations are compared with experimental data that have been recorded with the instruments at the CERN Cosmic Reference Field Facility (CERF), Geneva, Switzerland. This comparison is discussed in respect of the likely applications of these detector systems to high-energy neutron field measurement on-board aircraft and in the vicinity of high-energy particle accelerators. The former application is gaining considerable research attention following the revised estimates of relative biological effectiveness of cosmic neutron fields and the related recommendation that aircrew be regarded occupationally-exposed radiation workers, on behalf of the International Commission on Radiological Protection (ICRP) and the European Union. The latter application is of interest to accelerator operators and users who can be exposed to neutron fields with 100 MeV components as a result of scattering reactions from the materials comprising the accelerator and associated shielding. This is of growing concern to the medical field where the use of cyclotrons is often a key aspect of radiation treatment and therapy, in which the control and estimation of administered doses is a key objective.

The MEGA advanced Compton telescope project

The goal of the Medium Energy Gamma-ray Astronomy (MEGA) telescope is to improve sensitivity at medium gamma-ray energies (0.4–50 MeV) by at least an order of magnitude over that of COMPTEL. This will be achieved with a new compact design that allows for a very wide field of view, permitting a sensitive all-sky survey and the monitoring of transient and variable sources. The key science objectives for MEGA include the investigation of cosmic high-energy particle accelerators, studies of nucleosynthesis sites using gamma-ray lines, and determination of the large-scale structure of galactic and cosmic diffuse background emission. MEGA records and images gamma-ray events by completely tracking both Compton and pair creation interactions in a tracker of double-sided silicon strip detectors and a calorimeter of CsI crystals able to resolve in three dimensions. We present initial laboratory calibration results from a small prototype MEGA telescope.

Superconductivity in high energy particle accelerators

The basics of superconductivity are outlined with special emphasis on the features which are relevant for the application in magnets and radio frequency cavities for high energy particle accelerators. The special properties of superconducting accelerator magnets are described in detail: design principles, magnetic field calculations, magnetic forces, quench performance and persistent magnetization currents. The design principles and basic properties of superconducting cavities are explained as well as the observed performance limitations and the countermeasures. The ongoing research efforts towards maximum accelerating fields are addressed and the coupling of radio frequency power to the particle beam is treated.

Marcus Laurence Elwin Oliphant 1901 - 2000

With the death of Professor Sir Mark Oliphant, the first President of the Australian Academy of Science, Australia lost one of its most distinguished scientists. A tall, handsome man with a shock of white hair and a distinctive voice and laugh, he was well informed on a wide range of scientific matters and expressed firm views on their social consequences. He enjoyed wide respect throughout the nation as a great Australian, his influence spreading far beyond the discipline of physics, to which he made seminal contributions both through his own research and his leadership. The Academy will remember and honour him for his leading role in its establishment, and for his continuing association with it until the last years of his long life.Oliphant's outstanding international reputation was based on his pioneering discoveries in nuclear physics in Cambridge in the 1930s and his remarkable contributions to wartime radar research and to the development of the atomic bomb. In 1950, after an absence of 23 years, Oliphant returned to Australia, where he founded the Research School of Physical Sciences at the Australian National University and pioneered the creation in Canberra of a national university dedicated to the conduct of research at the highest international level.To the layman, Mark Oliphant was well known for his often outspoken comments on those matters about which he felt so strongly: social justice, peace, atomic warfare, the environment, academic freedom and autonomy, to name a few. The scientific community will remember him as a physicist for his pioneering experiments with Ernest Rutherford during momentous years that saw the birth of nuclear physics, as a physicist/engineer for his ingenuity and determination as one of the pioneers of high-energy particle accelerators, and as a science administrator and public advocate for science.

Chandraobservations of the X-ray jet in 3C 66B

Our Chandra observation of the FRI radio galaxy 3C66B has resulted in the first detection of an X-ray counterpart to the previously known radio, infra-red and optical jet. The X-ray jet is detected up to 7 arcsec from the core and has a steep X-ray spectrum, alpha ~ 1.3 +/- 0.1. The overall X-ray flux density and spectrum of the jet are consistent with a synchrotron origin for the X-ray emission. However, the inner knot in the jet has a higher ratio of X-ray to radio emission than the others. This suggests that either two distinct emission processes are present or that differences in the acceleration mechanism are required; there may be a contribution to the inner knot's emission from an inverse-Compton process or it may be the site of an early strong shock in the jet. The peak of the brightest radio and X-ray knot is significantly closer to the nucleus in the X-ray than in the radio, which may suggest that the knots are privileged sites for high-energy particle acceleration. 3C66B's jet is similar both in overall spectral shape and in structural detail to those in more nearby sources such as M87 and Centaurus A.

Radiation protection and environmental management at the relativistic heavy ion collider.

The Relativistic Heavy Ion Collider (RHIC) is a high energy hadron accelerator built to study basic nuclear physics. It consists of two counter-rotating beams of fully stripped gold ions that are accelerated in two rings to an energy of 100 GeV/nucleon or protons at 250 GeV/c. The beams can be stored for a period of five to ten hours and brought into collision for experiments during that time. The first major physics objective is to recreate a state of matter, the quark-gluon plasma, that has been predicted to have existed at a short time after the creation of the universe. Because there are only a few other high energy particle accelerators like RHIC in the world, the rules promulgated in the US Code of Federal Regulations under the Atomic Energy Act, State regulations, or international guidance documents do not cover prompt radiation from accelerators to govern directly the design and operation of a superconducting collider. Special design criteria for prompt radiation were developed to provide guidance tor the design of radiation shielding. Environmental Management at RHIC is accomplished through the ISO 14001 Environmental Management System. The applicability, benefits, and implementation of ISO 14001 within the framework of a large research accelerator complex are discussed in the paper.

On the hadronic beam model of TeV γ-ray flares from blazars

We propose two models, based on the hadronic beam-cloud collision, for production of TeV γ -ray flares in blazars. In the first model, a change in bulk Lorentz factor of the jet of the Active Galactic Nucleus (AGN) produces the flare. In the second model we consider a two-stage mechanism for high-energy particle acceleration in the jet. This system produces a power law spectrum with two different power indices at low and high energies, which is more efficient than one-stage shock acceleration at high energies. Using this spectrum in a hadronic beam-cloud model for γ -ray emission of blazars, a variable TeV as well as a stable GeV γ -ray flux is predicted. The break energy in the spectrum, related to distance between the jet base and terminal shock or boundary layer thickness, is the parameter used to obtain TeV flares.

Dynamic Current Injection into Magnetic Loops in Active Regions II. A 3D Magnetodynamic Model for Loop Flares

We have studied propagation along magnetic flux tubes in the active-region corona of large-amplitude torsional Alfvén wave packets (TAWP’s) coming up from a subphotospheric convection zone. TAWP’s can serve to transfer magnetic energy from the high-$\beta (\beta = P_{\mathrm{g}}/P_{\mathrm{m}})$ subphotospheric region to the low-$\beta$ coronal region. They dump part (or all) of their energy in the low-$\beta$ coronal region, which may result in very high temperature-plasma observed in X-rays (and in high energy particles). The supply of TAWPs from the photosphere, considered to be inefficient because the Alfvén velocity in the photosphere is small, turns out to be sufficiently effective for large-amplitude TAWP’s. This is due to the magnetic buoyancy acting on the magnetic twist packet and to the non-linear effect of squeezing out the gas from the twisted part of loops when it comes up near the photosphere. Both of these effects enhance the speed of emergence of the twist. We propose that loop flares may be due to the transport of energy and mass by torsional Alfvén waves. They may be the result of energy conversion of the magnetic twists and the kinetic energy of the accelerated hypersonic flows into thermal energy when two such TAWP’s collide high in a coronal loop. In order for such a collision of TAWP’s to occur, a TAWP is injected from one footpoint of a loop whilst another TAWP, from the other footpoint, is still propagating along the loop. The collision of these two TAWP’s at a high part of the loop explains the creation of a hyperhot region. The acceleration of high-energy particles is also explained as being due to the Fermi-I process between the approaching two hypersonic magnetic shocks.

Analytical calculation of the longitudinal space charge and resistive wall impedances in a smooth cylindrical pipe.

The longitudinal space charge and resistive wall impedances have been investigated in a smooth cylindrical beam pipe. At any point from the beam axis, we obtained an expression for the total impedance, which at the beam surface r=a for infinite pipe wall conductivity gives the expression for the total impedance that was derived by Zotter and Kheifets in studying the impedance of uniform beams in concentric cylindrical wall chambers, when a single cylindrical chamber is considered [B. W. Zotter and S. A. Kheifets, Impedances and Wakes in High-Energy Particle Accelerators (World Scientific, Singapore, 1998), Chap. 6]. A fitting formula for the space-charge impedance at the beam surface (r=a), which is valid for arbitrary wavelengths, is given. Rather than calculating the impedance with the field on the axis [Joseph J. Bisognano, Fifth European Particle Accelerator Conference (EPAC96), edited by S. Myers, A. Pacheco, R. Pascual, Ch. Petit-Jean-Genaz, and J. Poole (Institute of Physics, Bristol, 1996), Vol. 1, p. 328], the fitting formula is obtained by averaging over the transverse beam distribution. We also give another approach for the calculation of the resistive wall impedance using the flux of the Poynting vector at the pipe wall and then compare it with the expression obtained from the volume integral over the beam distribution.

A rudimentary electron energy analyzer for accelerator diagnostics

We have constructed a compact, planar retarding field analyzer for the diagnostics of low-energy, background electrons in a high-energy particle accelerator. Bench measurements of the analyzer have been made to characterize it, and the results are reasonable in light of models of this type of analyzer. Comparisons to results obtained using a beam-position monitor (BPM) show the advantages of this analyzer for electron diagnostics. Sample results from analyzers installed at the Advanced Photon Source storage ring at Argonne National Laboratory and the Proton Storage Ring at Los Alamos National Laboratory show how the analyzers can be used for studying the intensity, energy, and time structure of electrons in an accelerator environment.

Individual Dosimetry for High Energy Radiation Fields

The exposure of individuals on board aircraft increased interest in individual dosimetry in high energy radiation fields. These fields, both in the case of cosmic rays as primary radiation and at high energy particle accelerators are complex, with a large diversity of particle types, their energies, and linear energy transfer (LET). Several already existing individual dosemeters have been tested in such fields. For the component with high LET (mostly neutrons) etched track detectors were tested with and without fissile radiators, nuclear emulsions, bubble detectors of both types available and an albedo dosemeter. Individual dosimetry for the low LET component has been performed with thermoluminescent detectors (TLDs), photographic film dosemeters and two types of electronic individual dosemeters. It was found that individual dosimetry for the low LET component was satisfactory with the dosemeters tested. As far as the high LET component is concerned, there are problems with both the sensitivity and the energy response.

Symbolic modeling of high energy beam optics

A classical problem of computational physics consists of finding the minimum of a χ2 like function of many variables. Powerful optimization algorithms have been developed but do not guarantee convergence towards an absolute minimum. Analytical methods can improve the insight into a physical problem but calculations quickly exceed the power of a human brain. There comes the interest of optical design of high energy particle accelerators. The physics background is sketched and emphasis is put on the methodology. In practice, algebraic models may not be precise enough but they usually provide excellent initial conditions for a final numerical optimization.