Microparticle acceleration for hypervelocity experiments by A 3.75MV van de Graaff accelerator and a 100KV electrostatic accelerator in Japan

In-situ dust detectors have been calibrated by dust electrostatic accelerators that can accelerate projectiles to expected mass and velocity ranges of space debris and micrometeoroids. Unfortunately, In Japan, there was no such a facility dedicated to space science research until our research group was established a few years ago. Therefore, we have developed two high voltage accelerators. One is a modified 3.75MV Van de Graaff accelerator operated by High Fluence Irradiation Facility, Research Center for Nuclear Science and Technology, the University of Tokyo (HIT), and the other is a 100kV accelerator dedicated to dust experiment at the Institute of Space and Astronautical Science (ISAS). The particle velocity using the HIT Van de Graaff accelerator is higher than those reported in other accelerator facilities under the same particle mass conditions and encompasses the desired velocity range of micro-meteoroid. Time-Of-Flight dust mass spectrometer and Hybrid dust detector which are under development in Japan have been investigated using HIT dust accelerators. We have also constructed a 100kV electrostatic accelerator designed for easier handling and lower cost operation which is dedicated to dust acceleration, because the HIT Van de Graaff accelerator is being used for ion beam experiments mainly.     

Laser guiding for GeV laser-plasma accelerators

Guiding of relativistically intense laser beams in preformed plasma channels is discussed for development of GeV-class laser accelerators. Experiments using a channel guided laser wakefield accelerator at Lawrence Berkeley National Laboratory (LBNL) have demonstrated that near mono-energetic 100 MeV-class electron beams can be produced with a 10 TW laser system. Analysis, aided by particle-in-cell simulations, as well as experiments with various plasma lengths and densities, indicate that tailoring the length of the accelerator, together with loading of the accelerating structure with beam, is the key to production of mono-energetic electron beams. Increasing the energy towards a GeV and beyond will require reducing the plasma density and design criteria are discussed for an optimized accelerator module. The current progress and future directions are summarized through comparison with conventional accelerators, highlighting the unique short-term prospects for intense radiation sources based on laser-driven plasma accelerators.     

The history and future of accelerator radiological protection

The development of accelerator radiological protection from the mid-1930s, just after the invention of the cyclotron, to the present day is described. Three major themes--physics, personalities and politics--are developed. In the sections describing physics the development of shielding design though measurement, radiation transport calculations, the impact of accelerators on the environment and dosimetry in accelerator radiation fields are described. The discussion is limited to high-energy, high-intensity electron and proton accelerators. The impact of notable personalities on the development of both the basic science and on the accelerator health physics profession itself is described. The important role played by scholars and teachers is discussed. In the final section. which discusses the future of accelerator radiological protection, some emphasis is given to the social and political aspects that must he faced in the years ahead.     

Radiation protection at low energy proton accelerators

A sample is provided of the radiological safety issues particular to low energy proton accelerators. 'Low' energy in this context is taken to mean proton energies of less than about 1 GeV. Many of the radiation issues are common to all particle accelerators. Here, those issues are addressed that may require perhaps not unique treatment but those which benefit from a different approach. Among the problems discussed are the generation of prompt radiation and its transmission through shielding, the estimation of induced radioactivity, and the assessments of both the off-site prompt radiation hazard and the effect of releases of radioactive effluents to the environment.     

Estimation of bremsstrahlung photon energy in the environment of high-energy electron accelerator using CaSO4:Dy based TL dosemeter

High-energy bremsstrahlung X rays constitute the major radiation hazard to working personnel around the high-energy electron accelerators. Thermoluminescent (TL) dosemeter system based on CaSO4:Dy Teflon disc used in the routine individual monitoring was used to estimate the bremsstruhlung photon energy at different locations of the experimental hall of 450-MeV synchrotron accelerator. The response of TL discs under different filter regions of the dosemeter system undergo change with photon energy due to the lack of build up and interaction of photon in the metal filters. This change in the response of the discs used to estimate the energy of the bremsstrauhlung photon in conjunction with suitable calibration curve generated using known photon energy from medical linear accelerator. The photon energies estimated were in the range 1-4 MeV, depending on the locations.     

Application of particle accelerators in research

Since the beginning of the past century, accelerators have started to play a fundamental role as powerful tools to discover the world around us, how the universe has evolved since the big bang and to develop fundamental instruments for everyday life. Although more than 15 000 accelerators are operating around the world only a very few of them are dedicated to fundamental research. An overview of the present high energy physics (HEP) accelerator status and prospectives is presented.     

Characterization of plasma accelerators with RF linac terminology

The physics of plasma acceleration is described by using RF linac terminology such as shunt impedance, filling time, transit time factor, etc. It is shown that some differences between conventional RF accelerators and plasma accelerators make it difficult to import the RF linac terminology directly into the new field. For example, the shunt impedance is of limited use and the filling time is no use in wake-field accelerators with single-drive beams or single-pump pulses. The beatwave accelerator, a driven oscillator system, has in a sense more similarity to RF linacs than wake-field accelerators. It was shown that plasma wave decay due to collisions and modulational instability seriously deteriorate the quality factor.     

Applications of particle accelerators in medicine

There are nearly 20,000 particle accelerators in operation worldwide, about half of them employed for biomedical uses. This paper focuses on some recent advances in the two main medical domains where accelerators find their use, radionuclide production and radiation therapy. The paper first discusses the use of high-energy electron and proton accelerators for the potential, future production of (99)Mo, which is presently provided by fission reactors. Next, it reviews the rationale for the use of protons and carbon ions in cancer therapy, discussing the requirements imposed on accelerator technology and looking at some recent developments.     

Special radiation protection aspects of medical accelerators

Radiation protection aspects relevant to medical accelerators are discussed. An overview is first given of general safety requirements. Next, shielding and labyrinth design are discussed in some detail for the various types of accelerators, devoting more attention to hadron machines as they are far less conventional than electron linear accelerators. Some specific aspects related to patient protection are also addressed. Finally, induced radioactivity in accelerator components and shielding walls is briefly discussed. Three classes of machines are considered: (1) medical electron linacs for 'conventional' radiation therapy, (2) low energy cyclotrons for production of radionuclides mainly for medical diagnostics and (3) medium energy cyclotrons and synchrotrons for advanced radiation therapy with protons or light ion beams (hadron therapy).     

Electromagnetic acceleration studies with augmented rails

A comparative study of electromagnetic acceleration in rail-type accelerators with two kinds of rail geometry was carried out. The accelerators were energized by 200 kJ capacitor bank and the weight of loaded projectiles was about 1.3 grams, with a 10 mm×10 mm square bore. The velocity attained was 4.3 km/s in the augmented accelerator, while it was 3.8 km/s in the classical device. These differences in attained velocity are briefly discussed. A theoretical understanding of the rail erosion is also described     

The engineering needed for particle physics

Today's particle accelerators and detectors are among the most complicated and expensive scientific instruments ever built, and they exploit almost every aspect of today's cutting-edge engineering technologies. In many cases, accelerator needs have been the driving force behind these new technologies, necessity being the mother of invention. This paper gives an overview of some engineering requirements for the construction and operation of present-day accelerators and detectors.     

Concepts and limitations of macroparticle accelerators using travelling magnetic waves

The concept of an accelerator using a travelling magnetic wave that acts on magnetized projectiles is discussed. Although superconductors potentially may be good projectile material, their low critical temperature makes them unsuitable, Among ferromagnetic materials, dysprosium seems superior. For stable suspension and guidance, a high conductivity (preferrably superconducting) guide sheet is necessary. Magnetic field gradients of 10⁹A/m²travelling at 10⁶m/s should be achievable using present state-of-the-art components; resulting accelerations are ≳500 km/s². A linear accelerator for final speeds of 50 km/s needs a length of 2.5 km. Guidance forces sufficient to produce acceleration of2 times 10^{6}m/s²allow circular accelerators of reasonable size to achieve hypervelocities for small (50-100 mg) projectiles. An accelerator of 170-m diam would surpass the best results from light gas guns. Travelling waves suitable for accelerations of 10⁴m/s²can be produced without switching by means of flux displacing rotors and may be easily adapted to circular accelerators.     

Injection and dynamics of accelerated beams

This paper is a summary of the discussions undertaken by the working group on injection and accelerated beam dynamics at the 1st ICFA Novel and Advanced Accelerator Workshop on Second Generation Plasma Accelerators. The second generation of work on plasma accelerators is aimed to bring the accelerated beams up to the quality needed for applications such as high-energy physics linear colliders. To begin, first generation, or proof-of-principle, experiments and concepts were reviewed. To map the work needed in the second generation of development, the demands of the applications were examined, and an improved framework for discussing the viability of plasma accelerators was constructed. In particular, the issues scaling applications to the short wavelengths characteristic of plasma accelerators was discussed, as was the appropriate characterization of the beam quality in these devices, and the connection between plasma accelerator and conventional accelerator design. Within this framework, the working group discussed electron sources and injectors, the effects of drive beam evolution on accelerated beam dynamics, this effects of nonlinear plasma wave fields on beam phase space, stochastic processes, spatial and temporal beam-plasma wave matching, and future second-generation experimental goals and techniques.     

Superconducting magnets for accelerators and detectors

Accelerators and superconductivity have been good companions for 40 years. This paper is a review of the characteristics of present superconducting magnets for particle accelerators and particle detectors, in particular the ones used for high energy physics, emphasizing similarities and differences. Discussions on material characteristics and coil structure for accelerator magnets beyond 10 T are presented.     

Recent Activities of TIPC on Cryogenic Systems Used for Superconducting Accelerators in China

With the requirement of higher beam energy and luminosity, the cryogenic technologies are applied more and more widely in accelerator facilities. As a main research entity on cryogenics in China, Technical Institute of Physics and Chemistry (TIPC) makes significant contributions to the construction of cryogenic systems for several superconducting accelerators in China, i.e. the upgrade of the Beijing Electron-Positron Collider (BEPCII), the Shanghai Synchrotron Radiation Facility (SSRF) and the Peking University Free-Electron Laser Facility (PKU-FEL). In this paper the cryogenic systems for BEPCII, SSRF and PKU-FEL are introduced briefly, and our recent activities for these accelerators are described.     

Principles of high current electron beam acceleration

High current pulsed electron accelerators operate with beam currents exceeding 1 kA, pulse lengths from 20 ns to 1 μs, and output energies up to 50 MeV. Potential applications include pulsed radiography, intense microwave generation, free electron laser drivers, directed energy for defense, and industrial radiation processing applications. This paper gives a tutorial on the principles of high current electron accelerators. It is divided into four sections: (a) high current sources, (b) space charge dominated extractors, (c) beam transport with strong self-fields, and (d) methods of high power acceleration. In addition to discussions of conventional technology, such as the linear induction accelerator, promising new approaches to beam generation and acceleration are outlined. These include laser driven photocathodes, ion channel focusing, and high power rf accelerators.     

Pockels cell voltage probe for noninvasive electron-beam measurements

Accurate measurements of beam position and current are critical for the operation of the high-energy electron accelerators used for radiographic applications. Traditional short-pulse (e.g., 70 ns) machines utilize B-dot loops to monitor these parameters with great success. For long-pulse (e.g., 2 mus) accelerators, beam position and current measurements become more challenging and may require new technology. A novel electro-optic voltage probe has been developed for this application and provides the advantages of complete galvanic isolation, excellent low-frequency performance, and no time integration requirement. The design of a prototype sensor is presented along with preliminary accelerator test data.     

Present status of the theory of electron beam instabilities in storage rings

The coherent beam instabilities in circular accelerators are explained in terms of simple concepts of feedback devices. The notion of coupling impedance is introduced and interpreted by means of engineering circuit analysis. The condition of stability for the coherent motion is given in terms of the coupling impedance and accelerator and beam parameters.     

Measurement of the fluence response of the GSI neutron ball dosemeter in the energy range from thermal to 19 MeV

At high-energy particle accelerators, area monitoring needs to be performed in a wide range of neutron energies. In principle, neutrons occur from thermal energies up to the energy of the accelerated ions, which is for the present GSI (Gesellschaft für Schwerionenforschung) accelerator facility approximately 1-2 GeV per nucleon. There are no passive dosemeters available, which are designed for the use at high-energy accelerators. At GSI, a neutron dosemeter was developed, which is suitable for the measurement of high-energy neutron radiation by the insertion of a lead layer around Thermoluminescence (TL) detection elements (pairs of TL 600/700) at the centre of the dosemeter. The design of the sphere was derived from the construction of the extended range rem-counters for the measurement of ambient dose equivalent H(10). In this work, the dosemeter fluence response was measured in the quasi-monoenergetic neutron fields of the accelerator facility of the PTB in Braunschweig and in the thermal neutron field of the GKSS research reactor FRG-1 in Geesthacht. For the accelerator measurements, the reactions (7)Li(p,n)(7)Be, (3)H(p,n)(3)He and (2)H(d,n)(3)He were used to produce neutron fields with energy peaks between 144 keV and 19 MeV. The measured fluence responses are 27% too low for thermal energies and show an agreement with approximately 14% for the accelerator produced neutron fields related to the computed fluence responses (MCNP, FLUKA calculations). The measured as well as the computed fluence responses of the dosemeter are compared with the corresponding conversion coefficients.     

Gas-phase magnetohydrodynamic disk accelerator

A pulsed gas-phase magnetohydrodynamic (MHD) disk accelerator with a radial initial gas flow and radial electric current direction is described. Some working regime parameters and characteristics of the accelerated natural gas flow are reported. MHD accelerators of this type can be used for the investigation of chemical kinetics. Another promising application is related to the development of supersonic gas-phase endothermal chemical reactors with gasdynamic control.