Analytical studies on wakefield in a rectangular waveguide

Recent progress in laser-plasma accelerators has matured a concept of particle acceleration as a possible next-generation particle accelerator promising ultrahigh accelerating gradients in a compact size. Four major concepts of laser-plasma accelerators—the plasma beat wave accelerator, the laser wakefield accelerator, the self-modulated laser wakefield accelerator, and the plasma wakefield accelerator—are reviewed on accelerator physics issues and experiments demonstrating the basic mechanisms of their concepts. As a perspective to the future practical application, a design of 5-TeV linear colliders based on the laser wakefield accelerator is discussed.

In this article, we present the underlying physics and the present status of high gradient and high-energy plasma accelerators. With the development of compact short pulse high-brightness lasers and electron and positron beams, new areas of studies for laser/particle beam-matter interactions is opening up. A number of methods are being pursued vigorously to achieve ultra-high-acceleration gradients. These include the plasma beat wave accelerator (PBWA) mechanism which uses conventional long pulse ( approximately 100 ps) modest intensity lasers (I approximately 10(14)-10(16) W cm(-2)), the laser wakefield accelerator (LWFA) which uses the new breed of compact high-brightness lasers (<1 ps) and intensities >10(18) W cm(-2), self-modulated laser wakefield accelerator (SMLWFA) concept which combines elements of stimulated Raman forward scattering (SRFS) and electron acceleration by nonlinear plasma waves excited by relativistic electron and positron bunches the plasma wakefield accelerator. In the ultra-high intensity regime, laser/particle beam-plasma interactions are highly nonlinear and relativistic, leading to new phenomenon such as the plasma wakefield excitation for particle acceleration, relativistic self-focusing and guiding of laser beams, high-harmonic generation, acceleration of electrons, positrons, protons and photons. Fields greater than 1 GV cm(-1) have been generated with monoenergetic particle beams accelerated to about 100 MeV in millimetre distances recorded. Plasma wakefields driven by both electron and positron beams at the Stanford linear accelerator centre (SLAC) facility have accelerated the tail of the beams.

There have been recent articles in Notes and Records concerning James Chadwick’s contributions to the development of the atomic bomb, and it seemed worthwhile to supplement these with some remarks on Chadwick’s establishment of an important centre of nuclear physics research in Liverpool, especially since I believe this was the achievement which gave him more satisfaction than any other. The following is the abridged text of a lecture given at the Centenary Celebrations at the University of Liverpool in October 1991. Chadwick came to Liverpool in 1935, the year in which he was awarded the Nobel Prize, and held the Lyon Jones Chair of Physics for 13 years. During that time he transformed the department from one which was quite ill-equipped for research, into one which would be able to stand comparison with any in the world in the fields of nuclear physics and high-energy particle physics. The University had been able to attract him by promising to support him with the provision of new staff posts and with help in building up new facilities for research. In addition he already had friends within the university and the business community through his wife, who came from a well-known Liverpool family. He had also, I think, begun to feel that the time had come to leave Cambridge, perhaps because Rutherford was reluctant to contemplate the sort of expenditure which Chadwick realized was necessary to carry forward research in nuclear physics. Chadwick’s plans for Liverpool were centred around the construction of a cyclotron which would cost about £5000, roughly equal to Rutherford’s laboratory budget for one year

The Nuclear Physics Institute of the ASCR (NPI), a public research organization, is the major Czech institution in the field of nuclear physics. The institute, belonging to the Academy of Science of the Czech Republic, is located together with some other research organizations at the area of village Řež about 20 km north of Prague (see issue cover). The institute's staff comprises about 200 people including about 90 researchers. Moreover, about 35–40 diploma and Ph.D. students do their work at the NPI laboratories.

Our understanding of the dynamics of ion collisional energy loss in a plasma is still not complete, in part due to the difficulty and lack of high-quality experimental measurements. These measurements are crucial to benchmark existing models. Here, we show that such a measurement is possible using high-flux proton beams accelerated by high intensity short pulse lasers, where there is a high number of particles in a picosecond pulse, which is ideal for measurements in quickly expanding plasmas. By reducing the energy bandwidth of the protons using a passive selector, we have made proton stopping measurements in partially ionized Argon and fully ionized Hydrogen plasmas with electron temperatures of hundreds of eV and densities in the range 1020–1021 cm−3. In the first case, we have observed, consistently with previous reports, enhanced stopping of protons when compared to stopping power in non-ionized gas. In the second case, we have observed for the first time the regime of reduced stopping, which is theoretically predicted in such hot and fully ionized plasma. The versatility of these tunable short-pulse laser based ion sources, where the ion type and energy can be changed at will, could open up the possibility for a variety of ion stopping power measurements in plasmas so long as they are well characterized in terms of temperature and density. In turn, these measurements will allow tests of the validity of existing theoretical models.

The interaction of high intensity short pulse laser beams with plasmas can accelerate electrons to energies in excess of a GeV. These electron beams can subsequently be used to generate short-lived particles such as positrons, muons, and pions. In recent experiments, we have made the first measurements of pion production using ‘all optical’ methods. In particular, we have demonstrated that the interaction of bremsstrahlung generated by laser driven electron beams with aluminum atoms can produce the long lived isotope of magnesium (27Mg) which is a signature for pion (π+) production and subsequent muon decay. Using a 300 TW laser pulse, we have measured the generation of 150 ± 50 pions per shot. We also show that the energetic electron beam is a source of an intense, highly directional neutron beam resulting from (γ, n) reactions which contributes to the 27Mg measurement as background via the (n, p) process.

Experimental results are presented concerning the interaction of small molecules with high intensity short pulse laser light. The time-of-flight technique was used in order to study the ionization and fragmentation processes taking place. Laser pulses of different wavelengths and pulse durations were employed and preliminary results will be presented. Evidence for strong alignment of the multiply charged fragments along the electric field of the laser light will be discussed.

One of problems of physics of laser particle acceleration is increase of transformation of laser pulse energy in particle kinetic energy. Changing parametres of a laser target, it is possible to operate such ion characteristics as the maximum and average ion energy, angular divergence and spatial distribution. Rather recently [1], it was revealed, that transformation of laser energy in ion energy increases at use a thin foils limited in size. Occupying smaller effective volume hot electrons have higher density and temperature, accelerating ions more effectively. There is an optimum range for target thickness since too thin targets lead to a warming up a thermal wave of borders of a target, and too thick to electron energy losses. Optimization of some targets under geometrical characteristics was made, for example in [2]. The absorption of laser radiation of such targets reaches considerable values, however are not 100 %. In paper [3] using a periodic micro-relief on a target surface has been shown, that, it is capable to increase absorption of laser radiation up to 90 %. In the present paper it is offered to increase in such way absorption of thin targets and to choose parameters of a relief and basic part of a target so that the additional absorbed energy is transferred mainly to the accelerated protons. The choice of optimum characteristics of a target is made by means of analytical and numerical PIC modeling of a target set with characteristics near to optimum values. The calculations have shown that there is no necessity for ideal periodicity and a regularity of target relief for essential growth of absorption and energy of a proton. Replacement of a regular relief on randomly rough with characteristic scale comparable with regular considerably does not reduce neither absorption, nor energy of the accelerated ions.

Two-color ionization injection using a plasma beatwave accelerator

Electron dephasing is a major gain-inhibiting effect in plasma-based accelerators. A novel method is proposed to overcome dephasing, in which the modulation of a modest ( O(10 kG)), axial, uniform magnetic field in the acceleration channel leads to densification of the plasma through magnetic compression, enabling direct, time-resolved control of the plasma wave properties. The methodology is broadly applicable and can be optimized to improve the leading acceleration approaches, including plasma beat-wave, plasma wakefield, and laser wakefield acceleration. The advantages of magnetic compression compared to other proposed schemes to overcome dephasing are identified.

In recent years very high intensity short-pulse lasers with high repitition rates have been available in the laboratories. This has led to investigations of laser-atom interaction processes at hitherto unaccessable domains of double ionization signals vs. field intensity. Furthermore, new detection techniques have opend up the possibility of measurements of momentum distributions of the emitted electrons and ions in coincidence. Thus, for example, double ionization yields of He atom interacting with intense short pulse lasers have been measured (e.g., [1, 2, 3, 4, 5, 6]). More recently the momentum distributions of the two electrons emitted in double ionization of noble gas atoms have been determined via the measurement of the recoil momentum of the doubly charged ions in coincidence with an electron [7, 8]. These results provide important new tests of the mechanism of double ionization process in intense ultrashort laser pulses.

The year ended June 30, 1938 has been marked by energetic prosecution of experimental investigation and continued coordination and integration of various researches paving the way for more general formulation of geophysical facts. Good progress has been made in two major projects which open new fields of investigation and promise important advances. One of these is the completion of the Atomic‐Physics Observatory (see Fig. 1) and the considerable progress in the installation of the electrical equipment. The electrostatic generator and tube are designed to operate at potentials exceeding five million volts and offer unique opportunity for further studies in the expanding field of nuclear physics—a field to which we must look for additional understanding of magnetic phenomena.

The results of the development of the multifunctional accelerator complex of the NSC KIPT are considered. The magneto-optical structure of the recirculator, which is the basis of the complex, is presented, which ensures the production of an electron beam with a maximum energy of about 600 MeV when the beam passes through the superconducting accelerating structure three times. Variants of obtaining beams of electrons, gamma quanta, positrons and neutrons for performing fundamental and applied research in the field of nuclear physics and energy, solid-state physics, and nuclear medicine are presented.

The detection of neutrons in the presence of gamma-ray fields has important applications in the fields of nuclear physics, homeland security, and medical imaging. Organic scintillators provide several attractive qualities as neutron detection materials including low cost, fast response times, ease of scaling, and the ability to implement pulse shape discrimination (PSD) to discriminate between neutrons and gamma-rays. This talk will focus on amorphous organic scintillators both in plastic form and small-molecule organic glass form. The first section of this talk will describe recent advances and improvements in the performance of PSD-capable plastic scintillators. The primary advances described in regard to modification of the polymer matrix, evaluation of new scintillating dyes, improved fabrication conditions, and implementation of additives which impart superior performance and mechanical properties to PSD-capable plastics as compared to commercially-available plastics and performance comparable to PSD-capable liquids. The second section of this talk will focus on a class of small-molecule organic scintillators based on modified indoles and oligophenylenes which form amorphous glasses as PSD-capable neutron scintillation materials. Though indoles and oligophenylenes have been known for many decades, their PSD properties have not been investigated and their scintillation properties only scantily investigated. Well-developed synthetic methodologies have permitted the synthesis of a library of structural analogs of these compounds as well as the investigation of their scintillation properties. The emission wavelengths of many indoles are in the sensitive region of common photomultiplier tubes, making them appropriate to be used as scintillators in either pure or doped form. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. This work has been supported by the U.S. Department of Energy Office of Nonproliferation Research and Development (NA-22) and by the Defense Threat Reduction Agency (DTRA).

Previous articleNext article No AccessArchaeological NotesThe Applied Science Center for ArchaeologyFroelich RaineyFroelich Rainey Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by American Journal of Archaeology Volume 67, Number 3July 1963 The journal of the Archaeological Institute of America Article DOIhttps://doi.org/10.2307/501379 Copyright © 1963 by the Archaeological Institute of America. All rights reserved.PDF download Crossref reports no articles citing this article.