124130410
HEAVY-ION ACCELERATOR FACILITY FEATURING A SEPARATED-SECTOR ISOCHRONOUS CYCLOTRON.
An isochronous cyclotron of modest size with a model TU Tandem Van de Graaff as its injector would have the capability of accelerating the heaviest ions to well above the Coulomb barrier for the heaviest elements. An evaluation of several cyclotron designs has led to an isochronous cyclotron with four separate sectors. As now envisaged the cyclotron will be capable of accelerating heavy ions with a charge-to-mass ratio of 0.15 to an energy of 7.5 MeV1a.m.u. A unique feature of the plan is the use of a source of highly charged ions of the Dubna or LRL type in the terminal of the tandem. For example, to obtain energetic uranium ions, 9+ ions from the terminal ion source are accelerated to 144 MeV (0.605 MeV}a.m.u.), passed through a stripping foil to increase the ion charge to 36+, injected into the cyclotron, and accelerated to 1785 MeV (7.5 MeV1a.m.u.). The cyclotron will also accelerate light particles, for example, protons and a-particles to about 300 MeV. deuterons to 150 MeV, and 3 ~ e 2 ' ions to 400 MeV. For this added flexibility a small cyclotron will be provided as the alternate light-ion injector. When the tandem is used separately for experiments requiring its special capabilities, the two cyclotrons can also be used together for independent medium-energy research. When the tandem and large cyclotron are used together for heavy-ion acceleration, the injector cyclotron becomes an independent tool for low-energy nuclear chemistry or isotope production.
116322052
Accelerators for Heavy Ions
The use of heavy ion accelerators in nuclear physics, nuclear chemistry, atomic physics, and in material sciences studies is rapidly increasing. This paper reviews the present and developing scene in heavy ion accelerator concepts and technology. The area of applicability of various methods, likely avenues of future development and the trends of future requirements are discussed.
124286964
INNOVATIONS IN ISOCHRONOUS CYCLOTRONS.
Since the last International Conference on Isochronous Cyclotrons, three major projects have been approved: the 585 MeV proton cyclotron of the Swiss Institute for Nuclear Research (SIN) to be built at Villigen near Zurich; the 500 MeV Hcyclotron of the Tri-University Meson Facility (TRIUMF) at Vancouver, British Columbia; and the 200 MeV variable energy cyclotron of the Indiana University. A much smaller but unique project has been successfully brought into operation, the cyclograaff at Duke University which combines a small cyclotron with a tandem accelerator in a way which enhances the desirable characteristics of both. Finally, the most important happening since the last conference has been the renewed interest in accelerators for very heavy ions. In the United States alone, there will be more than ten major proposals. This paper reviews the activities and progress of the past several years and discusses some of the important innovations accomplished or foreseen.
93888470
Design Study for the Conversion of the Oak Ridge Isochronous Cyclotron from an Energy Constant of K=90 to K=300 MeV
A possible method of achieving a K=300 MeV cyclotron by increasing the average magnetic field of the Oak Ridge Isochronous Cyclotron (ORIC) from 18.6 to 33.9 kG with superconducting coils has been investigated.
122110697
The Holifield Heavy Ion Research Facility
The Holifield Heavy Ion Research Facility has been in routine operation since July 1982. Beams have been provided using both the tandem accelerator alone and a coupled mode in which the Oak Ridge Isochronous Cyclotron is used as an energy booster for tandem beams. The coupled mode has proved to be especially effective and has allowed us to provide a wide range of energetic beams for scheduled experiments. In this report we discuss our operational experience and recent development activities.
115550416
RECENT PROGRESS ON A SUPERCURRENT SEPARATED ORBIT CYCLOTRON.
119272967
Everything you always wanted to know about the cosmological constant problem (but were afraid to ask)
Abstract This article aims at discussing the cosmological constant problem at a pedagogical but fully technical level. We review how the vacuum energy can be regularized in flat and curved space–time and how it can be understood in terms of Feynman bubble diagrams. In particular, we show that the properly renormalized value of the zero-point energy density today (for a free theory) is in fact far from being 122 orders of magnitude larger than the critical energy density, as often quoted in the literature. We mainly consider the case of scalar fields but also treat the cases of fermions and gauge bosons which allows us to discuss the question of vacuum energy in super-symmetry. Then, we discuss how the cosmological constant can be measured in cosmology and constrained with experiments such as measurements of planet orbits in our solar system or atomic spectra. We also review why the Lamb shift and the Casimir effect seem to indicate that the quantum zero-point fluctuations are not an artifact of the quantum field theory formalism. We investigate how experiments on the universality of free fall can constrain the gravitational properties of vacuum energy and we discuss the status of the weak equivalence principle in quantum mechanics, in particular the Colella, Overhauser and Werner experiment and the quantum Galileo experiment performed with a Salecker–Wigner–Peres clock. Finally, we briefly conclude with a discussion on the solutions to the cosmological constant problem that have been proposed so far.
119353279
Stochastic Quintessence
The behavior of the quintessence field is studied during inflation. In order to have a satisfactory model of dark energy, the quintessence field value today should be as insensible to the initial conditions as possible. Usually, only the dependence on the initial conditions specified at the end of inflation or, equivalently, at the beginning of the radiation dominated era, is considered. Provided the quintessence field is initially within a large but, crucially, finite interval, its present value becomes independent of the initial value it started from. The question as to whether inflation naturally drives the quintessence field to the above-mentioned interval is addressed. Since the quantum effects turn out to be important, the formalism of stochastic inflation is used in order to calculate the evolution of the quintessence field. Moreover, the quantum effects originating from the inflaton field are also taken into account and are proved to be sub-dominant in most cases. Finally, the requirement that the quintessence field is on tracks today is shown to imply quite tight constraints on the initial values of the quintessence and inflaton fields at the beginning of inflation. In particular, the initial value of the inflaton field cannot be too large which indicates that the quintessential scenario seems to be compatible with inflation only if the total number of e-folds is quite small.
119068498
Reply to "Bouncing Universes and their perturbations: remarks on a toy model"
In this web note, we reply to a recent paper, gr-qc/0404126, confirming a previous work of ours in which a cosmological bouncing phase was shown to have the ability of modifying the spectrum of primordial perturbations (PRD 68, 103517 2003), but challenging its physical conditions of validity. Explicitly, Ref. gr-qc/0404126, besides pretending our Taylor series expansion of the scale factor close to the bounce amounts to choosing a family of polynomial scale factors, also claims that the bounce affects the spectrum only if the mass scale of the scalar field driving the dynamics is of the order of the Planck mass. We show that these objections are either misleading or incorrect since the minimum size of the Universe a_0 (value of the scale factor at the bounce) is either not physically specified, as required in a closed Universe, or implicitly assumed to be the Planck mass. We calculate this mass and obtain that, unsurprisingly, for a reasonable value of a_0, i.e. much larger than the Planck length, the scalar field mass is smaller than the Planck mass.
16915572
Precision of inflationary predictions and recent CMB anisotropy data
Inflationary predictions of the cosmic microwave background anisotropy are often based on the slow-roll approximation. We study the precision of these predictions and compare them with the recent data from BOOMERanG and MAXIMA-1.
119388182
Passing through the bounce in the ekpyrotic models
By considering a simplified but exact model for realizing the ekpyrotic scenario, we clarify various assumptions that have been used in the literature. In particular, we discuss the new ekpyrotic prescription for passing the perturbations through the singularity which we show to provide a spectrum depending on a nonphysical normalization function. We also show that this prescription does not reproduce the exact result for a sharp transition. Then, more generally, we demonstrate that, in the only case where a bounce can be obtained in Einstein general relativity without facing singularities and/or violation of the standard energy conditions, the bounce cannot be made arbitrarily short. This contrasts with the standard (inflationary) situation where the transition between two eras with different values of the equation of state can be considered as instantaneous. We then argue that the usually conserved quantities are not constant on a typical bounce time scale. Finally, we also examine the case of a test scalar field (or gravitational waves) where similar results are obtained. We conclude that the full dynamical equations of the underlying theory should be solved in a nonsingular case before any conclusion can be drawn.