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At least 793 records · Page 44
All sourcesNASA NTRSDOE OSTI
DOE OSTI2011

Study of a multi-beam accelerator driven thorium reactor

The primary advantages that accelerator driven systems have over critical reactors are: (1) Greater flexibility regarding the composition and placement of fissile, fertile, or fission product waste within the blanket surrounding the target, and (2) Potentially enhanced safety brought about by operating at a sufficiently low value of the multiplication factor to preclude reactivity induced events. The control of the power production can be achieved by vary the accelerator beam current. Furthermore, once the beam is shut off the system shuts down. The primary difference between the operation of an accelerator driven system and a critical system is the issue of beam interruptions of the accelerator. These beam interruptions impose thermo-mechanical loads on the fuel and mechanical components not found in critical systems. Studies have been performed to estimate an acceptable number of trips, and the value is significantly less stringent than had been previously estimated. The number of acceptable beam interruptions is a function of the length of the interruption and the mission of the system. Thus, for demonstration type systems and interruption durations of 1sec < t < 5mins, and t > 5mins 2500/yr and 50/yr are deemed acceptable. However, for industrial scale power generation without energy storage type systems and interruption durations of t < 1sec., 1sec < t < 10secs., 10secs < t < 5mins, and t > 5mins, the acceptable number of interruptions are 25000, 2500, 250, and 3 respectively. However, it has also been concluded that further development is required to reduce the number of trips. It is with this in mind that the following study was undertaken. The primary focus of this study will be the merit of a multi-beam target system, which allows for multiple spallation sources within the target/blanket assembly. In this manner it is possible to ameliorate the effects of sudden accelerator beam interruption on the surrounding reactor, since the remaining beams will still be supplying source neutrons. The proton beam will be assumed to have an energy of 1 GeV, and the target material will be natural lead, which will also be the coolant for the reactor assembly. Three proton beam arrangements will be considered, first a single beam (the traditional arrangement) with an entry at the assembly center, two more options will consist of three and six entry locations. The reactor fuel assembly parameters will be based on those of the S-PRISM fast reactor proposed by GE, and the fuel composition and type will be based on that proposed by Aker Solutions for use in their accelerator driven thorium reactor. The following table summarizes the parameters to be used in this study. The isotopic composition of the fertile material is 100% Th-232, and the plutonium isotopic distribution corresponds to that characteristic of the discharge from a typical LWR, following five years of decay. Thus, the isotopic distribution for the plutonium is; Pu-238 2.5%, Pu-239 53.3%, Pu-240 25.1%, Pu-241 11.8%, and Pu-242 7.3%.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2013

Development and Testing of Advanced Accelerator Structures and Technologies at 11.424 GHz (Final Report)

The areas of activity are grouped by Task. Task 1 involved a study of the key physics issues associated with the use of high gradient dielectric-loaded accelerating (DLA) structures in rf linear accelerators, and was carried out in collaboration with Argonne National Laboratory (ANL) and Euclid Techlabs LLC; Task 2 involved a study of high-gain active microwave pulse compressors, and was carried out in collaboration with Omega-P, Inc. and the Institute of Applied Physics of the Russian Academy of Sciences. The experiments were carried out in the X-band Magnicon Laboratory at the Naval Research Laboratory (NRL). The studies under Task 1 were focused on multipactor and breakdown in externally driven DLA structures at the 200-ns timescale. Suppression of multipactor and breakdown are essential to the practical application of dielectric structures in rf linear accelerators. During the first year of this program, we carried out a study of a doubly tapered clamped quartz traveling-wave (TW) structure that operated at up to 15 MV/m without breakdown by eliminating dielectric joints, thus avoiding the joint breakdown that had characterized many earlier experiments. However, strong multipactor loading was observed in the structure. In the second year, we carried out a successful test of a TW DLA structure with a sputtered copper exterior coating that eliminated the need for a clamped metal enclosure to form the outer metallic boundary, thus simplifying the fabrication of the structure. In the second year, we also carried out the first test of a dielectric-loaded standing-wave (SW) accelerating structure. Multipactor loading limited the achievable accelerating gradient in the structure to 9 MV/m, but the SW structure proved to be a useful configuration for studying multipactor physics. To continue this study, a new standing-wave structure is in preparation that will permit direct measurements of the energy stored in the structure for new studies of multipactor physics. Finally, in the third year of the program, we focused on the suppression of multipactor loading using an applied axial magnetic field, as proposed by Chang et al. [C. Chang et al., J. Appl. Phys. 110, 063304 (2011).]. Chang used an analytic model and PIC simulations to show that an axial magnetic field can reduce the period of the secondary electron trajectories on the dielectric surface, and thus spoil the multipactor resonance condition. The optimum effect occurs when the ratio of the gyrofrequency to the rf frequency is in the range of ~ 0.7 to 1. For an X-band structure, this is equivalent to a solenoidal field of 2.8–4 kG. This approach to multipactor suppression is attractive because it maintains the advantages of a DLA structure and is independent of other accelerator parameters.

43 PARTICLE ACCELERATORS↗
DOE OSTI2013

Experimental, Theoretical and Computational Studies of Plasma-Based Concepts for Future High Energy Accelerators

This is the final report on the DOE grant number DE-FG02-92ER40727 titled, “Experimental, Theoretical and Computational Studies of Plasma-Based Concepts for Future High Energy Accelerators.” During this grant period the UCLA program on Advanced Plasma Based Accelerators, headed by Professor C. Joshi has made many key scientific advances and trained a generation of students, many of whom have stayed in this research field and even started research programs of their own. In this final report however, we will focus on the last three years of the grant and report on the scientific progress made in each of the four tasks listed under this grant. Four tasks are focused on: Plasma Wakefield Accelerator Research at FACET, SLAC National Accelerator Laboratory, In House Research at UCLA’s Neptune and 20 TW Laser Laboratories, Laser-Wakefield Acceleration (LWFA) in Self Guided Regime: Experiments at the Callisto Laser at LLNL, and Theory and Simulations. Major scientific results have been obtained in each of the four tasks described in this report. These have led to publications in the prestigious scientific journals, graduation and continued training of high quality Ph.D. level students and have kept the U.S. at the forefront of plasma-based accelerators research field.

43 PARTICLE ACCELERATORS↗
DOE OSTI2014

Optics measurement and correction during beam acceleration in the Relativistic Heavy Ion Collider

To minimize operational complexities, setup of collisions in high energy circular colliders typically involves acceleration with near constant β-functions followed by application of strong focusing quadrupoles at the interaction points (IPs) for the final beta-squeeze. At the Relativistic Heavy Ion Collider (RHIC) beam acceleration and optics squeeze are performed simultaneously. In the past, beam optics correction at RHIC has taken place at injection and at final energy with some interpolation of corrections into the acceleration cycle. Recent measurements of the beam optics during acceleration and squeeze have evidenced significant beta-beats which if corrected could minimize undesirable emittance dilutions and maximize the spin polarization of polarized proton beams by avoidance of higher-order multipole fields sampled by particles within the bunch. In this report the methodology now operational at RHIC for beam optics corrections during acceleration with simultaneous beta-squeeze will be presented together with measurements which conclusively demonstrate the superior beam control. As a valuable by-product, the corrections have minimized the beta-beat at the profile monitors so reducing the dominant error in and providing more precise measurements of the evolution of the beam emittances during acceleration.

43 PARTICLE ACCELERATORS↗
DOE OSTI2015

Muon Accelerator Program Simulation Fellow

Muons are fundamental particles like electrons but much more massive. Muon accelerators can provide physics opportunities similar to those of electron accelerators, but because of the larger mass muons lose less energy to radiation, allowing more compact facilities with lower operating costs. The way muon beams are produced makes them too large to fit into the vacuum chamber of a cost-effective accelerator, and the short muon lifetime means that the beams must be reduced in size rather quickly, without losing too many of the muons. This reduction in size is called "cooling." Ionization cooling is a new technique that can accomplish such cooling. Intense muon beams can then be accelerated and injected into a storage ring, where they can be used to produce neutrino beams through their decays or collided with muons of the opposite charge to produce a muon collider, similar to an electron-positron collider. We report on the research carried out at the University of California, Riverside, towards producing such muon accelerators, as part of the Muon Accelerator Program based at Fermilab. Since this research was carried out in a university environment, we were able to involve both undergraduate and graduate students.

43 PARTICLE ACCELERATORS↗
DOE OSTI2016

Observation of 690 MV m -1 Electron Accelerating Gradient with a Laser-Driven Dielectric Microstructure

Acceleration of electrons using laser-driven dielectric microstructures is a promising technology for the miniaturization of particle accelerators. In this work, experimental results are presented of relativistic electron acceleration with 690±100 MVm -1 gradient. This is a record-high accelerating gradient for a dielectric microstructure accelerator, nearly doubling the previous record gradient. To reach higher acceleration gradients the present experiment employs 90 fs duration laser pulses.

43 PARTICLE ACCELERATORS↗
DOE OSTI2024

Direct Acceleration of an Electron Beam with a Radially Polarized Long-Wave Infrared Laser

Direct laser acceleration with radially polarized lasers is an intriguing variant of laser-based particle acceleration that has the potential of offering GeV/cm-level energy while avoiding the instabilities and complex beam dynamics associated with plasma wakefield accelerators. A major limiting factor is the difficulty of generating high-power radially polarized beams. In this paper, we propose the use of CO2-based long-wave infrared (LWIR) lasers as a driver for direct laser acceleration, as the polarization insensitivity of the gain medium allows a radially polarized beam to be amplified. Additionally, the larger waist sizes, Rayleigh lengths, and pulse lengths associated with the long wavelength could improve the injection efficiency of the electron beam. By comparing acceleration simulations using a near-infrared laser and an LWIR laser, we show that the injection efficiency is indeed improved by up to an order of magnitude with the longer wavelength. Furthermore, we show that even sub-TW peak powers with an LWIR laser can provide MeV-level energy gains. Thus, radially polarized LWIR lasers show significant promise as a driver of a direct laser-driven demonstration accelerator.

43 PARTICLE ACCELERATORS↗
DOE OSTI2014

The research progress of some key problems about the protection of industrial electron irradiation accelerator - Paper 9

In the last decades, electronic irradiation accelerator has made great progress and been widely used in fields. Because of its distinguishing feature of reliability and safety, electronic irradiation accelerator has attracted more attention of the investors, and created a huge economic value and social benefits. It will become the mainstream equipment of irradiation processing industry in future. So the further study of the shielding design around irradiation accelerator is of great significance. Different designs of ventilation duct will greatly influence dose rate of the exit. Because of the high dose rate under the target, it is suitable to use multi-tortuous duct when duct locating under target. It will reduce the dose rate about 3 orders of magnitude at the exit that add one backscattering interface in duct. Choose reasonable diameter and angle of embedded duct so that photons scatter as much as possible. We can use multiple small diameter ducts to replace large diameter duct. The system of Mini-DDL, Gamma detector and PC give a better reflection on the running statue of accelerator, its perfect usability can produce intuitive images for analyzed, it is important and helpful for workers and researchers to know about the radiation level of machine and environment. The measured results along the maze show that the maze must be long enough in order to achieve the desired shielding thickness. In future, we will combine the different kinds and motor patterns of body models, Monte Carlo programs, real time monitoring system with theoretical calculations to explore how the radiation field around accelerator has impact on human organs, get the dose distribution of body models so that improve the radiation protection to electron accelerator. (authors)

43 PARTICLE ACCELERATORS↗
DOE OSTI2014

Determination of activation products and resulting decommissioning implications for the Varian TruBeam linear accelerator - Paper 52

Modern medical linear accelerators used for the treatment of cancers are capable of operating at electron energies as high as 20 MeV. Above electron energies of 6 MeV, a measurable dose rate is obtained at the isocenter after beam termination. This is attributed to the activation of linear accelerator components through photonuclear reactions and neutron capture. Photons are produced as Bremsstrahlung during the collision of high-energy electrons with a heavy metal target, typically comprised of copper or tungsten. When photons exceeding the nucleon binding energy interact with a nucleus, neutrons are ejected. In the process of neutron capture, neutrons produced through ({gamma}, n) reactions are absorbed by a nucleus and the excess energy is emitted as a photon. Over the lifetime of an accelerator many components, such as the target, flattening filter, collimators, jaws, and treatment couch, are activated through these interactions. Although dependent on operating conditions, linear accelerators have an expected lifetime of 7 to 10 years. In Canada, at the end of their service, accelerators are typically sold for scrap, returned to a remanufacturing enterprise, or if the machine is still operational it can be retasked for continued use. Since many of the accelerator components have been exposed to a neutron fluence and activated to various extents, the requirements of the Canadian Nuclear Substance and Radiation Device regulations apply prior to final removal from the hospital. For shipments to the USA, there are exemption regulations to be considered. NRC regulation 10CFR 30.71 Schedule B lists a number of common radionuclides and the specific exemption quantity. Below these levels, radioactive materials may be freely transported from Canada to the USA without prior licensing from the Canadian Nuclear Safety Commission (CNSC) or United States Nuclear Regulatory Commission (NRC). (authors)

43 PARTICLE ACCELERATORS↗
DOE OSTI2011

Present Trends In The Configurations And Applications Of Electrostatic Accelerator Systems

Despite the worldwide economic meltdown during the past two years and preceding any stimulus program projects, the market for electrostatic accelerators has increased on three fronts: new applications developed in an expanding range of fields; technical enhancements that increase the range, precision, and sensitivity of existing systems; and new accelerator projects in a growing number of developing countries. From the single application of basic nuclear structure research from the 1930's into the 1970's, the continued expansion of new applications and the technical improvements in electrostatic accelerators have dramatically affected the configurations and capabilities of accelerator systems to meet new requirements. This paper describes examples of recent developments in cosmology, exotic materials, high resolution RBS, compact AMS, dust acceleration, ion implantation, etc.

43 PARTICLE ACCELERATORS↗
DOE OSTI2025

Experimental parameters for plasma wakefield acceleration in a narrow plasma column

Recent theoretical advancements propose multiple positron acceleration schemes in plasma wakefield acceleration (PWFA). One of the most promising ideas involves the creation of an electron-driven blowout wake within a finite-radius pre-ionized plasma column. This leads to the formation of an elongated region of sheath electrons at the closing of the first wake period capable of accelerating positrons while simultaneously providing a transverse focusing force. Additionally, the proposed scheme has shown to be a potential means of suppressing instabilities. We present an experimental opportunity to explore the narrow column PWFA at the Facility for Advanced Accelerator Experimental Tests II (FACET-II): the E333 experiment. As a pivotal first step towards achieving positron acceleration in PWFA, we have planned a precursor experiment utilizing the currently available single-bunch electron beam to study the physics of the narrow plasma PWFA scheme. We outline the feasible experimental parameters, including beam and ionization laser parameters, along with the required laser optics for the experiment. The primary observable signatures for this stage of the experiment are the final energy spectrum and transverse position of the electron bunch, anticipating reduced energy loss and enhanced beam guidance in the narrow plasma column compared to the nominal PWFA. Comprehensive simulations are used to detail our experimental plan.

Lee, Valentina [University of Colorado, Boulder, C↗
DOE OSTI2011

The Computer Program LIAR for Beam Dynamics Calculations in Linear Accelerators

Linear accelerators are the central components of the proposed next generation of linear colliders. They need to provide acceleration of up to 750 GeV per beam while maintaining very small normalized emittances. Standard simulation programs, mainly developed for storage rings, do not meet the specific requirements for high energy linear accelerators. We present a new program LIAR ('LInear Accelerator Research code') that includes wakefield effects, a 6D coupled beam description, specific optimization algorithms and other advanced features. Its modular structure allows to use and to extend it easily for different purposes. The program is available for UNIX workstations and Windows PC's. It can be applied to a broad range of accelerators. We present examples of simulations for SLC and NLC.

43 PARTICLE ACCELERATORS↗
DOE OSTI2011

Experimental Plans to Explore Dielectric Wakefield Acceleration in the THZ Regime

Dielectric wakefield accelerators have shown great promise toward high-gradient acceleration. We investigate the performances of a possible experiment under consideration at the FLASH facility in DESY to explore wakefield acceleration with an enhanced transformer ratio. The experiment capitalizes on a unique pulse shaping capability recently demonstrated at this facility. In addition, the facility incorporates a superconducting linear accelerator that could generate bunch trains with closely spaced bunches thereby opening the exploration of potential dynamical effects in dielectric wakefield accelerators.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Plasma-wakefield accelerator simultaneously boosts electron beam energy and brightness

High-energy particle colliders and X-ray free-electron lasers demand electron beams with qualities currently achieved only in kilometer-scale radio-frequency accelerators. Plasma accelerators promise a compact alternative but have faced challenges in delivering the needed beam quality at relevant energies. Here, we demonstrate that a plasma-wakefield accelerator operating in the nonlinear regime acts as a transformer to simultaneously boost the energy and brightness of an electron bunch injected from the plasma. Using a 10-GeV drive bunch and a three-stage meter-scale plasma source, we generated electron bunches exceeding 20 GeV with sub-percent energy spread, 2 mm·mrad normalized emittance, and multi-kA peak current. A significant number of drive-bunch electrons lost over 90% of their energy, a prerequisite for high energy-conversion efficiency. This demonstration of an energy transformer ratio exceeding two and a brightness enhancement over an order of magnitude opens a path towards cost-effective accelerators for future colliders and light sources.

experimental particle physics↗
DOE OSTI2011

Versatile Low Level RF System For Linear Accelerators

The Low Level RF (LLRF) system is the source of all of the rf signals required for an rf linear accelerator. These signals are amplified to drive accelerator and buncher cavities. It can even provide the synchronizing signal for the rf power for a synchrotron. The use of Direct Digital Synthesis (DDS) techniques results in a versatile system that can provide multiple coherent signals at the same or different frequencies with adjustable amplitudes and phase relations. Pulsing the DDS allows rf switching with an essentially infinite on/off ratio. The LLRF system includes a versatile phase detector that allows phase-locking the rf frequency to a cavity at any phase angle over the full 360 deg. range. With the use of stepper motor driven slug tuners multiple cavity resonant frequencies can be phase locked to the rf source frequency. No external phase shifters are required and there is no feedback loop phase setup required. All that is needed is to turn the frequency feedback on. The use of Digital Signal Processing (DSP) allows amplitude and phase control over the entire rf pulse. This paper describes the basic principles of a LLRF system that has been used for both proton accelerators and electron accelerators, including multiple tank accelerators, sub-harmonic and fundamental bunchers, and synchrotrons.

43 PARTICLE ACCELERATORS↗
DOE OSTI2011

General description of electromagnetic radiation processes based on instantaneous charge acceleration in ''endpoints''

We present a methodology for calculating the electromagnetic radiation from accelerated charged particles. Our formulation - the 'endpoint formulation' - combines numerous results developed in the literature in relation to radiation arising from particle acceleration using a complete, and completely general, treatment. We do this by describing particle motion via a series of discrete, instantaneous acceleration events, or 'endpoints', with each such event being treated as a source of emission. This method implicitly allows for particle creation and destruction, and is suited to direct numerical implementation in either the time or frequency domains. In this paper we demonstrate the complete generality of our method for calculating the radiated field from charged particle acceleration, and show how it reduces to the classical named radiation processes such as synchrotron, Tamm's description of Vavilov-Cherenkov, and transition radiation under appropriate limits. Using this formulation, we are immediately able to answer outstanding questions regarding the phenomenology of radio emission from ultra-high-energy particle interactions in both the earth's atmosphere and the moon. In particular, our formulation makes it apparent that the dominant emission component of the Askaryan effect (coherent radio-wave radiation from high-energy particle cascades in dense media) comes from coherent 'bremsstrahlung' from particle acceleration, rather than coherent Vavilov-Cherenkov radiation.

43 PARTICLE ACCELERATORS↗
DOE OSTI2011

Dielectric Wakefield Accelerator to drive the future FEL Light Source.

X-ray free-electron lasers (FELs) are expensive instruments and a large part of the cost of the entire facility is driven by the accelerator. Using a high-energy gain dielectric wake-field accelerator (DWA) instead of the conventional accelerator may provide a significant cost saving and reduction of the facility size. In this article, we investigate using a collinear dielectric wakefield accelerator to provide a high repetition rate, high current, high energy beam to drive a future FEL x-ray light source. As an initial case study, a {approx}100 MV/m loaded gradient, 850 GHz quartz dielectric based 2-stage, wakefield accelerator is proposed to generate a main electron beam of 8 GeV, 50 pC/bunch, {approx}1.2 kA of peak current, 10 x 10 kHz (10 beamlines) in just 100 meters with the fill factor and beam loading considered. This scheme provides 10 parallel main beams with one 100 kHz drive beam. A drive-to-main beam efficiency {approx}38.5% can be achieved with an advanced transformer ratio enhancement technique. rf power dissipation in the structure is only 5 W/cm{sup 2} in the high repetition rate, high gradient operation mode, which is in the range of advanced water cooling capability. Details of study presented in the article include the overall layout, the transform ratio enhancement scheme used to increase the drive to main beam efficiency, main wakefield linac design, cooling of the structure, etc.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Space-Borne Electron Accelerator Design

Renewed interest in active experiments with relativistic particle beams in space has led to the development of solid-state radio-frequency (RF) linear accelerators (linac) that can deliver MeV electron beams but operate with low-voltage DC power supplies. The solid-state RF amplifiers used to drive the accelerator are known as high-electron mobility transistors (HEMTs), and at C-band (5–6 GHz) are capable of generating up to 500 watts of RF power at 10% duty factor in a small package, i.e., the size of a postage stamp. In operation, the HEMTs are powered with 50 V DC as their bias voltage; they thus can tap into the spacecraft batteries or electrical bus as the primary power source. In this paper we describe the initial testing of a compact space-borne RF accelerator consisting of individual C-band cavities, each independently powered by a gallium nitride (GaN) HEMT. We show preliminary test results that demonstrate the beam acceleration in a single C-band cavity powered by a single HEMT operating at 10% duty factor. An example of active beam experiments in space that could benefit from the HEMT-powered accelerators is the proposed Magnetosphere-Ionosphere Connection (CONNEX) experiment (Dors et al., 2017).

43 PARTICLE ACCELERATORS↗