Saeed Assadi

The new SNS Allison emittance scanner measures emittances of 65 kV ion beams over a range of +/- 116 mrad. Its versatile control system allows for time-dependent emittance measurements using an external trigger to synchronize with pulsed ion beam systems. After an adjustable initial delay, the system acquires an array of equally-delayed beam current measurements, each averaged over a certain time span, where all three time parameters are user selectable. The zero offset of the beam current measurements is determined by averaging a fraction of 1 ms shortly before the start of the ion beam pulse. This paper discusses the optimization of the angular range. In addition it presents the first results and reports an unresolved artefact. Data are presented on the time evolution of emittance ellipses during 0.8 ms long H- beam pulses emerging from the SNS test LEBT, which is important for loss considerations in the SNS accelerator. Additional data explore the emittance growth observed with i...

Space charge effects, beam losses, wake fields, and orbital control are significant collective effects that affect beam dynamics. The strong-focusing cyclotron incorporates helical orbits with a strong-focusing lattice and high-gradient cavities. It makes it possible to fully separate orbits and suppress interaction between bunches on neighboring orbits. We simulate nonlinear synchrobetratron coupling and explore methods to use the tools of strong-focusing to suppress beam blowup mechanisms.

Results are presented from end-to-end simulation of a 100 MeV strong focusing cyclotron (SFC). The development of the high-current SFC is motivated by applications for production of medical isotopes and for a proton driver for subcritical fission. It uses a novel superconducting cavity to provide sufficient energy gain to fully separate all turns. An arc-contour F-D doublet, trim dipole winding, and sextupole are located along each turn within the aperture of each sector dipole to control the betatron and synchrotron motion and to stabilize non-linear dynamics with high-current operation. The phase space evolution of a proton bunch in the SFC was simulated using both the code OPAL and an ad hoc Runge-Kutta tracker. Iterative optimization of the dipole, quadrupole, and sextupole fields was used to provide precise isochronicity, favorable betatron phase advance, and cancellation of disper-

New information on magnetic fluctuations and transport in toroidal devices has been obtained in the MST reversed field pinch through measurement of nonlinear coupling of three waves in k-space, and measurement of current density fluctuations. Measurements of nonlinear coupling of magnetic fluctuations reveals that (1) two poloidal mode number m = 1 modes couple strongly to an m = 2

The strong-focusing cyclotron is an isochronous sector cyclotron in which slot-geometry superconducting half-cell cavities are used to provide sufficient energy gain per turn to fully separate orbits and superconducting quadrupoles are located in the aperture of each sector dipole to provide strong focusing and control betatron tune. The SFC offers the possibility to address the several effects that most limit beam current in a CW cyclotron: space charge, bunch-bunch interactions, resonance-crossing, and wake fields. Simulation of optical transport and beam dynamics entails several new challenges: the combined-function fields in the sectors must be properly treated in a strongly curving geometry, and the strong energy gain induces continuous mixing of horizontal betatron and synchrotron phase space. We present a systematic simulation of optical transport using modified versions of MAD-X and SYNERGIA. We report progress in introducing further elements that will set the stage for stud...

The Strong Focusing Cyclotron development at Texas A&M University has evolved from stacks of cyclotrons to a single layer high brightness, low emittance device to produce greater than 10 mA of proton beam to a desired target at 800 MeV. The latest design has a major geometric design optimization of strong focusing quadrupoles and a modified algorithm of high gradient cavities. These optimizations address the turn separation and interaction of radially neighbouring bunches and produced a reduced the number of turns necessary to reach the desired final energy under control conditions. In this paper, we present the new design, the physics of nonlinear synchrobetratron coupling, mνh+nνv=p causing beam blow-up in other form of cyclotrons and how this work has resolved it. The cavity beam loading, and space charge effects of multi turns at low energies to reduce losses, are discussed.

An adaptable architecture of a machine protection system (MPS) suitable for continuous wave (CW), high intensity accelerators like those proposed for Accelerator Driven Systems (ADS) for subcritical reactor strategies and heavy ion accelerators for the production of rare isotopes is presented. A system of databases, networks and nodes that can systematically and flexibly be reconfigured to rebalance the required metadata is used. Additional features include reconfigurable machine setup templates that can rigorously be tested with mirror redundant online backups, the utilization of external reconfigurable geometric algorithms for the data channels and the network distribution, and the inclusion of initial system requirements as well as envisioned upgrades.

A design is presented for a hadron collider in which the magnetic storage ring is configured as a circular pipeline, supported in neutral buoyancy in the sea at a depth of ~100 m. Each collider detector is housed in a bathysphere the size of the CMS hall at LHC, also neutral-buoyant. Each half-cell of the collider lattice is ~300 m long, housed in a single pipe that contains one dipole, one quadrupole, a correction package, and all umbilical connections. A choice of ~4 T dipole field, 2000 km circumference provides a collision energy of 700 TeV. Beam dynamics is dominated by synchrotron radiation damping, which sustains luminosity for >10 hours. Issues of radiation shielding and abort can be accommodated inexpensively. There are at least ten sites world-wide where the collider could be located, all near major urban centers. The paper summarizes several key issues; how to connect and disconnect half-cell segments of the pipeline at-depth using remote submersibles; how to maintain ...

High power, continuous wave (CW) accelerators are proposed for applications such as Accelerator Driven Systems (ADS) for subcritical reactor strategies and heavy ion accelerators for the production of rare isotopes. Because of the high beam powers and high energy loss with beam interception of material, the beam diagnostic designs are necessarily shifting to non-intercepting, realtime feedback devices that can be fully integrated with the accelerator machine protection system (MPS) and operation control system including online models. Appropriate for these applications, three types of beam diagnostics (lanthanum bromide scintillation coincidence detectors, GaN neutron and gamma detectors, and beam position monitors) are presented.

The proposed designs for polarized-beam electron-ion colliders require cooling of the ion beam to achieve and sustain high luminosity. One attractive approach is to make a fixed-energy storage ring in which ions are continuously cooled and stacked during a collider store, then transferred to the collider and accelerated for a new store when the luminosity decreases. An example design is reported for a 6 GeV/u superferric storage ring for this purpose, and for a d.c. electron cooling system in which electron space charge is fully neutralized so that highcurrent magnetized e-cooling can be used to best advantage.

A conceptual design is presented for a 100 TeV hadron collider based upon a 4.5 T NbTi cable-in-conduit dipole technology. It incorporates a side radiation channel to extract synchrotron radiation from the beam channel so that it does not produce limitations from heating on a beam liner or gas load limits on collider performance. Synchrotron damping can be used to support ‘bottom-up’ stacking to sustain maximum luminosity in the collisions.

The strong-focusing cyclotron is an isochronous sector cyclotron designed to accelerate >10 mA CW beams of protons and ions up to >500 MeV/u with low loss and high efficiency. Superconducting RF cavities are used to provide enough energy gain per turn to fully separate orbits, and arc-shaped beam transport channels in the sector dipole apertures provide strong focusing of all orbits. A design methodology is being developed to optimize the sector dipoles, the focal lattice, and the SRF cavities so that betatron tunes can be locked to favorable operating point. Provision is made for correction of dispersion and chromaticity. The methodology will provide a framework on which we can then proceed to study and optimize the nonlinear beam dynamics for high-current transport.

The Spallation Neutron Source (SNS) Project, a collaboration of six national laboratories, is constructing an accelerator based neutron facility at ORNL. The SNS accelerator systems will deliver a 1 GeV, 1.44 MW proton beam to a liquid mercury target. The high-beam power and desired high availability of the accelerator complex have had important consequences for the design and implementation of diagnostics at the SNS. Namely, diagnostic systems have been designed with high reliability, the ability for hands-on maintenance, redundancy in critical diagnostics, and commonality of subsystems in mind. The multi-laboratory diagnostics group has successfully implemented and commissioned a number of systems at LBNL during initial commissioning of the SNS Front-End systems. This talk reports on the team's progress in diagnostics commissioning and performance for the SNS, summarizes the approach that has been used in this multi-laboratory effort, describes the lessons learned and presents...

A 50 MeV, 5mA proton cyclotron is being developed as the injector for a high-current driver for an accelerator-driven subcritical fission power system (ADSMS), and also for production of isotopes for medical physics. Two innovations have made it possible to design a cyclotron capable of >5 mA beam current: strong-focusing of the bunches by quadrupole focusing channels integrated on the pole faces of the sector magnets, and superconducting rf accelerating cavities to provide sufficient energy gain per turn to cleanly separate the orbits. Simulation results will be presented for the beam dynamics of the intense proton bunches during injection, acceleration, and extraction. Key features for both applications will be discussed.

New technology is being developed for high-brightness, high-current cyclotrons with performance benefits for accelerator-driven subcritical fission power, medical isotope production, and proton beam cancer therapy. This paper describes the design for a 65 kV electron cyclotron resonance (ECR) ion source that will provide high-brightness beam for injection into the cyclotron. The ion source is modeled closely upon the one that is used at the Paul Scherrer Institute. Modifications are being made to provide enhanced brightness and compatibility for higher-current operation.

The Accelerator Research Lab at Texas A&M University is developing new accelerator technology for a high-brightness, high-current cyclotron with capabilities that will be beneficial for applications to accelerator-driven subcritical fission, medical isotope production, and proton therapy. As a first embodiment of the technology, we are developing a detailed design for TAMU-50, a 50 MeV, 5 mA proton cyclotron with high beam brightness. In this presentation we present devices and beamline components for injection, extraction, controls and diagnostics. We emphasize the system integration and implementation of TAMU-50 for production of medical radioisotopes.

Anomalous ion heating and superthermal electron populations have been studied in the MST reversed-field pinch. The ion heating is much stronger than that given by classical electron-ion friction, and is particularly strong during dynamo bursts. The heating displays a marked density dependence: in a 350-kA discharge with a maximum (bar n) = 0.9 x 10(exp 13) cm(exp -3), T(sub i) rises sharply as (bar n) drops below 0.4 x 10(exp 13) cm(exp -3) late in the discharge. Superthermal electrons are produced in the core, with temperatures of T(sub eh), = 350-700 eV while the bulk core temperature is T(sub e)o = 130-230 eV. The fraction of superthermal electrons decreases with increasing density, from 40 percent at (bar n) = 0.5 x 10(exp 13) cm(exp -3) to 8 percent at (bar n) = 1.9 x 10(exp 13) cm(exp -3) at I = 350 kA. However, data with similar plasma parameters but higher oxygen impurity content had a lower T(sub eh) and higher hot fraction. The edge superthermal electron distribution is we...

ABSTRACT We report the development of a conceptual design for accelerator-driven subcritical fission in a molten salt core (ADSMS). ADSMS is capable of destroying all of the transuranics at the same rate and proportion as they are produced in a conventional nuclear power plant. The ADSMS core is fueled solely by transuranics extracted from used nuclear fuel and reduces its radiotoxicity by a factor 10,000. ADSMS offers a way to close the nuclear fuel cycle so that the full energy potential in the fertile fuels uranium and thorium can be recovered.

Suggestions have been made for a 80-100 km circumference Future Circular Collider (FCC) that could ultimately contain a circular e+e- ring collider operating as a Higgs Factory as well as a 100 TeV hadron collider. Those suggestions have motivated us to propose an approach in which the project is sited at the location at the SSC tunnel, which has the lowest tunnel cost ever. The low tunnel cost would make it cost-effective to locate the 100 TeV Hadron Collider in a 270 km circumference tunne, using 4.5 Tesla superconducting magnets. The SSC tunnel itself would be used to house the Higgs Factory and the injector for the Hadron Collider. The injector for the Higgs Factory would be also used as a driver for an X-ray Free Electron Laser with unique capabilities for protein crystallography. The location of the project at a location with favorable geotechnology for minimum-cost tunneling, and low-cost/low-risk technology for the SRF and superconducting magnets, open the possibility to build the proposed laboratory within a decade.

MST is a large (Râ/a = 1.5/0.52 m) RFP which to date has obtained 80 ms discharges at a peak plasma current of 0.6 MA. Low loop voltages (15 volts) and modest temperatures (T{sub e}/T{sub i} â 350/250 eV) are routinely obtained giving estimated unoptimized energy confinement times of about 1 ms. Loop voltage and ion temperature are anomalous. Magnetic

Several attempts have been made to form a reversed field pinch (RFP) in a four-node, poloidal divertor configuration which positions the plasma far from a conducting wall. In this configuration, the plasma is localized within a magnetic separatrix formed by the combination of toroidal currents in the plasma and four, internal, conducting rings. These experiments were conducted on three devices: Tokapole II, the Wisconsin Levitated Octupole, and the modified Octupole with smaller conducting rings. Transient, RFP-like equilibria were obtained on Tokapole II and the Wisconsin Levitated Octupole. RFP-like equilibria with field reversal duration ~1 msec were obtained on the small ring Octupole. None of these plasmas was sustained against resistive magnetic diffusion. Local, internal measurements of the magnetic field in Tokapole II plasmas indicated the plasma current and density were mostly confined to the region inside the magnetic separatrix. The sharp drop in plasma pressure near the separatrix generated a large diamagnetic current in that region. Large magnetic perturbations were observed in the startup phase of these plasmas. On the small ring Octupole, the perturbation (delta B/B~ 40%) was measured to have a dominant poloidal mode number of m = 1 and toroidal mode numbers n~-5, i.e., internally resonant or nonresonant modes. This perturbation was stationary and was phase-locked to a magnetic field error. If the tenuous plasma region outside the separatrix is "vacuum-like," then this behavior might represent current -driven instability owing to the lack of a nearby, stabilizing boundary. Such instability is consistent with linear magnetohydrodynamic stability calculations and nonlinear simulations of a cylindrical RFP plasma bounded by a large vacuum region and a distant conducting wall.