T. Wilson

Characterization of superconducting bearings for lunar telescopes

The hybrid superconductor magnet bearing system for a lunar telescope has been developed based on passive magnetic levitation and the flux pinning effect of high-temperature superconductivity. The rationale lies in the unique capability of high-temperature superconductors (HTS) to adapt to the low temperature and vacuum environments in space or on the Moon, and to enhance system stability passively without power consumption. Characterization experiments have been conducted to understand its dynamic behavior and to estimate the required motor torque for its driving system design. Characterization experiments show that the hybrid HTS-magnet bearing system has periodical oscillation of drag torque. The bearing also suffers from small periodic oscillation on top of it due to discontinuous distribution of HTS. However, the magnitude of drag torque is velocity independent and very small. It makes the bearing attractive for high speed application. Finally, design guidelines for superconducting bearing systems are suggested based on experimental results.

High temperature superconducting bearings for lunar telescope mounts

A telescope to be installed on the lunar surface in the near future must work in a cold and dusty vacuum environment for long periods without on site human maintenance. To track stars, the drive mechanism must be capable of exceedingly fine steps and repeatability. Further, the use of lightweight telescopes for obvious economic benefits burdens the requirement for stable support and rotation. Conventional contact bearings and gear drives have numerous failure modes under such a restrictive and harsh environment. However, hybrid superconducting magnetic bearings (HSMB) fit in naturally. These bearings are stable, light, passive, and essentially frictionless, allowing high precision electronic positioning control. By passive levitation, the HSMB does not wear out and requires neither maintenance nor power. A prototype illustrating the feasibility of this application is presented.<<ETX>>

The application of FLUKA to dosimetry and radiation therapy

The FLUKA Monte Carlo code has been evolving over the last several decades and is now widely used for radiation shielding calculations. In order to facilitate the use of FLUKA in dosimetry and therapy applications, supporting software has been developed to allow the direct conversion of the output files from standard CT-scans directly into a voxel geometry for transport within FLUKA. Since the CT-scan information essentially contains only the electron density information over the scanned volume, one needs the specific compositions for each voxel individually. We present here the results of a simple algorithm to assign tissues in the human body to one of four categories: soft-tissue, hard-bone, trabecular-bone and porous-lung. In addition, we explore the problem of the pathlength distributions in porous media such as trabecular bone. A mechanism will be implemented within FLUKA to allow for variable multipal fixed density materials to accommodate the pathlength distributions discovered.

The FLUKA code: an overview

FLUKA is a multipurpose Monte Carlo code which can transport a variety of particles over a wide energy range in complex geometries. The code is a joint project of INFN and CERN: part of its development is also supported by the University of Houston and NASA. FLUKA is successfully applied in several fields, including but not only, particle physics, cosmic ray physics, dosimetry, radioprotection, hadron therapy, space radiation, accelerator design and neutronics. The code is the standard tool used at CERN for dosimetry, radioprotection and beam-machine interaction studies. Here we give a glimpse into the code physics models with a particular emphasis to the hadronic and nuclear sector.

Vibration isolation for space structures using HTS-magnet interaction

We employ the HTS-magnet interaction in the mechanical design of a vibration isolator. One common element of space structures is the coupling between multiple substructures or mechanical parts. Often, such coupling needs to provide a transmission of force between the two systems while blocking out the propagation of the vibration energy from one system to the other. A solution to this is to establish a soft link between the two systems. In this paper, we design a passive vibration isolation device employing the characteristics of the HTS-magnet interaction. The configuration of the vibration isolator consists of a ring magnet and a thin disk HTS where the HTS is located in the middle of the magnet and is levitated. Experiments show that the natural frequency of the system is 4 Hz and the frequencies above 10 Hz are successfully isolated. Such a passive device in space applications is superior to similar active devices that often require bulky control circuit boxes and consume considerable energy that is not readily available in the space environment. The concept can also be used as an isolation platform and can combine with the active vibration isolation technology so as to attenuate the vibration of all frequencies.

A high-temperature superconductor energy-momentum control system for small satellites

A method for angular momentum management in flywheel energy storage systems that employ superconducting bearings for spacecraft attitude control is presented. Success with high-temperature superconductor momentum wheels as practical energy storage systems has led to increased interest in their dual function for providing electrical power as well as attitude control of small satellites. The physics of angular momentum management is used to quantify how superconductor magnetic bearing flywheels as electro-mechanical devices serve as both energy storage and angular momentum storage systems within an end-to-end architecture. The result is a compound energy-momentum attitude and electrical power control system for satellites.

Superconductor-magnet bearings with inherent stability and velocity-independent drag torque

A hybrid superconductor magnet bearing system has been developed based on passive magnetic levitation and the flux pinning effect of high-temperature superconductivity. The rationale lies in the unique capability of a high-temperature superconductor (HTS) to enhance system stability passively without power consumption. Characterization experiments have been conducted understand its dynamic behavior and to estimate required motor torque for its driving system design. These experiments show that the hybrid HTS-magnet bearing system has a periodic oscillation of drag torque due mainly to the nonuniform magnetic field density of permanent magnets. Furthermore, such a system also suffers from a small superimposed periodic oscillation introduced by the use of multiple HTS disks rather than a uniform annulus of HTS material. The magnitude of drag torque is velocity independent and very small. These results make this bearing system appealing for high-speed application. Finally, design guidelines for superconducting bearing systems are suggested based on these experimental results.

A micro power supply for space micro-electromechanical systems using a high-temperature superconductor-magnet bearing

This paper investigates the possibility of using a high temperature superconductor (HTS) for a micro power supply in space micro-electromechanical systems (MEMS). Feasibility studies have been carried out to develop a micro HTS-magnet bearing system which can be used for wear prevention and as a power supply. The rationale lies in the unique capability of the HTS to adapt to low temperatures, radiation, and vacuum environments in space, and to enhance system stability passively without power consumption. This micro power supply consists of three components: an HTS magnet flywheel energy storage system, a motor/generator, and a lithium micro battery. The generator armature planar coil will be deposited on the surface of the stator of the flywheel which encloses the HTS. The rotor of the flywheel has alternating permanent magnet poles for the motor/generator. The HTS flywheel has high angular momentum storage since its drag torque is nearly velocity-independent and extremely small, enabling high-speed rotation. Preliminary investigations show that the micro-sized superconductor magnet bearing system is compatible with current micro-fabrication technology and is ideal for preventing wear and producing power in space applications.

Update On the Status of the FLUKA Monte Carlo Transport Code

The FLUKA Monte Carlo transport code is a well-known simulation tool in High Energy Physics. FLUKA is a dynamic tool in the sense that it is being continually updated and improved by the authors. We review the progress achieved since the last CHEP Conference on the physics models, some technical improvements to the code and some recent applications. From the point of view of the physics, improvements have been made with the extension of PEANUT to higher energies for p, n, pi, pbar/nbar and for nbars down to the lowest energies, the addition of the online capability to evolve radioactive products and get subsequent dose rates, upgrading of the treatment of EM interactions with the elimination of the need to separately prepare preprocessed files. A new coherent photon scattering model, an updated treatment of the photo-electric effect, an improved pair production model, new photon cross sections from the LLNL Cullen database have been implemented. In the field of nucleus-- nucleus interactions the electromagnetic dissociation of heavy ions has been added along with the extension of the interaction models for some nuclide pairs to energies below 100 MeV/A using the BME approach, as well as the development of an improved QMD model for intermediate energies. Both DPMJET 2.53 and 3 remain available along with rQMD 2.4 for heavy ion interactions above 100 MeV/A. Technical improvements include the ability to use parentheses in setting up the combinatorial geometry, the introduction of pre-processor directives in the input stream. a new random number generator with full 64 bit randomness, new routines for mathematical special functions (adapted from SLATEC). Finally, work is progressing on the deployment of a user-friendly GUI input interface as well as a CAD-like geometry creation and visualization tool. On the application front, FLUKA has been used to extensively evaluate the potential space radiation effects on astronauts for future deep space missions, the activation dose for beam target areas, dose calculations for radiation therapy as well as being adapted for use in the simulation of events in the ALICE detector at the LHC.

Developing a space radiation simulation and analysis package

The idea of blending a modern object-oriented graphics-based analysis program with a Monte Carlo radiation transport code for space-based applications is being assessed. This is part of an ongoing effort to restructure the FLUKA physics radiation transport simulation code for intimate compatibility with the ROOT analysis and visualization program at CERN. ROOT provides a full suite of powerful analysis tools in an environment based upon object-oriented data structures. It provides full 3-D Graphics support and allows the direct use of C++ as a scripting language. The FLUKA code is an alternative to the GEANT code as a tool for detailed simulation of radiation transport. Both of these physics codes have their strengths and at present can be provided for within the infrastructure of ROOT. GEANT has many well-known shortcomings that in some instances are significantly improved upon by FLUKA. Combining these types of transport codes with the ROOT analysis program into a single user-friendly software package w...