eLearning

A Noninteractive Beam Position and Size Monitor for Heavy Ions

John M. Bogaty IEEE Transactions on Nuclear Science, 1979

The Ion Beam Fusion development program at Argonne National Laboratory requires noninteractive size measurements of a pulsed, 30 mA, Xe+l particle beam. Pulses of 100 μs duration will be produced by the 1.5 MV preaccelerator; therefore, fast response diagnostics are required. Techniques of utilizing residual gas ionization to profile particle beams have been reported before. This paper discusses the development ...

A two-electron group model theory for radio-frequency ionization of noble gases with turbulent flow

M. E. Talaat IEEE Transactions on Plasma Science, 1991

Equations are derived for predicting the current-voltage characteristic curves of axial RF discharges in noble gases, with turbulent flow. The electrons are considered to be made up of two Maxwellian groups: bulk and tail electrons. The bulk electrons are described by a temperature Tb, and have kinetic energies (1/2 mv2=eV) from 0 to eV l (eVl=the threshold energy of the ...

RF discharge modeling considering time dependence and spatial nonlocality of the electron energy spectrum

V. A. Feoktistov; A. M. Popov; O. B. Popovicheva; A. T. Rakhimov; A. T. Rakhimova; E. A. Volkova IEEE Transactions on Plasma Science, 1991

RF discharge modeling in He is performed. New features of modeling are based on the solution of the nonstationary Boltzmann equation in the spatially nonuniform electric field, coupled with the equation for electric field and charged-particle densities. It is shown that the local equilibrium model for the electron energy spectrum in RF discharge is not valid for the pressure range ...

The Bevalac Radiotherapy Facility

J. R. Alonso; J. Howard; T. Criswell IEEE Transactions on Nuclear Science, 1979

The Patient Treatment Room at the Bevalac is now in full operation. In the design of this facility, emphasis has been placed on creating an atmosphere appropriate to a clinical facility; the usual features of an irradiation cave have been hidden behind carpets, curtains and paint. Patient positioning is done with a Philips Ram-style couch, with additional fixtures to accommodate ...

SEDS MIL-STD-1773 fiber optic data bus: Proton irradiation test results and spaceflight SEU data

K. A. LaBel; P. Marshall; C. Dale; C. M. Crabtree; E. G. Stassinopoulos; J. T. Miller; M. M. Gates IEEE Transactions on Nuclear Science, 1993

Proton test and space-flight single event effect data for NASA's first fiber optic data bus are presented. Bit error rate predictions based on a proton direct ionization model agree well with flight data for proton-belt and solar- flare effects. Specifically, the authors discuss the SEUs (single event upsets) seen in space during the first months of the SAMPEX (Solar Anomalous ...

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IEEE-USA E-Books

• Appendix B: Physical Phenomena

  This appendix contains sections titled: Drift Velocity and Mobility Diffusion Thermionic Emission Image-Force Lowering Recombination and Generation Impact Ionization and Avalanche Space-Charge Effect and Space-Charge-Limited Current Tunneling Ohmic Contact Hall Effect Heterojunction, Quantum Well, Superlattice, and Quantum Dot

• Fundamentals of Electrical Discharges

  Natural phenomena, such as gamma rays produced by radioactive decay processes in the soil and cosmic radiation originating from solar flares and other galactic objects, can ionize the air molecules. This chapter first discusses ionization and deionization processes in gases. This is followed by a discussion on ionization and attachment coefficients. Two typical breakdown mechanisms occur in gases, each of them operating under specifically favorable conditions: Townsend's mechanism and the streamer mechanism. Corona discharges in air can burn on the overstressed zones of hot electrodes. This kind of discharge occupies a short layer, attached to the energized conductor. When a conductor is in corona, then the electric field on the surface is somehow influenced by the surrounding ion space charge. Kaptzov's hypothesis (KH) relates to the assumption that the space charge emitted into the interelectrode gap is in amounts that hold the surface field at the onset level.

• Analysis of Neutron Damage in HighTemperature Silicon Carbide JFETs

  Neutron-induced displacement damage effects in n-channel, depletion-mode junction-fleld-effect transistors (JFETs) fabricated on 6H-silicon carbide are reported as a function of temperature from room temperature (RT) to 300°C. The data are analyzed in terms of a refined model that folds in recently reported information on the two-level ionization energy structure of the nitrogen donors. A value of 5 ± 1 cm-3 per n/cm2 is obtained for the deep- level defect introduction rate induced by the neutron irradiation. Due to partial ionization of the donor atoms at RT, the carrier removal rate is a function of temperature, varying from 3.5 cm-1 at RT to 4.75 cm-1 at 300°C. The relative neutron effect on carrier mobility varies with temperature approximately as T-7/2, dropping by an order of magnitude at 300°C compared with the RT effect. The results offer further support for the use of SiC devices in applications which combine high-temperature and severe radiation environments, where the use of Si and GaAs technologies is limited.

• Upsets Produced by Heavy Ion Nuclear Reactions

  This chapter contains sections titled: Heavy Ion Nuclear Reactions Upset Rate Calculations for Combined Ionization and Reactions Heavy Nuclear Ion Reactions Summary

• Principles of Substrate Crosstalk Generation in CMOS Circuits

  Substrate noise injection is evaluated for a O.2S-µm CMOS technology, to determine the mechanisms that contribute to substrate crosstalk. At the transistor level, we find that impact ionization current and capacitive coupling from the junctions are the most significant contributors to substrate current injection. An investigation of substrate fluctuations at a circuit level included switching transients, capacitive damping, and separate substrate biasing. This investigation revealed that voltage transients on power-supply lines can be the dominant source of substrate fluctuations. Finally, a statistical analysis of signal cancellation in an integrated circuit was performed. The results indicate that more cancellation will take place for the high-frequency noise components than for the average and low- frequency components. As a consequence, the de and low-frequency components of the transient that results from an individual switching event can not be neglected even if they are a relatively small fraction of the single transient.

• Space Charge in HVDC Extruded Insulation: Storage, Effects, and Measurement Methods

  This chapter discusses space-charge storage in HVDC extruded insulation, the relevant manifold effects, and the techniques developed by researchers in order to measure the amount and distribution of space charge stored in the insulation, and the electric field profile associated with such distribution. It reviews the theoretical background of charge injection and transport in insulating polymers. The chapter illustrates the processes that result in space-charge accumulation namely charge generation - via electronic charge injection, field-assisted thermal ionization of impurities, spatially inhomogeneous electric polarization, and steady DC current coupled with a spatially varying ratio ofpermittivity to conductivity. It also reviews the space-charge measurement methods for HVDC extruded insulation. The chapter focuses on the up-to-date developments of the best-suited techniques for measuring space charges in extruded insulation for HVDC cables. It provides a comparison between the best space-charge measurement methods for power cables: pulsed electro acoustic (PEA) versus thermal step method (TSM).

• Modeling Electron Impact Ionization

  Electron impact ionization is the mainstay for plasma-based flow control actuators because it actuates in less than microseconds and the electrode configuration can be made nonintrusive to oncoming stream. In addition, when the actuator is not needed, unlike most mechanical flow control devices, it will not be parasitic and degrade performance of aerospace vehicles. The space charges induce an additional electric field potential that makes it different from the corona discharge. This chapter presents the best physics-based, multifluid model for the electron impact ionization. The physics for electron impact ionization is well known through the luminary contributions by Townsend, the ionization is evolving from the electrons collision, secondary emission, and avalanche. The secondary emission from cathode arises as controlling mechanism for all electron impact ionization. A high concentration of positive charges over an electrode creates an extremely high electrical field potential, which is comparable to the magnitude in a nuclei.

• Ionization Processes

  The ionization process of atoms or molecules is through energizing the electrons causing them to leave stable orbit revolving around the nucleus and becoming free-moving charges. The main mechanisms for ionization consist of thermal, electron impact, chemical reactions, photoionization, and microwave or electron cyclotron resonance. This chapter describes the ionization that focus on the basic mechanisms of photoemission, thermal, and electron impact discharges. The equilibrium ionization of the mixture of electrons, ions, and neutral particles can be analyzed by the law of mass action and the electronic partition function. Under gas discharge conditions, ionization by electron impact dominates over the photoionization because the cross sections of photoionization close to the ionizing threshold are rather high. The chapter provides Saha equation of ionization. An important parameter for the ionization rate is the mean free path of the gas medium and is ultimately related to the collision cross section.

• Electrical Breakdown in Gases

  This chapter discusses a short treatise on atomic collisions in gases and a description of Townsend's experiments in the early twentieth century. It presents the Paschen curve, and describes the predominant theories of spark formation. The chapter also discusses other breakdown phenomena, such as coronas and the hollow electrode carrier generation used in pseudosparks. Electrical breakdown occurs in a gas when a high???conductivity channel is formed between cathode and anode. Before a study is made of the behavior of gases under the influence of an electric field, it is appropriate to review the basic principles of the kinetic theory of gases pertinent to gaseous ionization and breakdown. From there, the various concepts of ionic and electronic can be inferred. The chapter further discusses the efficient use of gaseous insulation with intershields. It concludes by discussing the important aspects of breakdown behavior in gaseous SF6.

• Specialized Silicon Carbide Devices and Applications

  The unique characteristics of SiC make it attractive for a variety of applications that are not well served by existing silicon technology. One such application is high-power, moderate-frequency microwave amplifiers and power sources based on devices such as MESFETs (metal-semiconductor field-effect transistors), static induction transistors (SITs), and IMPATT (impact ionization avalanche transit-time) diodes. Another important application involves high-temperature integrated circuits for sensing and control, where SiC bipolar and JFET (junction field-effect transistor) integrated circuits are the preferred implementations. A major emerging opportunity for SiC lies in the area of sensors for hostile environments. Developments to date include MEMS (micro-electro-mechanical sensor) devices for motion sensors, gas sensors for combustion control, and solar-blind UV optical detectors. In each area we describe the application requirements, highlight the advantages of SiC, and report the current status of SiC technology.