Showing papers in "IEEE Transactions on Nuclear Science in 1971"

RMS Envelope Equations with Space Charge

Abstract: Envelope equations for a continuous beam with uniform charge density and elliptical cross-section were first derived by Kapchinsky and Vladimirsky (K-V). In fact, the K-V equations are not restricted to uniformly charged beams, but are equally valid for any charge distribution with elliptical symmetry, provided the beam boundary and emittance are defined by rms (root-meansquare) values. This results because (i) the second moments of any particle distribution depend only on the linear part of the force (determined by least squares method), while (ii) this linear part of the force in turn depends only on the second moments of the distribution. This is also true in practice for three-dimensional bunched beams with ellipsoidal symmetry, and allows the formulation of envelope equations that include the effect of space charge on bunch length and energy spread. The utility of this rms approach was first demonstrated by Lapostolle for stationary distributions. Subsequently, Gluckstern proved that the rms version of the K-V equations remain valid for all continuous beams with axial symmetry. In this report these results are extended to continuous beams with elliptical symmetry as well as to bunched beams with ellipsoidal form, and also to one-dimensional motion.

Possible Emittance Increase through Filamentation Due to Space Charge in Continuous Beams

Abstract: The study of oscillations which can take place in a beam under space charge conditions has been extended to other distributions than the one described by Kapchinsky and Vladimirsky (K. V.) in 1959. Two sets of equations similar to the ones they established can be written provided axis and emittance values are replaced by rms expressions applicable to any type of distribution. In case of a non K. V. distribution, the comparison of these sets gives differential equations relating the rms emittances to correcting terms which depend on the charge distribution inside the beam. Such equations can be used to interpret some rms emittance increases observed either with a mismatch in a smooth focusing channel or with a matched beam in an AG focusing system.

Vacuum Ultraviolet Radiation Effects in SiO2

Abstract: Charging effects observed in MOS structures which have been exposed to sputtering plasmas or electron beam deposition suggest that Vacuum Ultraviolet (VUV) or soft X-radiation is important in producing these effects. Our experiments show that under positive gate bias VUV irradiation produces large positive charging effects for photon energies above 8.8 eV, the threshold for electron-hole pair creation in SiO2. This charging appears to be accompanied by an increase in interface state density. VUV radiation proves to be more useful than higher energy quanta or particles in studying radiation charging. This is true because one can control the depth of radiation absorption into the oxide. Etching experiments show that positive charge is induced near the Si-SiO2 interface even when radiation is absorbed near the gate electrode. This result is strong evidence in support of the hole transport and trapping model. We present evidence that under irradiation with positive bias, positive space charge is formed near both interfaces. We also show how a large positive space charge can be introduced into the oxide without a gate electrode.

Radiation Hardening of P-MOS Devices by Optimization of the Thermal Si02 Gate Insulator

Abstract: It has been found for p-channel MOS devices that considerably better radiation tolerance than generally believed possible can be obtained with gate insulators of thermally grown SiO2, provided that the processing conditions are optimized for radiation resistance. The oxidation ambient and temperature, the post-oxidation annealing temperature, the silicon orientation, and the method of depositing the gate metal all have pronounced effects on the radiation-induced degradation. With these parameters optimized for radiation hardness, gate threshold shifts of less than one volt after 1 × 106 rads (Si) can be obtained over the entire range of gate biases from 0 to -30 volts. This paper describes these findings and their applicability to the fabrication of radiation-hardened MOS circuits.

Defect Structure and Irradiation Behavior of Noncrystalline SiO2

Abstract: Various phenomena occuring during ionizing or particle irradiation of vitreous silica and Si-SiO2 interface structures are explained. Densification and changes in bond polarizability are due to the basic trend of maximizing ?-bonding between Si and O atoms with minimum bond strain. Hole trapping in SiO2, as exhibited, e.g., in irradiated MOS devices, is an intrinsic property of the Si-O bond. Irradiation generates trivalent Si and non-bridging O defects. These interact with impurities, especially SiOH and SiH groups, as well as with interstitial H. These defects determine the radiation behavior of vitreous silica and Si-SiO2 interfaces, as well as the stability of MOS devices.

High Purity Germanium for Detector Fabrication

Abstract: The preparation of large (100) oriented germanium crystals with net concentrations of electrically active impurities in the range 1-10 × 1010cm-3 is described. This material has been used successfully for the fabrication of semiconductor detectors having depletion layers up to 8 mm thick, without using lithium compensation. Electrical evaluation is performed by studying the Hall coefficient as a function of temperature, and by measuring the resistivity along the length at 77°K. Dislocation densities in most crystals range from 2000 to 5000 cm-2 Several dislocation-free crystals have also been grown. The oxygen concentration, measured by lithium precipitation, is approximately 1014 cm-3 in germanium grown from quartz crucibles and much less than this when grown from graphite. The solubility of lithium in pure, oxygen-free germanium is found to be 3.5 × 1013cm-3 at 23°C.

Plasma Contamination and Wall Erosion in Thermonuclear Reactors

Abstract: Plasma radiations striking the vacuum walls of fusion reactors may (a) seriously damage and erode the wall and (b) release major quantities of gas which will contaminate the plasma. The influence of various secondary particle-emission contributing to these two processes will be reviewed; special emphasis will be given to radiation blistering, sputtering, and the release of gaseous particles by energetic photon impact. From the best estimates of the yields of some of these processes, the lifetimes of walls made for example of Nb or Mo will be estimated.

Barium Fluoride as a Gamma Ray and Charged Particle Detector

Abstract: "Pure" Barium Fluoride has been found to scintillate to gamma rays and alpha and beta particles. Pulse height of 10% relative to NaI(Tl), emission decay of 0.63 microseconds, fluorescence emission maximum at 3250A have been measured for currently available crystals of BaF2. This paper describes the scintillation performance and pertinent physical properties of BaF2 in relation to some of the commercially available scintillators -- NaI (Tl), CsI(Na), CsI(Tl) and CaF2 (Eu). The low solubility, non-hygroscopic nature and a comparable absorption for gamma rays are particular advantages of BaF2 over the alkali iodide scintillators. Transmission to its fluorescence emission, shorter decay time and a better photelectric absorption cross-section favor BaF2 over CaF2 scintillators. However, the scintillation pulse height of BaF2 is presently lower than the other scintillators, but it is still sufficiently large enough to observe a resolvable Cs137 662 Kev photopeak. The mechanism responsible for scintillation in BaF2 is not well understood at present. A preliminary investigation to understand this mechanism was undertaken in the form of adding impurities of various valencies to BaF2 and also studying the behavior of scintillation with temperature. The data seems to indicate that hole-centers may be playing a primary role in the scintillation emission. An understanding of the mechanism and the improvement and development of BaF2 as a scintillator has been an integral part of the High Z Scintillator Research program maintained for some time by Harshaw.

Pulsed Feedback Tecniques for Semicondctor Detector Radiation Spectrometers

Abstract: Methods of applying pulsed-charge feedback to the charge-sensitive preamplifiers used with semiconductor detectors are discussed. All have in commn the accumulation of radiation-induced charge pulses on a feedback capacitor to produce a voltage ramp at the output of the feedback stage, which is reset at an appropriate point by pulsing a charge feedback path. Advantages of pulsed feedback over the conventional dc feedback techniques are discussed, together with the precautions required to reduce the effect of the large reset pulse on the later electronics. The application of pulsed-light feedback to low energy X-ray spectrometers is discussed and results are presented. We also discuss sane aspects of this system that tend to limit its high-rate performance. A brief account of the use of a transistor current-switch feedback system to reduce overload problems in high-energy ?-ray spectrometers is also given.

Dynamics of Pulsed High Current Relativistic Electron Beams

Abstract: Pulsed electron beams are formed by the slow charge of a pulse forming network (microseconds to D. C.) and the fast discharge (10 - 100 ns) onto a field emission diode. The resultant beams of kiloamps to megamps at hundreds of keV to ten MeV are passed through a window into the drift region. Ionization in the drift section allows the beam to be confined by its own magnetic field. Secondary electron currents in the plasma tend to neutralize this effect, Recent work on guiding intense beams with auxiliary fields has utilized applied Bz and B? (z-pinch) fields. Application of these beams extends from shock studies to ion acceleration.

Large Superconducting Magnet Designs for Fusion Reactors

Abstract: Fusion technology will require superconducting fields of larger working volume and higher field strengths than heretofore Designed. The forces that will result are so large that novel approaches to magnet design must be developed. This paper describes two complementary approaches that may he combined to yield a satisfactory design for very high field toroidal magnets. The first provides a cylindrical load-bearing, element in compression combined with return conductors in pure tension. The second follows the design techniques that have been developed in the studies of force-free toroidal magnets.

Detection of Low Energy X Rays with Si(Li) Detectors

Abstract: The continuing improvement in energy resolution of semiconductor detector X-ray spectrometers has led to interest in the use of these devices at energies less than 2 keV. This is an energy region of potential analytical interest since the K X rays of several elements of biological and chemical importance occur at these energies. However, the low X-ray fluorescence yield in low-Z elements, combined with the absorption of low-energy X rays due to the entry window of the vacuum chanber and that of the detector, have made work in this energy region impossible with the standard semiconductor detector X-ray spectrometers. In the present work, the X-ray absorption path has been reduced to a minimum to permit low-energy X ray studies of excitation, entry window thickness, detector linearity and resolution. Using electron beam excitation on low-Z targets, we have performed measurements of characteristic K X rays of elements down to and including carbon (277 eV).

Radiation-Induced Conductivity in Polymers: Poly-N-Vinylcarbazoie

Abstract: Experimental evidence is given which indicates that the yield of charge carriers excited by a given dose of x-rays in thin films of poly-N-vinylcarbazole (PVK) is dominated by geminate (initial) recombination of the ion pairs. The yield as a function of applied field gives a very good fit to the theory of initial recombination developed for gases by Onsager. Two competing mechanisms, the Poole-Frenkel effect and track recombination, may be rejected on the basis of the field dependence. A comparison of the charge transients in PVK with other organic materials is given along with a discussion of the possibility of trap modulation of the mobility in PVK. The role of three different kinds of carrier recombination, bulk, track and geminate, is described in terms of the experimental results expected for each of them.

Pulsed Power Technology for Controlled Thermonuclear Fusion

Abstract: Over the past few years, the technology of pulsed power generators has been developed to the level where it is possible to produce powers of the order of 1012 W for times of the order of 10-7 sec. Such generators are most commonly utilized to produce intense relativistic electron beams, and this paper briefly surveys the existing state of the art of generators and relativistic beams. As examples, recent work at NRL is considered in some detail. Finally, several potential applications of this technology in controlled fusion research will be discussed.

Marx - and Marx-Like - High-Voltage Generators

Abstract: Major developments have taken place in the art of Marx generating in recent years. The rationales, modi operandi and relative merits of these developments are discussed in an attempt at exegesis and classification.

Transformer Type Accelerators for Intense Electron Beams

Abstract: The principles and designs of transformer accelerators (TA) generating intense beams of charged particles over energy ranges 0.5-5 Mev are described. Pulse electron accelerators with pulse length of 10-8 to 10-5sec are investigated (some of them have a repetition rate of several hundreds pps) as well as one-phase d three-phase 50-cps transformers. The most models' power conversion efficiency is in the range of 60-95%, the averaged beam power comes up to or exceeds 10 kW and is in excess of 150 kW for one of the last models. The design of a 5 Mev single-pulse TA with peak current of 30 kA at pulse length of 40 nsec and of 1.2 Mev proton TA with average beam power of 10 kW are described. The features of main components of high voltage transformers and of intense current acceleration tubes are discussed.

Residual Fields in Superconducting Dipole and Quadrupole Magnets

Abstract: This paper discusses the magnetic measurements of residual field in superconducting dipole and quadrupole magnets. The technique used to measure residual fields is described herein. The results of the measurement are presented and compared with a simplified theory, which predicts the basic nature of residual fields. The theory and experiment agree reasonably well despite the simplifying assumptions made in the theory. The residual fields generated in a superconducting magnet do affect the uniformity of the field generated in such a magnet. The effects of residual field are worst at low field, which is precisely where one wants the most magnet uniformity in a superconducting synchrotron. The theory suggests that one can reduce the magnitude by: (1) reducing the strand diameter in the material (smaller strands require more twist to eliminate coupling); and (2) reducing the low-field critical current of the material, which also reduces ac loss and instabilities. The theory also suggests that superconducting synchrotrons with injection inductions as low as 1 kG must have superconductor strands as small as 1 to 2 ?m.

The Electrical Design of the NRL Gamble II, 100 Kilojoule, 50 Nanosecond, Water Dielectric Pulse Generator Used in Electron Beam Experiments

Abstract: The rationale for the choice of dielectric, size, and basic components of the system is summarized The technology available and the state of the art in designing large wxater dielectric energy storage systems will be discussed and the application of this technology to the design of the Gamble II pulse generator is described

Neutron Produced Trapping Centers in Junction Field Effect Transistors

Abstract: The junction field effect transistor has been employed to study trapping centers introduced in silicon by fast neutron irradiation. Extensive measurements have been made of both the static and dynamic characteristics of irradiated devices. The effects of neutron-produced traps have been explored in both n and p channel devices, as a function of neutron fluence and dopant concentration. The trapping center effects on small signal transconductance and large signal pulse response are characterized and the data are compared to appropriate theories to determine ionization energy values for the dominant traps. In n-type, trap energy levels of Ec - 0.38 ± 0.03 and Ec - 0.46 ± 0.03 eV are obtained, and in p-type an energy level of Ev + 0.29 ± 0.03 eV is observed.

Superconducting Niobium Cavity Measurements at SLAC

Abstract: The program of measurements at SLAC on superconducting niobium cavities is described. Results for TE and TM mode X-band cavities are presented. An RF magnetic breakdown field of 960 gauss and Q values greater than 1011 were measured for an electron beam welded TE011 mode cavity at 10.5 GHz. The best result for a TM mode cavity was a Q of 1.4 × 109 and a breakdown field of 360 gauss, limited probably by the quality of the electron beam weld. Data on the effect of exposure to air and to nitrogen are presented.

Short-Term Charge Annealing in Electron-Irradiated Silicon Dioxide

Abstract: The existence of a rapid annealing phase in the decay of space charge induced in silicon dioxide by pulsed irradiation has been demonstrated. This effect has been observed in MOS structures prepared from both wet and dry thermal oxides and also in several commercial N-channel MOSFET's. A simple model involving thermal release of the trapped positive charge from a distribution of oxide trapping levels conveniently approximates the major features of short-term annealing.

The ERA 4 MeV Injector

Abstract: A pulsed electron accelerator has been constructed and is now in operation at the Lawrence Radiation Laboratory, Berkeley. It was designed specifically for and is used as an injector for ERA (electron ring accelerator) studies. Electron bursts of 1200 amperes and 40 nanoseconds duration can be produced at energies of 1.0 MeV to 4.25 MeV. The present repetition rate is approximately one per second. Acceleration is accomplished by means of ferrite loaded accelerating sections, each of which is capable of maintaining a 250 kV voltage pulse across the accelerating gap for a period of 40 ns. The voltage pulse has a rise time of 12 ns and the total timing jitter is of the order of one nanosecond. Five sections stacked together and operated as a unit function as the electron gun. The gun employs a field emission cathode and is operated at approximately 1 MV. Additional acceleration is achieved by means of an iterated system of accelerator sections and solenoidal magnetic lenses.

Nereus, A 250 kV, 80 kA Electron Beam Generator

Abstract: A 250 - 400 kV, 80 kA, 30 ns electron beam generator has been developed. The machine consists of a 600 kV Marx generator, a water-dielectric transmission line, a diode, and a beam drift chamber. It was necessary to minimize prepulse for stable diode operation. Several cathodes were tested during development and results are reported. Diodes with 26 and 8 nH inductance are described.

Printed-Circuit Steering Coils

Abstract: Beam steering coils utilizing "turns" etched on printed-circuit boards have been constructed and tested. This approach offers an economical method for achieving high-quality, compact steering coils. The circuit-boards are rolled into a cylinder and inserted inside a short steel tube. Boards for vertical and horizontal steering are located in separate layers. For our application, three coil sizes were constructed with inside diameters of 25 cm. 20.6 cm, and 17.3 cm respectively. Active length is 0.6 of the inside diameter in all cases. The coils produce an integrated deflection field in either the vertical or horizontal direction of ~ 316 Gauss-cm when excited with 5 A at ~ 30V. The conductor pattern on the circuit-board was designed to produce a nearly uniform angular deflection for all rays transmitted, in spite of the short length/diameter ratio. The magnetic field integrated over a length of 152 cm was measured at several radii and azimuths. Values at 0.4 and 0.8 of bore radius were within ~ 0.5% and ~ 1.5% respectively of the central value. Suggestions for further refinement of deflection uniformity are presented.

Experiments with Megagauss Targets at SLAC

Abstract: The high pressures and current densities associated with MG fields limit their useful lifetime to 1 ?sec or less. The pulse duration of the SLAC electron beam being of the same order of magnitude, a successful marriage of the two techniques was achieved in experiments that use transverse fields in the range 1 to 2 MG as targets for a 19 GeV electron beam. The fields were generated in volumes of dia. 3 to 5 mm by discharging a very fast capacitor bank into small single turn coils, or by flux compression with electromagnetically driven aluminum foils. The termination of the capacitor bank, designed to minimize the destructive effects of the exploding coils, permitted a repetition rate of one shot per hour. Magnetic bremsstrahlung emitted by the electrons was recorded on X-ray film and nuclear emulsions. In an additional experiment, nuclear emulsions mounted in the high field region survived the violent self-destruction of the coils. In these, the magnetic deflection by far exceeds the multiple scattering, which is normally the dominant effect in nuclear emulsions.

Non-Intercepting Monitor of Beam Current and Position

Abstract: A compact monitor has been developed which measures beam current and beam position without intercepting or appreciably affecting the particle beam being measured. It is a broad band device which prevents the development of beam disturbing resonant modes. Although developed specifically for use on a short-pulse electron induction accelerator, it might be applied to other accelerator beams of pulsed or rf-bunched nature. The monitor consists of a resistive band inserted in the beam pipe wall with connections for reading the voltage across the band at each vertical and horizontal axis intercept. For pulsed or rf beams, return current equal in magnitude to the beam current flows on the beam pipe inside wall and through the resistive band. If the beam is centered, equal voltage appears on all four monitor connections. If the beam is off-center, the return currents are unsymmetrical and unequal voltages appear at the monitor connections. Beam current is proportional to the sum of all monitor voltages, while beam position is approximately proportional to the difference in voltage at opposing monitors. Tests and operating experience confirm its operation.

"ELRAFT" A Computer Program for the Efficient Logic Reduction Analysis of Fault Trees

Abstract: One of the most powerful and widely used techniques in the field of reliability analysis is the Fault Tree. In Fault Tree analysis, component failures or conditions (basic events) are graphically depicted in the necessary combinations to cause subsystem or system failures (secondary events). Application of probability theory to the logic scheme thus depicted permits computation of system failure probability where the probabilities of the basic events are known.

Charge-State Effects in Displacement Damage Invited Paper

Abstract: Charge-state effects in displacement damage in covalent semiconductors are reviewed. Specifically the influence on defect production mechanisms, configurations, mobility, annealing kinetics, interaction and dissociation are discussed. The recent theoretical work on the split-interstitial is mentioned, as is the new athermal migration mechanism.

Fault Tree Analysis with Probability Evaluaticn

Abstract: Reliability analysis is playing an increasingly important role in quantitative assessment of system performance for assuring nuclear safety, improving plant performance and plant life, and reducing plant operating costs. In particular, fault tree analysis with probability evaluation provides an all inclusive, versatile mathematical tool for analyzing complex systems. Its application can include a complete plant as well as any of the systems and subsystems. Fault tree analysis provides an objective basis for analyzing system design, performing trade-off studies, analyzing common mode failures, demonstrating compliance with AEC requirements, and justifying system changes or additions. The logic of the approach makes it readily understandable and, therefore, it serves as an effective visibility tool for both engineering and management.

A Method for the Routine Measurement of Dielectric Photoconductivity

Abstract: An instrumentation and data reduction technique for the routine analysis of dielectric photoconductivity data has been developed. This technique provides detailed conductivity versus time data during and shortly after an ionizing radiation pulse. Thus, it complements the timeintegral of conductivity technique, which can provide good long-term delayed conductivity data, and it offers some advantages over similar methods developed to measure conductivity. The unique features of this technique include the use of spline functions in the data reduction, the use of a sample designed to provide noise current cancellation, and circuit analysis that includes a mismatched transmission line.