Transit Time Effects Research Articles

Behavior of high-voltage gaps in the presence of large space-charge fields

It is shown in this paper that a high-voltage gap exhibits a nonlinear capacitance behavior in the presence of large space-charge fields. The existence of this nonlinear capacitor is quasi dc in nature and does not result from transit time effects, i.e., high-frequency effects. This nonlinear behavior can be used to tailor the shape of bunched intense relativistic electron beams.

A Unified Treatment of the Impedance of Transit-Time Devices

This paper proposes a simplified treatment of microwave transit-time devices by dividing the device operation into two regions: the injection and the drift regions. This division may simplify the mathematical formulation and bring out the physical mechanism of the operation more clearly; but it also imposes a limitation that only such devices in which this division can be drawn clearly may be analyzed. In other words, the carriers must be injected with a saturated velocity when entering the drift region. Fortunately, most microwave solid-state devices assume a saturated velocity. In fact, even in a vacuum diode in which the carrier velocity is constantly varying, we can still use this approach by modifying the formulation to include a continuous injection process. We assume an idealized simple two-terminal device. A simple formula for the impedance of the drift region due to the transit-time effect is derived. It includes a term to account for the injection phase of the operation. Different devices are differentiated by the injection mechanism which is characterized by its amplitude and phase. Examples for computing impedances in IMPATT, BARATT, TUNNETT, and vacuum diode devices are illustrated. This paper concludes with a discussion of a futuristic heterojunction device as a natural extension of the method of analysis. It is believed that the present approach will give students a clearer physical picture of the device operation without complicated mathematical derivations to obscure the essentials.

Analysis of the transit time effect on the stroboscopic voltage contrast in the scanning electron microscope

The transit time effect (TTE) on stroboscopic waveform measurements in the scanning electron microscope is analysed. Here the TTE means the voltage contrast variation due to the time-varying surface electric field near the measurement electrode. The results show that the TTE on waveform rise and fall times or amplitude measurements cannot be disregarded for waveforms with a time variation of the order of 100 ps or less. The TTE on pulse width measurements does not appear to be so large.

Absorption of starch by healthy ileostomates: effect of transit time and of carbohydrate load

Recently, breath hydrogen studies and intubation techniques have indicated that in excess of 10% of starch in normal foods may be malabsorbed in the small intestine and enter the colon. We evaluated starch absorption in healthy subjects with ileostomy. First, unabsorbed starch was quantified in ileostomy effluent from six ileostomates who ingested constant diets of wheat and potato starch for four days. Daily unabsorbed starch ranged from 1.3% to 5.0% of total ingested starch. Second, starch from a radiolabeled solid meal containing 50 g potato starch was measured under control conditions and after altering transit time with either loperamide, or magnesium citrate. Loperamide significantly decreased the amount of unabsorbed starch in all six ileostomates (p less than 0.05), while magnesium citrate significantly increased starch malabsorption in all six subjects (p less than 0.05). Third, starch absorption was measured after single solid meals containing 25, 50, 75, and 100 g potato starch. There was a linear relationship between starch input and output. Mean output expressed as a percent of input remained constant. We conclude that the degree of starch malabsorption by the small intestine of ileostomates may be less than that estimated by indirect methods in intact humans. The amount of unabsorbed starch is directly related to the quantity ingested and to the small intestinal transit time.

Stability of magnetically insulated ion diodes

Magnetically insulated ion diodes are examined for instability using analytical and numerical techniques. Two basic sources which drive instability are found: one due to a two-stream-type interaction between electrons and ions and the other due to ion transit time effects.

A SPICE modeling technique for GaAs MESFET IC's

A vertically integrated device modeling technique for GaAs IC's is presented for use in circuit simulation. Most of the SPICE2 capability can be utilized for modeling the gate transit time and parasitic effects. A computer program has also been developed to extract model parameters from the measured device data.

Transient P O 2 and P CO 2 differencese between end-tidal gas and arterial blood during rebreathing in awake dogs

O 2 and CO 2 partial pressures in end-tidal gas ( Pa) and carotid artery blood (Pa) were measured during non-steady-state gas exchange in unanesthetized dogs. In 5 experiments (A), low O 2 breathing in open circuit preceded prolonged rebreathing during maintained normoxia. In 6 experiments (B), steady-state hypoxia and hypercapnia were followed by rebreathing CO 2 in hyperoxia which caused Pa O 2 to rise and then fall while Pa CO 2 increased. Negative (Pa- Pa) CO 2 , averaging −5 torr, were observed 10 sec after starting rebreathing in B and values between −1 and −2 torr were noted later in A and B. ( Pa-Pa) O 2 showed considerable transient increases for 2 min in A and 20 sec in B. This behavior of ( Pa-Pa) O 2 could be explained by a lung model with unequal distribution of alveolar ventilation and perfusion to alveolar volume. The negative (Pa- Pa) CO 2 values observed during rebreathing with rapidly increasing Pa CO 2 were in part attributable to such unequal distribution effects, in part to lung-to-carotid artery transit time effects.

The BARITT diode — A low noise heterodyne photodetector with high integral gain

Optical detection properties of wellknown microwave BARITT diodes are described. As a result of bulk barrier modulation due to accumulation of photogenerated charge carriers the devices exhibit high internal gain when used as a direct photodetector. Moreover, transit time effects give rise to another kind of internal gain at certain microwave frequencies which can be advantageous in optical heterodyne techniques. Basic experimental results of photodetector sensitivity are discussed.

Noise properties and time response of the staircase avalanche photodiode

The staircase avalanche photodiode is a novel graded-gap superlattice device that is expected to detect photons quite noiselessly. It is designed in such a way that only electrons impact-ionize, thereby eliminating the feedback noise associated with conventional two-carrier avalanche devices. Because the electron multiplication can occur only at a small number of discrete locations in the device, the variability of the number of electrons generated per detected photon is minimized. The excess noise and the electron counting distribution are obtained as a function of the number of stages in the device and the impact-ionization probability per stage, for instantaneous multiplication. The (single-photon) impulse response function is calculated when the effects of (random) transit time are incorporated into the carrier multiplication process. Inclusion of the time dynamics is essential for determining the time course of the current generated by the device in response to pulses of light. This, in turn, permits bit error rates to be calculated for systems incorporating the device. For a five-stage quaternary device the gain-bandwidth product is calculated to be in the vicinity of 600 GHz.

Current research in optical pumping

In 1950, Professor Alfred Kastler described the way in which optical fields could be used to redistribute population among the Zeeman sublevels of a given atomic state. The « optical pumping » process discovered by Kastler continues to be a research topic of current interest. With developments in laser spectroscopy, it has become important to understand the interplay of optical pumping, transit-time and collisional effects to properly interpret experimental line shapes. A brief review of the current status of the theory is given, with special emphasis on what, as yet, appear to be unresolved problems. Velocity selective optical pumping and collision-induced resonances are discussed.

Gap transit-time effects in fast optoelectronic semiconductor switching devices

The output shape of an electric pulse, which traverses the gap of a fast optoelectronic semiconductor switching device, is influenced by the transit time of the pulse. This dependence as well as the use of transit-time effects for pulse shortening are studied. To this end in the present paper optical and electrical time-dependent properties of the central unit, I.e. the laser-excited semiconductor, and the external passive electric elements and sources are considered and a time-variant telegraphic equation obeying appropriate boundary conditions is established. Numerical solutions for physically important cases are calculated and discussed.

Numerical study of an n-gallium arsenide diode distributed oscillator

The dynamic electron velocity, electron temperature, etc., in an n-gallium arsenide ballistic diode have been calculated by solving the Boltzmann equation under a hydrodynamic approximation. It has been found from the results that an n-gallium arsenide ballistic diode exhibits a negative conductance at a fairly high frequency range and over a wide frequency range from 1500.0 to 2300.0 GHz. From the small signal analysis using a simplified diode model, it has been shown that the negative conductance arises as a result of density modulation effects of the carriers, namely, space-charge transit time effects. High growth rate, up to 300.0 Np/cm, has been predicted in an n-gallium arsenide ballistic diode distributed oscillator. The diode can be expected to act as a new solid-state source at a far infrared frequency range.

Transit-time effects in a strong field inverted lamb dip theory

The inverted Lamb dip theory for a spatially-bounded plane laser beam is presented, valid for arbitrary gas pressure levels and field intensities. Line shape, power-broadening, contribution of transit-time and gas pressure effects to the dip linewidth have been computed and are found to be in perfect agreement with experimental data. In the limit of low pressure and intensity, the dip linewidth is found to depend only on the beam radius and the mean thermal velocity of molecules.

Nonlinear evolution of magnetopause tearing modes

Since the magnetosheath plasma is highly turbulent, reconnection at the dayside magnetopause is likely to be temporally unsteady. The tearing mode can be viewed as a model for the unsteady development of a reconnecting magnetic topology. Magnetopause tearing occurs in the guide‐field limit and has a wave packet spatial structure in the east‐west direction. We solve for the nonlinear evolution of a single wavelength guide‐field tearing mode including the effects of finite transit time on the Landau resonant electrons. Short wavelength modes evolve algebraically in time with perturbation amplitudes proportional to t². Long wavelength modes are fully nonlinear, and the amplitude grows linearly in time.

On the transport noise of hydrophobic ions in lipid bilayer membranes.

Abstract The effect of transit time on the electrical transport noise of a closed one-barrier model at equilibrium as proposed by Kolb and Lauger [6] is studied using the master-equation approach. A transit time is the time for an ion to cross the energy barrier (membrane interior) when the energy of the ion reaches the barrier height. Both the time correlation function and the noise power spectrum are obtained as functions of the transit time of the ions. Possible effects of transit time on the time correlation function of transport of dipicrylamine ions in lipid bilayers as reported by Bruner and Hall [13] and on the noise power spectrum as reported by Kolb and Lauger [6] are discussed.

Electro-acoustic current fluctuations in CdS

Experimental data on electro-acoustic current fluctuations, in the frequency range 500 kHz to 100 MHz, are presented for semiconducting and photoconducting CdS single crystals. The measurements were carried out under pulsed-bias conditions to avoid excessive Joule heating of the samples. The experimental results are discussed in terms of our previously published theory. The latter is based on a model where bunches of conduction electrons can be trapped and detrapped in potential troughs associated with acoustic waves which are amplified from the thermal background. The experimental current-noise spectra showed local minima which can be related to the potential-trough transit-time. These transit-time effects are not described by the theory, because it did not take space-charge into account. Apart from these effects, however, in most cases the current-noise data for both semiconducting and photoconducting samples can be described by one or two Lorentzian spectra, in accordance with the theory. In some cases, however, deviating spectra showing minima and maxima which could not be related to potential-trough transit-times were observed. Values for the electron drift-mobility obtained from voltages marking the onset of electro-acoustic current fluctuations lie well within the range of the values published by others.

Transit-time effects on noise in planar crossed-field electron guns

A theory is developed for the noise in an unbounded parallel-plate crossed-field diode. The high-frequency regime is studied, where transit-time effects must be included. The diode is assumed to be operating in the space-charge-limited regime. Maxwell's equations and the Vlasov equation are expanded to first order. A key consideration in this expansion is the fluctuation in the boundaries of velocity space appearing in the integrals for the charge and current density. The first-order terms describe the linear response of the electric field and transmitted current resulting from the injection of a small additional cathode emission composed of electrons of a specified velocity. Using a statistical approach, these perturbations are combined to determine the noise factor. The special case of a parabolic average-potential distribution in space is considered.

Effect of formant transition time on the perception of the voiced stop consonants.

Effect of formant transition time on the perception of the voiced stop consonants.

Intercarrier Buss Phenomena Analysis and Cures

This partly tutorial paper defines buzz as the result of video related incidental phase modulation (IPM) of the intercarrier. The main sources of IPM are 1. parametric and transit time effects, both non-linear in character and 2. AM to PM conversion of a strictly linear character. 1. is the main source of transmitter visual IPM but can also take place in the receiver. Linear AM to PM is prominent in the receiver as Nyquist IPM.

The Argonne tandem as injector to a superconducting linac

The Argonne tandem uses pelletron chains, NEC accelerator tubes, and a dual closed-corona system. Its main function is to be an injector for a superconducting linear accelerator. As long as the transverse and longitudinal emittances are within the acceptance of the linac, the output beam quality of the tandem-linac system is essentially determined by the tandem. The sensitivity of the linac to the longitudinal emittance ΔEΔt of the incident beam makes the output beam quality dependent on the negative-ion velocity distribution in the source, transit-time effects in the tandem, molecular-beam dissociation, and stripper-foil uniformity. In this paper we discuss these beam-degrading effects.