Measurement Of Electron Drift Velocity Research Articles

A simple method for measuring electron drift velocity in gases using grid ionization chamber

A simple method for measuring the electron drift velocity in gases with a given electric field using a grid ionization chamber is proposed and demonstrated. By collimating incident α particles that are perpendicular to the electric field, the drift velocity can be derived easily using the electron drift distance from primary ionization to a grid divided by the time interval between the cathode and anode signal starting times. These experimental settings can avoid additional signal processing of signals and reduce the effect of electron diffusion. Using this method, the measurement of electron drift velocities in 90% Ar + 10% CO2 is presented. Measured results agree well with the simulated values and with existing experimental results.

Commissioning and Calibration of the ALICE TPC

ALICE (A Large Ion Collider Experiment) is the dedicated heavy ion experiment at the Large Hadron Collider at CERN. The main tracking device of ALICE is a large volume TPC. The milestones of the TPC commissioning as well as the current status of the detector calibration are presented. The obtained resolutions in transverse momentum, position as well as in specific energy loss (dE/dx) are presented and results from noise and electron drift velocity measurements are addressed.

Investigation of the E × B rotation of electrons and related plasma characteristics in a radio frequency magnetron sputtering discharge

Electron drift velocity caused by E × B motion is measured with the help of a Mach probe in a rf planar magnetron sputtering discharge at different powers of 25, 50 and 75 W. Radial variation of the drift velocity is observed at all the powers with the maximum velocity in the racetrack region. The electron temperature and ion density are also found to exhibit radial variation. The drift velocity in the near target region is found to have a higher value than the sheath edge. The sheath structure measured with the help of an emissive probe exhibits radial variation with the strongest electric field in the racetrack region. The maximum extension of the sheath is approximately 2.5 cm from the target. The results of electron drift velocity measurements are explained in terms of the measured variation of the magnetic field and cathode sheath structure. Quite good agreement is observed between the drift velocities measured from Mach probe characteristics and sheath characteristics.

Measurements of electron drift velocity in OCS

Measurements of drift velocity for electrons in carbonyl sulfide (OCS) in the range of reduced electric field 2 ÷ 100 Td are presented and compared with those in CO2 and N2O. The OCS data fall-in between these two gases, but their interpretation will require detailed numerical modeling using available electron-scattering cross sections.

Measurements of drift velocity in the ATLAS RPC gas mixture

We present here some results on measurements of electron drift velocity as a function of the electric field in a single gap, avalanche operated, small size (10 × 20 cm 2 ) RPC filled with a ternary gas mixture (94.3 % C 2 H 2 F 4 , 5 % C 4 H 10 , 0.3 % SF 6 ). A pulsed nitrogen laser is focused (∼ 20 μ m spot size at the focus) inside the gas gap to generate primary ionization via double photon ionization process. Results are presented and discussed.

Electron drift velocities in mixtures of helium and xenon and experimental verification of corrections to Blanc’s law

Measurements of electron drift velocities were performed in pure Xe and He and in a number of mixtures ranging up to 70% of Xe. The data were obtained by using a pulsed Townsend technique over the density-normalized electric field strength E/N between 1 and 100 Td . Even for pure gases there are no data in the entire range covered here, and these data represent an extension of accurate drift velocities to higher E/N. A selection of well-established cross sections for low energies, which was extended to higher energies, led to a reasonably good agreement of the calculated transport coefficients with the available data. At the same time we have applied the standard (common E/N) Blanc's law and two forms of common mean energy (CME, due to Chiflykian) procedures. Blanc's law fails for most mixtures at low and moderate E/N, while the CME procedure is capable of following the experimental data for the mixtures much more closely, and even predicting the negative differential conductivity region when such effect does not exist for pure gases. Thus the present paper also represents an experimental test of procedures to correct the standard Blanc's law. Finally, we have used the data for two mixtures to obtain results for the third mixture and in all cases this procedure gave excellent results even though only the standard Blanc's law was used in the process.

Measurement of Electron Drift Velocities in the Mixture of Xe and He for a New High-Pressure Xe Gamma-Ray Detector

Drift velocities of electrons in a mixture of Xe (20 atm)–He (3 atm) were measured using a cylindrical high-pressure xenon chamber. The drift velocities were found to be greater than 3 ×105 cm/s above the reduced electric field of 2.0 ×10-18 V·cm2 at room temperature, which are close to those in Xe–H2 (0.3%). The mixture of He gas into high-pressure xenon improved the resolving time of detectors because it increased the electron drift velocities. This implies that a high-pressure xenon chamber mixed with 3He instead of He gas operates as a gamma-ray detector sensitive to thermal neutrons.

Electron Interactions With BCl3

In this paper we review and assess the cross sections for collisions of low-energy electrons with boron trichloride (BCl3). The only available experimental cross section data are for partial and total ionization and electron attachment, and the electron attachment cross sections are uncertain. Calculated values are available for the total elastic, differential elastic, and momentum transfer cross sections, and derived cross sections have been published for vibrational excitation and dissociation. Other than some rather uncertain data on electron attachment rate constants and some measurements of electron drift velocities in BCl3/Ar and BCl3/He mixtures, there are no measurements of the electron attachment, ionization, or transport coefficients for this gas. Analysis of the experimental data on the electron affinity, electron attachment, and electron scattering, enabled identification of negative ion states of BCl3 at about −0.3, 1.0, 2.8, 5.2, 7.6, and 9.0 eV. Because the existing electron collision data are few and uncertain, relevant data are provided for photon impact on BCl3..

Electron drift velocity measurements at high electric fields

A method to measure the electron drift velocity is presented. A pulsed UV nitrogen laser is used to excite both the drift and cathode nickel micromeshes of a Micromegas detector. The signals induced on the anode are then readout by a fast current amplifier. Several results have been obtained for various gas mixtures and electric fields from 10 V/ cm to 14 kV/ cm . Relevant applications with low (TPCs mode) and high (pre-amplification mode) electric fields will be discussed.

Consistent measurements comparing the drift features of noble gas mixtures

We present a consistent set of measurements of electron drift velocities and Lorentz deflection angles for all noble gases with methane and ethane as quenchers in magnetic fields up to 0.8 T. Empirical descriptions are also presented. Details on the World Wide Web allow for guided design and optimization of future detectors.

Operation of microstrip gas counters with DME-based gas mixtures

This paper reports on the operation of MicroStrip Gas Counters (MSGC) with several dimethylether (DME)-based gas mixtures. We present measurements of signal amplitude, detection efficiency and spatial resolution for minimum ionizing particles. We also show measurements of electron drift velocity and transverse diffusion coefficient in the counting gases considered. These results are discussed regarding the use of MSGC’s for tracking at high-energy physics experiments that have to deal with high particle rates.

A New Method for Electron Drift Velocity Measurement Using Frequency Response Analysis

A simple method for the measurement of electron drift velocity in gases under electric fields is presented. In this method, sinusoidally modulated electron current through the drift space is measured with a lock-in amplifier in place of using two shutters. The phase delay of the electron current referred to the electron release rate from the cathode gives an accurate mean transit time of electrons through the drift distance between the cathode and anode. The results of preliminary measurements of the electron drift velocity in argon are in good agreement with formerly reported data. In spite of simple procedures, this method will be useful for accurate measurements of electron drift velocity in various gases over wide ranges of the reduced electric field.

Measurement of electron drift velocities and Lorentz angles in fast gas mixtures

Electron drift velocities and Lorentz angles have been measured in various fast gas mixtures: ArCH 4, ArC 2H 6, CO 2CF 4, ARCO 2CF 4, and also in pure CH 4, C 2H 6, CF 4, and CO 2. The measurements were carried out in crossed magnetic and electric fields using a new experimental method based on the detection of α-decay recoils in coincidence with α-particles. The magnitude of the B and E fields could be varied up to B = 1.4T and E = 6.5 kV/cm. The precision in the absolute measurements of the drift velocities was about 1%, and the Lorentz angles were measured with an accuracy of about 0.5°.

Measurements of electron drift velocities and positive ion mobilities for gases containing CF 4 II

Measurements of electron drift velocities and positive ion mobilities for gases containing CF 4 have been made. Our previous paper described the results on electron drift velocities for gas mixtures containing CF 4 and hydrocarbon, and ion mobility results for gas mixtures of CF 4 + hydrocarbon, Ar + C 2H 6 and Ar + C 3H 8. The present paper is the second and final paper of the series. It describes the results on electron drift velocities for the gas mixtures; Ar + CF 4 + hydrocarbon, where hydrocarbon is CH 4 or C 2H 6 or C 3H 8 or iso-C 4H 10. The fraction of each gas component was changed systematically for each set of gas mixtures, and the electron drift velocity was measured as a function of the applied drift field between 0.2 and 2.5 kV/cm. Indications were found for relatively large electron drift velocities, even for low electric fields, with better saturation properties than was the case for the gas mixtures of CF 4 + hydrocarbon previously measured. Positive ion mobility was measured for several kinds of gas mixtures; Ar + hydrocarbon, CF 4 + hydrocarbon and Ar + CF 4 + hydrocarbon. Since ion currents and their arrival times were actually measured, the word “positive ion” does not necessarily mean a specific kind of ions but rather a group of ion clusters. The positive ion mobilities were deduced from this measurement under the assumption that Blanc's law was valid. A consistent picture was obtained within this approximation.

High-field electron drift in a-Si:H

Recent high-field measurements of electron drift velocities in hydrogenated amorphous silicon (a-Si:H) are surveyed. The electron drift-mobility depends essentially exponentially upon electric field above 90 K; the characteristic field E 0 of the nonlinearity increases approximately linearly with temperature. Models for these high-field measurements are discussed.

A Study of the Vibrational Excitation of H2 by Measurements of the Drift Velocity of Electrons in H2−Ne Mixtures

Measurements of electron drift velocities have been made in 1�160% and 2�892% hydrogen-neon mixtures at 294 K and values of EI N from 0�12 to 1�7 Td. The measurements are highly sensitive to the region of the threshold of the v = 0 → 1 vibrational excitation cross section for hydrogen and have enabled more definitive tests of proposed cross sections to be made than was possible using drift velocity data for H2−He and H2−Ar mixtures. The theoretical v = 0 → 1 vibrational excitation cross section of Morrison et al. (1987) is shown to be incompatible with the present measurements. A new set of hydrogen cross sections has been derived from the available electron swarm measurements in pure hydrogen and hydrogen mixtures.

Momentum Transfer Cross Section for Electrons in Krypton Derived from Measurements of the Drift Velocity in H2?Kr Mixtures

Measurements of electron drift velocities have been made in 0�4673% and 1�686% hydrogenkrypton mixtures at 293 K and values of E/ N from 0�08 to 2�5 Td with an estimated uncertainty of <�0�7%. The data have been used in conjunction with the H2 cross sections of England et aL (1988) to derive the momentum transfer cross section for krypton over the energy range 0�05 to 6�0 eV. The drift velocity data have also been used to test the Kr momentum transfer cross sections of Koizumi et aL (1986) and Hunter (personal communication 1988). The cross section of Koizumi et aL is clearly incompatible with the present measurements while the cross section of Hunter has been used to predict these measurements to within 1% to 3%.

A Swarm Experiment in He–H2 Mixtures to Examine Vibrational Excitation of H2 by Electron Impact

Measurements of electron drift velocities have been made in pure helium and in a helium-hydrogen mixture in order to check the available inelastic cross sections for hydrogen. Although drift velocities in mixtures with helium as the buffer gas are less,sensitive to inelastic scattering by hydrogen than those with argon, the accuracy with which the momentum transfer cross section for helium is known enables the check to be made with virtually no error arising from uncertainty in the momentum transfer cross section for the buffer gas, in contrast to the situation when argon is used. A difference techrtique has been used to minimise the effect of systematic errors in the measurements. The results support the rotational and vibrational cross sections derived from the transport coefficients measured in pure hydrogen.

The Influence of the Cell Geometry on the Signal Shape in Electron Drift Velocity Measurements

An accurate determination of the “time-of-flight” in swarm experiments with a parallel plate drift chamber requires that the time evolution of the charge induced on the collector is linear. This is obtained in very large chambers where the edge effects can be neglected. However, the experimental conditions of high-mobility carriers and highly pressurized gases impose some constraints on the acceptable drift cell dimensions. We have numerically calculated the effects of the finite size of the collector by exploiting the methods of the images. The numerical results have been experimentally checked using a suitable drift cell of variable geometry. As a result, a quantitative limit on the ratio between the collector radius and the drift distance has been established in order to design drift cells for which the edge effects can be neglected. P.A.C.S. numbers: 2940. 4110 D, 3480 B

Self‐consistent analysis of electron drift velocity measurements with the STARE/SABRE System

Recent work with the STARE (Scandinavian Twin Auroral Radar Experiment) and SABRE (Sweden and Britain Radar Experiment) data sets has shown some inconsistency with existing theories (fluid and kinetic theory) of radar aurora. A new technique, which we call the superimposed grid point method, has proven to be a very valuable tool in the study of this inconsistency. This technique can be used under conditions where the electron drift velocity is approximately constant over an entire STARE (or SABRE) latitude interval and consists of superimposing all of the observed radial Doppler velocity components for the entire latitude interval together into one grid point. This yields, for a given electron drift velocity, a set of Doppler velocity vectors for typically more than 30 different flow angles. Thus this technique allows the study of the angular variation of the Doppler velocities observed with the radars, for a given electron drift velocity. One of the main results of using this technique has been strong evidence that very often the radar Doppler velocities are limited to near the ion acoustic velocity in a manner very similar to the equatorial electrojet. Doppler velocities at flow angles greater than some critical flow angle appear to follow a cosine law, as is usually assumed in the fluid and kinetic theory, while velocities at flow angles less than this critical flow angle seem to deviate greatly from the cosine law and are often limited to the ion acoustic velocity. We have reinterpreted the radar Doppler velocity measurements in the ion acoustic approach (Nielsen and Schlegel, 1985) and find consistency between the results of the superimposed grid point analysis and this new approach.