Effects of nonlocality on the dynamics of streamers in positive corona discharges

Computer simulation is used to study the effect on the parameters of the streamer plasma due to the nonlocality of the electron energy distribution near the head of a streamer in air. Taking into account the nonlocality increases the electron field strength in the head and the electron density in the channel. The streamer radius decreases, while the streamer velocity and current as well as the efficiency of generating chemically active particles remain essentially the same as in the local approach. Pis’ma Zh. Tekh. Fiz. 23, 89–94 (June 26, 1997)     

Performance of uranium liquid argon calorimeters

We present results on the performance of a uranium liquid argon calorimeter exposed to electrons, pions and muons up to 150 GeV energy.     

Detection of Cherenkov light emission in liquid argon

Detection of Cherenkov light emission in liquid argon has been obtained with an ICARUS prototype, during a dedicated test run at the Gran Sasso Laboratory external facility. Ionizing tracks from cosmic ray muons crossing the detector active volume have been collected in coincidence with visible light signals from a photo-multiplier (PMT) immersed in liquid argon. A 3D reconstruction of the tracks has been performed exploiting the ICARUS imaging capability. The angular distributions of the tracks triggered by the PMT signals show an evident directionality. By means of a detailed Monte Carlo simulation we show that the geometrical characteristics of the events are compatible with the hypothesis of Cherenkov light emission as the main source of the PMT signals.     

液氩泵机械故障分析

详细介绍液氩泵解体检查的情况,分析液氩泵转子铜质双头螺柱断裂和铜压块磨损的原因,最后阐述了液氩泵的操作经验。     

进粗氩塔Ⅰ顶部的粗液氩波动对氩馏分的影响

由于液位计负压管堵塞 ,造成自动控制系统出错 ,改用手动调节液氩进粗氩塔Ⅰ的阀调整液氩回流量 ,使工况正常     

减少液氩中含氮量的几点做法

本文以循序渐进的方法分析了一起因装置操作弹性小造成产品液氩中氮含量超标的原因 ,并简要介绍了操作中尽可能的减少液氩中氮含量的思路及方法     

Electron multiplication in liquid argon on a tip array

We have carried out a systematic study of the electron multiplication in liquid argon on an array of 52 sharp tips. We found a multiplication factor for a single tip of at least 100 and a plateau region in the counting-rate vs tip-voltage curve of about 150 V.

The results make us hopeful in exploiting such mechanism for a new kind of detectors.     

The calculation of the thermodynamic properties of liquid argon

Analysis and correlation of experimental p, v, and T data for liquid argon, limited to a pressure of 300 bar, and their extrapolation to pressures of 500 bar, yields a reference network of isotherms and isobars correlated to the saturation and freezing curves. An equation of state is derived to describe with sufficient accuracy the experimental and reference data in the temperature interval 83.78–170° K at pressures up to 500 bar. Results are presented for the comparison of the calculated quantitites with the experimental and tabular data on the thermodynamic properties of liquid argon.     

Monte Carlo investigations of aspects of liquid argon calorimeters

Using the EGS3 Monte Carlo program we have examined the response of liquid argon sampling calorimeters for different absorber materials. In particular, the response to electrons (compared to muons) has been studied as a function of the width of the argon gap. Effects due to cladding of absorber plates have also been investigated.     

液氩冷量回收技术

文章主要介绍液氩冷量回收装置的原理、流程及操作要点。将原来散失在大气中的冷量进行回收 ,用来液化氧气和液氩贮罐中保温不好而汽化的氩气 ,以增加液体产量 ,具有可观的经济效益。     

Fluctuation in energy-loss measurements in allene-doped liquid argon for heavy ions

Liquid argon (LAr) has suitable properties for use as a particle-detector medium, however, its response to heavy ions is not linear, because of the non-perfect collection of charge produced by the incident ions due to the strong recombination between the liberated electrons and argon ions. We were able to improve the linearity of the response by doping photoionization materials, such as allene (C₃H₄), to LAr. Using allene-doped LAr, we made some experiments of the heavy ion calorimeters for the mass identification of relativistic iron ions, but this approach was unsuccessful. We therefore investigated the cause of the failure using relativistic heavy ions of neon, argon and iron. The energy resolutions obtained experimentally were of the order of several percent at the full width at half maximum (FWHM) for neon to iron ions passing through a LAr gap of 10 mm. These values were 2 or 3 times worse than those predicted theoretically, and the poor energy resolution led to insufficient mass resolution. Here, we describe methods for measuring fluctuation in energy-loss signals in LAr, and discuss the factors determining the resolution.     

Investigating laser-induced ionization of purified liquid argon in a time projection chamber

A UV-wavelength laser beam was used to ionize a purified liquid argon medium in a time projection chamber environment, and for the first time, to our knowledge, ionization signals corresponding to ionization electrons were measured in the particle time projection chamber resulting in a laser calibration. Furthermore, the mechanism of the complicated ionization process has been postulated.     

A large liquid argon photon/hadron calorimeter for FNAL

This paper describes a new liguid argon photon/hadron detector currently under construction for Experiment E706 at the Fermi National Accelerator Laboratory.     

Performance of a large liquid argon shower detector used at Fermilab

Details of the construction and operation of a lead, liquid argon electromagnetic calorimeter used in Fermilab experiment E515 are presented. The system had an active projected area of 1.2×2.4 m². Its performance in low intensity electron beams and in exposure to intense, high multiplicity 200 GeV/c π^? Be interactions are described.     

A study of ionization electrons drifting large distances in liquid and solid argon

A two liter gridded ionization chamber was built and operated repeatedly to study electron transport in liquid and solid argon over distances up to 10 cm in drift fields of 0.01–2 kV/cm. A detailed analysis of the ionization pulse shape was performed, yielding information on both the degree of purity of the liquid and the electron drift velocity. Argon with an impurity concentration less than 0.2 ppb oxygen equivalent was obtained with a simple purification system. The measured attenuation length extrapolates to 7.5 m for liquid argon and to 1 m for solid argon at a drift field of 1 kV/cm.     

Modeling of the supersonic argon plasma jet at low gas pressure environment

Numerical simulation results are presented concerning the heat transfer and fluid flow within the supersonic argon plasma jet encountered in low pressure (or soft vacuum) plasma spraying (LPPS). The plasma parameters at the inlet section of the plasma jet are taken from our modeling results of the subsonic-to-supersonic d.c. arc plasma torch. The mach number, temperature and static pressure at the center of the plasma jet on the torch exit section are 2.8, 13 200 K and 6000 Pa, respectively, whereas the environment (i.e. vacuum chamber) pressure is 0.1 atm. Those parameters are typical for LPPS. The plasma jet is assumed to be axi-symmetrical and in local thermodynamic equilibrium state. The All-Speed SIMPLE algorithm is coupled with the FAST-2D program to simulate the whole plasma jet containing both the supersonic and subsonic flow regions. Modeling results clearly show that there exist several successive temperature, velocity and static wave crests and troughs. The fluctuation magnitudes of those parameters reduce rapidly in the flow direction, along with the flow transformation from the supersonic flow regime into the subsonic flow regime. The existence of a series of compression and expansion waves in the region near the torch nozzle exit shows clearly the over-expanded characteristics of the supersonic plasma flow.     

Time resolution of liquid argon detectors: Part I. Optimum filter

A simple dependence of the ultimate time resolution of a LAr detector on the transconductance of the FET, the capacitance of the detector, the ionization and purity of the argon is presented in this paper. For small capacitance of the detector (～ 100 pF) and for minimum ionization particles, the accuracy of time measurement is about ～ 10 ns.