This paper presents two-surface multipactor discharge with two-frequency rf fields using Monte Carlo simulations and Computer Simulation Technology (CST) Particle Studio. The effects of the relative strength and phase of the second carrier mode on multipactor susceptibility and time dependent physics are studied. Compared to single-frequency rf operation, shrinkage of multipactor susceptibility regions is observed for different configurations of two-frequency rf operation. The presence of a second carrier mode in the rf field results in mixed multipactor modes in which electrons take a fixed time period to complete a round trip between the two surfaces, while the time for electrons to traverse the gap in each direction is found to be different. CST simulation reveals that the space-charge effect reduces the electron growth rate and causes shrinkage of multipactor susceptibility bands.
Radon concentrations were measured in kucha, semikucha and pucka houses located on the sedimentary rocks of Early Pleistocene-Pliocene Soan Formation, Pleistocene Mirpur conglomerate and recent deposits. The radon concentration was measured using CN 85 nuclear tracks etch detectors in box type dosimeters installed in the bedrooms and kitchens of the houses. It was found to vary from 14 AE 7 Bqm À3 to 258 AE 28 Bqm À3 with an average of 105 AE 17 Bqm À3 . The average radon concentration in the kucha, semi-kucha and pucka houses was 78 AE 15 Bqm À3 , 108 AE 18 Bqm À3 and 108 AE 18 Bqm À3 respectively. The increase in radon concentration from kucha to pucka houses was attributed to the type of house, differing humidity related to the Mangla Dam, temperature, bed rock geology, structures (joints, fractures and faults), aggregates and uraniumbearing sand. This study shows that the average radon level is within the accepted safe health limit (200 Bqm
This work investigates secondary electron yield (SEY) mitigation from a metal surface with a microporous array fabricated using the laser drilling technique. We propose a general empirical model to fit the experimentally measured SEY of a flat gold surface for normal and oblique incidences of primary electrons. Using this empirical model, we develop a two-dimensional Monte Carlo (MC) simulation scheme to determine the effective SEY of a microporous array. It is found that the SEY from a porous surface is significantly reduced compared to that of the flat surface. By taking into account all the generations of secondary electrons inside a well, our MC results are found to be in very good agreement with the experimental data. The dependence of the SEY on the aspect ratio of the micropores and porosity of the surface is examined. A simple empirical formula has been proposed to evaluate the effective SEY of the gold microporous array for pores of arbitrary aspect ratios.
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