Modern Dielectric Materials for Output Windows of High-Power Microwave and Terahertz Sources
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Modern Dielectric Materials for Output Windows of High-Power Microwave and Terahertz Sources E. A. Serov 1
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& V. V. Parshin & K. V. Vlasova & A. I. Makarov
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Received: 10 June 2020 / Accepted: 8 September 2020/ # Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract
Analysis of dielectric properties of several materials, BN, AlN with BN additive, crystalline quartz, MgAl2O4 spinel, 6H-SiC in the millimeter and submillimeter (terahertz) ranges, is presented. Basing on the experimentally measured dielectric losses of these materials and on their thermal and mechanical properties, we made a calculation to estimate the maximal achievable output power that can be transmitted through disks made of such materials. Prospects for using these materials for gyrotron barrier window production are discussed. Keywords Dielectric losses . Gyrotron window . Millimeter and submillimeter waves . Thermal calculations . High power transmission
1 Introduction For achieving the optimal characteristics of a high-power microwave or terahertz vacuum source, e.g., gyrotron, it is necessary to choose a suitable material for a barrier window. The balance of relatively low dielectric losses having weak temperature dependence and relatively high thermal conductivity is required for effective heat removal. Different materials were considered to be used for these purposes: boron nitride (BN), aluminum nitride (AlN), αsapphire, quartz, silica glass, and silicon [1]. However, up to the end of the 1990s, the researchers have found that CVD diamond is the best material for the barrier windows because of its unique properties [2, 3]. It has very high thermal conductivity up to 2000 W/m∙K and ultra-low dielectric losses. Modern samples of CVD diamond may have tanδ value in the millimeter (MM) and submillimeter (SubMM) ranges of about 10−5 and even lower [4]. Nevertheless, a wide use of CVD diamond windows is limited by their high price. Therefore, CVD diamond windows are actually used only for megawatt power level sources, e.g., for the
* E. A. Serov [email protected]
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Institute of Applied Physics, Russian Academy of Sciences, 46 Ul’yanov St., Nizhny Novgorod, Russia 603950
Journal of Infrared, Millimeter, and Terahertz Waves
ITER project [5, 6]. Technological gyrotrons which can provide power of about several or tens of kilowatts in continuous wave operation are usually equipped with BN windows. The problem is the absence of relatively inexpensive material suitable for output windows of gyrotrons with ~ 50–500-kW power. In the previous paper [7], we considered the possible use of 6H-SiC for highpower gyrotrons in microwave and terahertz ranges. This study is devoted to the estimation of maximal output power which can be transmitted through the barrier windows made of different modern dielectric materials, including re-analysis of such estimations for 6H-SiC, taking into account recently measured temperature dependence of its thermal conductivity [8]. Calculations are based on experimentally measured dielectric pro
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