Abstract: The diamond disks for megawatt level gyrotron have been developed by microwave plasma chemical vapor deposition. Key parameters that affect the performance of diamond windows, such as compressive strength, thermal conductivity, coefficient of thermal expansion and dielectric loss tangent were characterized. The diamond disk with a diameter of 92 mm and a thickness of 1 mm can withstand a pressure of about 0.47 MPa. The thermal conductivity of diamond disk at room temperature reaches 20.1 W·cm⁻¹·℃⁻¹. The tanδ of 0.95 mm thick diamond disk is as low as 2.7×10⁻⁶. Finally, a low-microwave-loss diamond disk with a thickness of 1.8 mm was synthesized under optimized parameters and applied to a 140/105 GHz dual frequency gyrotron. A stable power output of 850 kW was achieved at 140 GHz with a window loss of approximately 0.11% and 760 kW was achieved at 105 GHz with loss of approximately 0.15%. The calculation results indicate that this 1.8mm diamond disk with tanδ=3.8×10⁻⁵ can be used for 1.5 MW long pulse gyrotron.

Key words: Microwave plasma chemical vapor deposition, Megawatt level microwave window, Diamond disk, Long pulse high-power gyrotron

摘要： 采用微波等离子体化学气相沉积对兆瓦级回旋管用金刚石微波窗片进行了研制。对影响金刚石窗口性能的耐压强度、热导率、热膨胀系数、介电损耗正切等关键参数进行了表征。实验结果表明，厚度 1 mm、通径 92 mm 的金刚石窗片可承受约 0.47 MPa 的压强；金刚石室温热导率达到 20.1 W·cm⁻¹·℃⁻¹；0.95 mm 厚金刚石窗片介电损耗正切低至 2.7×10⁻⁶。合成了 1.8 mm 厚低微波损耗金刚石窗片并应用于 140/105 GHz 双频回旋管中，在 140 GHz 频率下回旋管实现了 850 kW 的稳定功率输出，窗片损耗约 0.11%；在 105 GHz 频率下实现了 760 kW 的稳定功率输出，窗片损耗约 0.15%。实验数据计算结果表明，研制的 1.8 mm 厚、tanδ=3.8×10⁻⁵ 的金刚石窗片可满足 1.5 MW 长脉冲回旋管的应用需求。

关键词: MPCVD, 兆瓦级微波窗口, 金刚石窗片, 长脉冲大功率回旋管