长脉冲相对论速调管放大器的初步实验研究

 介绍了L波段长脉冲相对论速调管放大器(RKA)的强流相对论电子束(IREB)的调制及微波提取等方面的实验研究。重点分析了束流经过中间腔间隙调制后束流脉冲缩短和输出微波脉冲缩短问题，经过对注入微波、中间腔和输出腔等参数的调节，得到了比较强的基波调制电流和微波辐射。采用446kV/3.0kA/1.4μs的空心电子束，经过四腔放大后，得到381MW/200ns的辐射微波，束波转换效率28%，增益34dB。     

长脉冲相对论速调管中束流脉冲缩短的研究

介绍L波段长脉冲相对论速调管放大器研究中，长脉冲强流相对论电子束(IREB)经过输入腔和中间腔间隙后的脉冲缩短问题.分析了造成束流脉冲缩短的主要机理之一是高频系统的角向非均匀模式与电子束相互作用而使得束流扩散形成的，并经过实验参数的调节，减轻了长脉冲IREB的脉冲缩短问题，得到了较强的基波调制电流.从长脉冲加速器引出500 kV，3.5 kA，1.3 μs的电子束，经过输入腔和两个群聚腔的调制后，得到了2.0 kA的基波调制电流，束流脉冲宽度由0.3 μs增加到1 μs，束流脉冲缩短问题得到明显减轻. 关键词： 相对论速调管放大器 脉冲缩短 高功率微波 长脉冲强流相对论电子束     

L波段相对论速调管输入腔研究

 介绍L波段强流相对论速调管放大器输入腔的数值分析、新型的结构设计和实验调试及其应用等方面的情况, 对输入腔进行了特别的结构设计, 解决了大耦合孔对谐振腔参数的不良影响, 设计符合RKA应用的要求。均匀电子束经过输入腔后, 得到了约6％的最大基波调制电流深度。     

X波段同轴多注相对论速调管放大器的初步实验研究

为了提高相对论速调管放大器的工作频率和输出功率,结合三重轴相对论速调管和多注速调管的特点,设计了工作在X波段的同轴强流多注相对论速调管放大器,对强流多注电子束在多注器件结构中的传输、电子束经过输入腔和中间腔后的基波调制以及经过输出腔的微波提取过程进行了实验研究,得到了初步的实验结果.在输入微波功率30 kW,频率9.375 GHz,电子束电压670kV,束流5.3 kA,轴向引导磁感应强度0.8 T的条件下,得到了最大输出微波功率为420 MW,效率为12%,增益为41 dB,输出微波频率与输入微波一致.实验证实了采用同轴强流多注相对论速调管放大器实现X波段高功率微波放大的可行性,为后续更高功率研究打下了基础.     

相对论速调管三轴提取腔的分析与设计

分析了同轴漂移管中电子束的空间电荷限制流和能量分布，为了降低S波段相对论速调管放大器(RKA)中电子束空间电荷效应及势能，提高RKA的束波转换效率，提出了三轴结构的输出腔，理论分析RKA的束波转换效率达到36%，比同轴提取腔的束波转换效率提高了9个百分点. 采用数值计算程序设计了三轴提取腔，粒子模拟了S波段RKA的微波提取，取得了与理论分析一致的结果. 采用590kV/5kA的空心电子束，经过预调制腔和群聚腔等两个腔的调制后，采用三轴提取腔提取微波，得到了约1.0GW的微波功率，效率35%. 理论研究结果与实验结果吻合得较好. 关键词： 相对论速调管放大器 三轴提取腔 空间电荷限制流     

感性加载宽间隙腔相对论速调管的粒子模拟

 通过粒子模拟的方法研究了三腔结构的感性加载宽间隙腔相对论速调管放大器,分析了宽间隙腔中垫圈/杆等参数对于束流调制的影响。模拟结果表明:感性加载的宽间隙腔能够克服宽腔所带来的势垒效应,增加电子束与腔的作用时间,提高束流调制和能量提取的效率。模拟中采用500 keV,6 kA的电子束,经过两腔调制得到了约4.5 kA的调制电流,调制深度接近80%;采用渐变结构的输出腔,得到功率约1.2 GW,频率2.86 GHz,效率为40%的输出微波。     

X波段高功率相对论速调管放大器研究

为进一步提高X波段相对论速调管放大器的输出功率,采用理论分析与粒子模拟的方法对双群聚腔级联式相对论速调管放大器进行了研究。分析了提高注入腔对注入微波吸收效率的方法,分析了群聚腔调制能力与腔体模式、Q值等参数的关系,分析了输出腔提取效率与Q值的关系。在三维粒子仿真中,设计了模式反射器抑制TEM模式泄露与杂模振荡,得到了功率超过2.5 GW,频谱纯净,频率锁定为8.40 GHz,输出输入微波相位差稳定,抖动不超过2°的高功率微波输出。     

相对论速调管放大器一维非线性理论的数值分析

给出了相对论速调管放大器中归一化调制电流和电子束动能的积分微分方程,基于MATLAB平台编程并采用递推法、中心差分法、梯形积分法等数值计算方法计算了归一化束电流和电子束动能随归一化距离的关系,以及反映电荷守恒的归一化因子。最后计算了调制电流的n次谐波的模式强度随归一化距离的变化。     

S波段速调管双间隙输出腔的设计和实验研究

 介绍了S波段强流相对论速调管放大器(RKA)双间隙输出腔高频系统的设计,并利用3维粒子模拟程序模拟和优化了短脉冲强流相对论调制电子束经过双间隙输出腔后的微波提取。在束压640 kV、束流6 kA、基波调制深度80%的条件下,模拟得到功率为1.1 GW的微波,频率约为2.85 GHz,效率28%。在高频分析和粒子模拟的基础上进行了实验研究,实验中采用束压640 kV、束流6 kA的环行电子束,经过优化调节RKA参数,在中间腔后得到了约4.6 kA的基波调制电流,加上双间隙提取腔后从该RKA获得了频率为2.9 GHz、功率为1 GW、脉宽22 ns的输出微波,束波转换效率26%。     

双间隙输出腔开放腔的高频特性分析

 建立了S波段相对论速调管放大器双间隙输出腔开放腔的3维模型。采用时域有限差分法，通过监测激励电流源的响应计算了该双间隙输出腔的谐振频率、有载Q值、场分布以及特性阻抗，并分析了腔体结构尺寸对谐振频率、有载Q值和特性阻抗的影响。研究表明：腔体半径对开放腔的谐振频率影响很大，耦合孔尺寸对腔体谐振频率的影响较小；随着耦合孔张角增加，有载Q值逐渐减小；随着腔体半径增大、间隙的减小，腔体特性阻抗降低。研究结果可为S波段强流相对论速调管放大器双间隙输出腔的设计提供理论依据。     

An empirical model for the equivalent translational compliance of steel studs

The effect of the resilience of the steel studs on the sound insulation of steel stud cavity walls can be modeled as an equivalent translational compliance in simple models for predicting the sound insulation of walls. Recent numerical calculations have shown that this equivalent translational compliance varies with frequency. This paper determines the values of the equivalent translational compliance of steel studs which make a simple sound insulation theory agree best with experimental sound insulation data for 126 steel stud cavity walls with gypsum plaster board on each side of the steel studs and sound absorbing material in the wall cavity. These values are approximately constant as a function of frequency up to 400 Hz. Above 400 Hz they decrease approximately as a non-integer power of the frequency. The equivalent translational compliance also depends on the mass per unit surface area of the cladding on each side of the steel studs and on the width of the steel studs. Above 400 Hz, this compliance also depends on the stud spacing. The best fit approximation is used with a simple sound insulation prediction model to predict the sound insulation of steel stud cavity walls whose sound insulation has been determined experimentally.     

Theoretical investigation of an electron beam propagating through a wide gap cavity

This paper presents a self-consistent nonlinear theory of the current and energy modulations when an electron beam propagates through an inductively-loaded wide gap cavity. The integro-differential equations axe obtained to describe the modulation of the beam current and kinetic energy. A relativistic klystron amplifier （RKA） model is introduced, which uses an inductively-loaded wide gap cavity as an input cavity. And a numerical code is developed for the extended model based on the equations, from which some relations about the modulated current and modulated energy are numerically given.     

速调管输入腔开放腔的高频特性分析与实验研究

 建立了带输入波导结构的S波段速调管放大器输入腔开放腔模型,利用3维软件对其高频特性进行了数值计算研究,并对输入腔结构进行了优化设计。利用已加工的输入腔进行了高频参数的冷测实验研究,实验中的输入腔结构尺寸与高频分析中的完全相同,实验结果与高频分析结果一致。用3维PIC程序对电子束经过该输入腔后的束流调制以及注入微波的吸收情况进行了模拟。模拟结果表明：该输入腔与微波注入波导匹配很好,注入微波能被电子束和谐振腔全部吸收,在输入腔间隙后37 cm处得到了13%的基波电流调制深度。     

Conceptual Design Study of a Novel Gyrotron for NMR/DNP Spectroscopy

In this paper we present some initial results from a conceptual design study focused on the development of a novel frequency tunable gyrotron for nuclear magnetic resonance (NMR) spectroscopy with signal enhancement based on the utilization of high field radiation and dynamic nuclear polarization (DNP) technique. The first variants of both the electron optical system and the resonant cavity which have been designed aiming continuous frequency tunability in a broad frequency band are presented and discussed. The selected method for frequency tunability is based on the excitation of higher order axial modes and smooth transition between them. It was selected after a critical examination of the known theoretical and practical results related to the frequency control in gyrotrons. It is believed that the current conceptual design is an appropriate basis for development of the next (optimized) design which will include also a detailed design of other components (mode converter, output window etc.) and magnetic circuit (superconducting magnet and supplementary solenoids) as well as for the overall mechanical design and fabrication of the prospective gyrotron.     

S波段相对论速调管放大器输入腔的3维分析与模拟

 利用3维软件设计了适用于S波段相对论速调管放大器的单重入输入腔,该腔体采用了偏心设计,以便减小耦合孔处的不均匀场对腔间隙场的影响,分析了腔体耦合孔尺寸对腔间隙场均匀性的影响;建立了带输入波导结构的3维输入腔开放腔模型,并应用此模型,采用3维PIC程序模拟了注入微波功率、束直流对输入腔间隙后束流调制的影响。研究结果表明：耦合孔尺寸对腔间隙电场均匀性影响较大,当耦合孔离轴越近时,腔间隙场越不均匀;在结构参数和束参数固定的条件下,基波电流调制深度随着间隙电压的增加而增加,但达到最大基波调制电流的漂移距离几乎不变;在结构参数和注入微波参数固定的条件下,束直流越大,达到最大基波调制电流所需的漂移距离越短。研究结果为腔体的设计和输入腔束流调制实验提供了参考依据。     

Grating-based wavelength control of single- and two-color vertical-external-cavity-surface-emitting lasers

Wide wavelength tunability of single- and two-color operating vertical-external-cavity-surface-emitting lasers (VECSELs) is demonstrated. Employing an external feedback based on a diffractive grating outside the cavity of a narrow-line single-color VECSEL allows for a continuous tuning of the emission wavelength over 10 nm. Employing a dual-feedback-configuration for tunable two-color emission, a tunability of the difference frequency between the two lasing wavelengths from 300 gigahertz to up to 3.5 terahertz is demonstrated.     

相对论强流长脉冲速调管放大器

 为了研制高功率长脉冲速调管放大器,对其输入腔进行了3维粒子模拟研究。建立了S波段速调管放大器输入腔开放腔的3维模型,计算了开放腔的谐振频率和有载Q值。将束压束流从原来的600 kV,5.4 kA提高到837 kV,12.48 kA,实现了长脉冲100 ns的稳定运行,调制束流与实验结果一致。在结构不变的情况下,将束压束流提高到900 kV,16 kA时出现了模式竞争,只能稳定运行到50 ns。为了克服模式竞争,将耦合孔改为对称的双耦合孔后,输入腔系统可以稳定运行到100 ns。     

二维异质结光子晶体中含近邻点缺陷的弯曲波导的可调谐滤波特性

应用时域有限差分(FDTD)法,对光在二维异质结光子晶体中含两个近邻点缺陷直角弯曲波导的传输特性进行了数值模拟研究。计算结果表明,具有特定本征共振频率的光子晶体微腔(点缺陷),可将在其邻近波导中传播的相同频率成分的光波"引入"到微腔中。"引入"的频率依赖于异质结光子晶体弯曲波导和微腔的参量,从而能够实现调变"引入"频率。通过改变点缺陷周围介质材料(液晶)的折射率或相关介质柱半径,可分别实现约31 nm或12 nm的波长调谐范围。计算结果为光通信中的调谐、上/下载滤波器,提供了一条新的设计思路和依据。     

Study of inspection on metal sheet with subsurface defects using linear frequency modulated ultrasound excitation thermal-wave imaging (LFM-UTWI)

The linear frequency modulated ultrasound excitation thermal wave imaging (LFM-UTWI) was investigated on detection of subsurface defects of metal sheet. A numerical finite element analysis is carried out to calculate thermal wave signal dependence of time by linear frequency modulated ultrasonic wave excitation. Cross-correlation operation in time domain and frequency domain are used to extract the main peak value and the corresponding delay time, respectively. Fourier transform (FT) is applied to calculate the amplitude and phase angle of harmonic component of thermal wave. Experimental results show that various deep subsurface defects are readily detected using LFM-UTWI with once excitation, and LFM-UTWI has an advantage of better defect detectability compared to ultrasound lock-in thermography (ULIT).