Atomic ion frequency standards

The history and status of trapped-ion frequency standards are reviewed. In a trapped-ion frequency standard, the frequency of an oscillator is servoed to a resonance which corresponds to a transition between two energy levels of an atomic ion. The ions are suspended in space by a combination of electric and magnetic fields. In a conventional rubidium cell, the atoms are surrounded by a buffer gas having a pressure of about 10³ Pa (approximately 10 torr). In an ion trap, the ions are held either in a vacuum or in a low-pressure buffer gas (less than 10^-3 Pa). In an atomic beam, the atoms also move through a vacuum, without collisions. However, the time available for interaction with the electromagnetic field is limited to their flight time through the apparatus, usually about 10 ms or less. Trapped ions can be observed for much longer periods. Consequently clocks based on ions trapped in electromagnetic fields portend orders-of-magnitude improvement in the development of new frequency standards. Prospects for future standards are discussed     

X 波段无导引磁场Cerenkov 型振荡器的仿真研究

利用2.5 维粒子模拟软件Karat 对一种无导引磁场X 波段Cerenkov 型高功率微波振荡器开展了仿真研究,利用 冷腔色散曲线模型与Superfish 电磁场分布模拟软件选择了工作点,设计了基本模型。在基本模型的基础上进行仿真优化, 通过采用内外约束阴极环提高电子束质量,采用锥变型收集极优化器件Q 值、增加模转效率、纯化输出微波模式,优化 非均匀锥形慢波结构增强束波作用,最终使器件效率从17%优化到30%,输出功率达到1.8GW,输出微波模式为TEM 模,频率9.1GHz,对应二极管工作电压620kV、电流9.4kA.     

小回旋三次谐波0.52 THz回旋管

为了发展大功率高效率太赫兹辐射源,对小回旋电子注激励三次谐波太赫兹电子回旋脉塞进行了研究,分析了不同参数情况下的模式竞争.研究结果表明,采用近轴小回旋电子注能够实现三次谐波单模振荡.在此基础上设计了一只0.52 THz、TE37模三次谐波回旋管,数值计算表明,该回旋管在工作磁场为6.98 T下输出功率可以达到3.7 kW.对产生近轴小回旋电子注的高磁压缩比磁控注入式电子光学系统进行的粒子模拟研究结果表明,该电子枪能够产生满足实验要求的65 kV/2.5 A,横纵速度比为1.24,引导中心半径0.35 mm的小回旋电子注,其纵向速度离散6.6%,横向速度离散6.1%.     

A Kind of Magnetron Cavity used in Rubidium Atomic Frequency Standards Yang Shiyu(杨世宇), Cui Jingzhong(崔敬忠), Tu Jianhui(涂建辉), Liang Yaoting(梁耀廷)

研究了一种应用于铷原子频标的磁控管腔,其中包括磁控管腔的主要特征和参数计算,测试结果与计算理论吻合较好,所设计的磁控管腔能够满足铷原子频标的设计要求。     

3mm二次谐波回旋振荡管设计与数值模拟

二次谐波回旋振荡管的互作用磁场比基波回旋振荡管的磁场降低了一半,从而降低了设计难度,具有广阔的应用前景。通过对单腔结构的W波段二次谐波回旋振荡管高频结构、起振电流、模式竞争以及注波互作用研究,确定了W波段TE02模二次谐波回旋振荡管的基本工作参数,通过粒子模拟(PIC)软件进行计算,在电子注电压为60kV,注电流为6A及速度比为1.5时,获得了67.5kW的输出功率和超过18%的效率,且工作稳定。     

用于铷原子频标的磁控管腔研究

研究了一种应用于铷原子频标的磁控管腔，对用于磁控管腔的主要特征和参数计算进行了研究，主要包括磁控管腔的谐振频率、Q值、微波场模式。研究结果表明磁控管腔的谐振频率可以调谐至6.835GHz，Q值都能够调至600～1000之间，其微波场谐振模式是典型的TE011模式，频率温度系数较小（32.5KHz/℃－35.0 KHz/℃），所设计的磁控管腔能够满足铷原子钟物理部分的设计要求。     

A Microwave Frequency Standard Employing Optically Pumped Sodium Vapor

An instrument in which a simple microwave triode oscillator is stabilized by reference to a natural atomic resonance---the field-independent hyperfine resonance of sodium---is described. Light from a sodium lamp is transmitted through an absorption cell containing sodium vapor and argon, which is placed in a resonant cavity. This light produces population differences between the two quantum levels which are involved in the desired atomic resonance and provides a means of detecting resonance, The cavity is excited by an external microwave triode oscillator which is frequency modulated to a small degree at 60 cycles. When the exciting oscillator frequency coincides with the center of the atomic resonance line, the signal observed by a photocell will be a modulation of the transmitted light at 120 cycles and higher even-order harmonics. Any deviation from line center will introduce a 60-cycle component whose phase and magnitude may be detected to produce an error signal to retune the oscillator in the usual servo loop manner. Theory predicts that an accuracy of possibly one part in 10/sup 10/ can be achieved by systems using sodium and suitable local oscillators. It is evident also that such systems can be engineered into quite small packages, making possible many new applications of microwave oscillators stabilized to high order.     

Theory of resonant relativistic oscillator with nonuniform focusing field

The two-dimensional model of millimeter wave resonant O-type oscillator (as orotron, ledatron, resonant BWO, etc.) with a relativistic electron beam is analyzed. The selfconsistent nonlinear simultaneous equations have been obtained for the arbitrary space distribution of the magnetic guide field. The start generation characteristics are analyzed under small-signal conditions with an analytical solution taken for the case of inclined focusing magnetic field. It is found that the efficiency of electron-wave interaction appreciably depends on the focusing field strength and the relativistic mass factor. The results of numerical optimization of the guide field structure are presented to show possibility of improvement of the start characteristics of the oscillator.     

Large storage box hydrogen maser

An atomic hydrogen maser has been operated that confines atoms in a volume whose linear dimensions are approximately ten times larger than those of previous masers of this type. The uncertainties associated with the wall frequency shift, presently the principal limiting factor in the absolute accuracy of frequency measurements with the hydrogen maser, should be reduced with this device, since the fraction of time an atom spends on the storage box wall is inversely proportional to the diameter of the box. Oscillations are achieved by the use of two resonant cavities coupled by a high-gain amplifier. The strong field maintained in one cavity prestimulates the atoms to radiate at an enhanced rate in the weak field of the other. With enough gain, self-sustained oscillation can be achieved at normal hydrogen fluxes and normal cavityQ-factor values. The theory of the two-cavity large storage box maser is considered and preliminary results are discussed.     

Analysis of a low magnetic field TE m11 gyroklystron amplifier†

Large- and small-signal numerical calculations are presented for a two-cavity, low magnetic field gyroklystron amplifier operating in the TE _m11 whispering-gallery mode. The gyroklystron system modelled consists of a bunching cavity and an output cavity separated by a drift tube. For operation of both cavities at TE₅₁₁, gain and emission efficiency are studied for a high energy (γ = 1·6), low axial velocity (β_Verbar; = 0·1) electron beam. Prebunching prior to the output cavity in the gyroklystron leads to an increase of the maximum efficiency by more than a factor of two over that obtained from operating the output cavity as an oscillator. Model calculations are presented which show that magnetic field tapering greatly reduces the effects of any initial axial velocity spread in the electron beam, allowing high gain (?40 dB) and high efficiency (25-30%) to be achieved.     

CMOS prototype image sensor with edge enhancement to compensate for blurring

Small signal analytical analysis and large signal numerical calculations are presented for a gyroklystron in which a low order (TE₀₁₁) mode in the bunching cavity is coupled by the electron beam to a high order (TE₀₄₁) mode in the output cavity. A drift region separates the two cavities. We demonstrate that the probunching of the beam before entering the output cavity not only enhances the interaction efficiency of the TE₀₄₁ mode but also improves the mode stability by suppressing the TE₂₄₁ mode. The gyroklystron may be operated either as an oscillator or as an amplifier by a small variation of the applied magnetic field. The effect of the beam velocity spread on the efficiency is also investigated. It is found that the operation of the gyroklystron is more sensitive to beam velocity spread than that of a gyromonotron. Optimum conditions for a cold beam are not necessarily those for a wam beam.     

An Ultrahigh-order-mode, Higher-harmonic Coaxial Gyrotron Oscillator in Sub-terahertz Wave Range

A coaxial cavity gyrotron oscillator at a frequency of 0.34 THz is studied, which operates with a quite low magnetic field of 4.55 Tesla at the third cyclotron harmonic of the ultrahigh-order mode TE_43,4. Properly choosing the depth of the longitudinal corrugations on the inner rod and optimizing the electron-beam position significantly suppress the mode competition. Nonlinear multimode simulations show the feasibility of the single-mode operation with an output power of 163 kW by using an electron beam with a voltage of 70kV and a current of 30A, which corresponds to an interaction efficiency of 9.2 % with maxim density of ohmic losses 2.9 kW/cm².     

回旋管高频腔中金属膜片对谐振频率的影响

本文从多点反射的角度给出了高频腔中存在对称金属膜片时谐振频率的计算公式和特性曲线。并从实验上证实了金属膜片对机械加工误差的补偿作用。     

三腔分离腔振荡器高频特性分析

本文详细研究了三腔分离腔振荡器的高频特性,从圆柱坐标系下的Borgnis位函数的齐次标量Helmholtz方程出发,引入慢波驻波概念及其场表达式,利用Borgnis位函数的边界条件及相邻子区公共界面上的场匹配条件,导出了三腔分离腔振荡器内角向均匀TM模的色散关系及场分布,求得的谐振频率与实验中测得的微波频率一致.     

三腔分离腔振荡器高频特性分析

本文详细研究了三腔分离腔振荡器的高频特性,从圆柱坐标系下的Borgnis位函数的齐次标量Helmholtz方程出发,引入慢波驻波概念及其场表达式,利用Borgnis位函数的边界条件及相邻子区公共界面上的场匹配条件,导出了三腔分离腔振荡器内角向均匀TM模的色散关系及场分布,求得的谐振频率与实验中测得的微波频率一致.     

A Barkhausen-Kurz oscillator at centimeter wavelengths

This paper describes a new device for the generation of high-frequency oscillations in the centimeter wavelength region with high efficiency and low starting currents. The tube is fundamentally a Barkhausen-Kurz oscillator [1] utilizing a resonant cavity and a magnetically focused electron beam, but with no accelerating grids. The important features of this tube are the use of a parabolic potential distribution to utilize multiple transit electron motion, and the use of the magnetic field to control coupling between the electron stream and the resonator field and to reduce to negligible value the current intercepted at the resonator gap. A preliminary theory of the electronic energy interchange of this oscillator is provided, and the background theory of the oscillator design is discussed. Both X-band and K-band tubes have been tested. In the X-band tube, a maximum output power of 1.8 watts and a maximum efficiency of 13.5 per cent were obtained. At K band, the maximum power output was 430 milliwatts, and the maximum efficiency was 12.2 per cent. Starting currents belaw 0.1 ma have been observed at X band.     

高效率双波段同轴相对论返波管粒子模拟研究

提出了一种能在C 波段和X 波段实现稳定双频输出的带有谐振反射腔的单电子束同轴相对论返波振荡器,并使 用2.5 维全电磁粒子PIC 模拟软件进行了粒子模拟研究。模拟结果显示：在电子束电压510kV,电流9.03kA,引导磁场 0.73 T 的条件下,双频器件实现了8.1GHz 和9.9GHz 的双波段频率稳定输出,平均功率为0.95GW,波束互作用效率为 20.6%, 效率高于空心双波段返波管以及瓷绝缘线双频振荡器。     

A submillimeter free-electron laser experiment

A free-electron laser (FEL) Raman-backscattering oscillator, using afrac{1}{2}-1MeV, 20 kA electron beam pumped with a weak (∼ 250g) periodic (8 mm) transverse magnetic field, is operated as a source of high power millimeter and submillimeter radiation, with lasing developing during the 150 ns beam pulse. Measurements of lasing operation are described at 1.0 and 0.6 mm. The temporal behavior of cavity radiation is considered and effective gain is measured and compared with theory.     

Optical parametric oscillation with intracavity sum-frequencygeneration

Theoretical calculations of an optical parametric oscillator containing an intracavity sum-frequency crystal are presented for the case in which only the signal beam from the parametric generation process oscillates in the cavity. The pump beam that is not converted in the parametric generation process is summed with the signal beam to produce a beam at the desired frequency. The stable steady-state configurations that completely deplete the incident pump radiation are determined. When the sum-frequency crystal precedes the parametric-oscillator crystal, steady states with nearly complete pump depletion can occur for over a factor of twelve variation in the pump intensity. Other regimes of operation display period-doubling routes leading to chaotic solutions. A numerical calculation for conversion of 1.064-μm radiation to 589-nm light yields an intensity conversion efficiency of 86.6%     

高斯型耦合Tavis-Cummings模型中原子的量子特性

研究了原子与光场的耦合系数呈高斯型调制的双原子Tavis-Cummings模型中原子的量子特性.通过数值计算,分析了原子垂直于腔轴的运动以及系统初态对双原子能级布居数反转和双原子偶极压缩的影响.结果表明,原子垂直于腔轴的运动影响双原子能级布居数反转的崩塌和回复,但不改变双原子偶极压缩的最大压缩量,只改变最大压缩次数.光场初态为真空态,而两原子初始处在特定的非最大纠缠态时,双原子偶极压缩最大.