The design and construction of a pulsed beam generation system based on high intensity cyclotron

In order to perform the studies on a pulsed beam generation system based on a high intensity cyclotron, a test beam line with a pulsed beam generation for a 10 MeV compact cyclotron (CYCIAE-10) has been designed and constructed at China Institute of Atomic Energy (CIAE). A 70 MHz continuous H-beam can be pulsed to the pulse length of less than 10 ns with a repetition rate of 4.4 MHz. The sine waveform with a frequency of 2.2 MHz is adopted for the chopper and a mesh structure with single drift and dual gaps is used for the 70 MHz buncher. A helical resonator is designed and constructed based on simulations and experiments on the RF matching for the chopper. A helical inductance loop that is exceptionally large of its kind and equipped with water cooling for the resonator has been successfully wound and a 500 W solid RF amplifier has been manufactured. A special measuring device has been designed, which can be used to measure both the DC beam and the pulsed beam. The required pulsed beam was obtained after pulsed beam tuning.     

The design and construction of a pulsed beam generation system based on high intensity cyclotron

In order to perform the studies on a pulsed beam generation system based on a high intensity cyclotron, a test beam line with a pulsed beam generation for a 10 MeV compact cyclotron (CYCIAE-10) has been designed and constructed at China Institute of Atomic Energy (CIAE). A 70 MHz continuous H-beam can be pulsed to the pulse length of less than 10 ns with a repetition rate of 4.4 MHz. The sine waveform with a frequency of 2.2 MHz is adopted for the chopper and a mesh structure with single drift and dual gaps is used for the 70 MHz buncher. A helical resonator is designed and constructed based on simulations and experiments on the RF matching for the chopper. A helical inductance loop that is exceptionally large of its kind and equipped with water cooling for the resonator has been successfully wound and a 500 W solid RF amplifier has been manufactured. A special measuring device has been designed, which can be used to measure both the DC beam and the pulsed beam. The required pulsed beam was obtained after pulsed beam tuning.

     

Impedance model of helical resonator discharge

Modeling and measurement results of the RF input impedance of a helical resonator discharge are given. A simple microstrip transmission line model is used to extract an equivalent circuit of a helical resonator discharge. The transmission line model consists of a grounded cylinder for RF shielding, a helical copper coil for RF heating, and a high density plasma. Transmission line parameters for an experimental helical resonator discharge chamber are extracted, and the results are compared with the measured results. The measured transmission line parameters for the experimental reactor are the characteristic impedance of 200 Ω, the attenuation constant of 6×10^-3 Np/m, and the wave number of 0.36 rad/m, which have good agreement with the calculated values     

Properties of inductively coupled plasma source with helical coil

This paper presents modeling and experimental results of the voltage, current, and density profiles of a helical resonator plasma source. The source has a 5/4-wavelength (λ) helical resonator structure with the helical coil short-circuited at one end and open circuited at the other end. When the radio frequency (RF) tap for power feeding was located at an odd multiple of λ/4 from the short-circuited end, the observed voltage, current, and plasma density were higher in the short-circuited section than those in the open-circuited section. The opposite property was observed with the RF tap at an even multiple of λ/4. A microstrip transmission line model was used to explain the experimental results. The model accurately predicted the RF voltage and current profiles. After calculation of RF voltage and current, the plasma density was solved numerically. The difference between the calculated and measured plasma density was within a factor of two. The changes on the density profile indicate that the transport properties of plasma can be adjusted with the RF tap position     

On the application of radio frequency voltages to ion traps via helical resonators

Ions confined using a Paul trap require a stable, high voltage and low noise radio frequency (RF) potential. We present a guide for the design and construction of a helical coil resonator for a desired frequency that maximises the quality factor for a set of experimental constraints. We provide an in-depth analysis of the system formed from a shielded helical coil and an ion trap by treating the system as a lumped element model. This allows us to predict the resonant frequency and quality factor in terms of the physical parameters of the resonator and the properties of the ion trap. We also compare theoretical predictions with experimental data for different resonators, and predict the voltage applied to the ion trap as a function of the Q factor, input power and the properties of the resonant circuit.     

Coarse and Fine Control of the EPR Frequency of a Loop-Gap Resonator Using a Single-Turn Coil with a Varactor Diode Attached

Coarse control and fine control of the resonant frequency of a loop-gap resonator (LGR) operating at an electron paramagnetic resonance (EPR) frequency of ca. 650 MHz were achieved using a single-turn coil with a varactor diode attached (a frequency shift coil). When the distance between the LGR and the frequency shift coil was changed from 15 to 10 mm under the condition of constant voltage to the varactor diode (0 V), a shift of the resonant frequency of the LGR of ca. 20 MHz was observed (coarse frequency control). When the voltage applied to the varactor diode was changed from 0 to 15 V at the same distance between the LGR and the frequency shift coil (10 mm), a shift of the resonant frequency of the LGR of ca. 200 kHz was observed (fine frequency control). There were no significant changes in sensitivity of EPR measurements of a phantom (comprised of agar with a nitroxide radical and physiological saline solution) without and with the frequency shift coil. The EPR sensitivity did not change discernibly when the resonant frequency was shifted by the frequency shift coil. Furthermore, radio-frequency phase adjustment for homodyne detection could be performed by using the frequency shift coil without applying frequency modulation to the carrier wave.     

Two-Frequency Brillouin Fiber Laser Controlled by Temperature Difference in Fiber Ring Resonator

A Brillouin fiber laser (BFL) consisting of a fiber ring resonator with different fiber temperatures emits two-frequency light output. The two-frequency BFL yields an optical beat output which can be utilized as an optical frequency shifter. The output beat frequency is controllable by the temperature difference in the fiber ring resonator and changes with a step of a resonant frequency interval of BFL. The temperature dependence of the BFL output frequency was 2.4 MHz/°C. The stability of the output beat frequency to the temperature fluctuation was estimated as 1.04°C/2.5 MHz.     

用于高温射频超导量子干涉器的介质谐振器的性质研究

介质谐振器是目前高温射频超导量子干涉器较常采用的一种高品质因数微波谐振器.它是由10 mm×10 mm×1 mm的SrTiO₃(STO)标准衬底及覆盖在其上的YBa₂Cu₃O_7-δ(YBCO)薄膜磁通聚焦器共同构成的.为探明磁通聚焦器构形对介质谐振器谐振频率的影响,本文采用Ansoft公司出品的HFSS高频结构仿真软件对磁通聚焦器构形不同的若干介质谐振器的谐振特性进行了仿真.结果表明:增大磁通聚焦器开     

Study of a magnetic alloy-loaded RF cavity for bunch compression at the CSR

The Heavy Ion Research Facility and Cooling Storage Ring(HIRFL-CSR)accelerator in Lanzhou offers a unique possibility for the generation of high density and short pulse heavy ion beams by non-adiabatic bunch compression longitudinally,which is implemented by a fast jump of the RF-voltage amplitude.For this purpose,an RF cavity with high electric field gradient loaded with Magnetic Alloy cores has been developed.The results show that the resonant frequency range of the single-gap RF cavity is from 1.13 MHz to 1.42 MHz,and a maximum RF voltage of 40 kV with a total length of 100 cm can be obtained,which can be used to compress heavy ion beams of 238U72+ with 250 MeV/u from the initial bunch length of 200 ns to 50 ns with the coaction of the two single-gap RF cavity mentioned above.     

A new type of HTc superconducting film comb-shape resonator for radio frequency superconducting quantum interference devices

A new type of HTc superconducting film combshape resonator for radio frequency superconducting quantum interference devices (RF SQUID) has been designed. This new type of superconducting film comb-shape resonator is formed by a foursquare microstrip line without a flux concentrator. The range of the center frequency of this type of resonator varies from 800 MHz to 1 300 MHz by changing the length of the teeth. In this paper, we report on simulating the relationship of the value of the center frequency and the length of the teeth, and testing the noise of HTc RF SQUID coupling this comb-shape resonator. __________ Translated from Chinese Journal of Low Temperature Physics, 2005, 27(3) (in Chinese)     

Multi-physics analysis of the RFQ for Injector Scheme Ⅱ of C-ADS driver linac

A 162.5 MHz, 2.1 MeV radio frequency quadruples (RFQ) structure is being designed for the Injector Scheme Ⅱ of the China Accelerator Driven Sub-critical System (C-ADS) linac. The RFQ will operate in continuous wave (CW) mode as required. For the CW normal conducting machine, the heat management will be one of the most important issues, since the temperature fluctuation may cause cavity deformation and lead to the resonant frequency shift. Therefore a detailed multi-physics analysis is necessary to ensure that the cavity can stably work at the required power level. The multi-physics analysis process includes RF electromagnetic analysis, thermal analysis, mechanical analysis, and this process will be iterated for several cycles until a satisfactory solution can be found. As one of the widely accepted measures, the cooling water system is used for frequency fine tunning, so the tunning capability of the cooling water system is also studied under different conditions. The results indicate that with the cooling water system, both the temperature rise and the frequency shift can be controlled at an acceptable level.     

集成马赫-曾德尔热光耦合器的可调谐振环优化设计

根据耦合模理论,推导出可调谐光波导谐振环的光强和相位传递函数的表达式,并分析了可调谐谐振环的传输特性.结果表明,谐振环中集成的马赫-曾德尔耦合器的参量设定和调谐方式直接影响谐振环的谐振频率移动范围和调制功率.通过改变耦合器参量对谐振环进行优化设计,在中心波长为1550 am附近,谐振环半径2 cm,传输损耗0.08 dB/cm的情况下,实现了清晰度和最佳谐振深度的调谐,谐振频率的移动范围低于0.027 GHz,降低了谐振环对频率调制器的调频要求,同时降低了耦合器的调制功率.     

Transfer matrix methods for sound attenuation in resonators with perforated intruding inlets

A resonator with perforated intruding inlet (PII) is a superior silencer element, since the use of perforated inlet extensions can dramatically improve the acoustic performance. In this work, both a one-dimensional (1D) and a two-dimensional (2D) transfer matrix methods are developed to predict the transmission loss of the resonator without considering the mean flow. Based on the two groups of comparisons with tests, it is found out that the applicability of 1D method is limited by the resonator geometry even when the frequency is below the cut-off value of plane wave. Whereas the 2D approach is much more accurate while predicting the transmission losses within entire frequency range. Subsequently, five groups of resonators are chosen to determine the effects of structure parameters to transmission loss based on the 2D approach. The resonant frequency decreases and more resonant peaks appear when the length of inlet extension increases. A higher perforation rate leads to a shift of resonant peak towards higher frequencies. Besides, better acoustic performance could be obtained with the perforation being properly designed. Reducing the inlet/outlet radius can obviously improve the transmission loss without changing the frequency of resonant peak. The theories and conclusions in this study can be used for the design and optimization of resonators in various engineering applications.     

Direct EPR irradiation of a sample using a quartz oscillator operating at 250 MHz for EPR measurements

Direct irradiation of a sample using a quartz oscillator operating at 250 MHz was performed for EPR measurements. Because a quartz oscillator is a frequency fixed oscillator, the operating frequency of an EPR resonator (loop-gap type) was tuned to that of the quartz oscillator by using a single-turn coil with a varactor diode attached (frequency shift coil). Because the frequency shift coil was mobile, the distance between the EPR resonator and the coil could be changed. Coarse control of the resonant frequency was achieved by changing this distance mechanically, while fine frequency control was implemented by changing the capacitance of the varactor electrically. In this condition, EPR measurements of a phantom (comprised of agar with a nitroxide radical and physiological saline solution) were made. To compare the presented method with a conventional method, the EPR measurements were also done by using a synthesizer at the same EPR frequency. In the conventional method, the noise level increased at high irradiation power. Because such an increase in the noise was not observed in the presented method, high sensitivity was obtained at high irradiation power.     

Design and experimental verification of a dual-band metamaterial filter

In this paper, we present the design, simulation, and experimental verification of a dual-band free-standing metamaterial filter operating in a frequency range of 1 THz–30 THz. The proposed structure consists of periodically arranged composite air holes, and exhibits two broad and flat transmission bands. To clarify the effects of the structural parameters on both resonant transmission bands, three sets of experiments are performed. The first resonant transmission band shows a shift towards higher frequency when the side width w_1 of the main air hole is increased. In contrast, the second resonant transmission band displays a shift towards lower frequency when the side width w_2 of the sub-holes is increased, while the first resonant transmission band is unchanged. The measured results indicate that these resonant bands can be modulated individually by simply optimizing the relevant structural parameters(w_1 or w_2) for the required band. In addition, these resonant bands merge into a single resonant band with a bandwidth of 7.7 THz when w_1 and w_2 are optimized simultaneously. The structure proposed in this paper adopts different resonant mechanisms for transmission at different frequencies and thus offers a method to achieve a dual-band and low-loss filter.     

利用传输腔技术实现镱原子光钟光晶格场的频率稳定

为了获得高稳定度和高精确度的原子光晶格钟,光晶格场的频率必须得到锁定,线宽必须控制到特定水平用来消除交流斯塔克频移.本文提出利用传输腔技术来实现对镱原子光钟的光晶格场的频率锁定和抑制频率长期漂移的锁定方案.首先,将一个殷钢材料的传输腔锁定在基于调制转移谱技术锁定的780 nm激光场上,再将759 nm的光晶格光场锁定在传输腔上.实验结果表明,光晶格光场的线宽可以锁定和控制在1 MHz以下.光晶格光场与锁定于氢钟的光梳拍频结果显示,光晶格光场的长期频率稳定度优于3.6×10~(-10),可以确保实现镱原子光钟的不确定度进入10~(-17).     

S波段HYBRID聚束-加速结构的样机研制

Hybrid聚束-加速结构是把驻波预聚束器、行波聚束器和标准加速管集成到一起的新型RF结构。简述了对S波段Hybrid聚束-加速结构样机的束流动力学优化和微波设计结果,解释了Hybrid结构导致发射度增长的原因,对此样机进行了射频低功率测试。样机的冷测结果与RF设计结果一致性很好。在冷测频率2 855.21 MHz处,实测S₁₁小于?45 dB,腔间相移偏差小于±2°,VSWR≤1.2对应的带宽大于5 MHz,轴向场分布完全满足动力学要求。     

品质因子可调的石墨烯纳米机械振子

纳米机械振子尺寸小,质量轻,可以用来制作探测力、质量等微小物理量的超灵敏探测器.石墨烯拥有质量轻、密度低和杨氏模量高等特性,被认为是制作纳米机械振子的理想材料.石墨烯纳米机械振子因其具有的谐振频率高、品质因子高和谐振频率可调性高等优势,近年来得到了人们的广泛关注.作为表征纳米机械振子性能的一个重要指标,品质因子越高,意味着纳米机械振子耗散越低,纳米机械振子的灵敏度越高.本文通过微纳加工的工艺制备出一种谐振频率随栅压可调(调节的范围为73MHz~90MHz)的石墨烯纳米机械振子样品,研究其在极低温高真空环境下的品质因子与栅极电压之间的关系.实验表明通过栅压调节振子的内部应力,能够使石墨烯纳米机械振子品质因子从220提高到1000.我们的结果为二维材料纳米机械振子的耗散研究提供了一种新的研究思路.     

SSC直线注入器RFQ腔体多物理场分析

SSC-LINAC是为兰州重离子研究装置（HIRFL）设计的直线注入器,它将U34+离子加速到1 MeV/u注入到分离扇回旋加速器（SSC）中,为冷却储存环（CSR）提供10 MeV/u的U34+。该注入器可以将SSC引出的重离子流强提高一个量级以上。SSC-LINAC由一个RFQ（Radio Frequency Quadrupole）加速器和4个DTL（drift tube linac）组成,设计频率为53.667 MHz。RFQ工作在连续波模式,设计功率30 kW,如果不能有效地冷却,高频电流在电极表面产生的热量会使RFQ的腔壁和电极发生形变,从而导致腔体频率的漂移以及加速和聚焦电场的改变。因此,为了保证连续波工作的RFQ加速器稳定运行,对水冷模式和通道设计提出了很高的要求。作者用有限元软件ANSYS对RFQ进行高频电磁场、温度场、结构应力的耦合分析,验证了冷却方案设计的可行性和可靠性。Heavy Ion Research Facility at Lanzhou(HIRFL) consists of SFC, SSC, CSRm and CSRe. A new linac injector, which will increase U34+ to 1 MeV/u, is designed for SSC to increase the beam intensity to ten times higher. The new injector, whose frequency is 53.667 MHz, is composed by a RFQ (Radio Frequency Quadrupole) cavity and four DTL(Drift Tube Linac) cavities. The RFQ cavity, whose RF power is 30 kW, is operated at CW(continuous wave) mode. The heat produced by HF (high frequency) electromagnetic will cause deformation of RFQ structure, lead to the resonant frequency shift, and reduce the focusing efficiency of the cavity. An efficient cooling system is necessary to ensure that the RFQ cavity can stably be operated at the nominal frequency. A detailed multi-physics field coupling analysis of RFQ has been finished with 3D finite elements software ANSYS. The result of the analysis shows that the water cooling system can cool the RFQ cavity fully and keep the frequency drift be in a acceptable level.     

Magic Wavelength Measurement of the ~(87)Sr Optical Lattice Clock at NIM

We report on the magic wavelength measurement of our optical lattice clock based on fermion strontium atoms at the National Institute of Metrology(NIM).A Ti:sapphire solid state laser locked to a reference cavity inside a temperature-stabilized vacuum chamber is employed to generate the optical lattice.The laser frequency is measured by an erbium fiber frequency comb.The trap depth is modulated by varying the lattice laser power via an acousto-optic modulator.We obtain the frequency shift coefficient at this lattice wavelength by measuring the differential frequency shift of the clock transition of the strontium atoms at different trap depths,and the frequency shift coefficient at this lattice wavelength is obtained.We measure the frequency shift coefficients at different lattice frequencies around the magic wavelength and linearly fit the measurement data,and the magic wavelength is calculated to be 368554672(44) MHz.