Arm cavity resonant sideband control for laser interferometric gravitational wave detectors

We present a new optical control scheme for a laser interferometric gravitational wave detector that has a high degree of tolerance to interferometer spatial distortions and noise on the input light. The scheme involves resonating the rf sidebands in an interferometer arm cavity.     

Efficient Scheme for One-Way Quantum Computing with Radiofrequency SQUID Qubits byAdiabatic Passage

We proposed an efficient scheme for constructing a quantum controlled phase-shift gate and generating the cluster states with rf superconducting quantum interference devices (SQUIDs) coupled to a microwave cavity through adiabatic evolution of dark eigenstates. During the operation, the spontaneous emission is suppressed since the rf SQUIDs are always in the three lowest flux states. Considering the influence from the cavity decay with achievable
experimental parameters, we numerically analyze the success probability and the fidelity for generating the two-SQUID maximally entangled state and the controlled phase-shift gate by adiabatic passage.     

One-step implementation of the Toffoli gate via quantum Zeno dynamics

Based on the quantum Zeno dynamics, we present a scheme for one-step implementation of a Toffoli gate via manipulating three rf superconducting quantum interference device (SQUID) qubits to resonantly interact with a superconducting cavity. The effects of decoherence such as spontaneous emission and the loss of cavity are also considered.     

Experimental generation and characterization of uniformly filled ellipsoidal electron-beam distributions

For 40 years, uniformly filled ellipsoidal beam distributions have been studied theoretically, as they hold the promise of generating self-fields linear in the coordinate offset in all three directions. Recently, a scheme for producing such distributions, based on the strong longitudinal expansion of an initially very short beam under its own space-charge forces, has been proposed. In this Letter we present the experimental demonstration of this scheme, obtained by illuminating the cathode in a rf photogun with an ultrashort laser pulse (approximately 35 fs rms) with an appropriate transverse profile. The resulting 4 MeV beam spatiotemporal (x,t) distribution is imaged using a rf deflecting cavity with 50 fs resolution. A temporal asymmetry in the ellipsoidal profile, due to image charge effects at the photocathode, is observed at higher charge operation. This distortion is also found to degrade the transverse beam quality.     

关于热阴极微波电子枪中电子反轰问题的研究

 提出了热阴极微波电子枪的设计中可以通过缩短腔长减小电子反轰功率，并通过模拟计算详细研究了腔长对电子反轰及枪出口束流品质的影响。     

第一讲台面型电子加速器——激光尾波场加速器

近年来，随着超短超强激光脉冲技术的发展，利用超短超强激光在等离子体中激发出的高强度尾波场来实现电子加速的方案也取得了巨大进展．相对于传统的射频腔加速器，这种新型的加速器由于以等离子体为介质，可以突破传统加速器中加速梯度小于100MV／m的限制，其加速梯度可以达到100GV／m．电子在这样的加速场下，在厘米量级的距离内就可以获得GeV的能量．随着台面型超短超强激光器的发展，新一代实用化的台面型电子加速器有望在不远的将来得以实现．文章将从理论和实验上对激光尾波场加速中的尾波激发、电子注入、距离延长三个方面加以介绍，同时给出国内在这些方面的一些研究进展．     

Regenerative mode locking via superposition of higher-order cavity modes in composite cavity fiber lasers

We demonstrate a new method of optical pulse generation in regeneratively mode-locked fiber ring lasers (RML-FRLs). The method is based on generating dominant longitudinal modes in the fiber ring cavity by means of a composite cavity structure and their intermode beating at the photodetector incorporated in the regenerative feedback loop. The beat signal is then used as a modulation signal to generate optical pulses in a regenerative mode-locking scheme, thereby eliminating the requirement for a high-Q rf bandpass filter in a conventional RML-FRL. Optical pulses with a repetition frequency of 3.6 GHz have been generated successfully with a supermode noise suppression of more than 48 dB and a low phase noise of -85 dBc/Hz at 10 kHz offset from the carrier frequency.     

Low-power MRI by Frank-sequence excitation

Recently, a new NMR method employing an rf excitation scheme with strongly reduced power has been introduced, which is based on modulating rf pulses according to Frank sequences. For many applications, a reduction of rf power is essential, e.g. to eliminate bulky rf pre-amplifiers or in medical high-field MRI to preserve patient safety. Another benefit of the new scheme are very short dead times allowing for measurements of samples with short relaxation times. In this work, Frank-sequence excitation is used for low-power imaging for the first time. Results of one-, two-, and three-dimensional imaging experiments are presented and compared to conventional images.     

Coaxial cavity gyrotron with dual RF beam output

A 140-GHz, 1.5-MW, TE_28,16-coaxial cavity gyrotron with a dual RF beam output has been designed, built, and tested. For the first time, the generated RF power has been split into two parts and coupled out through two RF output windows in order to reduce the power loading in the windows. The quasioptical output system is based on a two-step mode conversion scheme. First, the cavity mode TE_-28,16 is converted into its degenerate whispering gallery mode TE_+76,2 using a rippled-wall mode converter. Then, this mode is transformed into two TEM₀₀ output wave beams. A maximum rf output power of about 950 kW with an output efficiency of 20% has been measured. According to numerical calculations, an rf power above 1.5 MW is expected to be generated in the cavity. Even if all losses are taken into account, a discrepancy between experiment and calculations remains. The power deficit seems to be partly caused by the influence of the stray radiation captured inside the tube. However, the two main reasons are probably an incomplete mode conversion from TE_-28,16 to TE_+76,2 and a large energy spread of the electron beam due to trapped electrons. An increased amount of captured stray radiation resulted in a reduced stability of operation. A single-stage depressed collector was used successfully, increasing the RF output efficiency from 20% to 29%     

Radiofrequency forward Mössbauer scattering method in study of magnetic materials

Mössbauer spectra in forward scattering scheme were measured for iron borate (FeBO ₃) exposed to radiofrequency (rf) field below the Neel temperature. The spectra have satellites spaced by doubled rf field frequency. The semiclassical model of Mössbauer transmission through a thick magnetic sample under rf reversals of a hyperfine field is proposed. This model reproduces all features of the measured spectra. Experiments and model calculations indicate additional possibilities of this measurement scheme for study the soft magnetic materials.     

Femtosecond synchronization of radio frequency signals with optical pulse trains

A synchronization scheme for extraction of low-jitter rf signals from optical pulse trains, which is robust against photodetector nonlinearities, is described. The scheme is based on a transfer of timing information into an intensity imbalance of the two output beams from a Sagnac loop. Sub-100-fs timing jitter between the extracted 2-GHz rf signal and the 100-MHz optical pulse train from a mode-locked Ti:sapphire laser is demonstrated.     

高亮度1（1／2）超导腔光阴极注入器的腔形设计

对高亮度1 1/2超导腔光阴极注入器进行了腔形的概念研究设计。通过计算比较发现,重入腔的轴电场分布特性,使它很适合做超导光阴极注入器的首腔。我们还通过模拟计算,研究了电子束动力学各种参数的相互依赖关系,最后我们给出1 1/2腔的一组腔及束动力学参数。     

High power acceleration of an HSC type injector for cancer therapy

A hybrid single cavity(HSC) linac, which is formed by combining a radio frequency quadrupole(RFQ)and a drift tube(DT) structure into one interdigital-H(IH) cavity, is fabricated and assembled as a proof of principle injector for cancer therapy synchrotron, based on the culmination of several years of research. The HSC linac adopts a direct plasma injection scheme(DPIS), which can inject a high intensity heavy ion beam produced by a laser ion source(LIS). The input beam current of the HSC is designed to be 20 m A C~(6+) ions. According to numerical simulations, the HSC linac can accelerate a 6-m AC~(6+) beam, which meets the requirement of the needed particle number for cancer therapy(108-9ions/pulse). The HSC injector with the DPIS method makes the existing multiturn injection system and stripping system unnecessary, and can also bring down the size of the beam pipe in existing synchrotron magnets, which could reduce the whole cost of synchrotron. The radio frequency(rf) measurements show excellent rf properties for the resonator, with a measured Q equal to 91% of the simulated value. AC~(6+) ion beam extracted from the LIS was used for the HSC commissioning. In beam testing, we found the measured beam parameters agreed with simulations. More details of the measurements and the results of the high power test are reported in this paper.     

Longitudinal phase-space coating of beam in a storage ring

In this Letter, I report on a novel scheme for beam stacking without any beam emittance dilution using a barrier rf system in synchrotrons. The general principle of the scheme called longitudinal phase-space coating, validation of the concept via multi-particle beam dynamics simulations applied to the Fermilab Recycler, and its experimental demonstration are presented. In addition, it has been shown and illustrated that the rf gymnastics involved in this scheme can be used in measuring the incoherent synchrotron tune spectrum of the beam in barrier buckets and in producing a clean hollow beam in longitudinal phase space. The method of beam stacking in synchrotrons presented here is the first of its kind.     

Compact narrow-band THz radiation source based on photocathode rf gun

Narrow-band THz coherent Cherenkov radiation can be driven by a subpicosecond electron bunch traveling along the axis of a hollow cylindrical dielectric-lined waveguide. We present a scheme of compact THz radiation source based on the photocathode rf gun. On the basis of our analytic result, the subpicosecond electron bunch with high charge (800 pC) can be generated directly in the photocathode rf gun. According to the analytical and simulated results, a narrow emission spectrum peaked at 0.24 THz with 2 megawatt (MW) peak power is expected to gain in the proposed scheme (the length of the facility is about 1.2 m).     

Broadband dipolar recoupling in rotating solids: a numerical comparison of some pulse schemes

A numerical comparison of the dipolar recoupling performance of several previously published homonuclear recoupling schemes under magic angle-spinning conditions is presented. Emphasis is put on the recoupled polarization transfer in a two-spin system where the efficiency is studied as a function of resonance offsets in the presence and absence of chemical-shielding anisotropies. In addition, the effect of the rf field strength is investigated. Powder pattern line shapes are shown in the on-resonance case that reveal the distribution of dipolar couplings for each recoupling scheme. These results are compared to data computed with a purposely misset rf field strength to estimate the pulse scheme sensitivity to rf-inhomogeneity and experimental missettings.     

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     

A laser system for the spectroscopy of highly charged bismuth ions

We present and characterize a laser system for the spectroscopy on highly charged ²⁰⁹Bi⁸²⁺ ions at a wavelength of 243.87?nm. For absolute frequency stabilization, the laser system is locked to a near-infra-red laser stabilized to a rubidium transition line using a transfer cavity based locking scheme. Tuning of the output frequency with high precision is achieved via a tunable rf offset lock. A?sample-and-hold technique gives an extended tuning range of several THz in the UV. This scheme is universally applicable to the stabilization of laser systems at wavelengths not directly accessible to atomic or molecular resonances. We determine the frequency accuracy of the laser system using Doppler-free absorption spectroscopy of Te₂ vapor at 488?nm. Scaled to the target wavelength of 244 nm, we achieve a frequency uncertainty of σ _{244 nm}=6.14?MHz (one standard deviation) over six days of operation.     

Design of a β=0.45, f=350 MHz Spoke Cavity

Recently intensive studies have been done on superconducting cavities (e.g. spoke cavity, reentrant cavity, and ch cavity), which are used as accelerating structures in the low and medium energy part of high power high intensity proton or ion accelerators. many experiments have shown that spoke cavity is a good candidate for low energy part. it is also promising to be used for the medium β area. so a β=0.45 spoke cavity is being studied at Peking university. in this paper, the structural and electromagnetic design of a β=0.45, f=350mhz spoke cavity is reported in detail. the calculated rf parameters (e.g. Q, r/Q, peak surface fields and dissipated power) indict a potential of good acceleration.     

Simply quantum information processing with RF superconducting qubit

Utilizing rf superconducting quantum interference devices coupled with transmission line resonator, we propose a scheme to implementing quantum information processing. In this system, the high fidelity two-qubit maximally entangled states and quantum logic gate are realized. Under the large detuning condition, the excited state of an rf superconducting quantum interference device is adiabatically eliminated. So the excited state spontaneous emission of the superconducting qubit can be effectively avoided in this paper. At last, the experimental feasibility and the challenge of our schemes have been discussed.