Harmonic Cavity Research Articles

Stability analysis of double-harmonic cavity system in heavy beam loading with its feedback loops by a mathematical method based on Pedersen model

With the high beam current in storage ring, it is necessary to consider the instability problem caused by the heavy beam loading effect. It has been demonstrated that direct RF feedback (DRFB), autolevel control loop (ALC) and phase-lock loop (PLL) in the main cavity can lessen the impact of the beam effect. This paper regarded the beam, main cavity, harmonic cavity and feedback loops as double harmonic cavity system, and extended the transfer functions in the Pedersen model to this system. Some quantitative evaluations of simulation results have been got and conclusions have been drawn. In the case of a passive harmonic cavity, the optimization strategy of the controller parameters in the pre-detuning, ALC and PLL, as well as the gain and phase shift of DRFB were discussed. Meanwhile, it also involved the impact of the harmonic cavity feedback loop on the system stability at the optimum stretching condition when an active harmonic cavity was present. The research results can be used as guidelines for beam operation with beam current increasing in the future.

Beam test of a harmonic kicker cavity

A harmonically resonant kicker cavity designed for beam exchange in a circulator cooler was built and successfully tested at the Upgraded Injector Test Facility (UITF) at Jefferson Lab. This type of cavity is being considered for the injection scheme of the Rapid Cycling Synchrotron at the Electron-Ion Collider, where the spacing of neighboring bunches demands very short kicks. Operating with five transversely deflecting modes simultaneously that resonate at 86.6 MHz and consecutive odd harmonics thereof, the prototype cavity selectively deflects 1 of 11 electron bunches while leaving the others unperturbed. An RF driver was developed to synthesize phase- and amplitude-controlled harmonic signals and combine them to drive the cavity while also separating the modes from a field-probe antenna for RF feedback and dynamic tuning. Beam deflection was measured by sweeping the cavity phase; the deflection waveform agrees with expectations, having sub-nanosecond rise and fall times. No emittance increase is observed. Harmonically resonant cavities like the one described provide a new capability for injection and extraction at circulators and rings.

Magnetic Alloy Core Loaded 2nd harmonic cavity design and testing for CSNS-II RCS

In this report, we present our recent progress in the design and high-power testing of the 2nd harmonic cavity for the China Spallation Neutron Source upgrade project. To achieve optimal performance, high-performance magnetic alloy (MA) cores with dimensions of Φ850mm × Φ316mm × 25mm were meticulously developed and fabricated to serve as the load material for the radio-frequency (RF) cavity. Through rigorous testing, we were able to achieve a remarkable cavity accelerating gradient of over 40 kV/m under 15% duty cycle. To ensure optimal cooling efficiency, we conducted a comprehensive fluid dynamics simulation analysis and verified our results through experiments. Finally, to assess the long-term stability and performance of the cavity, we conducted a series of extended operation tests. These experiments successfully confirmed the high-performance capabilities and exceptional stability of the 2nd harmonic cavity.

RF behavior of a second harmonic photonic band gap cavity gyrotron oscillator

RF behavior of a second harmonic photonic band gap cavity gyrotron oscillator

Continuously wavelength tunable, continuous wave laser ideal for UV Raman spectroscopy

AbstractWe utilize a novel, high‐power, tunable, continuous wave (CW) deep UV laser to measure resonance Raman spectra of phenolate solutions with high signal‐to‐noise ratios (SNR). In UV resonance Raman (UVRR), increased coupling of the excitation light with a chromophore can transfer molecules into excited states that cause increased heating and photochemistry. Deep UV lasers have traditionally utilized high peak powers to enable efficient single‐pass nonlinear conversion from visible into near infrared light. Nonlinear phenomena such as the formation of transient radical species, Raman saturation, thermal heating, and dielectric breakdown can introduce extraneous light sources that can complicate the interpretation of the Raman spectrum. Dielectric breakdown can increase the baseline, increase noise, and sometimes saturate the detector, preventing Raman detection. Spontaneous Raman scattering intensities should scale linearly with the excitation light intensity. However, this linear behavior does not always occur with pulsed laser excitation. This occurs because stimulated Raman scattering can cause a superlinear intensity response, or transient absorption can cause sublinear intensity responses. CW laser excitation excites samples with electric fields that are much lower than typical pulsed laser excitation. This eliminates the nonlinear responses. The geometry of our new CW laser enables high gain in the harmonic generation cavities that achieve high harmonic generation efficiencies. Average power in the deep UV is >30 mW for wavelengths as short as 206 nm. In the work here, we demonstrate that CW excitation is ideal for resonance Raman measurements in general to reduce spectral complexity.

Harmonic kicker cavity for high power operation

Harmonic kicker cavity for high power operation

A Method for non-destructive testing of resonant frequency in the W-band second harmonic gyrotron complex cavity

A Method for non-destructive testing of resonant frequency in the W-band second harmonic gyrotron complex cavity

Mode-zero Robinson instability in the presence of passive superconducting harmonic cavities

Mode-zero Robinson instability in the presence of passive superconducting harmonic cavities

Coherent qubit measurement in cavity-transmon quantum systems

A measurement of the time between quantum jumps implies the capability to measure the next jump. During the time between jumps the quantum system is not evolving in a closed or unitary manner. While the wave function maintains phase coherence it evolves according to a non-Hermitian effective Hamiltonian. So under null measurement the timing of the next quantum jump can change by very many orders of magnitude when compared to rates obtained by multiplying lifetimes with occupation probabilities obtained via unitary transformation. The theory developed in 1987 for atomic fluorescence is here extended to transitions in transmon qubits. These systems differ from atoms in that they are read out with a harmonic cavity whose resonance is determined by the state of the qubit. We extend our analysis of atomic fluorescence to this infinite level system by treating the cavity as a quantum system. We find that next photon statistics is highly nonexponential and when implemented will enable faster readout, such as on timescales shorter than the decay time of the cavity. Commonly used heterodyne measurements are applied on timescales longer than the cavity lifetime. The overlap between the next photon theory and the theory of heterodyne measurement which are described according to the stochastic Schr\"odinger equation is elucidated. In the limit of large dispersion the intrinsic error for next jump detection, at short time, tends to zero. Whereas for short-time dyne detection the error remains finite for all values of dispersion.

Design and low-power measurement of 1.5 GHz TM020-type harmonic cavity for KEK future synchrotron light source

We designed a normal-conducting (NC) 1.5 GHz harmonic cavity that can be used in a future synchrotron light source at High Energy Accelerator Research Organization (KEK). By utilizing a higher TM020 mode for beam acceleration, this cavity has lower R/Q and higher unloaded Q as compared to those of conventional NC cavities. These features are advantageous in reducing the fluctuations in harmonic RF voltages when the bunch gaps are introduced. Harmful parasitic modes other than the TM020 mode can be heavily damped using coaxial slots located at the node of the TM020 mode. We made a concerted effort to lower the coupling impedances of parasitic modes while maintaining high Q value of the accelerating mode. We found that maintaining the axial symmetry of the cavity is essential for minimizing the leakage power of the accelerating mode into the coaxial slots. In this article, we present the optimization of the cavity shape, low-power measurement, and the basic design of a high-power model.

Comparative thermodynamic analysis of China Spallation Neutron Source second phase (CSNSII) SRF system cooling Scheme

The China Spallation Neutron Source second phase (CSNS-II) accelerator upgrades consist of three major components: linac energy upgrade from 80 MeV to 300 MeV, injection system upgrade, and new magnetic alloy dual harmonic cavities. There are ten double spoke cavities cryomodules and eight elliptical cavities cryomodules in total. A comparative thermodynamic analysis of the superconducting radio frequency (SRF) systems can be of great importance to select a reliable, cost-effective and easy-maintenance cooling schemes. This is particularly critical for SRF systems that require long-term operation. A comparative thermodynamic analysis of both types of cooling schemes for SRF systems, referred to as Scheme 1 (a cryogenic distribution system with distributed heat exchangers) and Scheme 2 (a cryogenic distribution system with central heat exchangers), was presented in this paperThe length and size of process transfer lines, as well as the heat loads subjected to their components, of cryogenic distribution systems were introduced. In addition, the unsteady state cooldown process for the CSNS-II SRF cryomodules was investigated. The analysis results that included temperature and pressure profiles along the linac distance, as well as distributions of JT expansion effectiveness, mass flow rate, and cryomodule exegetic efficiency. Furthermore, the exergy analysis and refrigeration power are investigated using a neural network optimized by a novel sparrow search algorithm genetic algorithm (SSA-GA). Results show that, Scheme 1 is more advantageous than Scheme 2 because it can save maintenance time. From 300 K to 4.5 K, the total cooldown time of SRF cryomodules is approximately 28 h. The maximum ΔP is around 1.1 bara, which can be considered in the acceptable range. The prediction of ηex is stable at the 7th epoch after being optimized by SSA-GA, and the MSE is 1 × 10-5. And the error between the predicted and true values of the BP neural network after SSA optimization is very small (less than 0.1%), approaching zero, indicating that the BP optimized by SSA achieves good prediction. This paper's work can serve as a solid foundation for the construction and operation of the CSNS-II.

Toward 80% Efficiency in a Super Klystron-Like Relativistic Backward Wave Oscillator With Second and Third Harmonic Coaxial-Premodulation Cavity

To further increase the beam-wave conversion efficiency, a super klystron-like relativistic backward wave oscillator (RBWO) with coaxial-premodulation (CPM) cavity is proposed. Compared with previous dual-premodulation (DPM) cavities, the CPM cavity intensifies the second and the third harmonic components, resulting in a larger fundamental harmonic current both in the slow-wave structure (SWS) and the extraction cavity, and, consequently, leads to an enhanced microwave power generation by the Cherenkov radiation and transition radiation. In the particle-in-cell simulation, an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{X}$</tex-math> </inline-formula> -band microwave with a power of 3.44 GW and record efficiency of up to 80% has been achieved.

Optimization of Variable Parameters in Diode Pumped SHG Nd-YAG Lasers

Second Harmonic Generation (SHG) produces many parameters which are the consequences of interaction of fundamental incident power &nbsp;and those created inside the second harmonic cavity, external employing monolithic crystals. In this study, a low power of &nbsp;continuous wave (CW) Nd-YAG laser with principal output of &nbsp;and maximum power of &nbsp;theoretically was used. The crystal is [MgO: LiNbO3] which is lithium niobate, magnesium oxide doped with specific optical properties explained, the parameters in questions are both reflection &nbsp;and circulating &nbsp;powers in the second harmonic cavity. Both are functions of fundamental incident power . The results are compared with their experimental correspondents and interpretation for the causes is discussed.

RF design and frequency sensitivity analysis of a 1500 MHz passive third harmonic superconducting cavity for the SILF

To reduce Touschek scattering in the beam and extend the lifetime of the beam in the Shenzhen Innovation Light-source Facility (a fourth-generation light source), a 1500 MHz passive third harmonic system will be used. The present work is devoted to the RF design and frequency sensitivity analysis of the 1500 MHz passive third harmonic superconducting cavity, optimizing the RF parameters of the cavity, and giving a frequency scheme for the cavity in fabrication. The reliability of the cavity during operation is taken as the main goal for the optimization of the geometrical parameters, and its structural and RF parameters are obtained with E peak/E acc of 2.17, B peak/E acc of 5.12 mT/(MV/m) and G · R/Q of 25052 at 2 K. A pair of fluted beam pipes are used to propagate the higher order modes (HOMs) of the harmonic cavity, allowing a smooth transition of the first dipole mode to the absorber located at room temperature area. For the frequency sensitivity analysis, the frequency variations of the cavity in fabrication are obtained by multi-physics coupling simulation in the paper, which gives the target frequency of the cavity between welding and preloading. After electron beam welding (EBW), the resonant frequency of the cavity should be maintained at 1500.096 MHz, and the pre-tuning target frequency is 1497.456 MHz. The slow tuning range is ±400 kHz, the fast-tuning range is 600 Hz, and the maximum allowable tuning force is 15 kN.

Design and verification of a high-gradient and high-power 2nd harmonic cavity for the China Spallation Neutron Source upgrade project

Here, we report our recent progress in the design, fluid thermodynamics simulation, and high-power test of the2nd harmonic cavity for the China Spallation Neutron Source Phase II. A high-performance and large-size magnetic alloy (MA) core was developed as the load material for the radiofrequency cavity to achieve a high gradient of 40 kV/m. The water-cooling structure and cooling efficiency were studied and improved through numerical analysis and thermal experiments. The long-term stability of the cavity, especially the waterproofness of the MA cores with high heat load, was verified by high power tests.

Experimental verification and analysis of the beam loading effect based on precise bunch-by-bunch 3D position measurement

The beam loading effect is one of the main bottlenecks in further improving the performance of synchrotron radiation light sources. Although theoretical analysis and numerical simulation of the beam loading effect have been very well performed, the corresponding diagnostic tools were rather poor, and in most cases, only streak cameras were used to observe the synchronous phase distribution and the intensity distribution in bunch trains. SSRF developed a precise bunch-by-bunch 3D beam position measurement system. This system allows precise measurement and recording of both transient state data and steady-state beam parameters (filling pattern, synchronous phase). Therefore, experimental verification and analysis of the beam loading effect can be more comprehensive and accurate. In this paper, the measurement results of the synchronous phase, synchrotron frequency and synchrotron damping time with and without a third harmonic cavity are introduced and discussed.

Commissioning and First Results of the SSRF Phase-II Beamline Project

The SSRF Phase-II Beamline Project started November 20, 2016 with a 6-year construction period. This project is mainly to construct 18 new beamlines and more than 30 end-stations, as well as the corresponding storage ring upgrades, the user auxiliary laboratories, the beamline technology support laboratories, and the infrastructures. Till now, 11 beamlines have passed the technical acceptance test and been in running. The remaining seven beamlines will be finishing their technical acceptance test soon. The commissioning of the upgraded accelerator is successful including the lattice modification, the new 3rd harmonic superconducting cavity installation and the 650 W helium cryogenic system construction.

Study of longitudinal phase space for typical beam injector via analytical method

Longitudinal phase space (LPS) manipulation for high-brightness electron beams is critical for successful development of photocathode injectors, especially those are expected to generate ultra-short bunches. Compared with commonly used schemes involving dedicated devices and complicated peripheral sub-systems, a convenient approach for LPS linearization, which is based on adjusting injecting RF phase, has advantages in the typical injectors those consisting of RF cavities and a drift tube. Therein, instead of conventional higher-order harmonic cavities, natural evolutions in the following drift space have been applied to compensate nonlinearity of the LPS from the injector. Since adequate characterizations for the LPS are of importance to promote the application of such approach, elaborate analytical derivations from a new view have been conducted to demonstrate the manipulation scheme, and numerical simulations have been performed to further validate the theoretical results. Contributions of inevitable phase slippages have also been analyzed via analytical and numerical methods. Additionally, to cross-check the analysis results, multi-particle simulations have been performed as well. All of the results indicate that the LPS of the typical injector can be linearized through the natural evolutions during the drifting process. Then such method presents to be a conceivable supplement to conventional LPS manipulation approaches.

Rf cavity point-charge wakefield computation through a hybrid analytical and numerical approach

We study short-range geometric wakefields of a normal conducting third harmonic cavity, developed by ALBA, which is currently under investigation for the BESSY II main storage ring upgrade. As is commonly done to enhance the shunt impedance, the single cell cavity shape includes smooth nose-cone transitions to the outside beam pipe, which significantly affects the wakefields. Utilizing the general approach developed by the earlier work [B. Podobedov and G. Stupakov, Phys. Rev. ST Accel. Beams 16, 024401 (2013)], a model of point-charge wakefield for cavities of this type is suggested. The wakefield model consists of two parts: the singular part, inherently difficult for numerical codes, is found analytically, and the nonsingular part, which could be retrieved from relatively nondemanding numerical wakefield computations. Based on this hybrid approach, the wakefields due to arbitrary short bunches can be readily obtained both efficiently and accurately. The model was cross-checked against direct numerical simulations and a good agreement was found within the entire range of bunch lengths relevant to potential applications, from sub-millimeter down to $1\text{\ensuremath{-}}\ensuremath{\mu}\mathrm{m}\text{ }\text{ }\mathrm{rms}$. We also observed that the wakefield model of a single cavity applies equally well to a small number of coupled cavities after some straightforward parameter scaling.

Novel perturbation method for judging the stability of the equilibrium solution in the presence of passive harmonic cavities

When using the harmonic cavity to stretch the beam in electron storage rings, we expect the beam can be lengthened effectively and also stably. Semianalytical approaches can be used to obtain the equilibrium distribution but generally failed in the prediction of its stability. In this work, a novel perturbation method is proposed to check whether the calculated equilibrium solution can survive from the $l=1$ mode perturbation. For the case of uniform beam filling, we derive a simple formula that can determine the threshold of $l=1$ mode instability under specific parameters, which is well verified with tracking simulation for the Hefei Advanced Light Facility storage ring.