System For Superconducting Cavities Research Articles

Insights on grain boundary effects on crack formation and propagation in Nb3Sn coatings at low temperature and high strain rates: a molecular dynamics simulation study

Mechanical behavior of Nb3Sn coatings is inherently correlated with the anti-interference ability of the superconducting cavity system and the amplitude and phase stability of the cavity field. We report on atomic-scale simulation and analysis of grain boundary effects on the crack formation and propagation in Nb3Sn coatings at low temperature and high strain rates. For tensile-deformed single crystal Nb3Sn, accompanied by the occurrence of slips, micro voids propagate along the () and (210) planes (stretching the crystal along the [100] direction), and subsequently coalesce, leading to the cracks formation. For tensile-deformed single-crystal Nb3Sn coating on Nb substrate, it fails by crack propagation in the coating before showing significant yielding plateaus. In the Nb3Sn coating, the slip bands on the (201) and () planes meet and merge, inducing the breaking of atomic bonds and the formation of voids at the slip band intersections, and the subsequent micro-crack initiation. The misfit dislocations of Nb3Sn/Nb heterostructure interface and the dislocations nucleated on slip systems control the plastic deformation of the Nb substrate, causing the BCC-to-FCC and FCC-to-HCP phase transformation in the substrate, for which, ductile fracture occurs after necking. For polycrystalline Nb3Sn coating on Nb substrate, the simulations demonstrate that cracks propagate entirely along grain boundaries, exhibiting the intergranular fracture characteristics. The composite exhibits a significant strain rate effect. At high strain rates, crack propagation across grain boundaries in Nb3Sn is hindered, dislocations are emitted into the both adjacent grains from the grain boundary facets, they glide across the grain, and voids are nucleated at the intersections of dislocations inside the grains, which leads to the formation of voids and ultimately the occurrence of trans-crystalline fracture. The findings provide important information about the crack evolution in Nb3Sn coatings, which are critical to the fabrication and performance analysis of Nb3Sn superconducting radio frequency cavities.

Low beta superconducting cavity system design for HIAF iLinac

A superconducting ion-Linac (iLinac), which is supposed to work as the injector in the High Intensity heavy-ion Accelerator Facility project, is under development at the Institute of Modern Physics (IMP), Chinese Academy of Sciences. The iLinac is a superconducting heavy ion linear accelerator approximately 100 meters long and contains 96 superconducting cavities in two types of 17 cyromodules. Two types of superconducting resonators (quarter-wave resonators with a frequency of 81.25 MHz and an optimal beta β = v/c = 0.07 called QWR007 and half-wave resonators with a frequency of 162.5 MHz and an optimal beta β = 0.15 called HWR015) have been investigated. The cavity design included extensive multi-parameter electromagnetic simulations and mechanical analysis，and its results are described in details. The fundamental power coupler and cavity dynamic tuner designs are also presented in this article. The prototypes are under manufacturing and expected to be ready in 2023.

Research of the 499.8 MHz superconducting cavity system for HALF

A 499.8 MHz superconducting cavity system has been proposed to be used to in the storage ring of Hefei Advanced Light Facility (HALF). The cavity will be operated at 4.2 K providing 1.5 MV accelerating voltage and 140 kW of power to the electron beam. The research of the 499.8 MHz superconducting RF system has been made. The optimization design for the 499.8 MHz superconducting cavity and its ancillaries such as fundamental power coupler, HOM damper have been investigated. And some good results are also presented in this paper. Especially, the vertical test result shows that the Q0 of the new superconducting cavity is 1.00∗109 at the accelerating gradient being 16 MV/m (at the accelerating voltage being 3.84 MV). It should be noted that the loss of pure Ti flange was not deducted.

Numerical gate synthesis for quantum heuristics on bosonic quantum processors

There is a recent surge of interest and insights regarding the interplay of quantum optimal control and variational quantum algorithms. We study the framework in the context of qudits which are, for instance, definable as controllable electromagnetic modes of a superconducting cavity system coupled to a transmon. By employing recent quantum optimal control approaches described in (Petersson and Garcia, 2021), we showcase control of single-qudit operations up to eight states, and two-qutrit operations, mapped respectively onto a single mode and two modes of the resonator. We discuss the results of numerical pulse engineering on the closed system for parametrized gates useful to implement Quantum Approximate Optimization Algorithm (QAOA) for qudits. The results show that high fidelity (>0.99) is achievable with sufficient computational effort for most cases under study, and extensions to multiple modes and open, noisy systems are possible. The tailored pulses can be stored and used as calibrated primitives for a future compiler in circuit quantum electrodynamics (cQED) systems.

The development of the 499.8 MHz superconducting cavity system for BEPCII

In order to accommodate the luminosity improvement strategy, two superconducting 499.8 MHz radio frequency (rf) cavities have been adopted for the Upgrade project of Beijing Electron Positron Collider (BEPCII), a double-ring electron–positron collider as well as a synchrotron radiation (SR) light source. The in-house development of the 499.8 MHz superconducting cavity system was initiated at IHEP since 2008. One prototype niobium cavity with all the parts except for the flanges and the pickup port formed by spinning was fabricated and then vertical-tested successfully in July 2011. Four prototype input couplers were manufactured and high-power tested with one reaching a maximum rf power of continuous wave (cw) 420 kW. One prototype HOM damper with a satisfactory absorbing efficiency at the desired frequency band was also constructed and high power tested up to cw 4.4 kW. In the meanwhile, a frequency tuner consisting of a stepping motor and a piezoelectric oscillator was developed. Finally, the bare cavity was dressed with one input coupler, two HOM dampers and one frequency tuner, mounted in a domestic-developed cryostat and then high-power tested successfully in Oct. 2011. The achieved accelerating voltage is 2.2 MV with corresponding Q0 measured to be 5.8 × 108, beyond the designed goal. This is the first in-house developed 499.8 MHz HOM-damped superconducting cavity system in China. The design, fabrication, post processing and tests of the niobium bare cavity and its auxiliaries, as well as the horizontal high-power test of the cavity system are presented.

Cryomodule tests of four Tesla-like cavities in the Superconducting RF Test Facility at KEK

A 6-m cryomodule including four Tesla-like cavities was developed, and was tested in the Superconducting RF Test Facility phase-I at KEK. The performance as a total superconducting cavity system was checked in the cryomodule tests at 2 K with high rf power. One of the four cavities achieved a stable pulsed operation at $32\text{ }\text{ }\mathrm{MV}/\mathrm{m}$, which is higher than the operating accelerating gradient in the ILC. The maximum accelerating gradient (${E}_{\mathrm{acc},\mathrm{max}}$) obtained in the vertical cw tests was maintained or slightly improved in the cryomodule tests operating in a pulse mode. Compensation of the Lorentz force detuning at $31\text{ }\text{ }\mathrm{MV}/\mathrm{m}$ was successfully demonstrated by a piezo tuner and predetuning.