Mechanical Properties of High RRR Niobium at Cryogenic Temperatures

IEEE Trans. Appl. Supercond.

Wang

Furuya

et al. 2011

An SRF cavity is generally manufactured with a shell structure to decrease the temperature of the inner surface and consequently to decrease the rf surface resistance. During operation, the SRF cavity is immersed in a bath of liquid helium while its interior is maintained under ultra-high vacuum. To be loaded under a condition of external pressure at a cryogenic temperature, a pressure test at room temperature is requested for safety examination. Explicit calculation and estimation of buckling to prove its structural strength is thus essential. With a great stress on the cavity, the nonlinear behavior of the stress-strain curve of niobium generates the elastoplastic buckling behavior different from elastic buckling. The stress-strain curve of niobium depends on the formation, fabrication, and treatment, thus modifying the buckling behavior. We investigated the buckling behavior of a 500-MHz SRF cavity under external pressure, for which various stress-strain curves were applied. Finite-element software (ANSYS) was used to calculate the limit pressure and post-buckling behavior, with an incremental arc-length control scheme to include effects of nonlinearities of both the geometry and the material property. Not only the limit pressure but also the buckling mode vary with the assigned material property and boundary conditions.

Section: Materials Propertymentioning

confidence: 99%

“…The various tensile tests [4]- [6] all reveal the yielding stress of niobium increases dramatically when it is cooled down to the liquid helium temperature. Consequently the cavity strength is much worse at room temperature.…”

Section: Introductionmentioning

confidence: 97%

Effects of Material Properties on the Elastoplastic Buckling of an SRF Cavity Under External Pressure

IEEE Trans. Appl. Supercond.

Wang

Furuya

et al. 2011

“…According to the test results at room temperature [3], [4], the highly pure niobium has Young's modulus 105 GPa. Because copper has a similar Young's modulus and is much cheaper than niobium, some copper bent waveguides were manufactured for buckling tests.…”

Section: A Copper Waveguidementioning

confidence: 99%

Elastoplastic Buckling on the Bent Waveguide of CESR-Type SRF Cavity

IEEE Trans. Appl. Supercond.

Wang

Yang

et al. 2007

A superconducting radio-frequency (SRF) cavity module of CESR-type has been adopted for some advanced accelerators. During operation, the pressure in the liquid-helium vessel acts on the cavity wall, but an ultrahigh vacuum must prevail inside the cavity; the cavity structure must be thus pressure-tested at ambient temperature as a standard procedure for safety. During the pressure test elastoplastic buckling might occur on this SRF cavity and its bent waveguide section, being a shell-like structure. A nonlinear finite-element model for computation is established to assess the mechanism of buckling and post-buckling of the bent waveguide. Some test results with copper bent waveguides are presented. The critical pressure and buckling pattern are strongly affected by the material property and the thickness of the structure and the U-channel.

“…At cold, only the equivalent state is interested herein. From the available data [2,3], a coefficient of thermal expansion of 4.94×10 -6 K -1 ; Young's modulus of 125 GPa, and Poisson's ratio of 0.38 were selected as the default niobium properties for numerical computation at 4.22 K in this work, where no other values are specified.…”

Section: Computed Resultsmentioning

confidence: 99%

“…This cavity is immersed in liquid helium to be maintained in a superconducting state. The saturation temperature of He 4 at 1 atm (101.33 kPa) is 4.22 K. The mechanical properties of niobium at room temperature and at cryogenic temperature have been tested [2,3] to some extent, and found to depend very strongly on purity, manufacture, and the post treatment, like heat treatment. However, the cavity structure shrinks as it is cooled down to cryogenic temperature by liquid helium.…”

Section: Introductionmentioning

confidence: 99%

Effects of material properties on resonance frequency of a CESR-III type 500 MHz SRF cavity

Proceedings of the 2003 Bipolar/BiCMOS Circuits and Technology Meeting (IEEE Cat. No.03CH37440)

Chang

et al.

A simulation that links the calculation of mechanical structure and of radio frequency electromagnetic field with the finite element code ANSYS ® is employed in this study. Both efficiency and accuracy of the calculation are thus improved over those of the conventional computation that builds separate models with different codes for each computed domain because information related can be internally transferred between the different computation domains. The resonance frequency changes associated with mechanical properties of niobium are examined. The computed results indicate that the coefficient of thermal expansion significantly affects the shift in resonance frequency that occurs when the cavity is cooled from room temperature to liquid helium temperature. Young's modulus and Poisson's ratio have minor effects.