Many modern and future particle accelerators employ high gradient superconducting RF (SRF) to generate beams of high energy, high intensity and high brightness for research in high energy and nuclear physics, basic energy sciences, etc. In this paper we report the record performance large-scale SRF system with average beam accelerating gradient matching the International Linear Collider (ILC) specification of 31.5 MV m −1 . Design of the eight cavity 1.3 GHz SRF cryomodule, its performance without the beam and results of the system commissioning with high intensity electron beam at Fermilab Accelerator Science and Technology (FAST) facility are presented. We also briefly discuss opportunities for further beam studies and tests at FAST including those on even higher gradient and more efficient SRF acceleration, as well as exploration of the system performance with full ILC-type beam specifications.

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In a storage ring, turn-to-turn fluctuations in the intensity of spontaneous synchrotron radiation occur due to two mechanisms. The first mechanism is the quantum uncertainty in the number of emitted photons. The second mechanism is the turn-to-turn variations in the relative positions of classical pointlike electrons in the bunch. We present a unified description of both effects in the framework of quantum optics. We derive an equation for the fluctuations for an arbitrary degree of coherence, which generalizes previously reported results for temporally incoherent radiation. We compare the predictions of our calculation with a previous experiment at Brookhaven National Laboratory, where the latter mechanism was dominant and propose a new dedicated experiment in the Integrable Optics Test Accelerator (IOTA) at Fermilab, where the two mechanisms may have comparable contributions to the fluctuations. Finally, our calculation shows that the magnitude of the fluctuations is rather sensitive to the dimensions and the shape of the electron bunch, thereby indicating possible applications in beam instrumentation. In particular, the small vertical size of the flat beams in IOTA may be estimated via these fluctuations, whereas measurement by a conventional synchrotron radiation monitor is difficult due to the diffraction limit.

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The interaction of creep and fatigue in structural materials under high-cycle loading is modeled using isochronic limit stress diagrams. The hypothesis of a unified limit diagram invariant to the time to failure is used. The unified diagram is given by a cosine power function with the exponent describing creep-fatigue interaction and encompasses convex, concave, and S-like curves. The models build are tested for aluminum alloys, heat-resistant steels, creep-resistant steels and alloys, and laminates Keywords: creep-fatigue interaction, high-cyclic fatigue, isochronic limit stress diagram, time to failure, unified limit diagram, cyclic stressIntroduction. The majority of modern design rules and strength standards place high emphasis on endurance evaluation in the conditions of simultaneous creep and fatigue. This problem is of paramount importance for boilers, high-pressure vessels, blades and disks of gas turbines, pipelines, and other structures operating at high temperatures [1,5,7,13,15,16,19]. In polymeric and composite materials, the interaction of creep and fatigue is even manifested at room temperatures [17].The classical creep-fatigue analysis is based on the hypotheses of linear and nonlinear damage accumulation [15]. The measure of damage in this case is "partial times" [11, 18, etc.] and some hidden (internal) parameter [4, 8, 15, etc.] with the corresponding evolutionary equation. Though still inadequately validated, this approach produced good results in some cases, especially in the case of nonstationary loading.An efficient means for evaluation of creep-fatigue interaction under high-cycle loading is limit stresses diagrams [6,14]. These diagrams correlate the static and cyclic load components responsible for creep and fatigue, respectively. It was experimentally shown in [3,15] that there is a unified limit diagram, invariant to the time to failure, for the majority of structural materials. In the present paper, we will use the concept of unified limit stress diagram to model creep-fatigue interaction.

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The paper is concerned with the problem of predicting nonlinear creep strains and time to ductile rupture of prismatic rods under constant tension. The material of the rod is assumed isotropic, homogeneous, and perfectly plastic. The problem is solved using models that take into account the change in the geometry of the rod during creep, the finiteness of the creep strains, and the effect of the initial and actual elastic strains. The conditions whereby the characteristic dimension of the rod tends to infinity and the accumulated and real strains in the viscous flow are limited are used as a failure criterion. The calculated results are compared with experimental data for a number of steels and alloys to formulate the conditions for the ductile rupture and embrittlement of metallic materials under uniaxial creep Keywords: prismatic rod, metallic perfectly elastoplastic material, uniaxial tension, nonlinear creep, finite strains, actual stress, ductile rupture, required plasticity, initial (starting) plasticityIntroduction. The reliable prediction of the time to creep failure of materials and structural members is based on the concepts of ductile, brittle, and mixed rupture [10, 16-18, 20, 21].The concept of ductile rupture seems to be best justified. It presupposes analyzing the behavior of loaded bodies under large (finite) strains. Hoff's model [19] was apparently the first to implement the concept of ductile rupture to a tension rod. The model is based on the fact that the characteristic dimension of the rod tends to infinity and predicts the time to failure using the steady-state creep law.The ductile-rupture model was tested in [19] using the experimental data from [14] for smooth cylindrical aluminum-alloy specimens. It was shown that the calculated results are in good agreement with the experimental data for the majority of the alloys. Similar results were obtained in [1,4,6,7] in studying the creep rupture of samples made of some creep-resistant steels and alloys.It should be noted that Hoff's model was not widely used to predict the creep rupture of materials. This is due apparently to the intensive use of various empirical and semiempirical relations based on extensive experimental data. An important factor is the absence of clear quantitative criteria to identify ductile-rupture zones. As a consequence, incorrect use of the model may result in a substantial (from one to two orders of magnitude) disagreement between theory and experiment.The present paper uses Hoff's concept of viscous flow to construct a nonlinear creep model and a refined ductile-rupture model and validates them against some metallic materials to formulate a necessary ductile-rupture condition.1. Problem Formulation. Subject of Study. Let us consider creep and creep rupture of a viscoelastic homogeneous rod at constant temperature q and under a tensile force applied at the rod ends: