اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدCoaxial multi-mode cavities for fundamental SRF research in an unprecedented parameter space
89
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
Recent developments in superconducting radio-frequency (SRF) research have focused primarily on high frequency elliptical cavities for electron accelerators. Advances have been made in both reducing RF surface resistance and pushing the readily achievable accelerating gradient by using novel SRF cavity treatments including surface processing, custom heat treatments, and flux expulsion. Despite the global demand for SRF based hadron accelerators, the advancement of TEM mode cavities has lagged behind. To address this, two purpose-built research cavities, one quarter-wave and one half-wave resonator, have been designed and built to allow characterization of TEM-mode cavities with standard and novel surface treatments. The cavities are intended as the TEM mode equivalent to the 1.3GHz single cell cavity, which is the essential tool for high frequency cavity research. Given their coaxial structure, the cavities allow testing at the fundamental mode and higher harmonics, giving unique insight into the role of RF frequency on fundamental loss mechanisms from intrinsic and extrinsic sources. In this paper, the cavities and testing infrastructure are described and the first performance measurements of both cavities are presented.
قيم البحث
اقرأ أيضاً
In this letter, we present the frequency dependence of the vortex surface resistance of bulk niobium accelerating cavities as a function of different state-of-the-art surface treatments. Higher flux surface resistance per amount of trapped magnetic f
ield - sensitivity - is observed for higher frequencies, in agreement with our theoretical model. Higher sensitivity is observed for N-doped cavities, which possess an intermediate value of electron mean-free-path, compared to 120 C and EP/BCP cavities. Experimental results from our study showed that the sensitivity has a non-monotonic trend as a function of the mean-free-path, including at frequencies other than 1.3 GHz, and that the vortex response to the rf field can be tuned from the pinning regime to flux-flow regime by manipulating the frequency and/or the mean-free-path of the resonator, as reported in our previous studies. The frequency dependence of the trapped flux sensitivity to the amplitude of the accelerating gradient is also highlighted.
Buffered Chemical Polishing (BCP) was the most conventional polishing method for superconducting radio frequency (SRF) Niobium (Nb) cavity surface preparation before the discovery of Electropolishing (EP), which is superior to BCP in high gradient pe
rformance. The High Field Q-slope (HFQS) is perfectly eliminated by taking the low temperature bake (LTB) post EP, which guarantees high gradient performance in EPed cavities. The mechanism of the HFQS is well understood for EPed cavities. On the other hand, there is no common consensus on the HFQS with BCP, since even BCP with LTB does not always resolve the HFQS. BCP is much easier to apply and still an important preparation technology for very complicated SRF structures like low beta cavities. Therefore, overcoming the issue of HFQS with BCP is highly beneficial to the SRF community. This paper mines a large number of available data sets on BCPed cavity performance with fine grain, large grain, and even single crystal niobium materials under different experimental settings. We found that all existing explanations for HFQS with BCP are inconsistent with some experimental results, and propounded nitrogen contamination as a new model. We checked that nitrogen contamination agrees with all existing data and nicely explains unresolved phenomena. Combining these evidence, we deduce that nitrogen contamination is the cause of HFQS in BCP.
The surface resistance of an RF superconductor depends on the surface temperature, the residual resistance and various superconductor parameters, e.g. the energy gap, and the electron mean free path. These parameters can be determined by measuring th
e quality factor Q0 of a SRF cavity in helium-baths of different temperatures. The surface resistance can be computed from Q0 for any cavity geometry, but it is not trivial to determine the temperature of the surface when only the temperature of the helium bath is known. Traditionally, it was approximated that the surface temperature on the inner surface of the cavity was the same as the temperature of the helium bath. This is a good approximation at small RF-fields on the surface, but to determine the field dependence of Rs, one cannot be restricted to small field losses. Here we show the following: (1) How computer simulations can be used to determine the inside temperature Tin so that Rs(Tin) can then be used to extract the superconducting parameters. The computer code combines the well-known programs, the HEAT code and the SRIMP code. (2) How large an error is created when assuming the surface temperature is same as the temperature of the helium bath? It turns out that this error is at least 10% at high RF-fields in typical cases.
Cool-down dynamics of superconducting accelerating cavities became particularly important for obtaining very high quality factors in SRF cavities. Previous studies proved that when cavity is cooled fast, the quality factor is higher than when cavity
is cooled slowly. This has been discovered to derive from the fact that a fast cool-down allows better magnetic field expulsion during the superconducting transition. In this paper we describe the first experiment where the temperature all around the cavity was mapped during the cavity cool-down through transition temperature, proving the existence of two different transition dynamics: a sharp superconducting-normal conducting transition during fast cool-down which favors flux expulsion and nucleation phase transition during slow cool-down, which leads to full flux trapping.
In this Letter, we present a study of the confinement properties of point-defect resonators in finite-size photonic-bandgap structures composed of aperiodic arrangements of dielectric rods, with special emphasis on their use for the design of cavitie
s for particle accelerators. Specifically, for representative geometries, we study the properties of the fundamental mode (as a function of the filling fraction, structure size, and losses) via 2-D and 3-D full-wave numerical simulations, as well as microwave measurements at room temperature. Results indicate that, for reduced-size structures, aperiodic geometries exhibit superior confinement properties by comparison with periodic ones.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
