Heat Treatment for Jacketed Half-wave Resonator Cavity (original) (raw)
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Heat Treatment for a Prototype Half-Wave Resonator Cavity
29\textsuperscript{th} Linear Accelerator Conf. (LINAC'18), Beijing, China, 16-21 September 2018, 2019
Performance of a superconducting cavity, which is made of niobium, tends to be degraded easily depending on the surface resistance. Surface residual resistance of the cavity can be increased during the cavity fabrication process such as pressing, cutting and welding, because these multiple steps can lower the crystallinity of the cavity surface not only by disordering the lattice atoms but also by supplying lattice atoms with impurity atoms. Among the impurity atoms, hydrogen is a well-known impurity that lowers the cavity performance in the form of Q-disease. High temperature heat treatment was performed to remove impurity gas (mainly hydrogen) from the surface of a cavity, and to anneal the cavity to increase the crystllinity. Optical images of the heat treated niobium sample were investigated. Crystallinity was improved after the heat treatment by investigating X-ray diffraction (XRD), thus it confirmed that the annealing was successfully carried out. The residual gas analysis (RGA) was investigated and it confirmed that hydrogen was removed successfully during the heat treatment.
Investigation of High Temperature Baking of Jacketed Quarter Wave Resonators
2018
The Superconducting booster Linac at IUAC has been delivering accelerated ion beams for scheduled experiments since 2013 [1, 2]. It has three accelerating modules with eight Quarter Wave Resonators (QWR) (opt=0.08) in each module. The QWRs for the first module were built at Argonne National Laboratory while those for the second and third modules have been built in-house. During the electropolishing of one of the indigenously built resonators (QWR # I03) the RF surface got spoiled due to a wrong mixture of acid that was meant for etching. In subsequent cold tests of the cavity, its performance was poor (2.6 MV/m @ 4 W). There was evidence of Q disease also, as the performance deteriorated further (~20%) when the cavity was held at 100-120 K for ~8 hours .In an attempt to recover the cavity, it was baked at 650 °C for 10 hours along with its outer stainless steel jacket. A series of tests were conducted thereafter, wherein a substantial improvement (A factor of two) in the performanc...
Review of Scientific Instruments, 1995
A thermal-wave resonant cavity was constructed using a thin dUminUM foil wall as the intensity-modulated-laser-beam induced oscillator source opposite a pyroelectric polyvilidene fluoride wall acting as a signal transducer and cavity standing-wave-equivalent generator. It was shown that scanning the frequency of oscillation produces the fundamental and higher overtone resonant extrema albeit with increasingly attenuated amplitude-a characteristic of thermal-wave behavior. Experimentally, scanning the cavity length produced a sharp lock-in in-phase resonance with simple linewidth dependencies on oscillation (chopping) frequency and intracavity gas thermal diffusivity. The thermal diffusivity of air at 294 K was measured with three significant figure accuracy: 0.21 l&O.004 cm%. The novel resonator can be used as a high-resolution thermophysical property sensor of gaseous ambients. 0 1995 American Institute of Physics.
Measurements of SCRF Cavity Dynamic Heat Load in Horizontal Test Sysytem
2010
The Horizontal Test System (HTS) at Fermilab is currently testing fully assembled, dressed superconducting radio frequency (SCRF) cavities. These cavities are cooled in a bath of superfluid helium at 1.8K. Dissipated RF power from the cavities is a dynamic heat load on the cryogenic system. The magnitude of heat flux from these cavities into the helium is also an important variable for understanding cavity performance. Methods and hardware used to measure this dynamic heat load are presented. Results are presented from several cavity tests and testing accuracy is discussed.
Vertical Test of Pefp Prototype SRF Cavity
2011
The PEFP Proton linac is a 100-MeV machine which consists of a proton injector, RFQ and DTL. For the extension of the machine beyond 100 MeV, SRF technology is under consideration. As a prototyping activity, a superconducting RF cavity with a geometrical beta of 0.42 and a resonant frequency of 700 MHz has been designed, fabricated and tested. The cavity is an elliptical shape with 5 cells stiffened by double-ring structure. A design accelerating gradient is 8.0 MV/m at the operating temperature of 4.2 K and maximum duty factor is 9 %. For the vertical test of the cavity, a cryostat with vacuum jacket and multi-layer insulation was prepared. The RF system for driving the cavity is based on PLL to track the resonant frequency. In case of lack of RF power, a two-way RF power combiner based on split coaxial transmission line is considered. The details of the vertical test setup and test results will be presented in this paper.
Impact of Trapped Flux and Thermal Gradients on the SRF Cavity Quality Factor
2012
The obtained Q0 value of a superconducting niobium cavity is known to depend on various factors like the RRR of the Niobium material, crystallinity, chemical treatment history, the high-pressure rinsing process, or effectiveness of the magnetic shielding. We have observed that spatial thermal gradients over the cavity length during cool-down appear to contribute to a degradation of Q0. Measurements were performed in the Horizontal Bi-Cavity Test Facility (HoBiCaT) at HZB on TESLA type cavities as well as on discand rod-shaped niobium samples equipped with thermal, electrical and magnetic diagnostics. Possible explanations for the effect are discussed.
Low Temperature Test of HWR Cryomodule
Applied Science and Convergence Technology, 2016
Low temperature test for half-wave resonator (HWR) cryomodule is performed at the superfluid helium temperature of 2 K. The effective temperature is defined for non-uniform temperature distribution. Helium leak detection techniques are introduced for cryogenic system. Experimental set up is shown to make the low temperature test for the HWR cryomodule. The cooldown procedure of the HWR cryomodule is shown from room temperature to 2 K. The cryomodules is precooled with liquid nitrogen and then liquid helium is supplied to the helium reservoirs and cavities. The pressure of cavity and chamber are monitored as a function of time. The vacuum pressure of the cryomodule is not increased at 2 K, which shows leak-tight in the superfluid helium environment. Static heat load is also measured for the cryomodule at 2.5 K.
Thermal-wave resonant cavity signal processing
Review of Scientific Instruments, 2019
The thermal-wave resonant cavity (TWRC) technique has been used for thermal diffusivity measurements by many researchers. This study aims to reduce the uncertainty associated with TWRC signal processing (curve fitting) by means of numerical simulation and experimental verification. Simulations show that the plot of signal amplitude versus cavity length can be fitted to a simplified model reported previously when the initial fitting position is at least twice the thermal-wave diffusion length (2 µ g), and that the uncertainty caused by different end positions is negligible in the range of 6-10 µ g. Upon consideration of the simulation results, signal-to-noise ratio, and clearly defined amplitude curve shape, fitting ranges of about 2.2-8.0 µ g and 2.2-8.7 µ g were chosen for the experimental data. Thermal diffusivity values (1.438 ± 0.001) × 10 −7 and (1.436 ± 0.001) × 10 −7 m 2 s −1 , respectively, were obtained for distilled water, in excellent agreement with the accepted literature value. The ratio of standard deviation to the mean value is smaller than 0.07%, one order of magnitude lower than typical results reported in the literature. Similar simulation results were obtained for air and methanol as intra-cavity samples.
Review of Scientific Instruments, 1998
The operating thermal power transfer mechanisms in a thermal-wave resonant cavity were explored theoretically and experimentally. Both steady-state ac ͑thermal-wave͒ and dc temperature rise were considered, and conduction and radiation heat transfer modes were found to co-exist in the cavity. By introducing controlled variable offset dc resistive heating superposed on the fixed-amplitude thermal-wave oscillation, it was also found that the thermal-diffusivity values of the intracavity gas can vary sensitively as a function of the dc temperature rise within a thin boundary layer adjacent to the cavity thermal source ͑a metallic Cr-Ni alloy strip͒. This resulted in the measurement of the temperature dependence of the thermal diffusivity of air. Furthermore, the observed dominance of thermal-wave radiation power transfer in the phase channel of the thermal-wave signal at large cavity lengths allowed the measurement of the absolute infrared emissivity of the thin Cr-Ni strip source material: ϭ0.091Ϯ0.004.