Thermoacoustic heat pumping study : experimental and numerical approaches

The work presented in this thesis is a contribution to the study of the thermoacoustic heat pumping. The word 'thermoacoustic' refers to the specific thermodynamic interaction between two adjacent media - a compressible fluid and a solid with high heat capacity - subjected to acoustic propagation. While a fluid particle experiences pressure fluctuations and thus temperature changes, it moves along the solid resulting in energy transfer between the fluid and the solid. The present fundamental study focuses on a stack of parallel plane plates plunged in a gas subjected to an acoustic wave. The domain of research is turned towards application. Numerical and experimental approaches are associated allowing the validation of a two-dimensional nonlinear numerical tool. The model is based on the low Mach approximation of the complete set of Navier-Stokes equations. The resulting system is solved numerically at an acoustic time scale and the calculation reiterated on a solid thermal diffusion time scale. A first validation of this tool in the linear thermoacoustic domain is carried out on published results. It leads to some remarks on previous studies justifying the need for completing them. An experimental setup corresponding to the numerical tool was then designed and the interesting operating conditions established. A good comparison between our experimental and our numerical results is then presented

Natural convection in a stack of horizontal plates in a differentially heated cavity

International audienceNatural convection of gas in a differentially heated 2Dcavity partially filled with a stack of horizontal conductingplates is investigated numerically. This specific situationmay be encountered in thermoacoustic wave generators.The thin left and right fluid layers around the stack induceconvective movements which strongly affect thetemperature distribution. In order to predict the actualtemperature field for practical applications, the results areanalysed in terms of convection Darcy type flow througha strongly anisotropic porous medium

Cryogenic thermoacoustics in the SPIRAL2 LINAC

International audience•Investigation of thermo-acoustic oscillation in heavy ions superconducting linear accelerator.•Statistical study of amplitudes and frequencies of TAO.•Comparison of different TAO damping solutions.•Investigation of damping solutions side effects on cryogenic operation. SPIRAL2 is a superconducting LINAC subject to cryogenic thermoacoustic oscillations occurring in its valves boxes. 4 years of monitoring and experimental investigations with thousands of datasets turned these unwanted effects into an opportunity to study and understand thermoacoustics in a complex environment such as a real life accelerator. Without digging deep into Rott’s thermoacoustics theory, thoroughly shown in other works, this paper describes the instrumentation and the methods that prepare more advanced modeling of these phenomena either to damp or to harness the energy of cryogenic thermoacoustics

An Approach for Component-Level Analysis of Cryogenic Process in Superconducting LINAC Cryomodules

International audiencePowerful superconducting linear accelerators feature accelerating sections consisting in a series of cryomod-ules (CM), each hosting superconducting radiofrequency (SRF) cavities cooled by a cryogenic process. Despite the extensive instrumentation used for the tests and valida-tion of the prototype cryomodules, it is usually very complex to link the measured global thermodynamic efficiency to the individual component performance. Previous works showed methods for assessing the global efficiency and even for allocating performances to sets of components, but few went down to a component level. For that purpose, we developed a set of techniques based on customized instrumentation, on dedicated test proto-cols, and on model-based analysis tools. In practice, we exposed the components to various operating conditions and we compared the measured data to the results from a detailed dynamic component model at the same condi-tions. This method was applied to the cryogenic debug-ging phase of the tests of the MINERVA prototype cry-omodule, which, despite the liquid helium shortage, led to an extensively detailed characterisation, for its valida-tion towards the serial construction

ESS Spoke Cryomodule and Test Valve Box

International audienceESS project aims being the world’s most powerful neutron source feeding multidisplinary researches. The superconducting part of the ESS linear accelerator includes 28 b=0.5 352.2 MHz SRF niobium double Spoke cavities. Paired in 13 cryomodules and held at 2K in a saturated helium bath those cavities will generate of an accelerating field of 9MV/m. The prototype Spoke cryomodule holds two cavities and their RF power couplers and integrates all the interfaces necessary to be operational within the linac machine. It is now being fabricated and its assembly will be performed with dedicated tooling and procedures in and out of the clean room. This prototype will be tested by the end of 2015 at IPNO site and then at full power at FREIA (Uppsala university) test stand. A valve box has thus been designed to take into account the specific features of this prototype cryomodule and of the cryogenic environments of both test sites. This valve box is also considered as a prototype of the cryogenic distribution of the linac Spoke section. This element will then be used for the tests of the series cryomodules. We propose to present this prototype Spoke cryomodule for ESS and the test valve box

ESS SRF Linear Accelerator Components Preliminary Results and Integration

International audienceThe European Spallation Source (ESS) is a pan-European project and one of world's largest research infrastructures based on neutron sources. This collaborative project is funded by a collaboration of 17 European countries and is under construction in Lund, Sweden. The 5 MW, 2.86 ms long pulse proton accelerator has a repetition frequency of 14 Hz (4 % duty cycle), and a beam current of 62.5 mA. The Superconducting Radio-Frequency (SRF) linac is composed of three families of Superconducting Radio-Frequency (SRF) cavities, which are being prototyped, counting the spoke resonators with a geometric beta of 0.5, medium-beta elliptical cavities (beta_{g}=0.67) and high-beta elliptical cavities (beta_{g}=0.86). After a description of the ESS linear accelerator layout, this article will focus on the recent progress towards integration of the first test results of the main critical components to be assembled in cryomodules, then in the ESS tunnel

The Superconducting Radio-Frequency Linear Accelerator Components for the European Spallation Source: First Test Results

International audienceThe European Spallation Source requires a pulsed Linac with an average beam power on the target of 5MW which is about five times higher than the most powerful spallation source in operation today. Over 97% of the acceleration occurs in superconducting cavities. ESS will be the first accelerator to employ double spoke cavities to accelerate beam. Accelerating gradients of 9MV/meter is required in the spoke section. The spoke section will be followed by 36 elliptical 704 MHz cavities with a geometrical beta of 0.67 and elliptical 704 MHz cavities with a geometrical beta of 0.86. Accelerating gradients of 20MV/m is required in the elliptical section. Initial gradient test results will be presented in which results exceed expected requirements