Francois Millet | CEA - Academia.edu (original) (raw)

Papers by Francois Millet

Cryogenics

SPIRAL2 is a superconducting LINAC subject to cryogenic thermo-acoustic oscillations occurring in... more SPIRAL2 is a superconducting LINAC subject to cryogenic thermo-acoustic 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 thermo-acoustics 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 modelling of these phenomena either to damp or to harness the energy of cryogenic thermo-acoustics.

IOP Conference Series: Materials Science and Engineering, 2019

In the framework of an international collaboration, a 100 TeV hadron collider in a 100-km long tu... more In the framework of an international collaboration, a 100 TeV hadron collider in a 100-km long tunnel is under study as a future circular collider beyond LHC at CERN. Its design is based on 16-T superconducting magnets cooled at 1.9 K by 10 cryoplants with a unit equivalent capacity of 100 kW at 4.5 K, up to 4 times larger than the present state-of-the-art. Half of the entropic refrigeration load is due to the synchrotron radiation produced by the highenergy proton beams and deposited on beam screens cooled between 40 and 60 K. This nonconventional thermal load distribution is an additional challenge for the cryogenic system. An engineering study on FCC-hh cryoplants is undergoing in progress with world-leader industries to define the preliminary conceptual design of industrial solutions and to confirm innovative technologies. The paper recalls the FCC-hh cryogenic requirements, presents the main results of Linde Kryotechnik study and highlights some identified R&D efforts.

SPIRAL 2 (Caen, France) is a state of the art superconducting linear accelerator composed of 26 q... more SPIRAL 2 (Caen, France) is a state of the art superconducting linear accelerator composed of 26 quarter wave accelerating cavities. Each cavity is plunged in a liquid helium bath at 4.4 K itself surrounded by a thermal shield at 70 K. In this paper, a dynamic model of the cryogenic system of the LINAC is proposed. This model simulates the dynamic behaviour of the 19 cryomodules and their respective valves box connected through the cryodistribution. Model accuracy is evaluated through a comparison between simulation and experimental data. Using the model we should be able to predict the behaviour of the cryogenic system for different beam operating conditions of the accelerator. The model also highlights the link between the cryogenic system and the cavity RF losses through a dynamic estimator of those RF losses in the cavity walls. The latter could be used as a rough estimator of the quality factor of a cavity.

Physical Review Accelerators and Beams

… , 2007. PAC. IEEE, 2007

The LHC is an accelerator with unprecedented complexity where the energy stored in magnets and th... more The LHC is an accelerator with unprecedented complexity where the energy stored in magnets and the beams exceeds other accelerators by one-to-two orders of magnitude. To ensure a safe and efficient machine start-up without being plagued by technical problems, a phase of "hardware commissioning" was introduced: a thorough commissioning of technical systems without beam. This activity started in June 2005 with the commissioning of individual systems, followed by operating a full sector, one eighth of the machine; the commissioning is expected to last until spring 2008 when commissioning with beam will start. The LHC architecture allows the commissioning of each of the eight sectors independently from the others, before the installation of other sectors is complete. An important effort went into the definition of the programme and the organization of the coordination in the field, as well as in the preparation of the tools to record and analyze test results. This paper discusses the experience with this approach, presents results from the commissioning of the first LHC sector and gives an outlook for future activities.

AIP Conference Proceedings, 2006

A new test facility with a cooling capacity respectively of 400W at 1.8K or 800W at 4.5K, is now ... more A new test facility with a cooling capacity respectively of 400W at 1.8K or 800W at 4.5K, is now under nominal operation in SBT (Low Temperature Department) at CEA Grenoble. It has been recently used for thermohydraulic studies of two phase superfluid helium in autumn 2004. In the near future, this test bench will allow: - to test industrial components at 1.8K (magnets, cavities of accelerators) - to continue the present studies on thermohydraulics of two phase superfluid helium - to develop and simulate new cooling loops for ITER Cryogenics, and other applications such as high Reynolds number flows This new facility consists of a cold box connected to a warm compressor station (one subatmospheric oil ring pump in series with two screw compressors). The cold box, designed by AIR LIQUIDE, comprises two centrifugal cold compressors, a cold turbine, a wet piston expander, counter flow heat exchangers and two phase separators at 4.5K and 1.8K. The new facility uses a Programmable Logic Controller (PLC) connected to a bus for the measurements. The design is modular and will allow the use of saturated fluid flow (two phase flow at 1.8K or 4.5K) or single phase fluid forced flow. Experimental results and cooling capacity in different operation modes are detailed.

The LHC is made of eight circular arcs interspaced with eight Long Straight Sections (LSS). Most ... more The LHC is made of eight circular arcs interspaced with eight Long Straight Sections (LSS). Most powering interfaces to the LHC are located in these sections where the particle beams are focused and shaped for collision, cleaning and acceleration. The LSSs are constituted of several unique cryogenic devices and systems like electrical feed-boxes, standalone superconducting magnets, superconducting links, RF cavities and final focusing superconducting magnets. This paper presents the cryogenic commissioning and the main results obtained during the first operation of the LHC Long Straight Sections.

The main cryogenic users of ITER are the superconducting magnet system and the cryogenic vacuum p... more The main cryogenic users of ITER are the superconducting magnet system and the cryogenic vacuum pumps. The magnet system consists of 18 toroidal field and six poloidal field coils and the central solenoid coils. The cryogenic vacuum pumps contain eight pumps for the vacuum vessel, up to four pumps for the neutral beam injectors and two for the tokamak cryostat.

The ITER cryogenic system includes provision for cooling the eight cryo‐sorption pumps that maint... more The ITER cryogenic system includes provision for cooling the eight cryo‐sorption pumps that maintain vacuum conditions within the tokamak plasma vacuum vessel. The eight pumps are operated such that at any given instant four pumps pump the plasma vessel and four pumps are undergoing four sequential stages of regeneration, each having a duration of 150 s. The regeneration includes a cold helium exhaust stage, warm‐up from 4.5 K to 80–100 K, desorption and pump‐out of released gases and cool‐down from 80–100 K to 4.5 K. Thus after every 150 s of operation one of the four pumps is taken off‐line for regeneration and another just‐regenerated pump is restored to the set of four pumps that provide the nominal pumping.

The cooling capacity below 2 K for the superconducting magnets in the Large Hadron Collider (LHC)... more The cooling capacity below 2 K for the superconducting magnets in the Large Hadron Collider (LHC), at CERN, will be provided by eight refrigeration units of 2400 W at 1.8 K, each of them coupled to one 18 kW at 4.5 K refrigerator. The supply of the series units was linked to successful testing and acceptance of the pre-series units delivered by the two selected vendors. The two pre-series units were temporarily installed in a dedicated test station to validate the overall capacity and to properly assess the performance of specific components such as cold compressors. Then the cold compressor cartridges to be installed in the six series and associated spare cartridges have been intensively and systematically tested in the test station. After a brief description of the test bench and the main achieved features of the pre-series units, we will present the results of the tests of 35 cold compressor cartridges. These tests show isentropic efficiency in the 75% range, excellent reproducib...

EPJ Web of Conferences, 2013

ABSTRACT Using DPSSL (Diode Pumped Solid State Lasers) as pumping technology, PW-class lasers wit... more ABSTRACT Using DPSSL (Diode Pumped Solid State Lasers) as pumping technology, PW-class lasers with enhanced repetition rates are developed. Each of the Yb YAG amplifiers will be diode-pumped at a wavelength of 940 nm. This is a prerequisite for achieving high repetition rates (light amplification duration 1 millisecond and repetition rate 10 Hz). The efficiency of DPSSL is inversely proportional to the temperature, for this reason the slab amplifier have to be cooled at a temperature in the range of 100 K-170 K with a heat flux of 1 MW*m-2. This paper describes the thermo-mechanical analysis for the design of the amplification laser head, presents a preliminary proposal for the required cryogenic cooling system and finally outlines the gain of cryogenic operation for the efficiency of high pulsed laser.

Ogata et al. reported in 1996 results of international Round Robin tests on mechanical property m... more Ogata et al. reported in 1996 results of international Round Robin tests on mechanical property measurement of several metals at cryogenic temperatures. Following the report, the standard deviation of Young's modulus of 316L steel is much larger than those of yield and tensile strengths, that is, 4.6 % of the mean value for Young's modulus, while 1.4 % and 1.6

Proceedings of the Twentieth International Cryogenic Engineering Conference (ICEC20), 2005

The cooling capacity below 2 K for the superconducting magnets of the Large Hadron Collider (LHC)... more The cooling capacity below 2 K for the superconducting magnets of the Large Hadron Collider (LHC), at CERN, will be provided by eight refrigeration units of 2400 W at 1.8 K, each of them coupled to a 4.5 K refrigerator. The two selected vendors have proposed cycles based on centrifugal cold compressors combined with volumetric screw compressors with sub-atmospheric suction, as previously identified by CERN as "reference cycle". The supply of the series units was linked to successful testing and acceptance of the pre-series temporarily installed in a dedicated test station. The global capacity, the performance of cold compressors and some process specificities have been thoroughly tested and will be presented.

Advances in Cryogenic Engineering, 1998

The paper describes the thermo-mechanical validation of the first sector of cryogenic distributio... more The paper describes the thermo-mechanical validation of the first sector of cryogenic distribution line (QRL) [1]. The design of the line is recalled and the test methodology presented together with the main results of the reception test at cryogenic temperatures

Nuclear Fusion, 2006

ABSTRACT The refrigeration power associated with the superconducting magnets and cryopumps of a s... more ABSTRACT The refrigeration power associated with the superconducting magnets and cryopumps of a steady-state fusion reactor is not negligible. The power has to be minimized because it plays a role in the power station global efficiency and in the required amplification factor Q. On the one hand, the long plasma discharges obtained in December 2003 on TORE SUPRA give an insight of the cryogenic losses that might be expected for a steady-state fusion reactor equipped with superconducting magnets. The superfluid bath of the windings in TORE SUPRA allows a simple calorimetric estimation of the cryogenic losses through the temperature evolution of the bath during the long discharge. The different kinds of losses in TORE SUPRA are estimated, discussed and explained. Not all of them will be present in a real reactor. On the other hand, in the framework of ITER preparation, the magnet system and the associated refrigerator have been dimensioned taking into account again all kinds of cold losses. This exercise is important because ITER, by its size, could be relevant to the steady-state reactor situation regarding refrigeration. Based on TORE SUPRA experiment and ITER design it is, therefore, possible to propose for the first time a preliminary figure for the cryoplant power of a steady-state reactor. The order of magnitude of the cryoplant power is ten times lower than that of the fusion reactor recycled power which can be considered acceptable.

Fusion Engineering and Design, 2006