Cryogénie | EPFL Graph Search

vignette|Bonbonne contenant de l'azote liquide (en anglais, « nitrogen »). La cryogénie est l'étude et la production des basses températures (inférieures à ou 120 K) dans le but de comprendre les phénomènes physiques qui s'y manifestent. La limite de représente la limite à partir de laquelle les gaz de l'air se liquéfient. La cryogénie possède de très nombreuses applications notamment dans les secteurs alimentaire, médical, industriel, physique et de l'élevage. La cryogénie a ouvert beaucoup de possibilités comme :

la conservation des aliments à l'aide d'azote liquide,
la suspension du métabolisme,
l'étude de la supraconductivité (absence de résistance électrique),
l'étude de la superfluidité (absence de viscosité pour un liquide),
la transformation en une fine poudre de toutes sortes de matières,
la récupération de plus de 90 % des gaz destructeurs de la couche d'ozone,
la création, à partir d'azote liquide, de toutes sortes de neiges,
le transport sur de longues di

Longitudinal intensity effects in the CERN Large Hadron Collider

Juan Federico Esteban Müller

This PhD thesis provides an improved knowledge of the LHC longitudinal impedance model and a better understanding of the longitudinal intensity effects. These effects can limit the LHC performance and lead to a reduction of the integrated luminosity. The LHC longitudinal impedance was measured with beams. Results obtained using traditional techniques are consistent with the expectations based on the impedance model, although the measurement precision was proven insufficient for the low impedance of the LHC. Innovative methods to probe the LHC reactive impedance were successfully used. One of the methods is based on exciting the beam with a sinusoidal rf phase modulation to estimate the synchrotron frequency shift from potential-well distortion. In the second method, the impedance is estimated from the loss of Landau damping threshold, which is also found to be in good agreement with analytical estimations. Beam-based impedance measurements agree well with estimations using the LHC impedance model. Macroparticle simulations of loss of Landau damping reproduce the measurements precisely and are used to determine the current stability limits. The single-bunch stability is analyzed for the HL-LHC, for a bunch intensity almost twice higher than the nominal LHC intensity. The effect of an additional rf system installed for double rf operation provides an increased stability margin in the absence of a wideband longitudinal damper system. The differences between the bunch-shortening and bunch-lengthening operation modes are presented, as well as the effect of an error in the phase synchronization between both rf systems. Several options for the rf parameters are considered, and their advantages and drawbacks under different circumstances are analyzed. A novel diagnostic tool for e-cloud monitoring based on bunch phase measurements has been fully developed. An advanced post-processing was implemented to improve the measurement accuracy up to the required level by reducing systematic and random errors. The tool is available at the CERN Control Room and shows the e-cloud build-up structure along the bunch trains and the total beam power loss due to e-cloud. Phase shift measurements are in good agreement with simulations of the e-cloud buildup and can be used to estimate the heat load in the cryogenic system. The use of this method in operation has been proven to ease the scrubbing run optimization and can eventually be used as an additional input for the cryogenic system.

EPFL2016

Dissolution dynamic nuclear polarization of deuterated molecules enhanced by cross-polarization

Daniel Abergel, Geoffrey Bodenhausen, Estel Canet Martinez, Sami Jannin, Sina Marhabaie, Jonas Milani, Matthias Weller

We present novel means to hyperpolarize deuterium nuclei in (CD2)-C-13 groups at cryogenic temperatures. The method is based on cross-polarization from H-1 to C-13 and does not require any radio-frequency fields applied to the deuterium nuclei. After rapid dissolution, a new class of long-lived spin states can be detected indirectly by C-13 NMR in solution. These long-lived states result from a sextet-triplet imbalance (STI) that involves the two equivalent deuterons with spin I = 1. An STI has similar properties as a triplet-singlet imbalance that can occur in systems with two equivalent I = 1/2 spins. Although the lifetimes TSTI are shorter than T-1(C-z), they can exceed the life-time T-1(D-z) of deuterium Zeeman magnetization by a factor of more than 20. Published by AIP Publishing.

Amer Inst Physics2016

Performance and reproducibility of C-13 and N-15 hyperpolarization using a cryogen-free DNP polarizer

Arianna Ferrari, Hikari Ananda Infinity Yoshihara

The setup, operational procedures and performance of a cryogen-free device for producing hyperpolarized contrast agents using dissolution dynamic nuclear polarization (dDNP) in a preclinical imaging center is described. The polarization was optimized using the solid-state, DNP-enhanced NMR signal to calibrate the sample position, microwave and NMR frequency and power and flip angle. The polarization of a standard formulation to yield similar to 4 mL, 60 mM 1-C-13-pyruvic acid in an aqueous solution was quantified in five experiments to P(C-13) = (38 +/- 6) % (19 +/- 1) s after dissolution. The mono-exponential time constant of the build-up of the solid-state polarization was quantified to (1032 +/- 22) s. We achieved a duty cycle of 1.5 h that includes sample loading, monitoring the polarization build-up, dissolution and preparation for the next run. After injection of the contrast agent in vivo, pyruvate, pyruvate hydrate, lactate, and alanine were observed, by measuring metabolite maps. Based on this work sequence, hyperpolarized N-15 urea was obtained (P(N-15) = (5.6 +/- 0.8) % (30 +/- 3) s after dissolution).

NATURE PORTFOLIO2022

Longitudinal intensity effects in the CERN Large Hadron Collider

Juan Federico Esteban Müller

EPFL2016