Muon beams are generated with large transverse and longitudinal emittances. In order to achieve the low emittances required by a muon collider, within the short lifetime of the muons, ionization cooling is required. Cooling schemes have been developed to reduce the muon beam 6D emittances to $\ensuremath{\approx}300\text{ }\text{ }\ensuremath{\mu}\mathrm{m}\text{\ensuremath{-}}\mathrm{rad}$ in transverse and $\ensuremath{\approx}1--1.5\text{ }\text{ }\mathrm{mm}$ in longitudinal dimensions. The transverse emittance has to be further reduced to $\ensuremath{\approx}50--25\text{ }\text{ }\ensuremath{\mu}\mathrm{m}\text{\ensuremath{-}}\mathrm{rad}$ with an upper limit on the longitudinal emittance of $\ensuremath{\approx}76\text{ }\text{ }\mathrm{mm}$ in order to meet the high-energy muon collider luminosity requirements. Earlier studies of the transverse cooling of low energy muon beams in high field magnets showed a promising performance, but did not include transverse or longitudinal matching between the stages. In this study we present the first complete design of the high field-low energy ionization cooling channel with transverse and longitudinal matching. The channel design was based on strong focusing solenoids with fields of 25--30 T and low momentum muon beam starting at $135\text{ }\mathrm{MeV}/\mathrm{c}$ and gradually decreasing. The cooling channel design presented here is the first to reach $\ensuremath{\approx}50$ micron scale emittance beam. We present the channel's optimized design parameters including the focusing solenoid fields, absorber parameters and the transverse and longitudinal matching.

http://inspirehep.net/record/1391727/files/openaccess_PhysRevSTAB_18_091001.pdf

High Field – Low Energy Muon Ionization Cooling Channel

Dynamic nuclear polarization (DNP) can provide a powerful means to amplify neutron diffraction from biological crystals by 10-100-fold, while simultaneously enhancing the visibility of hydrogen by an order of magnitude. Polarizing the neutron beam and aligning the proton spins in a polarized sample modulates the coherent and incoherent neutron scattering cross-sections of hydrogen, in ideal cases amplifying the coherent scattering by almost an order of magnitude and suppressing the incoherent background to zero. This chapter describes current efforts to develop and apply DNP techniques for spin polarized neutron protein crystallography, highlighting concepts, experimental design, labeling strategies and recent results, as well as considering new strategies for data collection and analysis that these techniques could enable.

Dynamic nuclear polarization enhanced neutron crystallography: Amplifying hydrogen in biological crystals

Le travail presente dans cette these porte d’une part sur le developpement et la caracterisation d’une nouvelle generation de detecteurs Micromegas (MICROMEsh GAseous Structure) pour l’experience COMPASS au Cern, et d’autre part sur l’estimation de la contribution de canaux diffractifs a la production de pions et de kaons, dans le cadre de l’etude des fonctions de fragmentation de quarks en hadrons a COMPASS. De nouveaux detecteurs Micromegas d’une surface active de 40 x 40 cm² sont en cours de developpement pour le futur de l’experience COMPASS, a partir de 2015. Ces detecteurs devront fonctionner dans des flux de muons et hadrons approchant 8 MHz/cm². Pour cela, une zone centrale d’environ 5 cm de diametre, traversee par le faisceau, sera constituee de 1280 pixels, et des technologies permettant de fortement reduire l’impact des decharges seront adoptees. Quatre prototypes de geometrie finale utilisant deux types de technologies de reduction des decharges differentes ont ete produits au Cern et testes en conditions reelles a COMPASS entre 2010 et 2012. Trois d’entre eux sont des detecteurs hybrides utilisant une feuille GEM (Gas Electron Multiplier) en tant qu’etage de preamplification pour reduire la probabilite de decharge. Le dernier detecteur est equipe d’une structure resistive a « resistances enterrees », permettant la reduction de l’amplitude des decharges. Leurs performances sont presentees dans cette these. L’impact de ces resultats sur la production et la mise en œuvre de la serie finale de detecteurs est egalement discute. Les fonctions de fragmentation de quarks en hadrons l’hadronisation d’un quark de saveur q en un hadron h. Ces fonctions universelles interviennent dans l’expression de la section efficace de nombreux processus. Elles sont accessibles a COMPASS via la reaction de diffusion profondement inelastique semi-inclusive de muons sur des nucleons. Les observables permettant leur extraction dans ce cadre sont les multiplicites de hadrons, soit le nombre moyen de hadrons produits par evenement de diffusion profondement inelastique. Les mesons vecteurs issus de processus diffractifs produisent egalement des pions et kaons par leur desintegration. Ces processus n’impliquant pas l’hadronisation d’un quark, il semble justifie de ne pas les comptabiliser dans la mesure des multiplicites. Ce travail propose une etude Monte-Carlo des contributions de la production diffractive de mesons vecteurs rho et phi a la production de hadrons leger et aux evenements inclusifs. Des facteurs de correction des multiplicites sont finalement etablis. Enfin, l’effet de cette correction sur l’extraction des fonctions de fragmentation en pions est presente.

Développement de détecteurs Micromegas pixellisés pour les hauts flux de particules et évaluation de la contribution diffractive à la leptoproduction de hadrons à COMPASS

The IBARAKI Biological Crystal Diffractometer (iBIX) has been available for use at MLF (Material and Life Science Facility) in J-PARC (Japan Proton Accelerator Research Complex) since 2008. The development in state-of-the-art detector systems could enable iBIX to become one of the highest-performance neutron single-crystal diffractometers in the world. Here, together with other various developments, such as data reduction software, crystal growth, and new techniques in measurement coupled analysis, we provided new hydrogen and water structural data of several proteins and macromolecules. Although the proton power at MLF has not yet reached its planned maximum (1MW), a more powerful neutron source will be soon needed for neutron protein crystallography. A future idea is also proposed and discussed in this article.

Current status and near future plan of neutron protein crystallography at J-PARC.

Polarized Drell–Yan measurements require a strong homogeneous magnetic field. A 2.5 T longitudinal field is generated with a superconducting solenoid carrying a nominal current of 650 A, while high homogeneity is obtained by using additional shim—and compensation coils. Since the target needs to be transversely polarized, a second main coil is required. A superconducting dipole coil encloses the solenoid and together they are integrated in a common cryostat. Field rotation, from longitudinal to transverse and vice versa, is possible by simultaneously powering both coils. During the complete procedure, the absolute field strength is never allowed to drop below 0.48 T to guarantee a high polarization percentage. In the meantime, the forces between the coils need to be controlled, and therefore the coils cannot both be carrying the nominal operational current, since this will destroy the system. The magnetic field rotation procedure is therefore uniquely developed for this system. In this paper, the magnet system is described and a summary of the operational experience gained during data taking is provided.

Operational Experience With the Combined Solenoid/Dipole Magnet System of the COMPASS Experiment at CERN

A 2.5 m long liquid hydrogen target has been developed for the COMPASS experiment at CERN to investigate the nucleon spin structure via the Deeply Virtual Compton Scattering (DVCS) process. To recognize exclusive DVCS events, produced photons and slow protons need to be detected. In order to do so, the material budget around the target has to be minimal. A 0.125 mm thick Kapton ® target cell and a 1 mm thick carbon fiber vacuum chamber with a Mylar ® window have been constructed and tested. Finally, the target system was successfully employed during the DVCS pilot run in COMPASS at the end of 2012. The objective of this paper is to give a detailed description of this newly developed liquid hydrogen target apparatus.

A 2.5 m long liquid hydrogen target for COMPASS

To improve the sensitivity of hydrogen detection using neutrons, a proton-polarization technique together with a high-pressure cooling method is necessary. The highest pressure (200 MPa) used in the experiment described here enabled relatively large protein crystals to be cooled without any cryoprotectants while retaining the protein structure, and it was confirmed that high-pressure-cooled crystals diffracted to nearly the same resolution as flash-cooled small crystals soaked with cryoprotectants. Dynamic nuclear polarization was used as a proton-polarization technique for protein crystals, and ∼300 mg polycrystalline protein doped with TEMPOL gave a maximum proton polarization of 22.3% at a temperature of 0.5 K in a 2.5 T magnetic field.

/pdf/cryoprotectant-free-high-pressure-cooling-and-dynamic-q4pgcuohg5.pdf

Cryoprotectant-free high-pressure cooling and dynamic nuclear polarization for more sensitive detection of hydrogen in neutron protein crystallography

In the polarised Drell-Yan experiment at the COMPASS facility in CERN pion beam with momentum of 190 GeV/c and intensity about $10^8$ pions/s interacted with transversely polarised NH$_3$ target. Muon pairs produced in Drel-Yan process were detected. The measurement was done in 2015 as the 1st ever polarised Drell-Yan fixed target experiment. The hydrogen nuclei in the solid-state NH$_3$ were polarised by dynamic nuclear polarisation in 2.5 T field of large-acceptance superconducting magnet. Large helium dilution cryostat was used to cool the target down below 100 mK. Polarisation of hydrogen nuclei reached during the data taking was about 80 %. Two oppositely polarised target cells, each 55 cm long and 4 cm in diameter were used. Overview of COMPASS facility and the polarised target with emphasis on the dilution cryostat and magnet is given. Results of the polarisation measurement in the Drell-Yan run and overviews of the target material, cell and dynamic nuclear polarisation system are given in the part II.

/pdf/arxiv-polarised-target-for-drell-yan-experiment-in-compass-vh765bt0n0.pdf

arXiv : Polarised target for Drell-Yan experiment in COMPASS at CERN, part I

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A 2.5 m long liquid hydrogen target for COMPASS

Cryoprotectant-free high-pressure cooling and dynamic nuclear polarization for more sensitive detection of hydrogen in neutron protein crystallography

arXiv : Polarised target for Drell-Yan experiment in COMPASS at CERN, part I