| 1. |
- Oellers, D., et al.
(författare)
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Polarizing a stored proton beam by spin flip?
- 2009
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Ingår i: Physics Letters B. - : Elsevier. - 0370-2693 .- 1873-2445. ; 674:4-5, s. 269-275
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Tidskriftsartikel (refereegranskat)abstract
- We discuss polarizing a proton beam in a storage ring, either by selective removal or by spin flip of the stored ions. Prompted by recent, conflicting calculations, we have carried out a measurement of the spin-flip cross section in low-energy electron–proton scattering. The experiment uses the cooling electron beam at COSY as an electron target. The measured cross sections are too small for making spin flip a viable tool in polarizing a stored beam. This invalidates a recent proposal to use co-moving polarized positrons to polarize a stored antiproton beam.
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| 2. |
- Augustyniak, W., et al.
(författare)
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Polarization of a stored beam by spin-filtering
- 2012
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Ingår i: Physics Letters B. - : Elsevier. - 0370-2693 .- 1873-2445. ; 718:1, s. 64-69
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Tidskriftsartikel (refereegranskat)abstract
- The PAX Collaboration has successfully performed a spin-filtering experiment with protons at the COSY-ring. The measurement allowed the determination of the spin-dependent polarizing cross section, that compares well with the theoretical prediction from the nucleon-nucleon potential. The test confirms that spin-filtering can be adopted as a method to polarize a stored beam and that the present interpretation of the mechanism in terms of the proton-proton interaction is correct. The outcome of the experiment is of utmost importance in view of the possible application of the method to polarize a beam of stored antiprotons.
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| 3. |
- Eversmann, D., et al.
(författare)
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New Method for a Continuous Determination of the Spin Tune in Storage Rings and Implications for Precision Experiments
- 2015
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 115:9
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Tidskriftsartikel (refereegranskat)abstract
- A new method to determine the spin tune is described and tested. In an ideal planar magnetic ring, the spin tune-defined as the number of spin precessions per turn-is given by nu(s) = gamma G (gamma is the Lorentz factor, G the gyromagnetic anomaly). At 970 MeV/c, the deuteron spins coherently process at a frequency of approximate to 120 kHz in the Cooler Synchrotron COSY. The spin tune is deduced from the up-down asymmetry of deuteron-carbon scattering. In a time interval of 2.6 s, the spin tune was determined with a precision of the order 10(-8), and to 1 x 10(-10) for a continuous 100 s accelerator cycle. This renders the presented method a new precision tool for accelerator physics; controlling the spin motion of particles to high precision is mandatory, in particular, for the measurement of electric dipole moments of charged particles in a storage ring.
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| 4. |
- Guidoboni, G., et al.
(författare)
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How to Reach a Thousand-Second in-Plane Polarization Lifetime with 0.97-GeV/c Deuterons in a Storage Ring
- 2016
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Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 117:5
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Tidskriftsartikel (refereegranskat)abstract
- We observe a deuteron beam polarization lifetime near 1000 s in the horizontal plane of a magnetic storage ring (COSY). This long spin coherence time is maintained through a combination of beam bunching, electron cooling, sextupole field corrections, and the suppression of collective effects through beam current limits. This record lifetime is required for a storage ring search for an intrinsic electric dipole moment on the deuteron at a statistical sensitivity level approaching 10(-29) e cm.
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| 5. |
- Oellers, D., et al.
(författare)
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New experimental upper limit of the electron-proton spin-flip cross-section
- 2014
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 759, s. 6-9
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Tidskriftsartikel (refereegranskat)abstract
- In a previous publication, measurements of the depolarization of a stored proton beam by interaction with a co-propagating unpolarized electron beam at low relative energy have been presented and an upper limit of about 3 x 10(7) b for the electron-proton spin flip cross-section was determined. A refined analysis presented in this paper reduces the previous upper limit by a factor of three by the introduction of a new procedure that, also makes use of non-identified particles.
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| 6. |
- Duane Loh, N., et al.
(författare)
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Profiling structured beams using injected aerosols
- 2012
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Ingår i: Proceedings of SPIE. - : SPIE. - 9780819492210 ; , s. 850403-
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Konferensbidrag (refereegranskat)abstract
- Profiling structured beams produced by X-ray free-electron lasers (FELs) is crucial to both maximizing signal intensity for weakly scattering targets and interpreting their scattering patterns. Earlier ablative imprint studies describe how to infer the X-ray beam profile from the damage that an attenuated beam inflicts on a substrate. However, the beams in-situ profile is not directly accessible with imprint studies because the damage profile could be different from the actual beam profile. On the other hand, although a Shack-Hartmann sensor is capable of in-situ profiling, its lenses may be quickly damaged at the intense focus of hard X-ray FEL beams. We describe a new approach that probes the in-situ morphology of the intense FEL focus. By studying the translations in diffraction patterns from an ensemble of randomly injected sub-micron latex spheres, we were able to determine the non-Gaussian nature of the intense FEL beam at the Linac Coherent Light Source (SLAC National Laboratory) near the FEL focus. We discuss an experimental application of such a beam-profiling technique, and the limitations we need to overcome before it can be widely applied.
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| 7. |
- Hempelmann, N., et al.
(författare)
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Locking the Spin Precession in a Storage Ring
- 2017
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Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 119:1
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Tidskriftsartikel (refereegranskat)abstract
- This Letter reports the successful use of feedback from a spin polarization measurement to the revolution frequency of a 0.97 GeV= c bunched and polarized deuteron beam in the Cooler Synchrotron (COSY) storage ring in order to control both the precession rate (approximate to 121 kHz) and the phase of the horizontal polarization component. Real time synchronization with a radio frequency (rf) solenoid made possible the rotation of the polarization out of the horizontal plane, yielding a demonstration of the feedback method to manipulate the polarization. In particular, the rotation rate shows a sinusoidal function of the horizontal polarization phase (relative to the rf solenoid), which was controlled to within a 1 standard deviation range of sigma= 0.21 rad. The minimum possible adjustment was 3.7 mHz out of a revolution frequency of 753 kHz, which changes the precession rate by 26 mrad/s. Such a capability meets a requirement for the use of storage rings to look for an intrinsic electric dipole moment of charged particles.
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| 8. |
- Hempelmann, N., et al.
(författare)
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Phase measurement for driven spin oscillations in a storage ring
- 2018
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Ingår i: Physical Review Accelerators and Beams. - : American Physical Society. - 2469-9888. ; 21:4
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Tidskriftsartikel (refereegranskat)abstract
- This paper reports the first simultaneous measurement of the horizontal and vertical components of the polarization vector in a storage ring under the influence of a radio frequency (rf) solenoid. The experiments were performed at the Cooler Synchrotron COSY in Julich using a vector polarized, bunched 0.97 GeV/c deuteron beam. Using the new spin feedback system, we set the initial phase difference between the solenoid field and the precession of the polarization vector to a predefined value. The feedback system was then switched off, allowing the phase difference to change over time, and the solenoid was switched on to rotate the polarization vector. We observed an oscillation of the vertical polarization component and the phase difference. The oscillations can be described using an analytical model. The results of this experiment also apply to other rf devices with horizontal magnetic fields, such as Wien filters. The precise manipulation of particle spins in storage rings is a prerequisite for measuring the electric dipole moment (EDM) of charged particles.
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| 9. |
- Loh, N. D., et al.
(författare)
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Fractal morphology, imaging and mass spectrometry of single aerosol particles in flight
- 2012
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 486:7404, s. 513-517
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Tidskriftsartikel (refereegranskat)abstract
- The morphology of micrometre-size particulate matter is of critical importance in fields ranging from toxicology(1) to climate science(2), yet these properties are surprisingly difficult to measure in the particles' native environment. Electron microscopy requires collection of particles on a substrate(3); visible light scattering provides insufficient resolution(4); and X-ray synchrotron studies have been limited to ensembles of particles(5). Here we demonstrate an in situ method for imaging individual sub-micrometre particles to nanometre resolution in their native environment, using intense, coherent X-ray pulses from the Linac Coherent Light Source(6) free-electron laser. We introduced individual aerosol particles into the pulsed X-ray beam, which is sufficiently intense that diffraction from individual particles can be measured for morphological analysis. At the same time, ion fragments ejected from the beam were analysed using mass spectrometry, to determine the composition of single aerosol particles. Our results show the extent of internal dilation symmetry of individual soot particles subject to non-equilibrium aggregation, and the surprisingly large variability in their fractal dimensions. More broadly, our methods can be extended to resolve both static and dynamic morphology of general ensembles of disordered particles. Such general morphology has implications in topics such as solvent accessibilities in proteins(7), vibrational energy transfer by the hydrodynamic interaction of amino acids(8), and large-scale production of nanoscale structures by flame synthesis(9).
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| 10. |
- Pedersoli, E., et al.
(författare)
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Mesoscale morphology of airborne core-shell nanoparticle clusters : x-ray laser coherent diffraction imaging
- 2013
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Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 46:16 SI, s. 164033-
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Tidskriftsartikel (refereegranskat)abstract
- Unraveling the complex morphology of functional materials like core-shell nanoparticles and its evolution in different environments is still a challenge. Only recently has the single-particle coherent diffraction imaging (CDI), enabled by the ultrabright femtosecond free-electron laser pulses, provided breakthroughs in understanding mesoscopic morphology of nanoparticulate matter. Here, we report the first CDI results for Co@SiO2 core-shell nanoparticles randomly clustered in large airborne aggregates, obtained using the x-ray free-electron laser at the Linac Coherent Light Source. Our experimental results compare favourably with simulated diffraction patterns for clustered Co@SiO2 nanoparticles with similar to 10 nm core diameter and similar to 30 nm shell outer diameter, which confirms the ability to resolve the mesoscale morphology of complex metastable structures. The findings in this first morphological study of core-shell nanomaterials are a solid base for future time-resolved studies of dynamic phenomena in complex nanoparticulate matter using x-ray lasers.
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