We have performed experimental and theoretical investigation of the formation and behavior of Coulomb clusters of charged diamagnetic particles in a cusp magnetic trap under microgravity conditions aboard the International Space Station. Graphite particles of 100-400 μm in size were used in experiments due to the highest specific magnetic susceptibility. We have observed the formation of clusters in the shape of an oblate ellipsoid of revolution and their oscillations after dynamical action by changing the magnetic field. Observing the excitation and damping of oscillations we have made some estimations. Molecular dynamics simulations of the observed processes have been made. Their results are in reasonable agreement with experiments. Some differences are evidently due to some unaccounted-for reasons.
For the final running period of HERA, a recoil detector was
installed at the HERMES experiment to improve measurements of hard exclusive
processes in charged-lepton nucleon scattering. Here, deeply virtual Compton scattering
is of particular interest as this process provides constraints on generalised parton
distributions that give access to the total angular momenta of quarks within the
nucleon.
The HERMES recoil detector was designed to improve the selection of exclusive
events by a direct measurement of the four-momentum of the recoiling particle.
It consisted of three components: two layers of double-sided silicon strip sensors
inside the HERA beam vacuum, a two-barrel scintillating fibre tracker, and a
photon detector. All sub-detectors were located inside a solenoidal magnetic field
with a field strength of 1T.
The recoil detector was installed in late 2005. After the commissioning of all
components was finished in September 2006, it operated stably until the end
of data taking at HERA end of June 2007. The present paper gives a brief
overview of the physics processes of interest and the general detector design. The
recoil detector components, their calibration, the momentum reconstruction
of charged particles, and the event selection are described in detail.
The paper closes with a summary of the performance of the detection system.
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