Diplon, deuton, deuteron: under different names, the nucleus of deuterium, or diplogen, has been the subject of intense studies since its discovery in 1932. As the only two-nucleon bound state, its properties have continuously been viewed as important in nuclear theory as the hydrogen atom is in atomic theory. Yet, ambiguities remain in the relativistic description of this system and the two-nucleon picture is incomplete: meson exchange and nucleon excitation into resonances should be considered in the deuteron description. The question of rare configurations where the two nucleons overlap and loose their identity is still under debate. We are still looking for the elusive effects of quarks in the nuclear structure.

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The Deuteron: Structure and Form Factors

Elastic electron scattering from light nuclei

Measurements of the deuteron form factors over a wide range of momentum transfer can provide important clues to the role of subnucleon degrees of freedom in nuclear dynamics. For a meaningful calculation of the form factors it is essential that the current density operators and the deuteron wave function transform under Lorentz transformations in a mutually consistent manner. Standard nucleon-nucleon interactions can be used to construct unitary representations of the Poincare group on the two-nucleon Hilbert space. Deuteron wave functions represent eigenstates of the four-momentum operator. Existing parameterizations of measured single-nucleon form factors are used to construct a conserved covariant electromagnetic current operator. The light-front symmetry of the representation allows a clean separation of the effects of one- and two-body currents for arbitrary momentum transfers. Comparison with data indicates that for Q/sup 2/ < GeV/sup 2/ the elastic cross sections are not dominated by two-body currents.

Light-front dynamics of elastic electron-deuteron scattering

Electromagnetic reactions on light nuclei are fundamental to advance our understanding of nuclear structure and dynamics. The perturbative nature of the electromagnetic probes allows to clearly connect measured cross sections with the calculated structure properties of nuclear targets. We present an overview on recent theoretical ab initio calculations of electron-scattering and photonuclear reactions involving light nuclei. We encompass both the conventional approach and the novel theoretical framework provided by chiral effective field theories. Because both strong and electromagnetic interactions are involved in the processes under study, comparison with available experimental data provides stringent constraints on both many-body nuclear Hamiltonians and electromagnetic currents. We discuss what we have learned from studies on electromagnetic observables of light nuclei, starting from the deuteron and reaching up to nuclear systems with mass number A = 16.

https://iopscience.iop.org/article/10.1088/0954-3899/41/12/123002/pdf

Electromagnetic reactions on light nuclei

Electromagnetic reactions on light nuclei are fundamental to advance our understanding of nuclear structure and dynamics. The perturbative nature of the electromagnetic probes allows to clearly connect measured cross sections with the calculated structure properties of nuclear targets. We present an overview on recent theoretical ab-initio calculations of electron-scattering and photonuclear reactions involving light nuclei. We encompass both the conventional approach and the novel theoretical framework provided by chiral effective field theories. Because both strong and electromagnetic interactions are involved in the processes under study, comparison with available experimental data provides stringent constraints on both many-body nuclear Hamiltonians and electromagnetic currents. We discuss what we have learned from studies on electromagnetic observables of light nuclei, starting from the deuteron and reaching up to nuclear systems with mass number A=16.

An internal-target technique was used to make the first measurements of the tensor analyzing power {ital T}{sub 20} of electron-deuteron elastic scattering in the four-momentum-transfer range of 2--3 fm{sup {minus}1}. Polarized deuterium atoms were confined within a storage cell in the VEPP-3 electron storage ring in Novosibirsk to achieve a total target thickness of 3{times}10{sup 12} cm{sup {minus}2}, 15 times greater than was previously possible with an atomic-beam target alone. The results for {ital T}{sub 20} are in agreement with reasonable models of the deuteron wave function.

Measurement of tensor analyzing power in electron-deuteron elastic scattering.

The first experiment using a storage cell to increase the thickness of an internal polarized gas target in an electron beam storage ring was performed at the VEPP-3 facility. We describe the storage cell technique as applied in this measurement of elastic and inelastic electron scattering from tensor polarized deuterium. An analysis of electron-beam-induced depolarization of the target was performed and experimental tests were carried out which verify the effect. Other effects causing depolarization of the target are discussed as well as the means by which they are overcome. The effective p zz of the target, shown to be stable over 8 months, was 0.57±0.05; the total target thickness was increased over that of a jet target by a factor of fifteen.

A polarized gas internal target using a storage cell in an electron storage ring

A magnet system for cryogenic Atomic Beam Source (ABS) having five superconducting sextupoles has been designed, manufactured and tested to get high intensity of polarized hydrogen/deuterium atomic beams. The beams will be used to fill the storage cell of the internal polarized target at the VEPP-3 electron storage ring in Novosibirsk. The geometry of the magnet system, results of the computations and measurements of the magnetic field are presented. A 4.8 T pole tip magnetic field has been measured for the magnet with an aperture of 44mm.

High field superconducting sextupole magnets

An overview of the polarized electron source used at the NIKHEF accelerator facility is given. Since its first operation in September 1996 we have obtained currents in the source larger than 150 mA, and polarization degrees up to 88%. Approximately 350 hours have been dedicated to physics with a polarized 3He internal target. Using one InGaAsP photocathode, 2 μs long pulses were produced with a current of 2 mA in the local linac, with a polarization degree of 82.5%, at a repetition rate of 1 Hz. Source operations had to be interrupted about every eleventh day for approximately an hour for photocathode reactivation. A photocathode lifetime (1/e) of 180 hours has been achieved.

The polarized electron source at NIKHEF

Experiments on electron scattering from polarized deuterons were carried out on the VEPP-3 storage ring at the Novosibirsk Institute for Nuclear Physics. The e—D coincidences were detected for elastic scattering experiments, and the p—n coincidences for photo disintegration studies. The tensor analyzing power of the elastic scattering was measured in the range of momentum transfer up to 3 f−1, and of photo disintegration in the range of photon energy up to 500 MeV. The detector system created for these experiments and the data analysis procedures are described in this paper.

S. G. Popov

Papers

Measurement of tensor analyzing power in electron-deuteron elastic scattering.

A polarized gas internal target using a storage cell in an electron storage ring

High field superconducting sextupole magnets

The polarized electron source at NIKHEF

Detector system for e—d scattering experiments on the VEPP-3 storage ring