Project summary

The aim of the experiment is to investigate the nuclear polarization of the hydrogen and deuterium molecules after recombination of the polarized atoms. Hydrogen (or deuterium) beam with the polarized nucleus (spin of all nucleus is oriented in one direction – direction of the external magnetic field) goes from the Atomic Beam Source (ABS) to the cell. Cell is the T-shape tube with the open ends. T-shape tube works as a storage cell and the density in the horizontal direction increases. But this process needs many collisions of atoms with the walls of the cell. During the collisions we can loose polarization of the atoms and atoms can recombine to molecules on the cell surface. The internal surface of the cell is covered by the "dry film" or Teflon to minimize both these processes.

Holding magnetic field (up to 3000G) defines the direction of the nuclei polarization. Conductivity of the cell tubes depends on the temperature. Decreasing of the temperature decreases the conductivity and increases the quantity of the gas in the cell (increases the target density). For this we have cell cooling system 40K-200K. To increase and control the recombination inside the cell we added in the middle of the cell the small “recombination chamber” which separated from the cell by the "Teflon vacuum gate". When the gate is closed the polarized atoms does not see the recombination chamber and the recombination inside the cell is suppressed. When we open the Teflon gate primary beam goes to the "recombination chamber" and recombine there. The surface of recombination chamber is prepared in the special way – covered by platinum or Ni. After that hydrogen goes to the cell in form of the molecules and in the cell we have rest of the polarized atoms and the molecules of hydrogen which have been done from the polarized atoms. The task of the experiment is to measure the nuclear polarization in molecules. For the control of the recombination process we propose to use the "heat flux detector". Detector measures the heat flux and we can estimate the recombination rate inside the recombination chamber. For investigation of the temperature dependence of the recombination process we have the separate cooling system for the recombination chamber. For the measurements of the polarization we use the polarimeter. This type of polarimeter measures the polarization of protons and deuterons at the energy not more then 500 eV. For the production of the positive ions we are going to use electron gun which is placed in the "electron gun chamber". Electron gun produces the electron beam with the energy up to 3 keV with the direct current up to 100 µA. We are going to use the gun in the pulse regime. In this case the current will be up to 1 mA. Well collimated electron beam can be registered by the electron beam profile monitor placed on the linear drive. It gives possibility to define the electron beam position and the beam shape and to adjust the gun regarding to the cell. The beam profile monitor behind the cell on the same linear drive in the absence of the gas give you a possibility to adjust gun relative the cell. Electron beam can ionize the atoms and molecules in the cell in the different ways (we are interesting in the positive ions only).

1. H + e– = H+ + 2e–
2. H2 + e– = H+ + H + 2e–
3. H2 + e– = H+ + H– + e–
4. H2 + e– = H+ + H+ + 3e–
5. H2 + e– = H2+ + 2e–

The process of the dissociation of molecular hydrogen after the electron impact can be investigated by using the molecular hydrogen in the cell. For our measurements the important processes are 1 and 5. 2, 3, 4 are the background. In the holding field higher then 1000 G all this processes go without changing of the nuclear polarization. Electrostatic lens (32) extracts positive ions from the cell and guide them to the spectrometer chamber. Accelerating electrodes 50 kV gives positive ions H+ and H2+ energy 50 keV. After that ions go through the carbon film and molecules dissociated inside the film. After the film we have only the H+. But H+ which before the film were in H+ form have the energy about 50 keV, but the H+ from H2+ have only 25 keV and we can separate these to types of ions. Carbon film does not disturb the nuclear polarization (standard technique for the production of the polarized proton beams on the accelerator). Deceleration electrode decreases the energy of ions down to the 500 eV (this is the maximum energy to the polarimeter). Deflecting electrode choose the direction of the beam – to polarimeter or to the microchannel plate (polarity of the voltage) and separate the ions by energy (value of the voltage on ). By varying the voltage we can send to the detectors the ions of different energy. Micro channel plate measures only the beam intensity and uses for the background measurements and intensity measurements. For the polarimeter we need in the correction of the trajectory and we can measure by polarimeter the polarization of atoms with different origination. Additional magnets create the holding field in the spectrometer chamber (about 20-30 G).

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