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Hydrogen recycling measurements from AISI 316L stainless steel surfaces have been performed in an installation using a multiple ion source as plasma simulator. A cylindrical vessel of a diameter of 25 cm and a height of 10 cm, closed at one end, forms the anode. Strong permanent magnets are mounted on the outer surface of the anode and produce a multiple magnetic field of several kG at the inner surface of the anode. This increases the length of path of electrons emitted from two hot cathodes and the ionisation probability considerably. The target is a metallic disc of 24 cm diameter placed at the open end of the anode. Typical working conditions of this multiple ion source are 80-120 V for the discharge potential and some 1.0 E-3 mbar for the hydrogen gas pressure. A hydrogen plasma of about 1.0 E12 ions/cm3 and a plasma potential of some volts above the anode potential is produced. Positive hydrogen ions of a fixed energy from 50 to 200 eV are implanted in the stainless steel target of 400 cm2 surface area. The ion flux density ranges from 2 to 6 x 1.0 E16 ions/cm2.s and the target temperature from 300-600 C. The target bombardment lasts 100s. The pressure increase in the ion source volume immediately after the end of bombardment is then measured by a capacitive manometer. A characteristic recycling time t, after which 63% of the implanted hydrogen is released, is determined from this pressure increase. The measured values of t are between 0.5 and 1s and increase with increasing temperature. Hydrogen surface recombination rates on stainless steel surfaces are calculated from these characteristic recycling times, using a computer code which takes into consideration surface and bulk phenomena in the transport of hydrogen between gas and solid phase. The calculated surface recombination rates are discussed and compared with other experimental data and theoretical models.

Additional information

Bibliographic Reference: Paper presented: 4th International Conference on Fusion Reactor Materials, Kyoto (JP), Dec. 4-8, 1989
Availability: Available from (1) as Paper EN 34816 ORA
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