Desorption Behavior of Hydrogen Isotopes Implanted into
Stainless Steel by Glow Discharge
グロー放電によりステンレス鋼に注入した水素同位体の脱離挙動
Masamitu Kondou1), Kiyohiko Nishimura2), Msahiro Tanaka2), Nobuaki Noda1) and Masao Matsuyama1)
近藤将充 1)，西村清彦 2)，田中将裕 2)，野田信明 1)，松山政夫 1)
1) Hydrogen Isotope Research Center, University of Toyama, Gofuku 3190, Toyama 930-8555, Japan
富山大学水素同位体科学研究センター，〒930-8555 富山市五福 3190
2) National Institute for Fusion Science, 322-6 Oroshi-cho, Toki 509-5292, Japan
核融合科学研究所，〒509-5292 土岐市下石町 322-6
Desorption behavior of hydrogen and deuterium implanted into type 316L stainless steel by glow discharge has been studied by experiments and numerical calculation based on a diffusion-limited process.
Desorption spectra of hydrogen and deuterium observed by experiments agreed with the numerically calculated spectra. This result suggests that desorption rate of hydrogen isotopes implanted by glow discharge is limited by diffusion rate of hydrogen isotope in the bulk. Furthermore, no large isotope effects
were observed on the desorption behavior.

1. Introduction
Control of fuel particles in the reactor core isindispensable to make steady operation of a fusion
reactor. A part of fuel particles is implanted into theplasma-facing materials (PFM’s) and released fromthem during the operation. Therefore, it is of a great
important issue to make clear the desorption behavior of hydrogen isotopes from PFM’s from viewpoint of stable fuel balance.
From this view point, desorption behavior ofhydrogen isotopes implanted into stainless steel by
a glow discharge has been studied using temperature desorption spectroscopy (TDS), and analysis ofdesorption spectra was carried out by a numericalcalculation method.
2. Experimental
A square plate of type 316L stainless steel wasused as a sample and its size was 15x15x0.5 mm3,
which was mechanically polished and rinsed withacetone before use.
The sample was set in the experimental apparatus, which was specially designed and manufactured for the glow discharge and desorption experiments. Schematic diagram of the apparatus isshown in Fig. 1. This apparatus has an advantageous point that the sample exposed to glow discharge in the chamber of Glow-2 of hydrogen isotope atmosphere can be moved to Glow-1, where itFig. 1 Schematic diagram of the experimental
device used to investigate desorption behavior.

is analyzed with TDS without air exposure. Conditions of glow discharge are as follows:(1) Pressure of hydrogen isotope: 130 Pa(2) Applied voltage: 250 V (H2), 270 V (D2)(3) Total current: 20 mA(4) Exposure time after discharge: 60 min(5) Sample temperature: Room temperature
After glow discharge in the Glow-2, the sample
was kept exposing to hydrogen isotope. Subsequently, it was evacuated below 5x10-5 Pa and thesample was transferred to Glow-1. Evacuation time
was changed in the range from 1 to 5 hours. Afterevacuation for a given time, the sample temperature
was linearly raised from room temperature to 613 K
at a given temperature ramp. Each partial pressureof hydrogen isotopes desorbed from the sample was3. Numerical Calculation
Numerical calculations were carried out by applying a simple diffusion model as the first approximation. It was assumed that hydrogen isotope
atoms diffuse in stainless steel with no trapping or
agglomeration and the diffusion of them simplyobeys the Fick’s Law with a source term as shownin the following equation:
C ( x, t ) 2C ( x, t ) D(T (t )) G ( x)t
x 2,----- (1)where C(x, t) is the concentration of hydrogen isotope at a distance x from the surface at time t, T(t)the absolute temperature of the sample , D(T(t)) thediffusivity of hydrogen isotope at a given temperature, and G(x) the source term. The diffusivity canbe expressed by the following equation:
D(T (t ))  D0 exp(Ed / RT (t )).

----- (2)0.6Discharge time: 90 min
Evacuation time: 60 min
Heating rate: 20 K/min

10: Obs.
: Calc.
50300

0.40.2350

400
450500Temperature, T / K

550

0.0600Fig. 2 Desorption spectra observed and calculated for deuterium glow discharge.

Desorption rate (Calc.),
N / arb. unit

Desorption rate (Obs.),
N / 1013 D-atoms cm-2 s-1

4. Results and Discussion
A typical desorption spectrum of deuterium isshown in Fig. 2. It was observed under the following conditions: exposure time was 90 min at room
temperature, and evacuation time was 60 min. Thesample was heated using an infrared heating device.
Heating rate was 20 K/min. A single desorption
peak was observed and peak temperature wasaround 400K [1, 2]. Desorption species consisted ofD2, HD and H2, and a small amount of water species (HDO and D2O) was also observed.
Best fit to the observed deuterium spectrum wasobtained when Ed and D0 were assumed to be 51.0

Desorption rate,
N / 1013atoms cm-2 s-1

measured by a conventional quadrupole mass spectrometer.

Discharge time: 90 min
Evacuation time: 60 min
Heating rate: 20 K/min

10: H2: D250350 of400
450 spectra
500 observed
550600Fig. 3 300
Comparison
desorption
Temperature,T/Kfor hydrogen and deuterium.

kJ/mol and 1.7x10-7 m2/s, respectively. These diffusion parameters almost agreed with the values reported by Wilson and Baskes [1]: 52.9 kJ/mol and1.7x10-7 m2/s for as-received sample of type 316
stainless steel.
All of the desorption spectra observed undervarious conditions of discharge time, evacuation
time and heating rate could be reproduced using thesame diffusion parameters except for a low temperature region. Therefore, these results indicate that
desorption rate of deuterium implanted into thesample by glow discharge is limited by diffusion
rate in the bulk.
Comparison of two desorption spectra for hydrogen and deuterium is shown in Fig. 3. Bothspectra were measured under the same conditions:
namely, 90 min discharge, 60 min evacuation, and20 K/min heating rate. As clearly seen from thiscomparison, there were no large differences in bothpeak temperature and desorption rate. These results
suggest that isotope effects upon desorption behavior of hydrogen isotopes are negligibly small
above room temperature.
5. Acknowledgement
This work was partly performed with the support and under the auspices of the NIFS Collaboration Research Program. (NIFS07KOBS009)
References[1] K.L. Wilson and M.I. Basakes: J. Nucl. Mater.
74 (1978) 179.
[2] R.E.Clausing,
L.C.Emerson,
L.Heatherly,
R.J.Colchin: Proc. Intl. Conf. on Plasma Wall
Interactions, Julich, 1976, p.573.