Exhaust behavior of tritium from the large helical device in the first deuterium plasma experiment

Figures & data

Figure 1. The layout of the LHD vacuum pump, NBI, CHD systems, and glow discharge electrode

Table 1. Operating conditions for glow discharge, Boronization, and baking

Wall conditioning operation	Operation gas	Discharge current (Constant current)	Discharge voltage (Average)	Operation pressure* (Average)	Total operation time (minutes)
Glow discharge	He	15 A	227 V	3.0 Pa	840
	H2	10 A	336 V	0.9 Pa	3600
	D2	10 A	370 V	0.9 Pa	2040
Boronization	B2D8+ He	15 A	237 V	2.2 Pa	350
Baking (368 K)	-	-	-	< 10^−3 Pa	63,300**

* The pressure was measured by a diaphragm gauge.

** The total baking operation time contained with the temperature rise and fall time about 37,200 minutes.

Table 2. Comparison of tritium exhaust rate in the initial deuterium plasma phase among the large fusion test devices

Device	First wall material	Divertor material	Wall conditioning operation		Sampling or monitoring period	Tritium exhaust rate	Operation temperature on vacuum vessel	Remarks	Reference
			Baking temperature	Discharge cleaning and wall coating
JET	Be	Be	-*	Be evaporation	Shot by shot sampling (600 sec)	12 ~ 45%	573 K or 623 K	Limiter: Be	[7,8]
	C	C		-	Long term sampling (over a period of many hours)	20%		Limiter: C
	Be	Be		Be evaporation		40%		Limiter: C
	Be	Be		Be evaporation		39%		Limiter: Be
JT-60U	C	C	573 K	Tyler or glow discharge (He), Tokamak discharge, Boronization	July 1991 to October 1993	28%	573 K	Produced tritium: 31 GBq	[2]
LHD	SUS	C	368 K	Glow discharge (H2, D2, He),  Boronization	March 2017 to August 2017	32.8%	293 ~ 303 K	Produced tritium: 6.4 GBq	This study

* No information in ref. [8].

Figure 2. Schematic diagram of the LHD vacuum pumping system and the exhaust detritiation system

Figure 3. Variation of tritium concentration measured by an ionization chamber in the exhaust gas during the plasma experiments

Figure 4. An example of tritium exhaust behavior from LHD in ten days

Figure 5. The effect of gas species on the tritium release behavior by the glow discharge cleaning

Figure 6. The tritium release behavior on the repetition glow discharge operation

Figure 7. The hydrogen isotopes release behavior on the wall baking operation at 368 K: (a) the operating temperature of LHD vacuum vessel and tritium concentration at the inlet of EDS, (b) the gas species measured by a mass spectroscopy and the total pressure in the mass spectrometer (Q-mass) chamber

Figure 8. The behavior of tritium chemical forms in the exhaust gas during the plasma experiment

Figure 9. The relationships between tritiated hydrogen gas and tritiated hydrocarbons, water vapor in the exhaust gas

Figure 10. Accumulated tritium amount and the ratio of exhaust and inventory of tritium during the first deuterium plasma experiment

Figure 11. Tritium exhaust pathway from LHD during the first deuterium plasma experiment

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