problems the ratios e/m of 4 he + and d 2 + ions are very close: m d 2 = 4.0282 amu m he = 4.0026...
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![Page 1: Problems The ratios e/m of 4 He + and D 2 + ions are very close: m D 2 = 4.0282 amu m He = 4.0026 amu m = 0.0256 amu A high resolution mass spectrometer](https://reader033.vdocument.in/reader033/viewer/2022051614/5517e4c4550346c6568b4691/html5/thumbnails/1.jpg)
ProblemsProblems The ratios e/m of 4He+ and D2
+ ions are very close:
mD2 = 4.0282 amu
mHe = 4.0026 amum = 0.0256 amu
A high resolution mass spectrometer should be required in order to separate the two peaks.
D2 concentration » expected 4He concentration
Capability of on line analysis during the electrolytic experiment
![Page 2: Problems The ratios e/m of 4 He + and D 2 + ions are very close: m D 2 = 4.0282 amu m He = 4.0026 amu m = 0.0256 amu A high resolution mass spectrometer](https://reader033.vdocument.in/reader033/viewer/2022051614/5517e4c4550346c6568b4691/html5/thumbnails/2.jpg)
Conventional techniquesConventional techniques Dynamic analysis technique (differential
pumping or diffusion through large impedance circuits):
alter the original composition of the gas mixture; exhibit low sensitivity; do not allow for on line analysis.
Static analysis technique (Cryosorption pumps):
may erratically trap helium in the condensates; require a long cycle time and are not suitable for
on line analysis. Unable to pump hydrogen isotopes to high degree
![Page 3: Problems The ratios e/m of 4 He + and D 2 + ions are very close: m D 2 = 4.0282 amu m He = 4.0026 amu m = 0.0256 amu A high resolution mass spectrometer](https://reader033.vdocument.in/reader033/viewer/2022051614/5517e4c4550346c6568b4691/html5/thumbnails/3.jpg)
Innovative solutionsInnovative solutions Non evaporable getter (NEG) pumps:
remove to a high degree all non inert components of the gas mixture (especially hydrogen isotopes); all inert gases are obviously preserved;
exhibit very high pumping speeds (especially for hydrogen);
the pumping speed for other active gases depends on the operating temperature of the getter alloy;
do not require frequent regeneration, allowing periodic analysis of gas samples during the experiment (roughly every 40 minutes).
A storage circuit has been purposely designed, which:
allows to periodically sample the gas mixture without influence on the electrolytic process;
eliminates any alteration of the gas mixture composition; allows to easily compare the results of the analysis of
each sample.
![Page 4: Problems The ratios e/m of 4 He + and D 2 + ions are very close: m D 2 = 4.0282 amu m He = 4.0026 amu m = 0.0256 amu A high resolution mass spectrometer](https://reader033.vdocument.in/reader033/viewer/2022051614/5517e4c4550346c6568b4691/html5/thumbnails/4.jpg)
Main featuresMain features High resolution Mass
Spectrometer (Balzers QMA 410).
Two NEG pumps are used: SAES Capacitorr B 1300 (600 g of
ST185 TiV alloy) operating at high temperature (300 - 400°C)
SAES GP200 MK4 W (170 g of ST707 alloy) operating at RT.
Dynamic pumping: Main pump: Pfeiffer TMU 261
turbo molecular drag pump Backing pump: Pfeiffer TMU 071
+ MD4
No cryosorption pumps are used.
Automatic operation (Field-Point + LabView).
Pressure stabilized storage circuit.
![Page 5: Problems The ratios e/m of 4 He + and D 2 + ions are very close: m D 2 = 4.0282 amu m He = 4.0026 amu m = 0.0256 amu A high resolution mass spectrometer](https://reader033.vdocument.in/reader033/viewer/2022051614/5517e4c4550346c6568b4691/html5/thumbnails/5.jpg)
Schematic layout of the gas Schematic layout of the gas analysis systemanalysis system
QMAUHV
chamber
Thermostatic Box
Cell
UHVcontainment
vessel
Storagecircuit
Samplevolume
HT NEGpump
n.o.
n.o.
n.c.
n.o. = normally open valve
n.c. = normally closed valve
Gas mixture inert gases
RT NEGpump
GV1
GV3GV5
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High resolution spectra of a 4He-D2 mixture.
dwell time 1 s, scan width 10 amu, scan time for each cycle 10s.
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Analog spectrum of an air sampleAnalog spectrum of an air sample
0 15 20 355 10 25 30 40 45 50
Mass (amu)
Ion c
urr
ent
(x1
0-8
A)
0
1
2
3
4
5
640Ar+
40Ar++