Transcript Schematic layout of the gas analysis system

Problems

The ratios e/m of 4He+ and D2+ ions are very close:
mD2 = 4.0282 amu
mHe = 4.0026 amu

Dm = 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
Conventional 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
Innovative 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.
Main 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.
Schematic layout of the gas analysis
system
Gas mixture
inert gases
Thermostatic Box
n.o.
n.o.
Cell
UHV
containment
vessel
n.c.
Sample
volume
HT NEG
pump
GV5
QMA GV3
RT NEG
UHV
pump
chamber
Storage
circuit
n.o. = normally open valve
n.c. = normally closed valve
GV1
High resolution spectra of a
4He-D mixture.
2
dwell time 1 s, scan width 10 amu, scan time for each cycle 10s.
Analog spectrum of an air sample
6
40Ar+
Ion current (x10-8 A)
5
4
3
2
40Ar++
1
0
0
5
10
15
20
25
30
Mass (amu)
35
40
45
50