AVS 46th International Symposium
    Vacuum Technology Division Tuesday Sessions
       Session VT-TuP

Paper VT-TuP3
High Resolution Quadrupole Mass Spectrometer for Light Masses

Tuesday, October 26, 1999, 5:30 pm, Room 4C

Session: Poster Session
Presenter: H. Eppler, Balzers Instruments, Principality of Liechtenstein
Authors: A. Hofmänner, Balzers Instruments, Principality of Liechtenstein
N. Müller, Balzers Instruments, Principality of Liechtenstein
H. Eppler, Balzers Instruments, Principality of Liechtenstein
Correspondent: Click to Email
Nuclear fusion experiments are performed with gas mixtures containing several components of low mass number (H2, D2, T2, 3He, 4He etc.). Quadrupole mass spectrometers with unit resolution can not separate these gases because of spectral overlaps even if spectrum- deconvolution algorithms are used. So high resolution mass spectrometry is required to separate the components with identical nominal mass numbers. For high resolution measurements in the low mass range a radiofrequeny- generator was developed that operates in the second Mathieu stability region. It drives a 16 mm rod diameter, 300 mm long mass filter at a frequency of 2.05 MHz and covers the mass range from 0.4 to 16.4 m/e. A cross- beam ion source with magnets produces ions with very good definition of ionization volume and energy. The deflection of the ions by 90° onto an off-axis SEM acts as an energy filter and so improves the resolution of the system. For example resolution of >400 at m/e= 4 is obtained with selectable resolution from 0.008 to 0.050 m/e at 10% peak height. The good stability of the mass scale allows for long term measurements without readjustment.