An experimental set up for studying the fusion edge plasma facing materials using TOF mass spectrometry

• A new experimental set up for studies of fusion edge plasma has been developed.
• SID, SIR, and sputtering processes in low-energy molecular ion–surface interaction have been studied.
• Detection of ions from hydrocarbon covered platinum surface in collision with N2+ ions has been carried out using TOF mass spectrometry.
• Parameters (beam profile and energy spread) for ion-beam characterization have been determined.
• Survival probability of incident molecular ions has been estimated.

A new experimental set up is developed to study the fusion edge plasma facing materials under impact of low-energy (40–10,000 eV) atomic and molecular ions. The primary ions are obtained from a low-pressure D.C. gas discharge Colutron ion source. The product ions resulting from the ion–surface interactions involving different processes, for example, surface-induced dissociation (SID), surface-induced reaction (SIR), chemical- and sputtering are detected and identified by using a single-field linear time-of-flight (TOF) mass spectrometer coupled with a time- and position-sensitive dual micro-channel plate detector. The mass spectra of secondary ions are recorded by employing a pulsed extraction and acceleration technique. The experimental set up, experimental technique and data acquisition methodology are presented and discussed. A test experiment is conducted on the developed set up to demonstrate the performance and reliability of the apparatus. For this, a primary beam of 427 eV N2+ ions was chosen to interact with a hydrocarbons covered surface of platinum target kept at room temperature. SID of N2+ into N+ and TOF mass spectra of sputtered, reflected and chemically formed ions from the ion–surface interaction are analyzed. A noticeable feature in the spectra is observed which shows that the odd-electron ions of sputtered hydrocarbons are preferentially produced in the interaction in addition to the other product ions. The nominal mass resolution (M/ΔM) of the present tandem mass spectrometer system is estimated to be about 600, while energy and spatial spreads of the primary ion beam are determined to be about 518 meV and 2.8 ± 0.3 mm respectively. The survival probability of the incident ions is found to be 6.6% suggesting that the major process of ion–surface interaction at the considered impact energy is neutralization.

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