Design status of the differentially pumped gas cell for positive ion mass spectrometry (PIMS)

The CUPAC-NE (Cotton University Particle accelerator Centre and North East Collaboration) has proposed to construct a discovery class accelerator facility with (i) a 5 MV Van de Graff accelerator with an ECR ion source at the terminal and (ii) a PIMS accelerator which is also based on using an ECR ion source. Both the accelerators will be first of its kind in the nation and will open up new and emerging frontiers of modern science. PIMS is a new technique in which intense beam of ¹⁴C⁺ isotopes from an ECR ion source is converted into negative ¹⁴C^-- ions by passing through a high pressure isobutene gas target in a differentially pumped cell. Interestingly ¹⁴N⁺, the dominant isobaric contaminant does not form negative ions. A mass spectrometer downstream of the cell rejects ¹⁴N⁺ ensuring pure ¹⁴C^-- are measured at the focal plane. As PIMS is discovered only recently, very few investigations beyond proof of principle demonstrations were done so far. We plan to explore PIMS to verify some of our predictions: (i) It will be possible to achieve lower time resolution than AMS and (ii) PIMS will work with large number of isotopes as the fundamental physics of the process is very similar to the ones used in RIB injector at ORNL