Development of a multipurpose beam foil spectroscopy set-up for the low cross-section measurements Gaurav Sharma a , T. Nandi b , H.G. Berry c , Nitin K. Puri a,⇑ a Department of Applied Physics, Delhi Technological University, New Delhi, Delhi 110042, India b Inter University Accelerator Centre, New Delhi 110067, India c Department of Physics, University of Notre Dame, Notre Dame, IN 46556, United States article info Article history: Received 20 February 2016 Accepted 28 April 2016 Keywords: Optical spectroscopy X-ray spectroscopy Beam-foil spectroscopy Plasma Optical alignment abstract A multipurpose facility for low cross section measurements has been developed at Inter University Accelerator Centre, New Delhi, India. The facility consists of a multipurpose miniature chamber equipped with 1 m focal length normal incidence Monochromator and charge coupled device based detection sys- tem which has been aligned to realize the best resolution of the spectrometer. The chamber in this facility collects radiation 100 times more efficiently from the older system, without using any extra focusing mir- ror assembly. It is ensured to have the provision of mounting an X-ray detector and the spectrometer transverse to the beam direction simultaneously in the same chamber. The atomic spectroscopic studies can be performed by interaction of ions beams with both thin foil and gas targets. Provision for using pho- tomultiplier tube instead of charge coupled device, is employed in the system depending on the condition of the source strength or other detection issues. We observed the essence of a very weak atomic phe- nomenon, a triply excited autoionizing forbidden transition, using the above facility to demonstrate its capability for measuring such low cross section phenomena. The present developed facility covers a large spectroscopic region from X-rays to the near infrared (0.1–10,000 Å). Ó 2016 Elsevier B.V. All rights reserved. 1. Introduction Beam-foil spectroscopy (BFS) is popularly known for its poten- tial in producing highly stripped ions and excited states [1] includ- ing various ionic states up to H-like ions with one or multi electrons in Rydberg [2,3] or continuum states [4]. Therefore it pro- duces enormous atomic and nuclear data which should be inter- preted for understanding the weak transitions rarely measured by other spectroscopic techniques [5–9]. With the development of much faster heavier beams, ion-atom collision spectroscopy proves to be a milestone in confirming the theoretical transition energies, oscillator strengths and other parameters calculated by various theoretical models or spectroscopic codes [10,11]. After many decades of beam-foil spectroscopy many gaps still exist in the identification of many transitions that are not yet observed or difficult to observe. However, they have been predicted theoret- ically or observed in systems other than beam-foil [12–16], whereas some others have been claimed to be observed indirectly from delayed observation of X-rays [15,16]. To observe such low cross section transitions and all the compo- nents of any cascade at the same time we have developed a multi- purpose facility that covers the spectroscopic region from intense X-rays to Near infrared (0.1–10,000 Å). While the old set-up was able to be used with a beam-foil set-up only; the new system can be used for the study of beam-foil, beam-gas and plasma spec- troscopy. The collection efficiency is also enhanced by 100 times from our previous setup. The grating spectrometers are very sensi- tive to minute vibrations therefore optical alignment of a spec- trometer is the most challenging task during the development of the complete BFS set-up. So, the detailed optical alignment of spec- trometer is discussed to put more emphasis and understanding on it and its related configurations. 2. Instrumentation: implementation and function 2.1. Limitations of the existing setup The existing setup at the Inter University Accelerator Centre (IUAC), New Delhi, India can only be used with beam foil spec- troscopy covering the X-ray regime from 1 keV onwards. On the other hand the 300 mm diameter size of the chamber, although http://dx.doi.org/10.1016/j.nimb.2016.04.056 0168-583X/Ó 2016 Elsevier B.V. All rights reserved. ⇑ Corresponding author. E-mail address: nitin.phy@dce.edu (N.K. Puri). Nuclear Instruments and Methods in Physics Research B 380 (2016) 26–31 Contents lists available at ScienceDirect Nuclear Instruments and Methods in Physics Research B journal homepage: www.elsevier.com/locate/nimb