Indus-2 Synchrotron Radiation Source Research Articles

High pressure experiments at the XAFS Beamline, INDUS-2

The dispersive XAFS beamline BL-08 at the INDUS-2 synchrotron radiation source, RRCAT, Indore uses a bent Si (111) crystal as dispersive-cum-focusing element and a position sensitive CCD detector to enable instantaneous measurement of the whole XAFS spectrum around the absorption edge of interest. This beamline is ideal for characterisation of materials under high pressure using Diamond Anvil Cell with ∼50 μm spot size. For this setup, the theoretically determined spot size (Horizontal × Vertical) varies between 17 × 137 μm and 37 × 142 μm for the x-ray energy range 5 keV-20 keV. To reduce the vertical spot size to <50 μm, we have designed an additional focusing mirror between the polychromator and sample position. The mirror, procured from SESO (France), will be installed shortly. Meanwhile, we have developed a dummy mirror bender setup at CDM (B ARC) and have carried out feasibility tests to confirm reduction in spot size using the same. We have also conducted preliminary XAFS experiments (at BL-08) on SrRuO3 at ∼16 keV, under ambient conditions and inside diamond anvil cell, in order to assess the signal intensity and quality. We have obtained reasonably good signal.

Modular 20kW solid state RF amplifier for Indus-2 syncrotron radiation source

Abstract This article presents the design and development of 505.8 MHz modular solid state Radio frequency (RF) amplifier capable of delivering 20 kW continuous RF power. It has been successfully commissioned for serving as the modern RF power source in Indus-2 synchrotron radiation source. For this amplifier, design procedure has been formulated for the solid state amplifier modules, radial combiner, divider, directional coupler and overall system architecture, with specifications suited to RF source for particle accelerator. This article describes underlying design principles and indigenous development of this amplifier, consisting of 400 W amplifier modules, 5 kW 16-port radial combiner/divider and directional couplers. Detail performance characterization of amplifier on component level as well as system level serves as useful data for higher power solid state amplifier designers. Simple design, indigenous technology, high efficiency and ease of fabrication, are the main features of this design.

Chemical shifts of K-X-ray absorption edges on copper in different compounds by X-ray absorption spectroscopy (XAS) with Synchrotron radiation

Cu K X-ray absorption edges were measured in compounds such as CuO, Cu(CH3CO2)2, Cu(CO3)2, and CuSO4 where Cu is present in oxidation state of 2+, using the energy dispersive EXAFS beamline at INDUS-2 Synchrotron radiation source at RRCAT, Indore. Energy shifts of ∼4–7eV were observed for Cu K X-ray absorption edge in the above compounds compared to its value in elemental copper. The difference in the Cu K edge energy shifts in the different compounds having same oxidation state of Cu shows the effect of different chemical environments surrounding the cation in the above compounds. The above chemical effect has been quantitatively described by determining the effective charges on Cu cations in the above compounds.

Photo-absorption studies on carbonyl sulphide in 30,000–91,000 cm −1 region using synchrotron radiation

Photo-absorption spectrum of carbonyl sulphide (OCS) is recorded in 30,000–91,000 cm −1 (3300–1050 Å) region at an average resolution of 1.2 Å using Photo-physics beamline on the 450 MeV Indus-1 synchrotron radiation source at RRCAT Indore, India. Owing to significant absorption cross section dependence, spectra of OCS are recorded at various pressures (0.001–5 mbar) to optimize the S/N ratio for band systems appearing at different energy regions. The spectral region below 70,000 cm −1 has contributions from dissociation mechanism of the ground state of OCS and three valence band systems arising from promotion of a 3π electron to 4π and 10σ orbital. Improved S/N ratio helped in unambiguous assignment of the valence band progressions at 42,000–48,000 cm −1, 53,000–62,000 cm −1 and 63,500–70,000 cm −1 regions to the 1Δ←X 1Σ + transition, the relatively intense and sharp bands of 1Π←X 1Σ + transition and intense but broad bands of 1Σ +←X 1Σ + transition, respectively, and obtain the vibrational frequencies. Above 70,000 cm −1 Rydberg series arising from s, p, d and f orbitals converging to the ionic ground state X 2Π of OCS + (90,121 cm −1) are identified. Long progression in the first few members of the Rydberg series is suggestive of mixed valence character. Quantum defects are evaluated and used to discuss the nature of the molecular orbital. The present study provides a unifying picture of the VUV photo-absorption spectrum of OCS up to its first ionization limit.

Possible origin of photoconductivity in La0.7Ca0.3MnO3

The effect of photon energy on the density of states near Fermi level of pulsed laser deposited La0.7Ca0.3MnO3 thin film has been studied to investigate the possible origin of change in the conductivity of these manganites upon photon exposure. For this purpose the photoelectron spectroscopy measurements were carried out using CSR beamline (BL-2) on Indus-1 synchrotron radiation source. The valance band spectra were measured at room temperature with photon energy ranging from 40 to 60 eV. We could see huge change in the density of states near Fermi level and this change is observed to be highest at 56 eV which is due to the resonance between Mn 3p to Mn 3d level. Our results suggest that the probability of electron transfer from deep Mn 3p level to Mn 3d-eg level is higher than that of Mn 3d-t2g level. It appears that this transfer of electron from deep Mn level to Mn 3d-eg level not only modifies the density of state near Fermi level but also changes the mobility of electrons by modifying the electron lattice coupling due to presence of Mn+3 Jahn–Teller ion.

Observation and analysis of spectral interference modulations in thin film light scattering experiments using synchrotron radiation

Light scattering in thin films represents several essential microstructural, morphological and compositional parameters in thin film systems. Under the present investigation certain gadolinia, silica thin films and multilayer systems have been probed for their spectral scattering signals using the photophysics beamline of INDUS-1 synchrotron radiation source. The pulsed structure of synchrotron radiation and its interaction with certain non-wedge optical component has however led to the spectral interference (SI) modulations in scattering signals, which was tackled by an appropriate modelling and analysis technique. Under this technique the geometric mean of the SI amplitudes were computed and then de-convoluted into several Gaussian peaks. Each Gaussian peak was made to interfere with an appropriate temporally delayed peak having certain transformed amplitude factors. Superposition of all these Gaussian interference was computed and compared with the experimental profile in an iterative manner to determine the mean pulse delay introduced by the optical element. Finally the inverse fast Fourier transform of the experimental SI signal was carried out to compare the modelling results and both the approaches demonstrated a closed match. Spectral scattering signals recorded for various thin film layer combinations depicted close resemblances with the specular characteristics recorded using a spectrophotometric technique. This distinctly highlights the dominance of multilayer thin film interference phenomena on the spectral light scattering characteristics.

Development of Photophysics Beamline at Indus-1 Synchrotron Radiation Source

A beamline to carry out photoabsorption and fluorescence experiments using INDUS-1 synchrotron radiation source has been recently commissioned at the Centre for Advanced Technology, Indore India. The optical system for the beamline consists of a pre-focusing toroidal mirror, an indigenously developed one meter Seya-Namioka monochromator and a post-focusing toroidal mirror to cover the wavelength range of 500A–2000A. An experimental chamber for performing VUV excited fluorescence on solid samples is coupled to the beamline. A quarter meter gas cell has also been fitted with the experimental station. In this paper, we have presented the salient features of the beamline and the recorded photoabsorption spectra of benzene and benzene-d6.

Optimal design of a beam stop for Indus-2 using finite element heat transfer studies

This paper describes the design of an in-vacuum, water-cooled beam stop (X-ray shutter) for the materials science (X-ray diffraction) beamline proposed to be built on the wavelength shifter in the Indus-2 (2.5 GeV) synchrotron radiation source. The radiation source impinges ∼ 1 kW power on the beam stop and the heat transfer capabilities of the beam stop have been evaluated. Temperature distribution in the beam stop has been obtained under various cooling conditions using the finite element analysis calculations with ANSYS software. Design parameters of the beam stop have been optimised. It is also shown that radiation cooling alone is not sufficient for taking away the heat load. Water-cooling of the beam stop is essential.

Use of spherical gratings in a toroidal grating mount for vuv-soft x-ray synchrotron radiation

A toroidal grating monochromator (TGM) based beamline was designed earlier and it is being setup on the 450 MeV Indus-1 synchrotron radiation source. This beamline operates in 40–1000 A wavelength range and gives a moderate resolution (∼500) at high throughput. Now-a-days, spherical gratings are giving very high resolution in some complex monochromators. We have evaluated the use of spherical gratings in the simple rotation mount of a TGM. The motivation has been to evaluate if the existing TGM beamline, without any hardware changes, can be used with the much cheaper spherical gratings. The two monochromators, employing toroidal and spherical gratings respectively, have been compared by performing detailed ray tracing calculations. Our study shows that, with the same mechanical hardware, a real spherical grating monochromator gives better performance compared to the conventional TGM with respect to the spectral resolution and the flux. Furthermore, for moderate resolution this improvement is realized even when the exit slit is not moved to keep the spherical grating in-focus.