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ROBIN is a single RF driver based negative ion test bed currently in operation at IPR, Gandhinagar, India. To understand and have deeper insights of physical phenomena, several diagnostics have been interfaced with ROBIN system. To quantify the negative ion density, laser photo detachment (LPD) diagnostic is configured. LPD at ROBIN is based on single high power Nd:YAG laser which has a pulse width of 3 ns and repetition rate of 20 Hz. Successful integration of LPD needs control on laser energy, precise triggering and detection of weak signals. Precise triggering has two aspects. One is to control laser energy via a delay between the flash lamp and Q-switch pulses; the second is to trigger it in phase with the 1 MHz RF signal. This required a triggering system which can work with an accuracy of few nanoseconds. A triggering and synchronization system (TSS) based on a custom field programmable gate array(FPGA) is designed and integrated in order to assure reliable and synchronized operation of the laser. Precise delay between laser pulses is necessary to obtain appropriate laser energy and to prevent the active Nd:YAG rod medium from thermal damage. In order to synchronize the laser operation with 1 MHz RF, Rogowskii coil based peak detection is used and interfaced with TSS. The LPD setup is HV referenced; hence the interfaces were designed with optical isolation. Another challenge is to detect weak signals from the LPD probe. For this, a custom low-noise pre-amplifier circuit is designed to measure signal in the range of 1-2 mA in the presence of large RF noise. The engineering solution designed for LPD interface contains mix of analog and digital systems. The TSS is based on a low cost FPGA platform, with custom analog-based interfaces. The unit has been integrated without using any specific commercial system for the desired goal. The data from diagnostic is being currently analysed. This paper presents the details regarding the design of interfacing electronics of the LPD, along with some test results. In addition, the FPGA firmware, the control software and signal acquisition process are presented. [ABSTRACT FROM AUTHOR]

Negative ion-based inductively coupled plasma sources operate in a high RF power and HV environment for plasma production and beam transport. Due to plasma power coupling dynamics, RF power mismatch causes large reflected fields which affect all the diagnostic signals, degrading the signal to noise ratio. In addition to RF disturbances, during the beam extraction and acceleration, the diagnostic signals are also prone to suffer during HV breakdowns due to high dV/dt fast switching of the HV system. The breakdowns cause the generation of HV transients which in turn disturb the entire signal referencing system. Such an operational environment poses challenges for front end electronics design for low voltage signals like the one from thermocouple sensors, which are some of the most important diagnostic elements in such sources. The surface-mounted thermocouples referenced to floating potential pick up noise from HV transients and RF noise. A signal conditioning system is therefore needed to arrest the noise sources and provide clean signals for the acquisition and control system. Such signal conditioning needs specific RF filters and PCB design. Special attention is also required for shielding and grounding to help reduce noise interference. The present work discusses the measurements in light of the improvements made to the front end electronics for the thermocouples used on the ROBIN RF-based negative ion source test bed. The source operates at 1 MHz RF and with HV power supplies rated at 11 kV 35 A for extraction and 35 kV 15 A for acceleration. Mismatch fields of the order of 90 V/m have been observed. The overall signal chain from field to presentation layer shall be presented with the measures undertaken to solve the noise interference. [ABSTRACT FROM AUTHOR]

ROBIN, the first step in the Indian R&D program on negative ion beams has reached an important milestone, with the production of negative ions in the surface conversion mode through Cesium (Cs) vapor injection into the source. In the present set-up, negative hydrogen ion beam extraction is effected through an extraction area of ~ 73.38 cm² (146 apertures of 8mm diameter). The three grid electrostatic accelerator system of ROBIN is fed by high voltage DC power supplies (Extraction Power Supply System: 11kV, 35A and Acceleration Power Supply System: 35kV, 15A). Though, a considerable reduction of co-extracted electron current is usually observed during surface mode operation, in order to increase the negative ion current, various other parameters such as plasma grid temperature, plasma grid bias, extraction to acceleration voltage ratio, impurity control and Cs recycling need to be optimized. In the present experiments, to control and to understand the impurity behavior, a Cryopump (14,000 l/s for Hydrogen) is installed along with a Residual Gas Analyzer (RGA). To characterize the source plasma, two sets of Langmuir probes are inserted through the diagnostic flange ports available at the extraction plane. To characterize the beam properties, thermal differential calorimeter, Doppler Shift Spectroscopy and electrical current measurements are implemented in ROBIN. In the present set up, all the negative ion beam extraction experiments have been performed by varying different experimental parameters e.g. RF power (30-70 kW), source operational pressure (0.3 - 0.6Pa), plasma grid bias voltage, extraction & acceleration voltage combination etc. The experiments in surface mode operation is resulted a reduction of co-extracted electron current having electron to ion ratio (e/i) ~ 2 whereas the extracted negative ion current density was increased. However, further increase in negative ion current density is expected to be improved after a systematic optimization of the operational parameters and Cs conditioning of the source. It was also found out that a better performance of ROBIN is achieved in the pressure range: 0.5-0.6 Pa. In this paper, the preliminary results on parametric study of ROBIN operation and beam optimization in surface mode are discussed. [ABSTRACT FROM AUTHOR]

Light interaction of nanoparticles embedded in a tissue decides the amount of thermal energy absorbed, which is key to plasmonic photothermal therapy, a recent concept for treatment of cancer. The light interaction depends on the shape-size-type of nanoparticles, type of tissue and the wavelength of light used. A numerical model is developed to capture light interaction of a nanoparticle embedded tissue and subsequently estimate spatial heating of the tissue. [ABSTRACT FROM AUTHOR]

This paper explores different types of nanofluids (namely aluminium nanoparticles dispersed in water, ethylene glycol, propylene glycol and therminol VP-1) for their suitability as working fluid in direct absorption linear parabolic solar collectors. Lambert Beer's law has been invoked to compute intensity attenuation as it passes through the nanofluid. Intensity attenuation and subsequent energy transfer takes place through absorption and scattering of solar radiations by the participating media (nanofluid). The current analysis quantitatively compares the solar energy capturing capacity for the four nanofluids. Optical efficiency as a function of receiver radius and volume fraction of nanoparticles has been computed for the four nanofluids, also thermal efficiency as a function of volume fraction has been found out. [ABSTRACT FROM AUTHOR]

The gold nanoparticle coated cobalt-silica core-shell nanospheres have been synthesized via a multi-step, solution based chemical approach. While the plasmonic characteristics of gold nanoparticles (AuNPs) are retained in core shell configuration, the magnetic properties of core shell system change significantly after AuNP coating. It is found that the coercivity of magnetic core-shell significantly reduces after AuNP coating and system could not attain magnetic saturation at 300 K (even at large field of 5 T). At low temperature (10 K), AuNP coated cobalt-silica coreshell nanospheres exhibit reduced magnetization (Ms=4.3 emu/g) compared to bare cobalt-silica core-shell system (Ms=6 emu/g). [ABSTRACT FROM AUTHOR]

The stabilization of AuNPs by Poly-vinyl Alcohol (PVA) with ascorbic acid as a reducing agent has been investigated here. PVA and ascorbic acid are bio-compatible and water soluble compounds, thus the approach is green. We study the extent of stabilization provided by PVA under differing initial pH conditions and at different ascorbic acid (AA) to gold chloride (AuCl3) molar ratios. It is found that if the molar ratio AA:AuCl3 is below 3 then PVA is effective as an stabilizer otherwise not. Furthermore, an improvement in stabilization is observed when initial pH value of reaction mixture is adjusted to be above 7 and TEM imaging shows fairly monodisperse and medium sized AuNPs (52±9 nm) at pH- 11. A decrease in width of plasmon peak and disappearance of secondary surge near 750 nm with time in time dependent UV-Vis absorption spectra shows that in presence of PVA, the nucleation is not according to standard LaMer nucleation model but particles are formed via a complex intermediary. [ABSTRACT FROM AUTHOR]