Performance Characterization of a Solenoid-type Gas Valve for the H−H^{-} Magnetron Source at FNAL

The magnetron-style $H^{-}$ ion sources currently in operation at Fermilab use piezoelectric gas valves to function. This kind of gas valve is sensitive to small changes in ambient temperature, which affect the stability and performance of the ion source. This motivates the need to find an alternative way of feeding H2 gas into the source. A solenoid-type gas valve has been characterized in a dedicated off-line test stand to assess the feasibility of its use in the operational ion sources. $H^{-}$ ion beams have been extracted at 35 keV using this valve. In this study, the performance of the solenoid gas valve has been characterized measuring the beam current output of the magnetron source with respect to the voltage and pulse width of the signal applied to the gas valve.Comment: 4 pp. arXiv admin note: text overlap with arXiv:1701.0175

Validating side scan sonar as a fish survey tool

Hydroacoustic methods can be used to answer a variety of questions regarding fish populations and behavior. In this study, side scan sonar methodology was developed to quantify abundance and biomass and compared to established visual observation methods on SCUBA over artificial reef structures in the western Gulf of Mexico. Side scan sonar methods were equivalent to SCUBA surveys for measuring fish abundance over the same reef areas, however, abundances were significantly higher when the larger area sampled by side scan was utilized. Side scan sonar methods were also more time efficient than SCUBA, ROV and long line fishing methods (66.7%, 33.3%, 25.9% respectively). In addition, side scan methods allowed biomass and fish size class categories to be estimated over reef sites. Side scan methods allowed five reef sites to be surveyed in one day, demonstrating the capability for macro scale comparisons of fish abundance, biomass and behavior among sites

Determination of the Superconductor-Insulator Phase Diagram for One-Dimensional Wires

We establish the superconductor-insulator phase diagram for quasi-one dimensional wires by measuring a large set of MoGe nanowires. This diagram is consistent with the Chakravarty-Schmid-Bulgadaev phase boundary, namely with the critical resistance being equal to R_Q = h/4e^2. We find that transport properties of insulating nanowires exhibit a weak Coulomb blockade behavior.Comment: 5 pages, 4 figure

Implementation of Design Changes Towards a More Reliable, Hands-off Magnetron Ion Source

As the main $H^{-}$ ion source for the accelerator complex, magnetron ion sources have been used at Fermilab since the 1970s. At the offline test stand, new R&D is carried out to develop and upgrade the present magnetron-type sources of $H^{-}$ ions of up to 80 mA and 35 keV beam energy in the context of the Proton Improvement Plan. The aim of this plan is to provide high-power proton beams for the experiments at FNAL. In order to reduce the amount of tuning and monitoring of these ion sources, a new electronic system consisting of a current-regulated arc discharge modulator allow the ion source to run at a constant arc current for improved beam output and operation. A solenoid-type gas valve feeds $H_{2}$ gas into the source precisely and independently of ambient temperature. This summary will cover several studies and design changes that have been tested and will eventually be implemented on the operational magnetron sources at Fermilab. Innovative results for this type of ion source include cathode geometries, solenoid gas valves, current controlled arc pulser, cesium boiler redesign, gas mixtures of hydrogen and nitrogen, and duty factor reduction, with the aim to improve source lifetime, stability, and reducing the amount of tuning needed. In this summary, I will highlight the advances made in ion sources at Fermilab and will outline the directions of the continuing R&D effort.Comment: 4 pp. arXiv admin note: substantial text overlap with arXiv:1701.0175

Improvements on the Stability and Operation of a Magnetron H- Ion Source

The magnetron H- ion sources developed in the 1970s currently in operation at Fermilab provide beam to the rest of the accelerator complex. A series of modifications to these sources have been tested in a dedicated offline test stand with the aim of improving different operational issues. The solenoid type gas valve was tested as an alternative to the piezoelectric gas valve in order to avoid its temperature dependence. A new cesium oven was designed and tested in order to avoid glass pieces that were present with the previous oven, improve thermal insulation and fine tune its temperature. A current-regulated arc modulator was developed to run the ion source at a constant arc current, providing very stable beam outputs during operations. In order to reduce beam noise, the addition of small amounts of N2 gas was explored, as well as testing different cathode shapes with increasing plasma volume. This paper summarizes the studies and modifications done in the source over the last three years with the aim of improving its stability, reliability and overall performance.Comment: 8 pages, 19 figure