Commissioning Results of Superconducting Magnet System for the Neutrino Beam Line
The first commissioning of a magnet system for the neutrino beam line in the J-PARC has been performed from January to March, 2009. The magnet system could be cooled down successfully in 9 days. RRRs of all the magnets and joint resistances in the magnet string were measured to be reasonable values. The magnet string composed of 28 superconducting combined function magnets could be excited up to 5000 A after several shutdown tests without a spontaneous quench. A quench protection scheme with a magnet safety system developed by CEA/SACLAY were verified to work properly. As for beam commissioning, the proton beams could pass through the arc section including the superconducting magnet string on the first attempt, and the magnet protection system were verified to work quite well even in a beam induced quench test.
Performance Tests of Superconducting Combined Function Magnets in the First Full-Scale Prototype Cryostat for the J-PARC Neutrino Beam Line
The first full-scale prototype magnet system assembled with the cryostat for the J-PARC proton beam line of neutrino experiment was successfully developed and tested. Two superconducting combined function magnets have been installed into the cryostat. The magnets were successfully cooled down to 4.5 K by forced flow supercritical helium and excited up to the current of 7345 A which is the nominal current of 50 GeV proton beam. The spot heater quench test showed that the quench characteristics in the supercritical helium were very similar to that in the liquid helium at 4.2 K, 1 atm. The quench protection scheme with both cold diodes and quench protection heaters was tested, and it has been verified that the magnet can be protected with safe margin.
Modeling Coherent Backscattering Errors in Fiber Optic Gyroscopes for Sources of Arbitrary Line Width
We present a new model of the noise and drift induced by coherent backscattering in a fiber optic gyroscope (FOG) interrogated with a light source of arbitrary temporal coherence. This study is critical to understand whether a FOG driven with a laser instead of a broadband source can attain high sensitivity and stability, which would have the overwhelming benefit of improving the FOG scale factor stability by at least ten-fold and would enable the use of FOGs for inertial navigation of aircrafts. Analytical and numerical solutions bring to light two significant new predictions. First, coherent-backscattering noise can be made negligibly small by utilizing a laser with a very narrow linewidth (less than ~ 20 kHz), although in this regime the drift is high. Second, by using a laser with a broad linewidth (greater than ~ 10 MHz), both the noise and the drift are low enough for aircraft inertial navigation. The dependencies of the noise and drift on fiber loss, loop coupling coefficient, and backscattering coefficient are also presented to define the optimum mode of operation of this new class of FOGs.