Wideband current transformers for the surveillance of the beam extraction kicker system of the Large Hadron Collider

The LHC beam dumping system must protect the LHC machine from damage by reliably and safely extracting and absorbing the circulating beams when requested. Two sets of 15 extraction kicker magnets form the main active part of this system. A separate high voltage pulse generator powers each magnet. Because of the high beam energy and the consequences which could result from significant beam loss due to a malfunctioning of the dump system the magnets and generators are continuously surveyed in order to generate a beam abort as soon as an internal fault is detected. Amongst these surveillance systems, wideband current transformers have been designed to detect any erratic start in one of the generators. Output power should be enough to directly re-trigger all the power trigger units of the remaining 14 generators. The current transformers were developed in collaboration with industry. To minimize losses, high-resistivity cobalt alloy was chosen for the cores. The annealing techniques originally developed for LEP beam current measurement in collaboration between CERN and industry allowed to extend the frequency response beyond that of traditional core materials. The paper shows the results obtained, exposes the problems encountered with shielding, conductor position sensitivity, load resistor technology and their solutions. The know-how acquired during the collaboration was further applied by the industrial partner to cover a wider range of sensitivity, size and frequency

Compromising the Unfolded Protein Response Induces Autophagy-Mediated Cell Death in Multiple Myeloma Cells

OBJECTIVE: To determine whether the Unfolded Protein Response (UPR) sensors (PERK, ATF6 and IRE-1) can be targeted to promote death of Multiple Myeloma (MM) cells. METHODS: We have knocked-down separately each UPR stress sensor in human MM cell lines using RNA interference and followed MM cell death by monitoring the membrane, mitochondrial and nuclear alterations. Involvement of caspases in MM cell death consecutive to UPR sensor knock-down was analyzed by western blotting, measurement of their enzymatic activity using fluorigenic substrates and susceptibility to a pan-caspase inhibitor. Activation of the autophagic process was measured directly by detection of autophagosomes (electronic microscopy), monodansylcadaverine staining, production of the cleaved form of the microtubule-associated protein 1A/1B light chain 3 (LC3) and indirectly by analyzing the impact of pharmacological inhibitors of autophagy such as 3MA and bafilomycin A1. RESULTS: We show that extinction of a single UPR stress sensor (PERK) induces a non-apoptotic form of cell death in MM cells that requires autophagy for its execution. We also show that this cytotoxic autophagic process represses the apoptosis program by reducing the cytosolic release of the apoptogenic factors Smac/DIABLO and cytochrome c. INTERPRETATION: Altogether our findings suggest that autophagy can contribute to execution of death in mammalian cells that are exposed to mild ER stress. They also suggest that the autophagic process can regulate the intrinsic apoptotic pathway by inhibiting production of death effectors by the mitochondria, thus preventing formation of a functional apoptosome. Altogether these findings give credit to the idea that UPR sensors can be envisaged as therapeutic targets for the treatment of MM

Flat Low-Loss Silicon Gradient Index Lens for Millimeter and Submillimeter Wavelengths

We present the design, simulation, and planned fabrication process of a flat high resistivity silicon gradient index (GRIN) lens for millimeter and submillimeter wavelengths with very low absorption losses. The gradient index is created by sub wavelength holes whose size increases with the radius of the lens. The effective refractive index created by the subwavelength holes is constant over a very wide bandwidth, allowing the fabrication of achromatic lenses up to submillimeter wavelengths. The designed GRIN lens was successfully simulated and shows an expected efficiency better than that of a classic silicon plano-concave spherical lens with approximately the same thickness and focal length. Deep reactive ion etching (DRIE) and wafer-bonding of several patterned wafers will be used to realize our first GRIN lens prototype

1.6:1 bandwidth two-layer antireflection structure for silicon matched to the 190–310 GHz atmospheric window

Although high-resistivity, low-loss silicon is an excellent material for terahertz transmission optics, its high refractive index necessitates an antireflection treatment. We fabricated a wide-bandwidth, two-layer antireflection treatment by cutting subwavelength structures into the silicon surface using multi-depth deep reactive-ion etching (DRIE). A wafer with this treatment on both sides has <−20  dB (<1%) reflectance over 187–317 GHz at a 15° angle of incidence in TE polarization. We also demonstrated that bonding wafers introduce no reflection features above the −20  dB level (also in TE at 15°), reproducing previous work. Together these developments immediately enable construction of wide-bandwidth silicon vacuum windows and represent two important steps toward gradient-index silicon optics with integral broadband antireflection treatment