Mostrar 2107 resultados

The high magnetic fields needed for guiding particles around the Large Hadron Collider (LHC) ring are created by passing 12’500 amps of current through coils of superconducting wiring. At very low temperatures, superconductors have no electrical resistance and therefore no power loss. The LHC is the largest superconducting installation ever built. The magnetic field must also be extremely uniform. This means the current flowing in the coils has to be very precisely controlled. Indeed, nowhere before has such precision been achieved at such high currents. Magnet coils are made of copper-clad niobium–titanium cables — each wire in the cable consists of 9’000 niobium–titanium filaments ten times finer than a hair. The cables carry up to 12’500 amps and must withstand enormous electromagnetic forces. At full field, the force on one metre of magnet is comparable to the weight of a jumbo jet. Coil winding requires great care to prevent movements as the field changes. Friction can create hot spots which “quench” the magnet and ruin its superconductivity. A quench in any of the LHC superconducting magnets would stop machine operation. 50’000 tonnes of steel sheets are used to make the magnet yokes that keep the wiring firmly in place. The yokes constitute approximately 80% of the accelerator's weight and, placed side by side, stretch over 20 km!

One of the building blocks of the CMS Silicon Tracker: a part of the detector that reconstructs the trajectories of charged particles emerging from the proton-proton collisions. A lightweight structure, made mostly of carbon fibre, supports silicon detectors and their readout electronics. These detectors generate an electrical pulse when they are traversed by a charged particle, and they are segmented into fine strips (in this case the strips are 180 microns wide, about the size of a human hair) that collect those pulses, such that the position of the strip provides a coordinate on the particle trajectory. In this “rod” silicon detectors are arranged in back-to-back pairs, where the two detectors of each pair have the strips oriented at an angle, such that the crossing point of the strips provides a two-dimensional coordinate in the rod plane. Three pairs of detectors are mounted on each side of the rod structure, to fully cover its surface. In the Tracker, rods are arranged to form cylindrical layers in the central “barrel” region.

120 tonnes of liquid helium in use at the Large Hadron Collider, cooling 36'000 tonnes of superconducting magnets to just 1.9 degrees above absolute zero. The cryogenic valves were designed for the needs of CERN to develop valves for use with the very low temperature of liquid helium.

Under the microscope you can see a pixel of silicon from a new generation of high-precision detectors under development for ALICE. The ALICE detector is designed for the periods when the LHC collides the nuclei of lead atoms rather than protons. These lead collisions produce extremely dense tangles of particle tracks and many short-lived particles. Precision is key! The new silicon detectors are extremely thin and can measure the passage of particles with a precision of 5 thousandth’s of a millimetre. The connections to the electronics are integrated into the silicon.

Each of these straws is a complete mini–detector in its own right. Every one is filled with a gas mixture and threaded with a wire. Imagine assembling 300’000 fragile drinking straws up to 144 cm long, with no bends or kinks allowed! This layer of tracker plays two important roles. Firstly, it makes more position measurements, giving more dots for the computers to join up to recreate the particle tracks. Then it also helps distinguish between different types of particles depending on whether they emit radiation as they make the transition from the surrounding foil into the straws. An electric field is applied between the wire and the outside wall of the straw. As particles pass through, they collide with atoms in the gas, knocking out electrons. The avalanche of electrons is detected as an electrical signal on the wire in the centre.

LHCb measures muons using gold plated tungsten wires stretched over read-out pads. A high voltage is applied across the wires and pads and the set-up is bathed in a gas mixture. Passing muons interact with the gas, knocking out electrons from its atoms in a process called ionization. Both the ionized atoms and the electrons then drift in the electric field. This movement creates an electric signal in the wires and pads that is used to identify where the muon has passed. In total, the LHCb muon detectors contain about 2 million wires and are capable of making measurements 40 million times a second – every time the particle beams collide.

The innermost layers of all four LHC detectors are made of silicon. This piece comes from the ATLAS detector where its job is to record the paths of the particles close to the collision. Here, hundreds of particles spray outwards and the silicon detectors must identify the exact points from which the particles originate and make an accurate measurement of the curvature of every particle track. Inside ATLAS, the first layer is made of 80 million silicon pixels, each smaller than a grain of sand. Surrounding the pixels are six million silicon strips, each about the thickness of a hair. The object on display here contains 1536 such silicon strips. Together, the layers of tracking detectors are like a giant 92 mega pixel camera taking a photo 40 million times every second.

The ATLAS transition radiation tracker is made of 300'000 straw tubes, up to 144cm long. Filled with a gas mixture and threaded with a wire, each straw is a complete mini-detector in its own right. An electric field is applied between the wire and the outside wall of the straw. As particles pass through, they collide with atoms in the gas, knocking out electrons. The avalanche of electrons is detected as an electrical signal on the wire in the centre. The tracker plays two important roles. Firstly, it makes more position measurements, giving more dots for the computers to join up to recreate the particle tracks. Also, together with the ATLAS calorimeters, it distinguishes between different types of particles depending on whether they emit radiation as they make the transition from the surrounding foil into the straws.