Superconducting Sextupole Corrector Magnet for the LHC Main Dipoles

Each LHC main dipole will be equipped with small sextupole corrector ma g nets with a field strength of 1970 x2 T/m2 and a magnetic length of 100 mm designed to correct the sextupole field errors. The paper presents a cosine-q type of design where much emphasis has been put on the cost reduction because these magnets have to be made in large series of some 2500 pieces. We describe the design of a two-layer coil which can be wound automatically. The winding starts in the middle of the wire with the only joggle, the layer jump, which is housed in a corresponding groove in the end of the central island. The two layers are wound simultaneously turning in opposite directions to find their position without the need of local tooling. The coil ends are closely packed and need no end spacers. The 18 pole perturbation introduced by the ends is corrected by the position of the coil block in the straight part. The yoke is made of iron laminations of the "Scissors type" which transmit the pre-stress from the outer aluminium shrink ring to the coil. This allows the iron to be close to the coil for field enhancement and also boosts the pre-stress in the coil due to the cool down contractions. The paper describes the experience with the magnet construction and gives the first test results

Simulation of the Effect of a Series of Superconducting Magnets on a Quenching Magnet using a Controlled Current Pulse

In the LHC, the superconducting corrector magnets will be powered in series of up to 154 magnets. For protection in case of a quench, each magnet has been equipped with a parallel resistor as a bypass for the current. To validate and optimize the parallel resistor value, a test arrangement has been set up which allows quenching a single magnet as if it were connected in a large series of magnets. This simulation is obtained by maintaining the current for a certain time interval after the quench occurred. Calculations have shown that, depending on the magnet type, a current duration (after quench) of 0.2 s to 1 s simulates correctly the effect of the series of magnets. The paper gives calculation results comparing the real situation with the simulated one and reports on the test set-up that will be used to optimize the parallel resistors

Online optimization of swimming and crawling in an amphibious snake robot

An important problem in the control of locomotion of robots with multiple degrees of freedom (e.g., biomimetic robots) is to adapt the locomotor patterns to the properties of the environment. This article addresses this problem for the locomotion of an amphibious snake robot, and aims at identifying fast swimming and crawling gaits for a variety of environments. Our approach uses a locomotion controller based on the biological concept of central pattern generators (CPGs) together with a gradient-free optimization method, Powell’s method. A key aspect of our approach is that the gaits are optimized online, i.e., while moving, rather than as an off-line optimization process. We present various experiments with the real robot and in simulation: swimming, crawling on horizontal ground, and crawling on slopes. For each of these different situations, the optimized gaits are compared with the results of systematic explorations of the parameter space. The main outcomes of the experiments are: 1) optimal gaits are significantly different from one medium to the other; 2) the optimums are usually peaked, i.e., speed rapidly becomes suboptimal when the parameters are moved away from the optimal values; 3) our approach finds optimal gaits in much fewer iterations than the systematic search; and 4) the CPG has no problem dealing with the abrupt parameter changes during the optimization process. The relevance for robotic locomotion control is discussed