Elastic modulus measurements of the LHC dipole superconducting coil at 300 K and at 77 K

Abstract

We present measurements of the stress-displacement relation for the superconducting coils used in the Large Hadron Collider main magnets (dipoles and quadrupoles). This mechanical property is relevant to determine the correct amount of azimuthal pre-stress to be imposed on the coil. The hysteresis pattern in the loading and unloading curves is discussed. The stress-displacement curves are used to compute the corresponding elastic moduli and deformations. Measurements are also carried out at liquid nitrogen temperature, using the same framework to interpret experimental data. ABSTRACTWe present measurements of the stress-displacement relation for the superconducting coils used in the Large Hadron Collider main magnets (dipoles and quadrupoles). This mechanical property is relevant to determine the correct amount of azimuthal pre-stress to be imposed on the coil. The hysteresis pattern in the loading and unloading curves is discussed. The stress-displacement curves are used to compute the corresponding elastic moduli and deformations. Measurements are also carried out at liquid nitrogen temperature, using the same framework to interpret experimental data.

Thermal contraction measurements of the superconducting coil of the main magnets for the Large Hadron Collider

“…We generalise equation (4) to include also the non-linear behaviour of the stack presented in [7] and deformations of the mould. Let E wf and E cf be the elastic moduli of the cavity at warm and cold temperature respectively: then one has ( ) ( )…”

“…Indeed, the unloaded height of a stack of insulated superconducting cable is ill-defined [9], equation (1) cannot be used for the evaluation of the thermal contraction coefficient of the stack in a direct manner. In fact, considering the stress-displacement curve presented in [7], at low pressure an increase of just 1 MPa (for instance from 0 MPa to 1 MPa) in the compression stress determines a strain of the same order of the thermal contraction of the stack [10][11][12], i.e. about 1 %.…”

“…This procedure has been chosen taking into account the loading path followed by the coil during the LHC dipole assembly before the cool-down [15]. The strain ε ws has been computed as the difference between the stack height at 0.4 MPa on the loading curve (that we assumed as unloaded stack height [7]) and the height on the unloading curve at a stress of σ w . At cryogenic temperature the strain ε cs can be evaluated in the same way.…”

“…For the evaluation of the thermal contraction coefficient of the stack we use the following scheme: we performed five different cool-downs and we consider the stressdisplacement curves presented in [7] to determine the strain before and after the cool-down. The strains are then used to compute by equation (5) the thermal contraction.…”

“…In this paper we present the measurements of the thermal contraction coefficient of a stack of conductors used in the outer layer coil of the LHC dipole [7]: the measurements have been performed taking into account the stress path followed by the coil during the magnet assembly.…”