Speaker
Marco Morrone
(Imperial College Sci., Tech. & Med. (GB))
Description
In the framework of the high luminosity large hadron collider (HL-LHC) project, important upgrades will take place by 2024 including the installation of new superconducting magnets in which new beam screens will be placed. The beam screen is an octagonally shaped pipe inserted into the cold bore of superconducting quadrupoles a few tens of meters from the proton beam interaction points (ATLAS and CMS). It ensures vacuum stability by means of small holes along its uncovered surfaces, and shields the 1.9 K magnet cryogenic system from the heat loads and damage to the coils that would be otherwise induced by the highly penetrating collision debris. This is obtained by dense tungsten blocks placed on four of the flat surfaces of the screen. The remaining surfaces accommodate four cooling capillaries whose purpose is to transfer the heat absorbed by the tungsten to the capillaries through highly conductive thermal links.
The main subject of this study concerns the investigation of the magnetic, thermal, and mechanical behaviours of the beam screen during an LHC worst-case scenario, namely, a magnet quench. In this case, the beam screen has to guarantee its mechanical integrity to ensure vacuum and thermal stability.
A numerical FEM (Finite Element Method) model has been developed to quantify the eddy currents and the resulting Lorentz forces induced by the rapid quadrupole magnetic field decay (from 140 to about 0 T/m in 0.4 sec). As these forces greatly depend on the electrical conductivity of the material which in turn depends on temperature, thermal analyses have taken into account the change of material conductivities as well as the temperature increase due to resistive losses. Therefore, the multiphysics nature of the phenomenon calls for a fully coupled model where electro-magnetic, thermal and mechanical effects could interact simultaneously in a unique Jacobian matrix during each sub-step of the quench. Since the induced forces turn out to be considerable (peaks equal to 310 N/mm) some of the most important outcomes of the model are the assessment of the equivalent stress and displacement of all the assembly components. They, in fact, have to stay within certain safety values to protect the magnet coils in the vicinity of the cold bore, and the assembly itself.
A beam screen prototype has already been manufactured according to the main results of the simulations. This will help validate the numerical models since an ad-hoc magnet quench set up has been envisaged to take place in mid-2016.
Research supported by the High Luminosity LHC project.
Primary author
Marco Morrone
(Imperial College Sci., Tech. & Med. (GB))
Co-authors
Cedric Garion
(CERN)
Paolo Chiggiato
(CERN)
