By Florence Thompson (CERN)
Engineers have started to use a life-sized mockup, named GALLUS V2, of the highly restricted region between the collision points and the tunnel at ATLAS and CMS, to test alignment and handling procedures.
The test bench was designed at CERN and recently completed - and two out of four of the TAXS modules to be handled in this challenging zone have been delivered to CERN - marking the start of the testing campaign.
TAXS
To protect the equipment in the tunnel from secondary particles produced by the collisions, there are four Target Absorber Secondary (TAS) modules. These are collimators (machine protection devices which absorb particles) made of copper which absorb the charged and neutral secondary particles.
One of these modules sits each side of both the ATLAS and CMS experiments, between the collision point and the final focusing quadrupole magnet (named Q1) in the tunnel on either side. For the HL-LHC, four new Target Absorber Secondary modules called TAXS will be installed to replace the previous LHC TAS modules.
Figure 2. Model showing the region of the HL-LHC on one side of the collision point. The TAXS (right hand side of the image) sits between the collision point and the first quadrupole, Q1, in the tunnel. The GALLUS V2 mockup mimics the region between Q1 and the experiment. Image: CERN
The mockup: why and what?
Particular handling of the TAXS is needed due to the tight space and radiation protection measures of the area, hence the use of a test bench to experiment different methods and equipment for installation, adjustment and alignment.
‘As the TAXS contains the beam pipe on the interior and will be installed in a complicated area for radiation protection and space, its alignment must be precise and remote,’ explains Antonio Alonso, project engineer in the team dealing with the collider-experiment interface of the HL-LHC. ‘The solution we have found is hanging the TAXS by several rods which can be moved from afar, allowing its position and tilt to be changed, following the natural movements of the experimental caverns.’
The way in which this is done – i.e. the exact equipment and methodology to be used for installation and adjustment – is now being experimented in a test bench mimicking this hanging system and the constraints of the tunnel.
‘The GALLUS V2 test bench was designed at CERN as an improved version of the one done by the US-LHC collaboration in 2002 for the LHC,’ continues Antonio. ‘We can adjust the configuration to mimic the tilt of the tunnel as it is in reality, and it allows us to simulate all the movement the TAXS may be required to do in its lifetime.’
There are effectively two types of mockup in one, with a removable part of the model to mimic the difference between ATLAS and CMS, so the TAXS modules for the different positions can be tested as close to the real constraints as possible. It can also be integrated with mockups of the sections of the tunnel side of this region (containing equipment like the vacuum devices), meaning that behaviour in a more complex setup can be observed.
Figure 3. The life-sized mockup of the collider-experiment interface of the HL-LHC is being used to test alignment and manoeuvring of the new TAXS modules. Florence Thompson / CERN
The testing campaign
As the first two TAXS modules – the ones to go either side of ATLAS – arrived a few months ago, and now that the test bench is completed, the team has performed the first real hanging of the first TAXS. This begins the testing campaign, which will include testing different TAXS subsystems – including handling, alignment, cooling and survey systems.
‘A dedicated testing campaign will be done with the different stakeholders of the project,’ explains Antonio, ‘It will allow us to make decisions about equipment and procedures for installation and handling, including testing new ideas and prototypes – collecting data to refine the process. We’ll also test the new survey and alignment systems, verify space between the TAXS and other equipment that will be present, and practise the removal of the LHC TAS and installation of the new TAXS in a way that would not be possible in the real or simulated environment.’