3.11.1 Introduction
Radiation levels in the collider scale with energy and, as LHC has shown, degrada
tion o f com ponents exposed to radiation can becom e a show stopper. A structured
3.11.2 Reference radiation levels
Radiation to electronics (R2E) is an issue in the design o f any high energy and high intensity machine [205]. Radiation effects in electronic devices can be divided into two main categories: cumulative effects and stochastic effects (Single Event Effects - SEE). Cumulative effects are proportional to the total ionising dose (TID ) - the dam
age induced by ionising radiation, and the 1 M eV neutron-equivalent fluence which radiation on the machine equipment, but it relies on both a refined implementation o f physics models o f the particle interaction with matter and an accurate 3D-description o f the region o f interest. In this context, FL U K A [206,207] which is widely employed at CERN, is a well benchmarked, multi-purpose and fully integrated particle physics MC code for calculations o f particle transport and interactions with matter. For a high intensity and high energy machine like the HE-LHC, typical sources o f radiation are luminosity debris, direct losses on collimators and dumps and beam interactions with the residual gas in the vacuum [208].
A FLU K A model o f the HE-LHC arc, for both optics solutions (18 x 90 and 23 x 90) is currently under development. Although FLU K A simulation allows a detailed study o f the radiation environment, taking the infrastructure around the accelerator into acount, the order o f magnitude o f the radiation levels can be esti
mated from the measured and calculated values from LHC. Scaling with the beam energy, beam current and assuming the maximum residual gas-density design value o f 1.0 x 1015 H2/m 3 (corresponding to beam lifetime o f 100 h), the annual HEH fluence and absorbed dose distribution at the locations where electronic racks are typically placed below the magnets in the arc are expected to be ^ 4 x 1010 cm -2 y -1 and
^ 8 0 G y y -1 respectively. These values are about a factor 2.5 lower than FCC-hh, assuming the same residual gas-density. Such values impose serious constraints on the selection and qualification o f electronic components for operation in distributed systems in the machine arc. because o f the infrastructure, which is fixed by the current machine layout. Indeed, in the case o f FCC-hh, ad-hoc shielded alcoves for electronics were designed to ensure adequate protection o f all the electronic systems from the severe radiation levels expected in the arc, even for a residual gas-density o f 1.0 x 1015 H2/m 3. W ith regard
1230 The European Physical Journal Special Topics
to HE-LHC, the existing RE alcoves need to be studied with FLU K A simulations, to verify that the shielding already available provides adequate protection and, poten
tially, to support civil engineering studies for the redesign o f these areas.
3 .1 1 .3 Radiation hardness
Radiation hardness assurance (RH A ) comprises all if the activities undertaken to ensure that the electronics and materials perform to their design specification after exposure to the HE-LHC radiation environment. Several strategies are being developed. essential means to independently assess the radiation hardness o f electronic com po
nents, assemblies and systems in the collider environment. An analysis o f the main shortcomings o f C E R N ’s facilities and possible solutions has been carried out and the main conclusions are outlined elsewhere [209]. For cumulative TID effects, facilities such as the CC60 [210] and G I F + + [211] will have to be upgraded with more pow
erful sources. This will allow higher doses to be reached in shorter times and it has the potential o f running more users in parallel. For the assessment o f the single event effects, the C H A R M facility [212] can be upgraded by increasing the beam intensity and the space available for the users to make parallel and multiple testing possible.
The extensive qualification programme required needs the upgrade o f existing and well-known irradiation facilities, by collaboratively exploiting the expertise and test capacity worldwide.
The HE-LHC R H A strategy is founded on a full-availability approach based on: (i) remote control, moving the processing tasks away from the equipment under control and (ii) failure self-diagnosis, online hot swapping and remote handling. Therefore system designs are based on a modular approach that will allow switching to a redun
dant sub-system without any impact on operation. This will be particularly beneficial for transient errors, which can typically be corrected with a reset. The approach will also relax the constraints on the error qualification limits, which will be obtained through accelerated radiation testing. In the case o f events which cause permanent effects such as hard SEEs (occurring stochastically) or cumulative damage, online hot-swapping will need to be complemented by the substitution o f the faulty board.
This procedure will need to be carefully optimised, especially for cumulative dam
age, where similar sub-systems exposed to similar radiation levels are expected to
curement and qualification processes can be optimised and the impact o f variability in sensitivity across batches and deliveries can be reduced. In specific cases, the use o f radiation-hardened solutions at com ponent level (e.g. F P G A ) can be considered in com bination with the use o f C O TS devices.
Finally, intensive work on radiation hardening o f electronics, components, mate
rials and detectors, as it is currently happening for HL-LHC, will continue in par
allel to technology scouting and early technology analysis to cope with the rapid advance o f electronics development and market trends. K ey technology areas for HE-LHC include, to name but a few, the development o f radiation-hard, fast and