1. However, it has not been clear to which extend all possible beam loss scenarios were fully computed. Therefore, the auditors would like to encourage the BLM team to summarize the results of the impressive simulation studies and measurements done so far. It might be beneficial to describe the different measurements and results using the same physical units, which are relevant for the BLMs under the specific conditions of LHC operation.
It should be pointed out in which domains improvements are ongoing, like the activity by the BLM & FLUKA teams on the implementation and computation of the LHC setup in the collimation regions.
Also, the limits of the
computations should be discussed. This
relates to the difficulty to get all information of correct geometry and
material compositions of some LHC components.
Barbara
We should estimate the error due to
geometry/material uncertainties by comparing a detailed model to a coarse
model. We do not expect very big effects (compared to required accuracy of 5
and 2 respectively).
Mariusz:
Agree with recommendation! It is not possible to
compute all loss scenarios, but the conservative thresholds which correspond to
high energy deposition and low BLM signal can be identified and will be used as
initial thresholds.
2.
The signal development as
function of different loss scenarios was studied. In particular, the response
functions of the monitors and the electronics response have been calculated. Saturation
effects should be studied in more detail, and the limits of the current monitor design should be summarized.
Mariusz:
The procedure of safe re-adjustement
of the thresholds thanks experience gain during the LHC operation is foreseen.
3. As the monitors are exposed to high radiation, the activation/de-activation as function of LHC operation should be computed in order to determine the baseline shifts of the BLM signal.
We
propose to use the measured BLM signal to determine the activation with time of
the monitors (plus the activation of the surrounding equipment). Shouldn’t that
be more precise than simulation?
4. A more detailed description of the materials and geometry of the monitors and a summary of the total material budget should be added.
5.
Quite a series of sophisticated simulations on shower propagation due to
beam losses have been made. However, the systematic errors on the results are
quite large (up to 50%).
(But still rather reasonable with
respect to the required accuracy of a factor of 5 at start-up.)
Therefore, and due to
the aforementioned points, the auditors share doubts that the monitors would
guarantee a safe and efficient operation of the LHC without a re-adjustment of
the thresholds.
The initial threshold settings have to be sufficiently conservative in
order not to damage the LHC magnets. During the initial runs of the LHC, they must
then be iteratively adjusted.
6.
The first operation of LHC will give the BLM team the possibility to
compare the behavior of the monitors with the predictions. As the monitors have
to cover an enormous range of radiation intensity, specific tests during LHC
operation have to be performed.
Dedicated test procedure
should be proposed by the BLM team.
For example, tests with provoked beam losses should be conducted in order
to verify the proper detection of those beam losses.
Mariusz:
We are very happy to see that tests with provoked beam
losses are recommended by auditors!
Mariusz:
7:
Documentation is being produced and will be put in EDMS