The initial operation of the MPD Detector during the commissioning phase of the NICA Accelerator complex will need to proceed in stages. In particular in the initial setup, the MPD Detector will be located in the “Service” position, away from the NICA beampipe. This presents the need to develop a detector setup, limited in scope, level of complication and timescale, which will operate outside of the normal MPD setup, on the temporary beam pipe, during the commissionning stage.
The tasks for such temporary detector setup include, but are not limited to:
Provide feedback to the NICA Accelerator Complex on relative changes of luminosity around the MPD interaction point, preferably “on-line” (with minimum latency)
Provide data which would distinguish true beam-beam collisions around the interaction point from possible background, such as beam-gas collisions, collisions far away from the expected interaction zone, beam-beampipe collisions, cosmic ray interactions, etc.
Test and commission the data and triggering interlink between MPD and NICA
Provide real-world experience in coordination of operation and datataking between operators of MPD and operators of NICA
Test critical general-purpose systems of MPD, such as data acquisition, on-line and off-line data storage and processing, engineering support systems (power supply, gas systems, safety equipment, etc.)
Provide input for calibration of selected detector subsystems with real collision data.
I think that we should first discuss why at all do we need to have the detector in a service position during the commissioning phase of NICA. In other similar situations that I know, RHIC and LHC, the detectors were not in a retracted position during the collider commissioning phase.
In case of ALICE it was not possible to move the detector, so there was no option to have it in “service” position. However during the beam commissioning the majority of detectors (most notably the TPC and TOF) were disconnected. Similarly the CMS and ATLAS detectors were fully switched off due to detector safety concerns. As far as I remember only the beam counters and the silicon tracker in ALICE were powered on. In case of MPD the possibility to have the detector in the “service” position exists. The proposition is to only switch on the “safe” detectors - in our case detectors based on scintillators.
According to the preliminary plan the injection of beams into collider will start on September 2022.
The accelerator team will use their own vacuum pipe made of stainless still with diameter of 100 mm.
This don’t guarantee that beam avoids hitting the wall of the beam pipe.
In case detector at that time stays on the beam line and 22 billions of gold ions (22 bunches x10**9) hit the beam pipe, they could destroy electronics of detectors close to the beam pipe. They are FFD, FHCal and possibly innermost layers of TPC. The maximum what we can see in this mode is beam-gas interactions which products mostly stays inside of beam pipe.
It is better that at that time the MPD stays in assembling doc. In optimistic case all systems will be under test with comics.
The solenoid will be cooled down at the temperature of liquid nitrogen. In less optimistic case we will work to finish assembling and tests of the MPD elements.
In December 2022 there is a plan to start the first run. MPD will be moved into the beam line with its own beam pipe.
I estimate as two weeks the required time to put detector on the beam.
We will not have ITS, which is a critical subsystem as far as radiation damage is concerned during the first phase.
Also I am sure that the accelerator people will not start the commissioning phase with full design luminosity. I believe it will be order(s) of magnitude lower.
Was there any study done that shows potential damage to the forward detectors?
The Collider starts with low luminosity but beam intensity could be 10**8 per bunch. We did some estimations of secondary particles density when beam hits the wall of beam. The result was that per one ion of gold there are 10 secondary particles per cm ** 2. The maximum flux is on the radius 30-40 cm and moves along the beam pipe. So for 10 ** 8 x 22 bunches= 2*10 ** 9 of Au one may have density of secondary particles more than 10 ** 10/cm ** 2. I plan to do more careful study of radiation dose in detector elements from interaction beam with pipe wall using Fluka.
Last week we presented an updated study of the beam-monitoring tasks for the temporary detector set-up. In this particular study we include MCORD, miniBeBe and BMD, in order to improve beam-gas vs beam-beam trigger and vertex determination.
We have new updated studies in progress that we will continue to present. We welcome your comments and suggestions.