by Giacinto De Cataldo. Published: 30 June 2016

At the CERN accelerator complex, ALICE is located after the beam injection line TI2 feeding LHC with Beam1, as shown in Fig.1. Due to the importance of its specific position, for a synchronized and safe operation of the experiment-accelerator complex, a control software named ALICE-LHC Interface (LHC_IF) is in place in ALICE.

Figure 1. The CERN accelerator complex

The LHC_IF project provides the online data exchange between the LHC and the experiment. It subscribes to the published beam parameters, monitors the quality of collisions in ALICE and provides feedback to LHC publishing a set of variables and parameters useful for the machine operation and collision optimization at IP2.  To achieve this it integrates some beam instrumentation such as Beam Condition Monitor (BCM), Beam Loss Scintillators (BLS) and ALICE detectors. Via the BCM the LHC_IF can dump the beams or inhibit the injection via dedicated control lines. It also provides basic tools for a preliminary offline data analysis of the beam and experiment conditions during a fill.

Fig.2 shows the LHC-IF display in the ARC with the most relevant information on the beams and collision quality at IP2.

Figure 2: The LHC_IF display.  The three sections, from left to right, show: Beam Information, Luminosity and Background.

The LHC-IF provides information (experiment status, Instantaneous luminosity, target luminosity, beam background, etc.) for the LHC web pages: LHC Page 1LHC Operation (shown in Fig.3), LHC Luminosity and LPC luminosity plots.

Figure 3: LHC Operation web page

Lately, in collaboration with Reyes Alemany and Jorg Wenninger of the Accelerator Operation Group, the LHC_IF has deployed in ALICE an automatic luminosity levelling routine. It is based on the instantaneous luminosity measurement and provides feedback to LHC on how fast the beams can be moved while approaching the target luminosity. In this way, automatically during STABLE BEAMS, LHC can safely deliver the nominal luminosity to ALICE minimising the setting time.

After a careful discussion with ALICE Run Coordinators about the main functionalities needed to be used by the shift leader, the LHC-IF has provided a compact shift leader user interface (SL_UI) to the main experiment online systems: CTP, ECS, DCS, LHC instrumentations, Luminosity and beam background monitoring (see Fig. 4). Soon the SL_UI will also include the monitoring of the LHC data files for the Offline pre-processor and Offline Condition Database (OCDB). The SL_UI has revealed to be an indispensable tool for the Shift Leader for an effective experiment operation.

Figure 4: The compact Shift Leader User Interface (SL_UI) where tabs (on top) and buttons (on the left) permit the Shift Leader an easy monitoring/operation of the Experiment.

Fig. 5 shows the collision monitoring that the LHC_IF had provided to the machine during the preliminary  tests with pp collisions at 13 TeV carried out on 5 May 2015.

Figure 5: The T0VX collision rate (red curve) in ALICE during the first unofficial test with pp collisions at 13 TeV carried out on 5 May 2015.

In Fig.6 ALICE members are commenting the first results during the official test with pp collisions at 13 TeV with stable beams in June 2015.

Figure 6: First considerations on the pp collisions at 13 TeV in June 2015.

A bit of history and an anecdote

The LHC Interface took its first shape in 2006, with a different name, in the ALICE DCS environment. In 2010 the project moved to the technical coordination, took its actual name and its mandate was defined and approved. Later it became a branch of the ALICE Online project. Fig. 7 is a photograph from 23 November 2009, showing a trend view of LHC_IF monitoring of the injection intensities and beam intensities respectively of B1 and B2 during the beam mode CIRCULATE AND DUMP.

Figure7: LHC_IF trends with injection intensities B1 (red peaks) and B2 ( green peak) and beam intensities measurements (blue and green curves) on the LHC_IF display in the ALICE control room on 23 November 2009.

LHC_IF is an international project and the institutions involved are: INFN Bari, Italy; Academy of Science, Kosice, Slovakia; INFN Bologna, Italy, CERN and lately University of Malta.

To conclude the presentation of the project here is  a funny story which must have happened during the first half of 2008.

As you might know in the beginning of the film Angels & Demons, from the ATLAS control room, the operator monitoring the beam injection says something like: “….as far as the heavy ion guys will not screw up the beams….”. During the screening of the film in May 2009 I heard that phrase, and immediately an episode from the year before  came to my mind.  In the middle of the night I was called on my private phone number (the CERN portable was switched off) and a woman kindly asked me if I were sleeping. Yes, I think so, I answered. It was Reyes Alemany from the Accelerator Operation Group saying that LHC and of course all four experiments were blocked since some time (…three of them were apparently complaining about that!). This was due to problems with removing the beam injection inhibits at IP2! I was not on call but I was the designer in ALICE of part of the automatic control software for that and then supposed to have a solution. In fact the poor shifter in ALICE was facing a tremendous slowing down of the control software due to an unexpectedly high number of commands that the different detectors in ALICE were sending at the same time during the first exciting INJECT AND DUMP tests of LHC! Once in the control room I realised, frightened, that I had no solution other than suspending all the automatic crosschecks of the experiment safe state and operating the inhibit lines manually. Fortunately the action was successful. The full unwanted machine stop took about three hours: I have the suspicion that the ATLAS colleagues cited this episode when the film was shot in their control room, making in some way the …heavy ion guys…  have a role in the film!