1) Message boards : LHC@home Science : LHC magnet is being repaired, no collisions for at least several weeks (Message 48303)
Posted 22 Jul 2023 by Sesson
Post:
https://home.cern/news/news/accelerators/accelerator-report-quench-lhc-inner-triplet-magnet-causes-small-leak-major

At 1.00 a.m. + 17 seconds on Monday, 17 July, the LHC beams were dumped after only 9 minutes in collision due to a radiofrequency interlock caused by an electrical perturbation. Approximately 300 milliseconds after the beams were cleanly dumped, several superconducting magnets around the LHC quenched – i.e. they lost their superconducting state.
...
Unfortunately, in the case of the inner triplet magnet located to the left of Point 8, a small leak has appeared between the cryogenic circuit, which contains the liquid helium, and the insulation vacuum that separates the cold magnet from the warm outer vessel, known as the cryostat. This vacuum barrier is crucial for preventing heat transfer from the surrounding LHC tunnel to the interior of the cryostat (this is similar to the functioning of a thermos flask). As a result of the leak, this insulation was lost: the insulation vacuum filled with helium gas, cooling down the cryostat and causing condensation to form and freeze on the outside.
...
it is clear that an intervention with the inner triplet magnet at room temperature will be required. This incident will probably have a great impact on the LHC schedule, with machine operation unlikely to resume for at least several weeks.

Looks like LHC has an MTBF of several days. The power of LHC is too large for a UPS. Time to have a summer break in the extremely hot days!
2) Message boards : CMS Application : no new WUs available (Message 48232)
Posted 19 Jun 2023 by Sesson
Post:
It's the LHC technical stop! ATLAS and CMS stopped working!
3) Message boards : ATLAS application : ATLAS vbox and native 3.01 (Message 48105)
Posted 16 May 2023 by Sesson
Post:
ATLAS Athena framework undergoes important renovation

I hope the ATLAS project can set a smaller default memory limit for VirtualBox VMs that is appropriate for Run 3 tasks.
4) Message boards : LHC@home Science : LHC's Winter Pause (Message 47953)
Posted 31 Mar 2023 by Sesson
Post:
It looks like the 2023 run is still stuck at 13.6 TeV.
I wish the LHC runs more smoothly at 13.6 TeV in 2023.
5) Message boards : LHC@home Science : LHCb releases first set of data (Message 47869)
Posted 17 Mar 2023 by Sesson
Post:
The most exciting news from LHCb is that “flavour anomalies” is not supported by most recent LHCb experiment. Instead LHCb found nothing that could challenge lepton flavour universality, a key property of Standard Model, and marked the end of years of speculation on possible “flavour anomalies”. This means physicsts have to come up with another theory that could challenge Standard Model.
6) Message boards : LHC@home Science : Most useful subproject (Message 47868)
Posted 17 Mar 2023 by Sesson
Post:
ATLAS and CMS of course, they are the flagship experiments of the LHC. CERN is running these applications in their own datacenters too.
However these applications may be too heavy. If you can't run them, Theory simulation and Sixtrack are also a good choice.
7) Message boards : LHC@home Science : Ready to restart! (Message 47263)
Posted 18 Sep 2022 by Sesson
Post:
I'm intrigued by the cryptic references to UFOs in that blog post - sounds suspiciously like someone's dropping their spanners on the machine. (Unless that's a dated baguette reference?)

Large particle accelerators like the Large Hadron Collider (LHC) are extremely sensitive to tiny vibrations. In fact, physicsts have discussed the possibility of detecting gravitational waves using large particle accelerators. The most interesting point is that particle accelerators are not only sensitive to gravitational waves, but also are probably capable of creating artificial gravitational waves! I wonder when will we build the next particle accelerator after the FCC that could enable unimaginable science fields in both cosmology and particle physics.

Anyway, we still don't have the HL-LHC. The most exciting results obtainable by LHC run 3 include:

    Either confirm or exclude lepton flavour universality (LFU) anomalies, and further searches on leptoquark models
    New experiements FASER and SND
    Results from significantly upgraded LHCb and ALICE experiment, like new exotic hardron discoveries and studies on quark–gluon plasma (QGP)
    Higher precision experiments and search of rare decay modes may find the first deviations from the SM

8) Message boards : LHC@home Science : Ready to restart! (Message 47221)
Posted 4 Sep 2022 by Sesson
Post:
An encouraging start for Run 3
9) Message boards : LHC@home Science : Ready to restart! (Message 47196)
Posted 28 Aug 2022 by Sesson
Post:
Meanwhile the LHC magnets remain at 2K, allowing more time to train the magnets.

From https://home.cern/science/engineering/restarting-lhc-why-13-tev
At LHC beam energies, the electric currents are extremely high, up to 12,000 Amperes, and superconducting cables have to be used. Superconductivity is a low-temperature phenomenon, so the coils have to be kept very cold, just 1.9 degrees above absolute zero to be precise, or about -271°C. Even a tiny amount of energy released into the magnet for any reason can warm the coils up, stopping them from superconducting. When this happens, the current has to be safely extracted in a very short time. This is called a quench, and just one millijoule – the energy deposited by a 1-centime euro coin falling from 5 cm – is enough to provoke one. Magnet protection in case of quenches is a crucial part of the design of the LHC’s magnetic system.

When a new superconducting magnet is qualified for use, it needs to be trained. That involves steadily increasing the current until the magnet quenches, then starting again. At first, the quenches may occur at relatively low current, but over time, as the components of the magnet settle in, the current increases until the magnet can be operated routinely at its nominal current. If a new training cycle is started after an extended period during which the magnet is warm, the magnet usually restarts training at a value that is higher than first quench in the first training cycle but lower than the maximum previously reached. In other words, the magnet’s ‘memory’ is usually less than 100%.

A magnet quench can be observed from the LHC Cryogenics dashboard, where you see the temperature suddenly jumps from 2K to over 3K, and then cools down slowly. Magnet quench is a common problem that can halt LHC operation for many hours :(

Of course there is magnet quench protection system which dumps the electric currents quickly and safely. Due to electromagnetic inductance U=L*di/dt, high voltage will appear as well when a magnet quenches. An electrical breakdown at this critical moment can boil the helium in a very short time, creating a strong explosion. The LHC was hit badly by this accident at run 1 and took 1 year to repair.

It looks like they are indeed training the magnets these days, there are magnet quenches with no beam. Now the LHC is at run 3 and at 13.6 TeV. After the extended repairs and possibly upgrades, maybe the LHC can try 14 TeV next time?
10) Message boards : LHC@home Science : Ready to restart! (Message 47175)
Posted 26 Aug 2022 by Sesson
Post:
RF will be warmed up to room temperature following the cooling tower fault in point 4.
No beam for the next ~4 weeks

The LHC RF system tripped frequently to the point that klystron is replaced for a new one.

Hopefully with this opportunity the LHC engineers can repair the RF system.

Meanwhile the LHC magnets remain at 2K, allowing more time to train the magnets.

The LHC run 3 performance is excellent, but the LHC is stopped for repairs too many times.
If the LHC is still that unreliable, I can't imagine what the feeling would be that the 100km FCC sits idle almost all the time waiting for things to be repaired here and there!
11) Message boards : LHC@home Science : Ready to restart! (Message 47032)
Posted 17 Jul 2022 by Sesson
Post:
The LHC has restarted, but every few days it's stopped for repairing, scrubbing, cooling, rather than running.
There is no physics beam in LHC for over a day. I hope the problems do not recur again and again, there be protons colliding at 13.6Tev nonstop.
12) Message boards : Theory Application : New release of Theory Application is around the corner (Message 46801)
Posted 19 May 2022 by Sesson
Post:
A latest commit at https://gitlab.cern.ch/MCPLOTS/mcplots/-/commit/6faa41d14f091cae6ac738ef5c7559fd0daeb81d named "release preparation" hints that a new release on 2022-05-19 is possible.
Recently Theory code has been very active, with many more latest results from the LHC added. It seems we will begin crunching through these latest data with latest generator version very soon.
13) Message boards : ATLAS application : ATLAS long simulation 1.00 (Message 45057)
Posted 16 Jun 2021 by Sesson
Post:
The long task could be much more attractive if it has more credits. The long tasks reduces network usage and improves efficiency, which is excellent! I would like to participate in it if I have more memory for a 4 core task.
14) Message boards : News : Theory application reaches 5 TRILLION events !! (Message 44961)
Posted 18 May 2021 by Sesson
Post:
Rivet currently has 991 analyses, see https://rivet.hepforge.org/rivet-coverage . However only 110 are available on mcplots, while it is stated it is almost automatic to add a Rivet analysis to mcplots. Are there any plans to add all of them? Seems only some basic information needs to be filled for each paper.
15) Message boards : Number crunching : GPU advertised for LHC, but they don't do it? (Message 44456)
Posted 7 Mar 2021 by Sesson
Post:
An article published in 2013 found that by using GPU, event generators can simulate Standard Model predictions at over 10x speed up compared to CPU, in some cases as much as 90x~100x.
16) Message boards : Theory Application : Tasks run 4 days and finish with error (Message 43993)
Posted 26 Dec 2020 by Sesson
Post:
Four days with success, Pythia8 - [boinc pp jets 8000 170,-,2960 - pythia8 8.301 dire-default 48000 158]


Yes, some time ago it was a job with 100k events and could take a week to complete, now it contains only 48k events. Some scientist must have changed that.
17) Message boards : Number crunching : Could you please enable IPV6 at LHC@home? (Message 43648)
Posted 18 Nov 2020 by Sesson
Post:
Could you please enable IPV6 for lhcathome.cern.ch and lhcathome-upload.cern.ch ?

There is good IPV6 connectivity at CERN. cern.ch, lhcathome.web.cern.ch , as well as CVMFS and Frontier is already IPV6 enabled. By using IPV6 the massive ATLAS downloads and uploads will be more stable and probably faster.

Thank you very much for providing us a way to support particle physics!
18) Message boards : Number crunching : GPU advertised for LHC, but they don't do it? (Message 43478)
Posted 7 Oct 2020 by Sesson
Post:
https://docs.oracle.com/cd/E19957-01/806-3568/ncg_goldberg.html
This might be a good starting point to understand why it is not a good idea to work with reduced precision.


I know reduced precision is bad. I don't have enough maths skills to understand any papers on it. But can't more calculations be done at FP32 to make it more accurate? Even if it requires several, it would still be faster than FP64 on most cards.


One of the features of Sixtrack is that it always try to produce the same result across all platforms they support. In order to do that the scientists even added brackets to expressions to prohibit the compiler from freely choose a mathematically equivalent computation. You can see scientific publications of Sixtrack and LHC@home for stories like that.

Now here comes GPU. Not only it cannot reproduce the bit-exact result as CPU, but must operate at reduced precision for best performance. I'd doubt if scientists would ever accept it.
19) Message boards : ATLAS application : error on Atlas native: 195 (0x000000C3) EXIT_CHILD_FAILED (Message 43037)
Posted 12 Jul 2020 by Sesson
Post:
My (theory-only) Ubuntu VM generated similar errors when I upgrade to 20.04. Then I executed the following command and my VM can continue working

sudo /sbin/create-boinc-cgroup
sudo systemctl daemon-reload
sudo systemctl restart boinc-client

I don't know if this applies to ATLAS as well or if it works after reboot. Since it is a VM, I don't need to shut down it when I turn off my computer.
20) Message boards : LHC@home Science : LHCb and the GPU (Message 42821)
Posted 10 Jun 2020 by Sesson
Post:
The application LHCb run on GPU is the trigger system HLT 1, which reduces data rate from 40Tbps to 1-2Tbps. I don't think you have 40Tbps internet connection at home, so we certainly won't participate in running this application.

However any application migration from CPU to GPU will be huge improvement, as CERN needs huge amount of CPU computing power everywhere. The CPU time saved here could be used to do something more complex.

It is very typical that HEP application suffers from low precision, numerical overflow and underflow, as the numbers encountered in particle physics can have a value subatomic tiny or astronomically large. Double precision is certainly needed, they even want quad-precision if available and fast enough. GPUs are not well-prepared for the tough challenge of high-precision computation, and people at CERN would want to embrace GPU computation more than we would.


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