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LHC@home: News





Last Build Date: Mon, 05 Feb 2018 08:16:44 GMT

Copyright: CERN
 



Task creation delayed - database maintenance

Mon, 05 Feb 2018 08:16:44 GMT

Due to a database issue last week, task generation is delayed and we need to clean up stuck workunits. The project daemons will be on and off this morning while we try to debug a problem with the BOINC transitioner.



Thanks for supporting SixTrack at LHC@Home and updates

Tue, 23 Jan 2018 17:08:14 GMT

Dear volunteers, All members of the SixTrack team would like to thank each of you for supporting our project at LHC@Home. The last weeks saw a significant increase in work load, and your constant help did not pause even during the Christmas holidays, which is something that we really appreciate! As you know, we are interested in simulating the dynamics of the beam in ultra-relativistic storage rings, like the LHC. As in other fields of physics, the dynamics is complex, and it can be decomposed into a linear and a non-linear part. The former allows the expected performance of the machine to be at reach, whereas the latter might dramatically affect the stability of the circulating beam. While the former can be analysed with the computing power of a laptop, the latter requires BOINC, and hence you! In fact, we perform very large scans of parameter spaces to see how non-linearities affect the motion of beam particles in different regions of the beam phase space and for different values of key machine parameters. Our main observable is the dynamic aperture (DA), i.e. the boundary between stable, i.e. bounded, and unstable, i.e., unbounded, motion of particles. The studies mainly target the LHC and its upgrade in luminosity, the so-called HL-LHC. Thanks to this new accelerator, by ~2035, the LHC will be able to deliver to experiments x10 more data than what is foreseen in the first 10/15y of operation of LHC in a comparable time. We are in full swing in designing the upgraded machine, and the present operation of the LHC is a unique occasion to benchmark our models and simulation results. The deep knowledge of the DA of the LHC is essential to properly tune the working point of the HL-LHC. If you have crunched simulations named "workspace1_hl13_collision_scan_*" (Frederik), then you have helped us in mapping the effects of unavoidable magnetic errors expected from the new hardware of the HL-LHC on dynamic aperture, and identify the best working point of the machine and correction strategies. Tasks named like "w2_hllhc10_sqz700_Qinj_chr20_w2*" (Yuri) focus the attention onto the magnets responsible for squeezing the beams before colliding them; due to their prominent role, these magnets, very few in number, have such a big impact on the non-linear dynamics that the knobs controlling the linear part of the machine can offer relevant remedial strategies. Many recent tasks are aimed at relating the beam lifetime to the dynamic aperture. The beam lifetime is a measured quantity that tells us how long the beams are going to stay in the machine, based on the current rate of losses. A theoretical model relating beam lifetime and dynamic aperture was developed; a large simulation campaign has started, to benchmark the model against plenty of measurements taken with the LHC in the past three years. One set of studies, named "w16_ats2017_b2_qp_0_ats2017_b2_QP_0_IOCT_0" (Pascal), considers as main source of non-linearities the unavoidable multipolar errors of the magnets, whereas tasks named as "LHC_2015*" (Javier) take into account the parasitic encounters nearby the collision points, i.e. the so called "long-range beam-beam effects". One of our users (Ewen) is carrying out two studies thanks to your help. In 2017 DA was directly measured for the first time in the LHC at top energy, and nonlinear magnets on either side of ATLAS and CMS experiments were used to vary the DA. He wants to see how well the simulated DA compares to these measurements. The second study seeks to look systematically at how the time dependence of DA in simulation depends on the strength of linear transverse coupling, and the way it is generated in the machine. In fact, some previous simulations and measurements at injection energy have indicated that linear coupling between the horizontal and vertical planes can have a large impact on how the dynamic aperture evolves over time. In all this, your help is fundamental, since you let us carry out the simulations and studies we are interested in, running the tasks we su[...]



LHC@home down-time due to system updates

Tue, 23 Jan 2018 09:19:32 GMT

Tomorrow Wednesday 24/1, the LHC@home servers will be unavailable for a short period while our storage backend is taken down for a system update.

Today, Tuesday 23/1, some of the Condor servers that handle CMS, LHCb and Theory tasks will be down for a while. Regarding the on-going issues with upload of files, please refer to this thread.

Thanks for your understanding and happy crunching!



Short interruptions Tuesday

Tue, 16 Jan 2018 07:05:48 GMT

There will be a couple of short server outages while our BOINC service pass to fail-over nodes today, Tuesday 16th of January. Similar interruptions will happen next week, as we carry out security updates on our computing infrastructure.



File upload issues

Mon, 08 Jan 2018 09:25:05 GMT

Our NFS storage backend got saturated and hence uploads are failing intermittently.

The underlying cause is an issue with file deletion, we are trying to resolve that.

Sorry for the trouble and thanks for your patience with transfers to LHC@home.



Increased file server capacity

Thu, 14 Dec 2017 10:05:32 GMT

Since Tuesday evening, we have had intermittent issues with upload failures due to a combination of a large number of new hosts running BOINC that co-incidentally joined at the same time as larger ATLAS tasks had been introduced. Our file server capacity has been increased and backlog tasks waiting for upload should upload again soon. (Please refer to the ATLAS application and Number crunching forums for more details.)



Missing accounts

Wed, 13 Dec 2017 08:46:45 GMT

Due to a too aggressive spam-cleaning campaign (our fault), we have accidentally deleted some valid accounts on Monday. We have restored a backup copy of the BOINC database, and will recover the missing account data.

If you get a message "missing account key" from your BOINC client, you may be affected. We expect that we can fix this later today, once we have verified the data sets. Hence there is no need to register again.

My apologies for this mishap.



BOINC server update Thursday

Tue, 05 Dec 2017 09:07:45 GMT

We will upgrade the LHC@home web servers to the new BOINC server code with the "Bootstrap" theme on Thursday 7 December. The new style and layout can already be seen on the LHC@home development project..

During the intervention, from 09 UTC on Thursday, there may be intermittent availability of the LHC@home servers, so BOINC clients may back off and try to upload data later.