LHC@home

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 submit to BOINC. Hence, the warmest "thank you" to you all!
Happy crunching to everyone, and stay tuned!

Alessio and Massimo, for the LHC SixTrack team.

Thanks for this information Alessio,

I have been here 24/7 since 2004 so you can tell I will run any tests you send my way (especially the most important ones)

-Samson

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Volunteer Mad Scientist For Life

Thanks a lot, Samson!
Indeed, I see a remarkable ranking for SixTrack! We are all extremely grateful for that :)
We will expand our basis of simulations, including FCC, collimation studies, etc... so counting more and more on the help of people like you
Thanks!
A.

Alessio and the team.

Thanks for the update and for letting us know how our help fits into the "grand scheme of things". It really does help to know that our work is both useful and appreciated.

jp

Thank you very much indeed! Great summary, exactly what I have been looking for!

I've been thinking about another great addition (sorry ...). On the ATLAS site we had progress bars for individual simulations (i.e. all of workspace1_hl13_collision_scan_*). Even with the limited amount of work I can contribute, it really feels like an accomplishment to see those progress bars running down. Otherwise the individual volunteers progress is too slow and the transition to a new simulation often gradual and uneventful.

https://lhcathome.cern.ch/ATLAS/index.php

Again, thank you for the update!

Hello!
Thanks you very much for this very good explanation and news!

I'd like to join the others in thanking Alessio and Massimo for their informative bulletin. I'm sure none of us contributors of CPU time are in it for any reward, but one does wonder at times what exactly we're doing.

Many thanks for keeping us informed; it makes a difference.

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Rgds
Peter.

i cannot see my graphics on Show graphics button. Kindly assist me in this..Anyone!!

Did you install the Extension Pack of VirtualBox?
Tullio

i cannot see my graphics on Show graphics button. Kindly assist me in this..Anyone!!

Since so far you ran only Sixtrack on linux:
1. there is no graphics, e.g. a screensaver
2. It doesn't need VirtualBox or parts of it like the Extension Pack

Thanks a lot, Samson!
Indeed, I see a remarkable ranking for SixTrack! We are all extremely grateful for that :)
We will expand our basis of simulations, including FCC, collimation studies, etc... so counting more and more on the help of people like you
Thanks!
A.

Much appreciated Alessio

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Volunteer Mad Scientist For Life

I'm very glad to hear that the relationship between the LHC personnel and the volunteer crunchers has improved to this level, where we are regularly updated on the project's status and kept in the loop about how our work is assisting yours. It seems like it was not very long ago, when this was not the case. I hope that this can continue, and that everyone is able to make contributions (even small ones) to the science. I anticipate sticking around with LHC as one of my go-to projects to keep my humble fleet of computers processing away, for the foreseeable future.

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Click here to see My Detailed BOINC Stats

I'd like to extend my gratitude also, not only for the tacit consideration of our efforts, but for making the language accessible to people like me, who don't know much about particle physics. It's nice to get an overview of what the calculations are trying to achieve. Thank you!

Greetings,

I was wondering if there are any LHC projects that take advantage of GPU's

I have a AMD r9-390x G1 and a NVIDIA GTX1060 6GB running concurrently. setup for 0.33 each card can run 3 instantses with the most efficient work per device. with other projects I see for comparison between cpu only and cpu-gpu, CPU 60-360min GPU 6-10min for the same project file name thats running..

I do not notice you user computer config that specifies use of GPU's. do you have a specific project that could utilize gpu's I would like to run your project with this advantage due to my GPU's available. your project uses 11GB of my SSD complete que'ed and running data set so I assume this is impossible to run on GPU?

Donotneedtono

Hello Donotneedtono, wellcome, 1st post.

The project does not have any GPU work units currently so your not missing out.

In theory there would be a speed to use a GPU but in practice I think it would be limited, when you think about sixtrack you have to calculate the path of a particle at close the the speed of light, I imgaine the caculations are done in double precision to get the most accurate possiable results. With consumer GPUs the double precision performance is lowered to ensure there is value in the profession products. In addition there is probally singinificant work to port the code to GPU and ensure numerical accuracy, even with different OS's there is a challenge here. So unlikly that there would be a GPU app but never say never :)

Many of us still retain GPUs like the Radeon HD 7970 that has 1/4 DP performance. I would be willing to bet there is a significant amount of untapped potential out there, check the volume of Milkyway@Home results for an idea, that project uses DP.

Thanks for the interest in GPUs!
The potential is there, true; on the other hand, as correctly pointed out by Toby, there is a significant effort in porting the code to GPUs - of course, I mainly speak about SixTrack. But this does not mean that we are not looking into that... :)
No time scales yet, but something is moving behind the scenes.
A.

I believe some work has been done in using GPUs for CMS, but our parallelism lies more in the fact that each event is independent rather than having parallelism within the event. Each event will have a differing number of tracks, detector hits, etc, so it would be difficult to use the whole GPU efficiently. As well, a lot of the code is still serial, so Amdahl's Law will probably drag down the advantage.

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How complex GPU work is, was seen in WCG for example.
They had a project (Cancer) to be finished in a faster time.
They let GPU's work. NVIDIA was with the most GPU's out of using.
The most work was done with AMD Radeon.
This work was finished in months. It was the only project in more than 14 years to be finished in this way.
So, it is more difficult, than the most volunteers think. (OpenCL...)

This are some stats from this time:
Date Years:months:days..
05/02/2013 93:224:20:49:21 603,341,099 1,420,371
05/01/2013 52:364:15:11:31 335,510,832 784,982
04/30/2013 82:185:22:09:09 507,133,427 1,176,595
04/29/2013 83:152:13:26:22 506,252,113 1,165,648
04/28/2013 77:094:00:17:09 499,363,186 1,166,754
04/27/2013 76:103:04:02:59 500,958,581 1,177,896
04/26/2013 84:130:16:20:22 517,293,338 1,207,218
04/25/2013 87:259:04:51:27 523,637,976 1,214,811
04/24/2013 86:324:14:26:41 511,755,323 1,183,610
04/23/2013 89:108:13:29:53 528,373,889 1,219,023

Thankyou for pushing this news to the clients.

In my experience, very few users running BOINC will come to the message boards to read the news so using the client notifications is a very nice way to keep everyone up to date.