SPACE CHARGE 2013

SC-13 Workshop Summary

Summary of the Space Charge Workshop 2013 (SC-13)
(PDF Copy)
 
G. Franchetti & F. Schmidt
 
The Space charge 2013 workshop took place at CERN from April 16^th to 19^th 2013. The scientific program of the workshop has been set up following suggestions by an International advisory committee composed of: Y.Alexahin (FNAL), O. Boine‐Frankenheim (TUD/GSI), I. Hofmann (GSI/HI-Jena), J. Holmes (SNS), S. Machida (RAL), E. Metral (CERN), K. Ohmi (KEK), J. Qiang (LBL) and F. Zimmermann (CERN).  The mini workshop was approved by ICFA and sponsored by EUCARD, ACCNET, ICFA, HIC4FAIR and LIU.  The program, the presentations and session summaries are available at the indico page:
             https://indico.cern.ch/conferenceDisplay.py?confId=221441
 
There have been 82 registrants distributed over the following countries, laboratories and companies:
 
Switzerland (CERN) 38
Germany (GSI, Frankfurt University) 13
UK (STFC) 12
USA (Fermilab, SNS, LANL, LBNL, MIT, Tech-X Cor., Muon Inc.) 11
Japan (KEK) 2
Austria (MedAustron) 1
China (IHEP) 1
France (Saclay) 1
Mexico (universidad de sonora) 1
Russia (ITEP) 1
Sweden (ESS) 1
 
The workshop lasted for 3 and half days and the program has been grouped in the following sessions:

18th of April High intensity effects Synergies   19th of April Mitigation and advanced techniques Joint Discussion/Outlook.

 

16^th of April
Stimulus/Project
Modeling/Theory/Overview
Space Charge Studies
 
17^th of April
Machine model (Theory and Instruments)
Code development
 
 
 
In each of the 3 full days and after the sessions with invited talks there has been 1 hour of contributed talks, followed by another hour for discussions on all the topics being covered during that day. These latter discussion sessions were led by I. Hofmann (Tuesday 16^th), J. Holmes (Wednesday 17^th) and E. Metral (Thursday 18^th). The joint discussion on Friday 19^th was co-convened also by I. Hofmann, J. Holmes and E. Metral.
 
Summary of the discussion
 
It is important to mention that the following scientific secretaries have contributed substantially to this workshop by taking note of all responses to the questions and comments during the discussions:
 
H. Bartosik, A. Huschauer,  M. Fitterer, V. Forte, J. Wagner, S. Aumon, D. Noll, L. Hein, R. Wasef, C. Hernalsteens, T. Rijoff
 
The main topics of the workshop have been the following:
 
1) The workshop has shown a rich activity on space charge related topics at CERN (LIU), GSI (FAIR), and RAL (ISIS upgrade). Several studies have been presented on experimental work and in particular concerning the LIU studies and ISIS upgrade.
 
2) In the session of code developments, the issue of code benchmarking has found a lot of attention with regards to long-term tracking. The presentation of the status of code benchmarking has been discussed and the issue about the noise created by PIC codes has evoked intense discussions.  
This topic has raised broader interest, in particular by J. Amudson, Eric Stern, J. Holmes, Ji Qiang, and Jean-Luc Vay. The decision has been taken to use the GSI test suite for benchmarking of frozen space charge models also for the benchmarking of PIC codes, both 2.5D and 3D.  Firm plans have been made to benchmark Synergia and Orbit and hopefully also IMPACT and WARP.
 
3) Some discussion has focused on role of GPU in the high intensity beam dynamics. Effort reported by GSI, RAL, FNAL were discussed at a deep technical level, and the present difficulties were highlighted.
 
4) Interesting from a theoretical standpoint has been a discussion about possibly equating PIC noise with intrabeam-scattering. To this end, previous work by J. Struckmeier has been reviewed on the effect of PIC noise on emittance growth. The audience has expressed the interest to study this topic in some detail.
 
 
Discussion/Outlook
 
The space charge teams at CERN and GSI have had various discussions to set up a list of questions to be addressed by the space charge world community coming to this workshop. This list consists of 7 questions and we have added some responses as a result of the workshop discussions:
 
 
 
 DISCUSSION TOPICS
 
 

1. What we are really missing at the moment is a better description of our machines WRT to nonlinearities and in particular the variation from magnet to magnet. How can we determine this true non-linear model of the machine and how shall we treat our limited knowledge about it (keywords: sigma of the individual multipolar component, how many seeds). What are the different methods, which can be used to make some progress in this aspect (and time scale)? Which instrumentation do we need to measure "properly" the machine nonlinearities? 

 

1. 1    What is the meaning of “properly” in a space charge dominated regime that require 10^5 turns of storage time? In particular, the requirements are significantly affected by the physics: there are regimes in which 10% error in the knowledge of nonlinear components is enough for a good description of the machine, but there are other regimes where the concept of “good” or “properly” is difficult to be defined.

 

• Responses:  What we really need is a better description of the machines; our simulations codes are more or less fine; The question is how we can improve the nonlinear description of our machines? What are the possible methods?
  • linear and nonlinear chromaticity
  • resonance driving terms (correct chromaticity, kick in both planes, )
    • some data in PS, PSB: difficult since only 1 family of sextupoles
  • experience at other labs:
    • chromaticity, DTA
    • ISIS: turn-by-turn
    • octupolar components by local bumps
• There has been a significant amount of work being done for the PS in particular. But we still need a reliable magnet by magnet model which would require a more structured effort.

 

2. For the actual necessity of projects what are the mechanisms for beam loss and emittance growth that are most important  => Review of the relevant issue of each project and review of their relevant mechanisms including a comparison with some simple formulae. Do we have good agreement?

 

• Responses: There seems to be consensus that resonances due to non-linear fields in conjunction with the tune spread due to space charge  seems to lead to both problems: just approaching a resonance leads to emittance blow-up and resonance crossings may lead to losses. On a deeper level the community is split about the questions if these incoherent or also coherent effects are important, as being discussed concerning the half integer resonance crossing in the PSB.

 

3. Which instrumentation do we need to measure our space charge effects? What has been the progress in instrumentation in the past years and what are the plans for the future?

 

• Responses: Concerning instrumentation there has mainly been proposals to provide 1000 turn BPM systems with good resolution and further the developments concerning wire scanners to allow for instance a better resolution of beam halo, i.e. improving existing instrumentation.

 

• Transverse tomography and collimators to reconstruct the transverse profile have been proposed as possible new tools.

 

• It was also mentioned that kickers in both planes are important to study coupled resonances.

 

• There has been a proposal to study coherent effects:  A quadrupolar pickup should allow to measure coherent response of the beam to the half integer resonance. In fact, this pickup would allow for the first time the measurement of the real space charge tune spreads in a machine.

 
 

4. The numerical aspects of beam physics codes with space charge are very important => In particular when we benchmark codes of either type frozen model or PIC type: which difference is "normal" and which is not.

 

• Responses: This issue has been central in the discussion during the workshop.

 

• On the one hand, benchmarking of several PIC codes have now been pursued and compared with the results of frozen space charge codes. This effort will take the better part of this year.

 

• On the other hand, renewed interest has been expressed to look into the noise issue of PIC codes in long-term storage ring simulations in more detail by several teams.

 

• It has been mentioned by PIC code developers that the single particle behavior allows a lot of in-sight into the understanding of the working of PIC codes.  

 

5. There seem to be some beams in the PS with most of the beam below the integer resonance and with not too many losses and emittance growth. Can we explain this?

 

• No clear position from the audience except that the experimental data would have to be well documented to allow for a clarification.

 
 

6. What is the maximum space charge tune shift evolution over the past years / decade in the different machines. Did we make progress? Can we dream to reach more than 0.4? What are all the possibilities to push forward the limit? Is the only possibility to fight space charge to increase the injection energy? 

 

7. What can we do from the optics point of view to reduce space charge effects?

 

• Both of the last 2 questions simply would need more studies. In fact, our simulation tools have to be better understood and benchmarked with experiments before a reliable answer can be given.

 
The final discussion at the workshop has not given definite answers to the list of topics, but has triggered a general consensus that these topics still require further studies. Progress will be presented in the upcoming HB2014 workshop or in earlier publications.