Loss maps of RHIC

1. Loss maps of RHIC Guillaume Robert-Demolaize, BNL CERN-GSI Meeting on Collective Effects, 2-3 October 2007 Beam losses, halo generation, and Collimation

2. Outline • Introduction • Required tools – a new aperture model • Measurements vs. predictions • Conclusion

3. Introduction • Main objective is to try to reproduce RHIC loss maps, using the tracking tools developed for LHC collimation studies (extended version of the SixTrack code, see talk by S. Redaelli) for the purpose of code benchmarking. These codes can: • provide longitudinal beam loss maps for the Blue and Yellow rings, • predict the cleaning inefficiency of the collimation system, • give an estimate for the maximum allowed intensity in the machine. • By reproducing real RHIC conditionsin the tracking code, one can then compare the predictions with “live” BLM measurements. • Studies presented in the following focus on the code accuracy to predict the halo loss locations along the machine.

4. The RHIC machine collimation regions

5. Collimation at RHIC • RHIC collimators only intercept one side of the beam per transverse plane (LHC = 2 parallel jaws per plane); RHIC primary jaw is also L-shaped: RHIC primary scraper LHC horizontal collimator • The full RHIC betatron collimation system is made of 1 primary and 3 secondary collimators per beam in IR8 (LHC = 4 primary and 16 secondary collimators per beam in IR7).

6. RHIC collimation layout • Pin diodes are installed at least 1m downstream of each collimator to get a direct loss signal when setting their position. • An additional secondary vertical collimator is located one arc downstream for both Blue and Yellow (not used).

7. Outline • Introduction • Required tools – a new aperture model • Measurements vs. predictions • Conclusion

8. Required tools • Numerical models for the RHIC lattice and beam are already available via MAD files. A “Teapot” aperture model was created for previous RHIC collimation studies (PhD thesis by R. Fliller). • Problem: encoding language for that model is significantly different from the one used for LHC tools; data was also missing for the latest machine changes => need for a dedicated RHIC aperture model !! • The L-shaped primary jaw also requires a specific treatment in SixTrack to allow collimation in both planes at the same time. • CPU resources (time & disk space) should allow tracking of large particle ensembles (at least 200k particles in parallel jobs)…

9. Creating the aperture model • The new aperture model consists of: • a spreadsheet with the transverse dimensions for all lattice elements, • an appropriate software to superimpose the recorded trajectories of scattered particles with the datasets from that spreadsheet. • Since the original aperture model was generated, some elements were either moved, removed or replaced => any and all modifications must be included !! • The various databases only list the transverse dimensions at the beginning or the end of a given element => one needs the complete description along that element !!

10. From the LHC aperture model… • To obtain accurate beam loss maps, a detailed LHC aperture program was developed. It allows locating proton losses with a precision of10 cm. S. Redaelli et al. => the idea is to generate a similar model for the two beam lines of RHIC.

11. … to the RHIC aperture model • Generating the new model was split into 3 steps: • step 1: get all the latest files from every source of aperture database (incl. mechanical drawings). • step 2: generate the new aperture database with 10 cm bins already implemented => allows to apply “real shape” of all elements. • step 3: run a cross-reference with MAD-X model of the machine: the aperture model MUST match the simulated lattice. • As for the LHC studies, collimator tanks are considered as drift spacesin the aperture model, since the corresponding aperture restrictions are applied in the scattering routines of the tracking. • Some elements required extra attention when modeling…

12. Sample case: DX magnet top view side view

13. Outline • Introduction • Required tools – a new aperture model • Measurements vs. predictions • Conclusion

14. Measurements vs. predictions • Live measurements data come from the 2005 proton run:

15. Dedicated datasets • Fill #6981, 4/28/2005, Blue beam:

16. Collimator movements • Positions and PIN diode signals once Blue beam is at store:

17. Loss monitors signal horizontal jaw movement

18. BLM signal at the STAR triplet STORE RAMP INJECTION => RHIC collimators are designed to lower beam loss induced background

19. Horizontal jaw movement zoom in collimation region (jaw movement from LVDT signal)

20. Horizontal jaw movement zoom in STAR triplet area (jaw movement from LVDT signal)

21. Simulated loss map – horizontal jaw • Tracked 240000 particles, impact parameter = 5 µm, 20 turns => about 59% of impacting protons are absorbed at the collimator (blue spike)

22. Zoom in the collimation region • Compare loss locations with live measurements:

23. Notes on simulated loss maps • Results from SixTrack simulations only list locations of direct proton losses, i.e. elements in which the transverse coordinates of tracked protons get larger than the available mechanical aperture => comparison with live BLM measurements need to take the “zero” signal into account (when collimators are out). • The aperture model allows to spot proton losses with a 10 cm resolution, while in the machine loss monitors are only installed at predetermined locations, mostly looking in the horizontal plane and are color blind (i.e. measure and display losses coming from both beam lines at the same time) => for later studies with the full system, Blue and Yellow simulated losses should be put on the same plot to allow proper analysis and predictions • Lattice studied was generated from MAD-X model with the ideal STAR and PHENIX β* values (1.0 m) and measured tune values (QX = 28.690, QY = 28.685). Other real machine conditions like orbit perturbations and β-beating can be derived from logged datasets and inserted into the tracking model.

24. Zoom in the STAR triplet region • Compare loss locations with live measurements:

25. Vertical jaw movement zoom in collimation region (jaw movement from LVDT signal)

26. Vertical jaw movement zoom in STAR triplet area (jaw movement from LVDT signal)

27. Simulated loss map – vertical jaw • Tracked 240000 particles, impact parameter = 5 µm, 20 turns => about 59% of impacting protons are absorbed at the collimator (blue spike)

28. Zoom in the collimation region • Compare loss locations with live measurements:

29. Zoom in the STAR triplet region • Compare loss locations with live measurements:

30. Outline • Introduction • Required tools – a new aperture model • Measurements vs. predictions • Conclusion

31. Conclusion • The simulated lattice features some of the magnet non-linearities and measured tune values but does not include beta-beating and real chromaticity values => should be included in the future. • During the tracking in SixTrack, particles with large amplitudes (i.e. close to usual collimator openings) get lost close to the triplet magnet in STAR => similar behavior as the one seen in live BLM signal !! • Predicted loss locations mostly correspond to what is observed on real time BLM signal (when integrated): downstream of collimators and at the front end of the STAR triplet magnet. One might want to reconsider the precision level of the aperture model to get better comparisons with live measurements. • Future studies should focus on the loss levels at the collimators and the corresponding rates at the low β* insertions, using both beams and the full RHIC collimation system => predictions of the most efficient settings for collimator openings !!