RF-TTC FAQs. September 24. Typical questions about timing signals generated by the RF system and transmitted over fibres to TTC system

Transcription

1 RF-TTC FAQs September Typical questins abut timing signals generated by the RF system and transmitted ver fibres t TTC system

2 A. Questins abut setup perid (10-19 Sept 2008) RF-TTC FAQs Was BCref in sync with the beam during this perid? N, the equipment t rephase the beam t the reference clck is nt peratinal yet. During the setup perid, BCref was a fixed MHz nt related t the beam frequency. It was (almst) never resynchrnized (nly when rebting the VME crate), and was derived frm a cmmercial Signal Generatr at MHz driving the Divider-by Were BC1 and BC2 synchrnus ne t each ther? Yes, they were synchrnized ne t each ther, and always at the same frequency (except when ne lp wuld unlck ). First MHz Then MHz frm Sept 10, 19:30 Then MHz frm Sept 11, 22:00 Capture beam 2, -0.4 mm They were re-synchrnized when needed: after re-bt, after pening synchr lp r fr test. And they were nrmally lcked with the beam Hwever, this situatin is nt ging t last, as the 2 beams will be cntrlled separately by 2 RF systems, and then may be asynchrnus during filling and ramping fr MD mdes r when nly ne ring is used (see questin: will the BC1 and BC2 be synchrnus? ) Figure 1: BC2 Frequency mnitring at CMS during Setup Perid- curtesy f A. Hlzner, CMS. 3. In case f future setup perids: When will the BC1 and BC2 be guaranteed? Fr further setup perids, the presence f the BCs will be guaranteed nly when the beam is circulating. When may the BC1 and BC2 disappear withut warning? During beam setup perids, the RF has t be adjusted. The BCs may thus be resynchrnized, interrupted r changed withut ntice between runs. During access perids, the BCs can be interrupted fr maintenance reasns and the experiments have t wrk n internal clck. S. Barn PH/ESE, P. Baudrenghien AB/RF Page 2 f 6

3 4. Will BC1 and BC2 disappear during 1ms fr resynchrnizatin befre injectins during the setup test perids? Nrmally n, as the runs are very shrt. Hwever, they may change r be shrtly interrupted between runs fr adjustment purpses. 5. Which Beam Mdes sequences are used during the setup perid Setup (2), inject&dump (16), circulate&dump(17) 6. Was the bunch always at a fixed psitin with respect t the rbit signal during all this perid? The bunch psitin was randm with respect t the rbit during the first 2 days. But it shuld have been stable as frm September 12. B. Questins abut final system 1. What are the BC1 and BC2? BC1 and BC2 are the Bunch Clcks 1 and 2. Fr each ring the Bunch Clck is a square wave at the RF frequency divided by 10. Its rising edge has a fixed delay with respect t bunch passage. This delay is reprducible frm run t run. When present, BCx is always lcked t the crrespnding beam. 2. Will BC1 and BC2 be synchrnus? They will always be synchrnus during physics. Hwever, they may be asynchrnus during filling and ramping fr MD mdes r when nly ne ring is used. If yu wish t bserve the beam in such situatins yu shuld use BC1 t track beam 1 and BC2 t track beam 2. If physics is intended, they wuld be synchrnus frm injectin n, but this decisin culd be reviewed. 3. What is BCref? BCref is the Reference Bunch Clck. It is a square wave at a fixed frequency equal t the cllisin RF frequency divided by 10. It is lcked t the beam during cllisins nly, and was freseen t prvide a very pure radi frequency clck allwing a better lifetime f the beam in case the Digital Direct Synthesizers generating BC1 and BC2 wuld nt be pure enugh. During cllisin its rising edge has a fixed delay w.r.t. bunch passage. But the equipment t rephase the beam t the reference clck is nt peratinal yet. In the meantime use BC1 r BC2 OP wishes t fine-tune the reference frequency during physics t cmpensate fr very slw drift in machine circumference (effect f tides, ). This will crrespnd t very smth shifts f the BCref, f the rder f less than 1 Hz/s. 4. What are the Orbit signals? Fr each ring the Orbit is a train f 5 ns lng pulses at the Revlutin Frequency. The pulse has a fixed delay w.r.t. passage f a bunch in bucket 1. This delay is reprducible frm run t run. When present, Orbitx is always lcked t the crrespnding beam. S. Barn PH/ESE, P. Baudrenghien AB/RF Page 3 f 6

4 5. What are the typical values f BC1, BC2 and BCref at 450GeV (at injectin) and at 7TeV (after ramping)? At 450 GeV: BC1 and BC2 = MHz BCref = MHz At 7 TeV: BC1 = BC2 = BCref = MHz Frequency variatin during ramping: 87Hz. 6. What is bucket1? A bucket is a ptential psitin t which the beam culd be lcked. Each bucket is lcked t a rising edge f the HMz. There are buckets per turn. There are 10 buckets per 25ns perid, and fr a specific type f run, bunches will always be psitined n the same bucket ut f 10. Fr each ring, bucket 1 is the first bucket after the 3 ms lng abrt gap (defined frm bucket t 35640) Tw bunches in buckets 1 f the tw rings cllide in IP1 (and IP5) 7. Will the BCref be used in the final system? If the radi frequencies prvided by the Digital Direct Synthesizer generating BC1 and BC2 are pure enugh t ensure a gd beam life time, the BCref may nt be useful. 8. Will the BCref (and the BCs) be fixed during the flat tp? N, they may mve very smthly t shift the beam (< 1Hz/s) and cmpensate fr very slw drifts in machine circumference. 9. What is the typical sequence f beam mdes during a physics run, and n which mdes will the main RF events ccur? 1. N Beam 2. Setup - Abrt 3. Injectin prbe beam 4. Injectin setup beam 5. Injectin Physics Beam 6. Prepare ramp 7. Ramp 8. Flat tp 9. Squeeze 10. Adjust 11. Stable Beam Unstable beams 12. Beam Dump Warning 13. Beam dump 14. Recver-cycling The resynchrnizatin (r reset) f the 5 timing signals will ccur during setup. Injectin set-up: Machine must g thrugh INJECTION PROBE BEAM and INJECTION SETUP BEAM (pilt, intermediate,dump, pilt) and then finally INJECTION PHYSICS BEAM (>30 min) BC1, BC2 and BCref are nt suppsed t be synchrnus until the end f ramp mde. S. Barn PH/ESE, P. Baudrenghien AB/RF Page 4 f 6

5 The resynchrnizatin f BC1, BC2 and BCref will happen during flat tp mde. Smth adjustments f the 3 BCs may happen during flat tp, squeeze, Adjust, Stable Beam, Unstable Beam During Beam Dump, the BCs stay running and are nt interrupted until at least 5-10 minutes after 10. Timing signals resynchrnizatin befre pre-injectin plateau Why are they resynchrnized? T ensure a prper reset is dne befre each new run. Which signals are ging t disappear? All f them (BC1, BC2, BCref, Orb1, Orb2). During which beam mde will it happen? During SETUP mde. 11. What is the typical delay between SETUP mde and the end f the RAMP mde? Prbably arund 1 hur 12. Which are the beam mdes (defined by EDMS (LHC-OP-ES-0005 v1.0)) during which the BCs are guaranteed? The presence f the BCs is guaranteed frm the end f Setup mde (Setup mde nt included) until the end f Beam Dump mde (included). In general, after BEAM DUMP, the signals will still be there but it is nt excluded that an interventin n the RF equipment interrupts them. They will then be re-started during the fllwing SETUP mde. 13. Which are the beam mdes during which the BCs are stable? BCref is stable frm the end f SETUP mde until the end f BEAM DUMP (and mst f the time during all mdes except SETUP ) BC1 and BC2 are stable frm the end f FLAT TOP mde until the end f BEAM DUMP mde. Hwever, all f them may smthly change (at a rate f less than 1Hz/s) between FLAT TOP and BEAM DUMP fr adjustment purpses. 14. Will the phase between ORBn and BCn be stable between runs? If yes, hw and when will it be fixed? Yes, the phase between ORBn and BCn is stable and is always the same frm run t run. It is set during setup mde and des nt change. 15. Will it be it pssible t test a full ramping and rephrasing sequence withut the beam? Yes. It is being scheduled fr the end f 2008 in agreement with the LHC Operatin team, RF and experiments. 16. Practically, what happens n RF side where there is a beam dump? D the signals disappear with the beam autmatically, r des their frequency slwly/quickly ramp back dwn t their injectin values? In general, after BEAM DUMP, the signals will still be there, keeping the same value they had during flat tp, but it is nt excluded that an interventin n the RF equipment interrupts them. S. Barn PH/ESE, P. Baudrenghien AB/RF Page 5 f 6

6 C. Questins abut QPLL behaviral 1. What is the typical lcking range f QPLLs It depends n the way the bard has been designed, but it is usually between : MHz and MHz. 2. What happens fr the utput clcks when there is a change f BC surce in the RF2TTC? Depending n the phase between the previus clck and the new ne, the QPLL f the RF2TTC may lse the lck and begin t scan the frequency range. Hwever, this des nt necessarily mean that the next QPLL in the chain is ging t lse its lck t. A dcument is available n: S. Barn PH/ESE, P. Baudrenghien AB/RF Page 6 f 6