News from the LHC J. Wenninger CERN Beams Department Operation Group LHC news - CMS - J. Wenninger Evian – 19th October 2009 16th Nov. 2009

Outline Recap of joint story and operating energy Status of the LHC: HWC and beam tests 2009/10 LHC run Outlook LHC news - CMS - J. Wenninger 16th Nov. 2009

Joint recap & maximum energy LHC news - CMS - J. Wenninger 16th Nov. 2009

High current busbar joints He heat exchanger Quadrupole Busbars (M1,M2) LHC news - CMS - J. Wenninger Vac. chamber Dipole busbar (M3) 16th Nov. 2009

Busbar soldering problems Careful inspection of all joints was performed when sector 34 was repaired, including systematic X-rays of interconnections. The repair team found to quality issues (systematic !): Overheating leading to SnAg solder flowing out of the busbar and leaving empty spaces. Un-melted SnAg solder. B25R3-M3 (dipole) before disconnection LHC news - CMS - J. Wenninger 16th Nov. 2009 Courtesy C. Scheuerlein

Joint problem summary Case A: Small – 10’s of nW level - anomalous resistance within the joint when the magnets are at 1.9 K: may trigger S34 type accidents (bad soldering of the 2 busbar cables). Detectable at 1.9 K with an upgrade of the quench detection and protection system. Case B: Poor joint quality (voids…) - excess resistance of 10’s of mW at room T - that do not pose an immediate threat, but can trigger a S34 incident in the event a quench (busbar or magnet). Detectable at room temperature with a DC resistance measurement. LHC news - CMS - J. Wenninger B B 16th Nov. 2009 A

Dipole magnets in arc cryostat 154 dipole magnets are connected as one circuit to the power converter. Time for the energy/field ramp is about 20-30 min (energy from the grid) Time for regular discharge (ramp down) is about the same (energy to the grid) Power Converter Energy Extraction: switch closed Magnet 3 Magnet 2 Magnet 152 Magnet 154 Magnet 4 DFB Magnet 1 Magnet 153 Magnet 5

Quench protection Quench detected: energy stored in magnet dissipated inside the magnet (time constant of 200 ms). Parallel diode becomes conducting: current of other magnets through diode. Resistances are switched into the circuit: up to 1 GJ of energy is dissipated in the resistances (nominal decay time constant: 100 s). DFB DFB Magnet 2 Magnet 4 Magnet 152 Magnet 154 Magnet 1 Magnet 3 Magnet 5 Magnet 153 Energy Extraction: switch open Energy Extraction: switch open Bus-bar must carry the current during the discharge through interconnections Power Converter

‘Safe’ energy for 2009/10 run The energy at which the LHC can be operated safely is determined by a number of factors: Maximum additional room T joint resistance (wrt nominal value). - recommendation: 90 mW (measurement uncertainties). Copper resistance (RRR value, resistance ratio 300K/4.2K). - recommendation : RRR = 120 Quench propagation (time) from magnet to busbar. - ten’s of seconds Discharge time of the circuits. - dipole : reduced from 103 s to 50 s - quads : reduced from 15 s to 10 s >> sets an absolute max of 5 TeV (induced voltage during discharge) Direct busbar quenches by the beam. - not a problem (geometry and loss monitor protection) LHC news - CMS - J. Wenninger 16th Nov. 2009

Simulations for dipoles LHC news - CMS - J. Wenninger 3.5 TeV 16th Nov. 2009 Courtesy A. Verweij

3.5 TeV and…. The decision on the energy in August 2009: Initial operation at 3.5 TeV. Increase energy to 4-5 TeV once sufficient experience has been gained at 3.5 TeV. It is not evident what facts can be used to decide on an energy increase, since the risk will still be present (hidden in the joints, can only be measured at room temperature). Simulations clearly indicate considerable risk. LHC news - CMS - J. Wenninger 16th Nov. 2009

LHC status LHC news - CMS - J. Wenninger 16th Nov. 2009

Cryogenics All sectors are ready for powering or in the last phase of cool-down (< 4K). This year cryogenic conditions are more stable – much better than 2008. 67 34 45 81 23 01.09 01.10 01.11

Quench protection system upgrades nQPS: joint protection system covering all busbar joints of the dipole and quadrupole circuits. Up to 2 kA/1.1 TeV the system is used for monitoring & measurements of the busbar resistances (not needed for protection). For 3.5 TeV operation the system must be fully commissioned and connected to the magnet protection (energy discharge) system. SymQ: protection system against symmetry quenches of the 2 magnet apertures (beam 1 and beam 2 of the same magnet). Required for operation > 5 TeV. Design, installation and commissioning of those systems (mostly nQPS) have largely dictated the pace of LHC re-commissioning. LHC news - CMS - J. Wenninger 16th Nov. 2009

Hardware Commissioning (HWC) HWC of all sectors in progress. HWC now split into 2 phases (personnel safety – Helium release): Phase 1: max current 1 kA, access authorized. Phase 2: current above 1 kA, 3 sectors closed for access. The commissioning progress of the nQPS was not fast enough to commission all sector to 6 kA/3.5 TeV for this week. Some time ago it was decided to fall back to 2kA – 1.1 TeV – to be able to stick to the schedule. Commissioning to 3.5 TeV (~3 weeks) will be done after the Christmas break. Planning to be defined… LHC news - CMS - J. Wenninger 16th Nov. 2009

Largest excess resistance (nΩ) nQPS commissioning (1) Commissioning of the new quench protection system was THE major activity of the HWC for the main dipoles and quadrupoles. Measurement results are very good: First measurements up to 2 kA for indicate no anomalous R above few nW in the busbars (limited by noise). Sector circuit Missing channels Largest excess resistance (nΩ) Sector 12 RB   RQ Sector 23  2.5±0.3 Sector 34   2.5±0.3 Sector 45  6 Sector 56  2.0±0.4 Sector 67 Sector 78 Sector 81 1 2 LHC news - CMS - J. Wenninger Status 15.11.2009 16th Nov. 2009

nQPS results LHC news - CMS - J. Wenninger Measurement of the joint resistance at 1.9K with a current of 2 kA (dipoles) for sector 78. Average R = 300 pW, all values < 1 nW 16th Nov. 2009 Courtesy K. Dahlerup Petersen

nQPS commissioning (2) Commissioning progress of the new quench protection system was not as fast as expected. The system is complex, Thorough testing of all cables & connections is required since it is a protection system. A problem with the connectors of the new QPS system was discovered during ELQA (Electrical Quality Assurance) tests. Main circuits are tested at 1.9 kV for 1 minute. Breakdowns were observed in certain sectors (most prominently 81) and they were traced to insulation problems of the nQPS cables (at the level of the connectors). 4 sectors were only tested to 1.2 kV. >> ~3000 connectors must (most likely) be redone before going to 3.5 TeV (approx. 3 days/sector). LHC news - CMS - J. Wenninger 16th Nov. 2009

nQPS cable damage G. J. Coelingh, LMC Nov 09 LHC news - CMS - J. Wenninger 16th Nov. 2009

HWC status 16th Nov 2009 98% of all circuits ready for 2 kA/1.2TeV. All circuits, except the main dipoles (RB) and main quadrupoles (RQ), are commissioned directly to 3.5 TeV LHC news - CMS - J. Wenninger 16th Nov. 2009

Main circuits Sector 12 is the ‘test sector’ for going to 6 kA / 3.5 TeV. Sectors 23, 56, 78 in the process of being handed over to OP group. Status 16.11.2009 Sector circuit Commissioned to injection current to 2 kA to 4 kA Sector 12 RB Y RQ - Sector 23 Sector 34 Sector 45  Sector 56 Sector 67 Sector 78 Sector 81 LHC news - CMS - J. Wenninger 16th Nov. 2009

Other issues… An insulation vacuum leak appeared a few week ago in S34 during cool-down to 4.2 K. Helium flowing from magnet enclosure into insulation vacuum Situation stabilized using groups of turbo-pumps. Cool-down & HWC to 1.9 K could proceed as foreseen. So far so good… LHC news - CMS - J. Wenninger 16th Nov. 2009

Injection tests The 2 injection tests were successful. No major issues were un-covered, some follow up… Vertical aperture bottleneck around injection point of beam 2 (IR8). Alignment being checked (looking for ~5 mm error !). LHCb very sensitive to beam loss on injection dump (‘TDI’), while ALICE seems to be fine. Arghh !! LHC news - CMS - J. Wenninger 16th Nov. 2009

Apertures Horizontal beam2 aperture scan Excellent !! IR7 IR6 IR5 IR8 Horizontal beam2 aperture scan x (m) Excellent !! LHC news - CMS - J. Wenninger IR7 IR6 IR5 IR8 y (m) Vertical beam2 aperture scan 16th Nov. 2009

Dump Beam was extracted into the dump channel. The bucket number was varied to probe the beam dilution trace on the dump block. Superposition of beam impacts on the dump block for different bucket numbers. Follows nicely expected dilution shape. LHC news - CMS - J. Wenninger y (cm) x (cm) 16th Nov. 2009

LHC Run 2009 (10) LHC news - CMS - J. Wenninger 16th Nov. 2009

LHC run 2009 LHC news - CMS - J. Wenninger Beam commissioning so far scheduled to start next Friday evening. All CERN machines will stop on 17th December and be put on standby until the ~7th January: we have ~27 days before Xmas break. 16th Nov. 2009

The Grand Plan Beam ‘safety’ Essential 450 GeV commissioning Energy ‘Safe’ Pretty Safe 450 GeV 1 e12 1 e11 1 TeV 2.5 e11 2.5 e10 3.5 TeV 3.0 e10 5 e9 Machine protection commissioning 1 Experiments’ magnets at 450 GeV 450 GeV collisions Ramp commissioning to 1.2 TeV LHC news - CMS - J. Wenninger Machine protection commissioning 1.5 First collisions at 1.2 TeV System/beam commissioning Machine protection commissioning 2 3.5 TeV beam & first collisions Full machine protection qualification Pilot physics 16th Nov. 2009

End of 2009 beam commissioning Very ambitious 4 week plan (in fact the plan requires ~30 days with 100% availability): Commissioning at 450 GeV. Collisions at 450 GeV (a few shifts). Ramp to 1.2 TeV. Collisions at 1.2 TeV with max. 2 bunches per beam, 2e10 p/bunch. >> In theory feasible if everything works very well… Predictions are difficult to make, but there is a good chance that we will be able to go as far as item 3. Depends a lot on how we manage (or not) the ramp… LHC news - CMS - J. Wenninger 16th Nov. 2009

In more details (1) Days 1-3: Days 4-10: First turn, closed orbit, RF capture for both beams. Days 4-10: Optics measurement and correction. Basic beam instrumentation. RF commissioning. Basic protection and collimation setup. Aperture. Beam dumping system. Fundamental machine protection (beam loss monitors). LHC news - CMS - J. Wenninger 16th Nov. 2009

In more details (2) Days 11-15: Days 15++: 2 beam operation. Exp. magnets. Exp. machine protection (IR aperture, IR loss monitors, BCMs). Ramp attempts… … leading to first collisions at 450 GeV Days 15++: Ramp to 1.2 TeV. Beam dumping system & machine protection in the ramp. Low intensity operation at 1.2 TeV. Optics at 1.2 TeV. Protection and collimation at 1.2 TeV. … leading to collisions at 1.2 TeV. LHC news - CMS - J. Wenninger In practice many activities will be interleaved. 16th Nov. 2009

450 GeV conditions No squeeze (beta* = 10 m): large beam sizes (~0.27 mm). Limited intensity (machine protection commissioning). ~ 2 weeks after first beam. LHC news - CMS - J. Wenninger Number of bunches / beam 2 4 Collision schedule 2-1-2-1 4-3-4-1 Particles per bunch 3x1010 4x1010 6x1010 Beam intensity* 1.6x1011 2.4x1011 beta* [m] 10 Luminosity [cm-2s-1] 1.1x1027 5.9x1027 1.3 x 1028 16th Nov. 2009

Beam operation at 3.5 TeV Luminosity (head on case, no crossing angle) : Nominal parameters k = number of bunches = 2808 N = no. protons per bunch = 1.15×1011 f = revolution frequency = 11.25 kHz s*x,s*y = beam sizes at collision point (hor./vert.) = 16 mm LHC news - CMS - J. Wenninger The beam size s depends on the betatron function b* and on beam emittance en: Everywhere in the ring the beam size scales with 1/g ~ 1/E. Aperture margins are reduced wrt 7 TeV ! The quench levels at 3.5 TeV are a factor ~10 higher wrt 7 TeV and the stored beam energy is lower: advantage in the early days. 16th Nov. 2009

b* and triplets Triplets Triplets ARC cells CMS collision point LHC news - CMS - J. Wenninger At the IP the beams have a small size but a large DIVERGENCE (phase space conservation): >> size grows rapidly between IR and triplets where it reaches a maximum. >> aperture limit during collisions. 16th Nov. 2009

>> overall factor ~8 Luminosity at 3.5 TeV A consequence of the small beam size at the IP (small b*) is a large beam size in the triplet magnets. The physical aperture in the triplet quadrupoles defines the minimum of b*. Limits b* to ~ 2 m at 3.5 TeV (instead of 0.55 m at 7 TeV) LHC news - CMS - J. Wenninger Beam size s* increase by: Factor 2 (‘naturally’ larger size) Factor ~2 (b* limit) Luminosity loss wrt 7 TeV of: Factor ~22 per plane (s*) >> overall factor ~8 for same beam intensity 16th Nov. 2009

(Possible) luminosity evolution in 2010 Comment energy bunches p/bunch b* (m) Peak L (cm-2 s-1) No crossing angle 3.5 43 x 43 3x1010 4 9x1029 5x1010 2.4x1030 156 x 156 2 1.7x1031 7x1010 3.4x1031 10x1010 6.9x1031 50 ns trains 144 x 144 3.1x1031 432 x 432 9.4x1031 9x1010 1.5x1032 LHC news - CMS - J. Wenninger ~1 event/crossing for b* = 2 m and intensity per bunch of 7x1010 Achievable integrated luminosity: ~300 pb-1. 16th Nov. 2009

Stored energy – a challenge !!!! 100 1k 10k 100k 1M 10M 100M 1T Pilot b 3 kJ Nominal b 65 kJ Safe Beam Limit - 2x1010 p 12 kJ Nominal beam 181 MJ Stored Energy (J) ‘156 b’ physics 3.5-7 MJ 3.5 TeV LHC news - CMS - J. Wenninger TEVATRON : ~2 MJ The stored energy in the LHC for the possible luminosity options will exceed what is done at TEVATRON by a factor ~10 for 50 ns operation! 16th Nov. 2009

Summary More than one year after 19.09 the beams are knocking on the LHC door again. If all goes very well, by Xmas we have collisions at 450 GeV and ramps to 1.1 TeV. If it goes incredibly well, we may even see collisions at 1.1 TeV. Machine uptime will be a key factor – don’t ask for too many accesses ! The way to 3.5 TeV will lead us through another commissioning period of the main circuits of ~ 3 weeks in 2010. LHC news - CMS - J. Wenninger 16th Nov. 2009