B.Goddard 08/11/04 HHH 2004 Workshop, CERN Beam Dump Brennan GODDARD CERN AB/BT The existing LHC beam dump is described, together with the relevant design aspects, technological and operational limitations. The issues and challenges presented by the various LHC luminosity upgrade options are detailed, together with some possible upgrade paths. Thanks to V.Mertens, E.Vossenberg.

B.Goddard 08/11/04 HHH 2004 Workshop, CERN Outline of talk Existing LHC beam dumping system –overview, parameters, design aspects and limitations; Issues and challenges of LHC luminosity upgrades –Extraction, dilution, absoption, protection; Possible beam dump upgrade paths Conclusion

B.Goddard 08/11/04 HHH 2004 Workshop, CERN Present system - concept Loss-free fast extraction system –Laminated steel kickers; DC Lambertson septum; Dilution system –Laminated steel kickers; passive ~650m drift length. Beam dump (absorber) block –Graphite cylinder, steel and concrete shielding Protection devices –Graphite protection (dilution) for septum and LHC machine extract  dilute  dump

B.Goddard 08/11/04 HHH 2004 Workshop, CERN Present design - schematic layout 15 x MSD septa 15 x MKD kickers TCDS protection 10 x MKB kickers TCDQ protection TDE dump block Total ‘beamline’ length : 975m from kicker MKD to dump TDE

B.Goddard 08/11/04 HHH 2004 Workshop, CERN 40 m Present design - tunnel layout Total ‘beamline’ length : 975m from kicker MKD to dump block TDE Dump cavern

B.Goddard 08/11/04 HHH 2004 Workshop, CERN Present design – main parameters SystemInstalled length [m]Field [T]System kick [mrad] MKD extraction kickers MSD extraction septa MKBH dilution kicker110.85±0.14 MKBV dilution kicker110.85±0.14 Septum protection7-- Q4 / LHC protection12-- ParameterUnitValue Total beamline length (start MKD – end TDE)m975 Particle-free abort gap ss 3.0 Beta function at beam dump block TDE (H / V)m5000 Beam size at TDE - 1  (H / V) mm1.5 Sweep length on TDE facecm109 Maximum temperature in TDE graphite˚C˚C1250

B.Goddard 08/11/04 HHH 2004 Workshop, CERN Present system – TDE absorber  0.7m  7.7 m C cylinder

B.Goddard 08/11/04 HHH 2004 Workshop, CERN Present system – TDE absorber –Density is graded to minimise  T: graphite with  = g/cc –Full sweep  T = 1250 O C in the dump block (LHC ultimate 0.86 A, 7 TeV)

B.Goddard 08/11/04 HHH 2004 Workshop, CERN Present system - protection –Unsynchronised dump would destroy septum and downstream elements –2 long (6m), low density (carbon) absorbers to intercept undiluted bunches

B.Goddard 08/11/04 HHH 2004 Workshop, CERN Present system - limitations Extraction system –Intensity : not limited –Energy : 7.5 TeV by kicker and septum strength –Filling scheme : not limited (need 3  s abort gap) Dilution system –Intensity : not limited; –Energy : limited to 7.5 TeV by kicker strength –Filling scheme : fails for superbunch (sweep length)

B.Goddard 08/11/04 HHH 2004 Workshop, CERN Present system - limitations Beam dump absorber block –Intensity : 1 A (at 7 TeV) with  T max of ~1500 O C –Energy : 7.5 TeV (at 0.7 A) with  T max of ~1500 O C –Filling scheme : not limited (if adequate dilution). Protection devices –Intensity : 1 A at 7 TeV by  T in septum and Q4 –Energy : 7.5 TeV (at 0.7 A) by  T in septum and Q4 –Filling scheme : protection fails for superbunch.

B.Goddard 08/11/04 HHH 2004 Workshop, CERN Increasing Intensity to 1.7 A - issues Extraction system –Kicker - no problems (unless RF heating??). Feasible –Septum – no problems. Feasible Dilution system –x2 sweep length. Feasible Beam dump Absorber block –Reduce  T max by reduced C density. Feasible Protection devices – Reduce  T max by reduced C density. Feasible

B.Goddard 08/11/04 HHH 2004 Workshop, CERN Increasing Energy to 14 TeV - issues Extraction system –Kicker x2  B.dl – x2 length or x2 rise-time (6  s). Feasible –Septum x2  B.dl – x2 length. Feasible Dilution system –x4 sweep  x4 kicker f 0 ; plus x2  B.dl  x8 length. Difficult –Increase dump tunnel length Difficult Beam dump Absorber block –Reduce  T max by reduced C density – x4 length. Difficult Protection devices – Reduce  T max by reduced C density – x4 length. Difficult

B.Goddard 08/11/04 HHH 2004 Workshop, CERN Superbunch with 0.86 A - issues Extraction system –Kicker - no problems. Feasible –Septum – no problems. Feasible Dilution system –x100 sweep length. Impossible Beam dump Absorber block –Reduce DT max with C density – increase length. Feasible Protection devices – Dilute full beam current without damage. Impossible

B.Goddard 08/11/04 HHH 2004 Workshop, CERN Upgrades – Higher I at 7 TeV Total intensity in distributed bunches Upgrades required for dump system –Increase sweep length (higher f 0  more dilution kickers) –Upgrade dump block (longer, lower density C); –Upgrade protection devices (longer, lower density C, more r ). Feasible for 1.7 A with ‘modest’ upgrades (e.g. avoiding civil engineering)

B.Goddard 08/11/04 HHH 2004 Workshop, CERN Upgrades – 14 TeV Intensity in distributed bunches Considerable upgrades required for dump system –Increase kicker and septum strength (6  s kicker rise time OR x2 kickers; x2 septa) –Increase dilution sweep length higher f 0, more kickers OR SC dilution quadrupole OR longer beam dump tunnel –Upgrade dump block (longer, lower density) –Upgrade protection devices (longer, sacrificial elements) Main Challenges –Beam dilution and energy deposition in dump block (small spot) –Machine protection for failure cases (slower rise time bad)

B.Goddard 08/11/04 HHH 2004 Workshop, CERN Upgrades – superbunch All intensity in 1  s superbunch at 7 TeV Major dump system upgrades required –Dilution with SC quadrupole –Upgrade dump block (longer, lower density C, larger diameter) –Lengthen (+500m) and possibly widen dump tunnel; new cavern –Sacrificial protection devices OR 100% reliable ‘active’ machine protection… Main challenges –Achieving sufficient dilution (sweeping beam impossible) –Machine protection against synchronisation error

B.Goddard 08/11/04 HHH 2004 Workshop, CERN Dilution with spiral sweep 108 cm sweep length 400 cm sweep length Increase dilution kicker frequency and sweep length –14 to 56 kHz… would require ~4 times more kicker length –At 7 TeV would allow currents of ~3 A in distributed bunches –At 14 TeV would allow ~0.8 A in distributed bunches

B.Goddard 08/11/04 HHH 2004 Workshop, CERN Dilution with SC quadrupole Present optics  max ~5km,  ~1.5mm 20 m 200 T/m –Works for any filling pattern :  constant at ≈ 20 mm (need ‘squeeze’) –Need extra 500 m beam dump tunnel…. –Quad design ~OK : L T/m, ~70mm aperture –Very orbit sensitive : 2 mm  0.35 mrad  ~0.4 m at dump (1150m drift). Absorber block size :  ≈ 1.5 m (±0.5 m orbit, ±0.25 m for 8  beam) Dilution quad  max ~1000km,  ~20mm

B.Goddard 08/11/04 HHH 2004 Workshop, CERN Protection – difficult with increasing E –Low material density essential to avoid material damage –More total material required to dilute energy density –Very long objects as a result… –10 7 dilution factor, need ~16 r of C 1.8 g/cc, or ~6 m at 7 TeV. –For 10 7 at 14 TeV, ~0.8 g/cc to avoid damage  14 m. –Some optimisation with graded density to get more r Peak GeV/cc in Cu vs beam size at 450 GeV and 7 TeV  T and density in LHC diluter for 7 TeV sweep (47 bunches)

B.Goddard 08/11/04 HHH 2004 Workshop, CERN Conclusion Dump upgrade for ~1.7 A at 7 TeV looks feasible –Some changes to dilution, absorption and protection Upgrading for 0.8 A superbunch is more difficult: –Achieving sufficient dilution to allow safe absorption (SC quadrupole dilution, absorber, tunnel, cavern, orbit…) –Machine protection (use sacrificial elements? depends on reliability…)