LHC beam dump 7.56 TeV operation W.Bartmann, C.Bracco, E.Carlier, L.Ducimetiere, B.Goddard, N.Magnin, A.Sanz Ull, V.Senaj, N.Voumard, C.Wiesner 3/7/17

Layout of subsystems Extraction septa MSD Dump block TDE + shielding Extraction kickers MKD Passive protection TCDS Dilution kickers MKB Passive protection TCDQ TCDQ [m] Entrance window VDWB Vacuum line Exit window Plus beam position and loss monitors, and dedicated interlocking (not shown)

Main subsystem characteristics at 7 TeV 15 magnets of 1.4 m 15 magnets of 4.5 m 6 magnets of 1.3 m 4 magnets of 1.9 m Fixed extraction angle requires active energy tracking for extraction and dilution kickers, and extraction septum

Beam dilution – drift length and sweep Need to reduce beam density from ~1015 p+/mm2 to ~1011 p+/mm2… Dilution kicker waveforms b and Dx functions for dump line (TD62) ~900 m drift  4-5 km bx,y at dump  s ~ 1.5 mm Dilution  1200 mm sweep length,  ~400 mm Peak p+ density is ~1.21011 p+/mm2 (cf 6.81014 p+/mm2 for undiluted beam, bx,y ~150 m)

Systems affected by higher energy exploitation Intercepting devices TCDS/Q and beam dump block TDE, plus entrance (VDVB) and exit windows More energy deposited, smaller beam size Extraction kickers Higher operating field (voltage and current) Dilution kickers Extraction septum Higher operating field (current) Beam Energy Tracking System (BETS) Larger dynamic range

Intercepting devices TCDQ/S, TDE and VSWB Being upgraded for HL-LHC design of 7.00 TeV, 2.3e11 p+/b in 2.1 um Operating limits not easy to define (needs FLUKA+ANSYS for each use-case, and highly sensitive to assumed materials properties In worst-case, any new constraints will mean scaling down peak intensity by some amount (~7.56/7.00) to keep dynamic stresses at ‘HL-LHC’ design limits These upgrades will take place in LS3 Might place a limit on brightness, but no hard limit on energy Would require dedicated FLUKA/ANSYS campaign for 7.56 TeV energy to define the intensity limits (as could be done for present devices of course, before LS3…)

Extraction kicker MKD Upgrade in progress to improve voltage holding New switch stack geometry Increased main capacitance New trigger transformers New power trigger modules Replacement of triggering cables DC powering of Ross relay Better protection against dust ingress Abort gap increase 3.0 us to ~3.1 us Implementation for LS2 Design operating energy: 7.00 TeV 7.5 TeV for reliability run, tests, …

Extraction kicker MKD operating at 7.56 TeV? Operating/test voltage corresponding to 7.56/8.1 TeV 31.2/33.4 kV without upgrade Will be 28.7/30.7 kV after the LS2 upgrade Compare to 26.8/28.9 kV today at 6.5 TeV Issue with maximum 30 kV rating of proposed additional capacitor to solve Otherwise MKD should be OK for 7.56 TeV operation after LS2 Performance at given voltage improved wrt today by new stack geometry No hard threshold Operational voltage lower than today’s test voltage

Dilution kickers MKBH/V operating at 7.56 TeV? Current very high (~26 kA), possible implications for contact erosion to be studied for both systems For MKBH: CONS upgrades planned for LS2 to improve performance Basically as for MKD generators (capacitance, triggering, geometry, Ross relays) Nothing planned for MKBV For MKBV: looks OK without changes Voltages today at 6.5/7.0 TeV are 13.7/14.8 kV respectively Voltages will increase to 16.0 kV in operation at 7.56 TeV, and 17.1 kV in tests at 8.1 TeV, which should be OK

Dilution kickers MKBH operating at 7.56 TeV? MKBH will be upgraded in LS2 for improved voltage holdoff Operating/test voltage corresponding to 7.56/8.1 TeV 28.8/30.8 kV without upgrade Will be 25.5/27.3 kV after the LS2 upgrade Compare to 24.7/26.7 kV today at 6.5/7.0 TeV Otherwise MKBH OK for 7.56 TeV No hard voltage threshold Performance at given voltage will be improved wrt today by new stack geometry (after LS2) Operational voltage lower than today’s test voltage (after LS2) Installing 2 additional MKBH to reduce failure probability is being studied (for LS3) New retriggering system to be installed to mitigate erratics (but maybe only in LS3)

MSD septa operating at 7.56 TeV? Assuming nominal septa kicks of: Total kick of all MSDs: αtot = 2.4 mrad with individual kicks of αMSDA = 0.128 mrad, αMSDB = 0.16 mrad and αMSDC = 0.192 mrad From 7.0 TeV to 7.56 TeV, B-rho increases by 𝐵𝜌 new 𝐵𝜌 nom ≈108.0%. Increasing MSD current from 880 A to 972 A (by ≈10.5%) gives a field increase of: MSDA: 0.86T/0.79T = 108.86% MSDB: 1.06T/0.99T = 107.1% MSDC: 1.24T/1.16T = 106.9% (Field simulations by A. Sanz – checked for 7.50 TeV values) Thus, relative weight of the kicks from the 3 septa families changes (saturation effects). The new total deflection is then given by: 𝛼 tot new =5∙ 𝐵𝜌 nom 𝐵𝜌 new 𝛼 msda nom ∙ 𝐵d𝑙 msda new 𝐵d𝑙 msda nom + 𝛼 msdb nom ∙ 𝐵d𝑙 msdb new 𝐵d𝑙 msdb nom + 𝛼 msdc nom ∙ 𝐵d𝑙 msdc new 𝐵d𝑙 msdc nom and has to be rescaled accordingly.

MSD septa operating at 7.56 TeV? Only 0.35 mm position error at TDE from new trajectory – negligible Saturation effects might introduce slightly more harmonic content for circulating beam, but small additional effect only, which could anyway be corrected at high energy MSD power converter maximum current increases from 880 to 980 A Should also be feasible (1000 A/ 600 V conveter) No issues expected from cooling (outlet temperature would increase from ~21 to ~24°C) Other systems should be OK (FMCM, BETS, etc.) Overall no issues expected from MSD

BETS operating at 7.56 TeV? Currently the tracking system BETS/PLC has a scale of 120 MeV per bit, encoded on 16bits. This is also what is sent by the BEM cards to Safe Machine Parameters (SMP), and then broadcasted over timing for all LHC systems. This means that currently the maximum energy that we can measure is 7.8462 TeV Operation at 7.56 TeV should not be a problem, but testing/reliability runs at 8.1 TeV (above 7.8 TeV) is not straightforward We might have to renovate the BETS, or to change the energy encoding over 16bits = loss of precision. Impact on LBDS (BETS, PLC, etc) and other systems (SMP, timing, etc) must be evaluated

Conclusions All dump subsystems impacted by operation at 7.56 TeV For TDE and beam intercepting devices, HL-LHC performance upgrades will be in LS3. Studies needed to define performance limits at 7.56 TeV (post LS2 and post LS3) After planned LS2 upgrades, extraction and dilution kicker operating voltages will be essentially same as present test voltages Completion of LS2 upgrades mandatory Issue of 30 kV additional capacitor voltage rating to solve for MKD Retriggering for MKBH might only be in LS3 Other improvements for voltage holdoff mean system reliability at 7.56 TeV should be similar to today’s reliability at 6.5 TeV One unknown is contact erosion with higher currents – difficult to test for. Could propose R&D activity to devise on-line ELQA for pulsed currents – will be challenging Upgrades should help keep SEB failure probability acceptable at 7.56 TeV – but need more accurate measurement of HEH fluency in UA63/67 & simulations for 7.56 TeV Impact on BETS, controls and SMP to be evaluated – may need upgrade MSD septa should not pose a problem – will operate at ~980 kA

References ABT Technical Coordination Meeting, LBDS 7.x TeV operation, https://indico.cern.ch/event/566833/ ABT CONS Project Review, CONS for MKB and MKD switches, https://indico.cern.ch/event/608322/ A. Sanz Ull, The LHC MSD septa at 7.5 TeV, EDMS 1736186