LHC Beam Dumping system R2E/Availability workshop Viliam Senaj 15/10/2014

LHC beam dumping system 15 deflection generators (MKD) and 10 dilution generators (MKB) per beam Altogether 800 HV GTO like Thyristors (GTO) and 480 HV triggering IGBTs Main concern – Single Event Burnout (SEB) of HV semiconductor switches due to High Energy Hadron (HEH) flux leaking from tunnel to the gallery through cable ducts SEB on MKD HV semiconductors = asynchronous beam dump (AD) and beam losses with risk of damage to downstream instruments and machine down-time (reparation) SEB on MKB = synchronous beam dump (SD) = machine down time

MKB generators: 10 per beam

MKD generators: 15 per beam

Stack of 10 GTO-like thyristors ABB - 5STH20H4502 DYNEX - DG648BH45-185 Similar specifications for both: Umax: 4.5 kV Udc: 2.8 kV (100 FIT) Imax: 80 kA dI/dt: 20 kA/µs Load integral ~ 106 A2s wafer diameter ~ 60 mm

Run1 and actions taken during LS1: extraction generators - MKD Run1: E < 4 TeV = reduced voltage on HV switches; no SEB observed LHC safety request: < 1 AD/y Internal request < 0.2 AD/y due to SEB on GTO SEB = destruction of GTO/IGBT = need to replace it: intervention + re-testing procedure = 6 – 12 h of machine down time Measurement of SEB cross-section (c-s) of 2 GTO families used (Dynex & ABB) and of triggering IGBT done in H4IRRAD showed significant difference in GTO SEB c-s at nominal voltage (2.9 kV per GTO at 7 TeV): ABB SEBc-s: ~ 8e-9 cm2 Dynex SEBc-s: ~ 5e-7 cm2 – factor of 60 higher! IXDN75N120 (triggering IGBT @ 1 kV) SEBc-s: ~ 1e-7 cm2 Replacement of 300 GTO make Dynex by ABB ones in MKD generators: Total of 600 GTO in MKD generators; SEB = AD Replacement of 360 triggering HV IGBT 1.2 kV rated by 1.7 kV ones and increase of triggering voltage to 1.17 kV per IGBT; SEB = AD

Run1 and actions taken during LS1: extraction generators - MKD Simplified estimation that HEH flux exists only at full beam energy (full GTO voltage) Request of 0.2 SEB/y on GTO leads to HEH fluence target value of ~ 5e4 HEH/cm2.y ~ 1/4 of cosmic rays at sea level SEB rate of HV IGBT at 5e4 HEH/cm2.y ~ 0.1 SEB/y Total of 0.3 SEB/y (AD) Simulations predict maximum fluence in UA area in front of cable duct of up to 1e6 HEH/cm2.y Shielding of the most exposed duct (the one close to TCDQ) during Run1 confirmed shielding factor of ~ 10 HEH flux during Run1 is estimated to < 1e5 HEH/cm2.y (measurement with insufficient accuracy) Filling of the remaining 2 big cable ducts will be completed in LS1 (UA side) In case of need – shielding can be added from RA (tunnel) side as well

Run1 and actions taken during LS1: dilution generators - MKB Run1: E < 4 TeV = reduced voltage on HV switches; no SEB observed. Replacement of 120 triggering HV IGBT 1.2 kV rated by 1.7 kV ones (SEB = SD) GTO exposed to max voltage of 2.9 kV only in MKBH generators = 80 GTO; (SEB = SD) GTO in MKBV (120 x) operates at voltage up to 1.6 kV only; SEB probability can be neglected MKBH and MKBV generators remains with Dynex GTO Filling of 3 big cable ducts will be completed in LS1 (UA side only)

R2E related failure rate estimation 6.5 TeV 7 TeV (without LS1 modifications) 2.7 kV/GTO (MKD + MKBH); 1.5 kV/GTO (MKBV) 2.9 kV/GTO (MKD + MKBH); 1.6 kV/GTO (MKBV) ABB SEBc-s [cm2] 2e-10 8e-9 Dynex SEBc-s [cm2] 7e-8 5e-7 IXGN100N170 SEBc-s [cm2] 5e-9 1e-7 IXDN75N120 HEH fluence estimation [HEH.cm-2.y] 5e4 4e5 Failure probability MKD (GTO) [y-1] 6e-3 0.2 61 (60 due to Dynex GTO) MKD (IGBT) [y-1] 9e-2 15 MKBH (GTO) [y-1] 0.3 2 16 MKB (IGBT) [y-1] 3e-2 5 Total AD (MKD GTO + IGBT) [y-1] 0.1 76 Total SD (MKB GTO + IGBT) [y-1] 0.35 2.2 21

Prevision of actions for Run3 and HL LHC MKD: based on more precise measurements of radiation in UA63/67 during Run2: Shielding of cable ducts from RA side Population of the most exposed positions in front of ducts by the generators with the old production of GTO (GV.xxx series ~ order of magnitude less sensitive to HEH; ~ 6 generators still have them) Installing of new trigger transformers (under development) to ensure improved triggering conditions with reduced voltage on triggering IGBTs MKB: Replacement of Dynex GTO by ABB ones Shielding of ducts from RA side IGBT SEB rate can be reduced by a factor of 5 by reducing the trigger supply voltage from 3.5 kV to 3.4 kV

Cumulative effects on LBDS Dose observed in UA63/67 during Run1 < 0.5mGy/y HV semiconductors: GTO/IGBT tested at H4IRAD with dose up to 10 Gy and cumulated HEH fluencies up to 1e10 HEH/cm2 showed only slight increase of leakage current Further tests of the influence of irradiation to switching properties of GTO/IGBTs to be done Control electronics: With all cable ducts shielded the total dose should be low enough to not expect particular problems Influence on commercial electronics (HV power supplies): To be determined. Multiple failures observed in the past but without clear correlation with beam presence

GTO SEB c-s measurement: ABB (5STH20H4502) vs. DYNEX (DG648BH45-185) Graphics representation of the measurement results: cosmic rays measurement at 4 kV and 3.4 kV with low statistics and hence low accuracy. Results at nominal voltage shows significant difference in SEB sensitivity of both GTO families – ABB being better and Dynex worse than claimed

Triggering IGBT SEB c-s measurement: IXYS IXDN75N120 vs. IXGN100N170