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

2. 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

3. MKB generators: 10 per beam

4. MKD generators: 15 per beam

5. 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

6. 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 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

7. 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

8. 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)

9. 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

10. 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

11. 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

12. 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

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