1. Safe Injection into the LHC V.Kain AB/CO
Contents and scope
The need for machine protection at injection
Interlocking – hardware and software
Passive protection systems – collimators
Protection level simulation results
Commissioning aspects
Conclusions
Input from B. Goddard, M. Lamont, J. Wenninger, H. Burkhardt
1/19/2005
Verena Kain, AB-CO

2. Machine Protection at Injection
2.4MJ in 450 GeV injected beam
Damage limit around 100 J/cc
~2x1012p+, ~5 % of injected batch
7.5s LHC aperture at 450GeV
Tight aperture in transfer line (MSI ~7s)
Holes in Cu : 450 GeV LHC p+ beam
(from 2004 TT40 materials test)
8x1012p+ = ¼ of full batch
5.3x1012p+ = 1/6 of full batch
Inside, damage visible over ~1m (melted steel)
1/19/2005
Verena Kain, AB-CO

3. What can go wrong: magnet trips, kicker flashovers, wrong settings…
Magnet trips can move trajectory by many s in short time (MSE: 40s in 1ms)
Kicker erratics, missings, timing etc.
Operator error
Corrupted settings
Slow failures:
10s in > 2-3ms: relying on interlocking
Fast failures:
10s in < 2-3ms: interlocking + collimators
Ultra-fast failures:
10s in few ms: collimators
1/19/2005
Verena Kain, AB-CO

4. Machine Protection Strategy
Avoidance:
Procedures to avoid dangerous situations
e.g. never inject intensity above damage level into empty LHC (beam presence condition)
Protection systems:
Active: surveillance + interlocks to inhibit injection
Software – typical reaction time: ~seconds
Hardwired – typical reaction time:
normal power converter surveillance (PCS): ≥2-3ms
(possible) fast current decay monitors (FCDM): ~ 1ms
Passive: collimators for fast and ultra-fast faults
Collimators must be robust enough to withstand full injected batch → low Z material (C, hBN).
1/19/2005
Verena Kain, AB-CO

5. Beam Presence condition
Injection of beam above damage level only possible if beam already circulating in LHC (beam presence)
Hardwired interlock !
SPS and LHC intensity must be monitored reliably
Reliability and availability – 2 independent BCTs per machine/ring?
LHC beam permit
SPS beam “safe”
LHC beam presence
Injection permit NO X
YES
YES (low Intensity)
YES (high Intensity)
Protects against many of the failures in the LHC (trips, settings, …)
1/19/2005
Verena Kain, AB-CO

6. TDI injection stopper + TCDD
Hardwired Interlocks
LHC energy
SPS intensity
LHC intensity
SPS beam
SPS HW
Extraction HW
bumped BP
MSE current, girder
MKE
bumper currents
Settings
Transfer line HW
Fast beam losses
LHC beam permit
LHC Settings
LHC HW
Injection HW
BTV screens
Transfer line collimators
SPS
Beam
Interlock
Controller
LHC
Beam
Interlock
Controller +
SLP
Extraction permit
TED position
Injection permit
TDI position
Movable TED beam
dumps (stoppers)
+TBSE
beam
SPS extraction kicker
LHC injection kicker
Timing
Timing
TDI injection stopper + TCDD
SPS
Transfer Line
LHC
Power Convertor Surveillance (PCS) and Fast Current Decay Monitoring (FCDM) are critical parts of the HW interlock system !
1/19/2005
Verena Kain, AB-CO

7. Software interlocks Software interlocks
Mostly used for less critical parameters and for redundancy:
beam quality, trajectory and losses in transfer line, etc.
Much slower than hardware interlocks, not failsafe…
Local reference values in front-ends for equipment surveillance compared with central reference values
Reference values are machine mode dependent
1/19/2005
Verena Kain, AB-CO

8. Passive Protection for fast and ultra-fast failures
Protection of LHC aperture and MSI aperture:
TCDI collimators for failures upstream of injection regions
“generic” protection system with full phase coverage
Dedicated collimators for kicker failures:
MKI (LHC) failure: TDI + TCLI are 90° downstream
MKE (SPS) failure: TPSG is 90° downstream
No dedicated collimators for septum failures
Protection from MSE and MSI failures  interlocking
1/19/2005
Verena Kain, AB-CO

9. TCDI Transfer Line Collimators
Close to LHC and MSI (last 300m matching section of TLs)
Robust, based on TCS design (1.2m C jaw)
FLUKA model of 300m of TI 8  local shield for each TCDI
3 collimators / plane ( °)
Setting: 4.5s, tolerances: ≤1.4 s
2 motors/ jaw (angular control)
Protection level 6.9 s (simulated with Monte-Carlo including all imperfections: b beat, mismatch from SPS, tolerances…)
degree
collimators x’ 6s x
120o
60o
amax
6.9 s
LHC aperture
to protect at
7.5 s
1/19/2005
Verena Kain, AB-CO

10. TDI – TCDD - TCLI Protects LHC (especially D1) against MKI failures
90° downstream of the MKI. ~4m long hBN jaws
local protection of D1 with mask -> TCDD (1m, Cu)
Auxiliary collimators TCLIs to complete system
For MKI-TDI phase advance ≠90°, and for flexibility (halo load…)
At nx180°±20° from TDI (1.2m long C jaws)
1-2 years after LHC start-up
MKI
1/19/2005
Verena Kain, AB-CO

11. TDI – TCDD - TCLI TCT design, half jaw, low Z two beams in one pipe
MKI +90˚
TCDD
TCLIB
TDI +340˚
TCLIA
TDI +200˚
Kicker
MKI
LEFT OF IP2
RIGHT OF IP2
TCLIM
TCT design, half jaw, low Z
two beams in one pipe
TCS design, beams in
separate pipes
1/19/2005
Verena Kain, AB-CO

12. Protection level simulations
Safe LHC injection  losses on aperture below 5% damage limit during injection
Extensive tracking simulations to check performance
MKI flashover scanned with TDI, TCLI setting
Full Monte Carlo of single failures at injection
All magnet and kicker families (SPS extraction, Transfer Line, LHC injection) for LSS4 - TI 8 – IR8
Full TL + LHC injection region aperture model
All imperfections and errors included
1/19/2005
Verena Kain, AB-CO

13. MKI flashover simulations
TDI, TCLI setting of 6.8s, to guarantee max. 5% above 7.5s
Increasing opening increases risk of damage
N/N0 of particles with amplitudes >7.5 sy
1/19/2005
Verena Kain, AB-CO

14. Single failure tracking Monte Carlo results (1000 runs per failure)
Family
Tolerable error
[Dk/k0]
required reaction time [ms]
Covered by
LHC TL
MPLH (LSS4 bumper)
0.185
201.0
TCDI
PCS
MKE (LSS4 kicker)
0.125 -
MSE (LSS4 septum)
0.005
0.1
MBHC (TT40 H bend)
5.1
PCS / FCDM
MBHA (TT40 H bend)
0.015
39.4
MBI (main TI 8 bends)
0.003
2.7
FCDM
MCIBH (start TI 8 H bend)
0.630
389.0
MBIAH (end TI 8 H bend)
13.2
MBIBV (end TI 8 V bend)
39.5
3MCIAV (end TI 8 V bend)
0.225
124.0
MSI (LHC injection septum)
3.0
n/a
PCS = standard Power Convertor Surveillance (≥3ms)
FCDM = Fast Current Decay Monitor (~1ms), dedicated new system
1/19/2005
Verena Kain, AB-CO

15. Discussion of results LHC protection looks OK, provided FCDM for MSI
Detect and react to 0.3% change in 2.5ms
TL needs FCDM for MSE septum (reduce risk window), MBI and MBHC
MKE and MSE faults can still cause damage to the TL… possible solutions being studied
All other single failures are covered for TL & LHC
TCDI system gives full protection from upstream failures
Failures at end of line: slow enough for PCS and FCDM
More complicated scenarios not yet studied
Grouped powering failures: e.g. general power cut
Combined failures
Fault of machine protection system + other failure
e.g. wrong setting of passive absorber + trip of magnet family
1/19/2005
Verena Kain, AB-CO

16. Commissioning aspects
Limited role of protection systems for early stage of LHC commissioning. (SPS extraction, SPS safe beam, TI 8 interlocks and LHC injection BIC needed !)
Injection protection must be fully operational for injected intensity above damage level ≈ 15 bunches
Many parts can be commissioned without beam:
LHC injection BIC + matrices + data exchange; collimator movements + interlocks; FCDM, PCS, logging, software, failsafe behavior, etc. etc.
Beam is essential for commissioning of:
SPS & LHC safe beam and beam presence (BCTs)
TDI/TCLI/TCDI jaw alignment
Tests of full interlock system (EMC, …)
1/19/2005
Verena Kain, AB-CO

17. Commissioning of TCDI system
Setting up collimators:
1) finding beam axis
2) align jaws with beam envelope
3) set jaws to required gap
Setting up with beam: Transmission Measurement
Angular jaw alignment
Beam size measurement
Use BCTs in SPS and downstream of TCDI (in LHC injection region - not in layout yet)
Move TCDI jaws through beam, measuring transmission…
Required beam intensity ~1010 depending on BCT resolution
Impact on LHC: ”inject – TDI dump” or “inject and dump” mode

18. TCDI setting up with beam - tests
First Results of transmission measurement for TCDI (TCS) setting up.
Measured transmission
vs. angular misalignment – looks promising
Simulated data
Methods tested in simulation
with realistic parameters and tolerances
Attainable accuracy can be predicted – expect able to align to ~100mrad.
Simulated transmission vs.
angular misalignment:
1/19/2005
Verena Kain, AB-CO

19. Commissioning of TDI /TCLI
Setting up TDI and TCLI with beam
Beam axis measurement : circulating pilot
Transmission Measurement for jaw alignment
similar to TCDI
inject-dump required, intensity depending on BCT resolution (max. ~1010)
Beam size measurement : circulating pilot (max. ~1010)
jaw moved through beam
reconstitute transverse beam profile from surviving beam intensity vs. position
1/19/2005
Verena Kain, AB-CO

20. Conclusions Injection protection
has to ensure only “safe” beam is injected into LHC during commissioning
is absolutely mandatory if injected intensities exceed p+
LHC protected against many failures by “beam presence” condition
Comprehensive tracking simulations extensively used to define protection systems and to determine protection levels
LHC fully protected with foreseen active and passive protection
Require Fast Current Decay Monitor to measure 0.3% DI in 2.5ms
Hardware and software interlocking is being specified → InjWG
At present the protection systems cannot fully exclude TL damage
Simulations will be extended to grouped and combined failures
Commissioning of the injection protection system is being prepared
Methods for setting up protection collimators being worked out
1/19/2005
Verena Kain, AB-CO