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Rüdiger Schmidt 1
The LHC collider project II The LHC collider project II Rüdiger Schmidt - CERN
SUSSP Sumer School
St.Andrews
Challenges
LHC accelerator physics
LHC technology
Operation and protection
Rüdiger Schmidt 2
summarising constraints and summarising constraints and consequences….consequences….
Centre-of-mass energy must well exceed 1 TeV, LHC installed into LEP tunnel:
Colliding protons, and also heavy ions Magnetic field of 8.3 T with superconducting magnets Large amount of energy stored in magnets
Luminosity of 1034: Need for “two accelerators” in one tunnel with beam parameters
pushed to the extreme – with opposite magnetic dipole field Large amount of energy stored in beams
Economical constraints and limited space: Two-in-one superconducting magnets
Accelerator Physics: An Introduction• Why protons? Why in the LEP tunnel? Why superconducting magnets? Why “two”
accelerators in one tunnel?
LHC Layout The quest for high luminosity and the consequences Beam-Beam interaction Crossing angle and insertion layout Wrapping up: LHC Parameters The CERN accelerator complex: injectors and transfer
LHC technology LHC operation and machine protection Conclusions
OutlineOutline
Rüdiger Schmidt 4
Getting beam into the LHCGetting beam into the LHC
Beam size of protons decreases with energy: 2 = 1 / E Beam size large at injection Beam fills vacuum chamber at 450 GeV
If the energy would be lower ... larger vacuum chamber and larger magnets – increased cost magnets and power converter limitations (dynamic effects,
stability, …) issues of beam stability
Injection from the SPS at 450 GeV, via two transfer lines, into the LHC
Rüdiger Schmidt 5
LHC injector complex - pre-accelerators existLHC injector complex - pre-accelerators exist
Rüdiger Schmidt 6
Injector ComplexInjector Complex
Pre-injectors: Linac, PS Booster and Proton Synchrotron deliver protons at 26 GeV to the SPS
The SPS accelerates protons from 26 GeV to 450 GeV
Both, the pre-injectors and the SPS were upgraded for the operation with nominal LHC beam parameters
Already today, beams are available close to the nominal beam parameters required for the LHC
Transfer Lines SPS - LHCTransfer Lines SPS - LHC
Two new transfer line tunnels from SPS to LHC are being built. The beam lines use normal conducting magnets.
Length of each line:about 2.8 km
Magnets are all available, made by BINP / Novosibirsk
Commissioning of thefirst line for 2004
Dipole magnets waiting for installation
Rüdiger Schmidt 8
LHC accelerator in the tunnelLHC accelerator in the tunnel
Rüdiger Schmidt 9
LHC TechnologyLHC Technology
…in particular superconducting dipole magnets…in particular superconducting dipole magnets
Challenges:
Superconducting magnetsCryogenicsVacuum systemPowering (industrial use of High Temperature Superconducting material)
Rüdiger Schmidt 10
1232 main dipoles +
3700 multipole corrector magnets
392 main quadrupoles +
2500 corrector magnets
Regular arc:
Magnets
Rüdiger Schmidt 11
Regular arc:
Cryogenics
Supply and recovery of helium with 26 km long cryogenic distribution line
Static bath of superfluid helium at 1.9 K in cooling loops of 110 m length
Connection via service module and jumper
Rüdiger Schmidt 12
Insulation vacuum for the cryogenic distribution line
Regular arc:
Vacuum
Insulation vacuum for the magnet cryostats
Beam vacuum for
Beam 1 + Beam 2
Rüdiger Schmidt 13
Regular arc:
Electronics
Along the arc about several thousand electronic crates (radiation tolerant) for:
quench protection, power converters for orbit correctors and instrumentation (beam, vacuum + cryogenics)
Rüdiger Schmidt 14
1232 DipolmagnetsLength about 15 mMagnetic Field 8.3 TTwo beamtubes with an opening of 56 mm
Dipole magnets for the LHCDipole magnets for the LHC
Rüdiger Schmidt
Coils for DipolmagnetsCoils for Dipolmagnets
Rüdiger Schmidt 16
Dipole field – approximate cosine teta current Dipole field – approximate cosine teta current distributiondistribution
In practice the above current distributions are approximated by real conductors, so the field contains also higher order harmonics (see later).
Intersecting ellipses generate uniform field.
Two intersecting ellipses, rotated of 90, generate a perfect quadrupole fields:.
ba
JbdB y +
= 0mSuch configuration follows:
Js = Jcos()
Rüdiger Schmidt 17
Superconducting cable for 12 kA
15 mm / 2 mm
Temperature 1.9 K cooled with Helium
Force on the cable:
F = B * I0 * L
with
B = 8.33 T
I0 = 12000 Ampere
L = 15 m
F = 165 tons
56 mm
Rüdiger Schmidt 18
Rüdiger Schmidt 19
Two - in One MagnetTwo - in One Magnet
Rüdiger Schmidt 20
Beam tubes
Supraconducting coil
Nonmagetic collars
Ferromagnetic iron
Steelcylinder for Helium
Insulationvacuum
Supports
Vacuumtank
Rüdiger Schmidt
The Dipolmagnet in a cryostatThe Dipolmagnet in a cryostat
Rüdiger Schmidt 22
Discovery of Discovery of superconductivitysuperconductivity
1908 -- Kamerlingh Onnes liqufies Helium.
1911 -- R-T for Mercury
?"…. Mercury has passed into a new state, which on account
of its extraordinary electrical properties may be called the superconductive state …."
Copyright A.Verweij
Rüdiger Schmidt 23
Magnetic field - current density - temperatureMagnetic field - current density - temperature
Superconducting
material determines:
Tc critical temperature
Bc critical field
Production process:
Jc critical current density
Temperature [K]A
pplie
d fie
ld [
T]
Superconductingstate
Normal state
Bc
TcLower temperature
increased current density
Typical for NbTi:
2000 A/mm2
@ 4.2K, 6TFür 10 T, Operation less than 1.9 K required
Copyright A.Verweij
Rüdiger Schmidt 24
Typical SupraconductorsTypical Supraconductors
The high critical field of supraconductor type II allows the construction of high field magnets.
1962 – commerically available supraconducting wires
Niobium-Titan (NbTi)
Charactersisation of superconductors:• Temperature• Magnetic Field• Current density
Copyright A.Verweij
Rüdiger Schmidt 25
Helium:Helium:PhasediagramPhasediagram
T>T: He I
T<T: He II(superfluid Helium)
T=2.17 K
LHC:
T=1.9 K
P1.2 bar
Copyright A.Verweij
Rüdiger Schmidt 26
Helium ParameterHelium Parameter
0
2
4
6
8
10
12
0 1 2 3 4 5 6 7Temperature (K)
Cp
(J
/g/K
)
T
Specific heat of Helium as function of T
Phasetransition at 2.18 Kelvin
Superfluid Helium (He II)
Copyright A.Verweij
He II, 1.9K He I, 4.2K Water, 300K SC @ 8T,1.9K
SC @ 8T,4.2K
thermal cond. ~100,000 0.02 1 ~400 ~400
viscosity 0.01 – 0.1 3 1000
Cp 4 5 0.0001 0.0004
Rüdiger Schmidt 27
Supraconducting wireSupraconducting wire
1 mm6 mm
Typical value for operation at 8 T and 1.9 K: 800 A
Copyright A.Verweij
Rutherford cableRutherford cable
width 15 mm
Rüdiger Schmidt 28
Fabrication of superconducting dipolesFabrication of superconducting dipoles
Dipole assembly in industry
Rüdiger Schmidt 29
Snapshot at industrySnapshot at industry
L.Rossi
Rüdiger Schmidt 30
Cryostating and measurements (main Cryostating and measurements (main dipoles and other magnets)dipoles and other magnets)
SMA18 cryostating hallat CERN for installing dipole magnets into cryostats
SM18: 12 measurement stations are prepared for cold tests of possibly all superconducting magnets
Rüdiger Schmidt 31
Challenges for dipole productionChallenges for dipole production
The magnets must reach without quenching a field of at least 8.3 Tesla, and possibly 9 Tesla
The field quality must be excellent (relative field errors much less than 0.1 %, positioning of collars to some 10 mm)
The geometry must be respected – and the magnet must be correctly bent
All magnets must be produced in time, delivered to CERN, installed in the cryostats, cold tested, and finally installed into the LHC tunnel
Rüdiger Schmidt 32
LHC Progress Dashboard - on the WEBLHC Progress Dashboard - on the WEB
Rüdiger Schmidt 33
Operation and machine Operation and machine protectionprotection
Rüdiger Schmidt 34
OutlineOutline
Energy stored in the LHC magnets and beams Charging the energy LHC dipole magnets - discharging the energy
• irregular discharge - magnet quenches
LHC Beams - discharging the energy• regular and irregular discharge
Magnets facing Beams Strategy for Protection of the LHC machine
Rüdiger Schmidt 35
Energy stored in LHC magnetsEnergy stored in LHC magnets
Approximation: energy is proportional to volume inside magnet aperture and to the square of the magnet field
about 5 MJ per magnet
Accurate calculation with the magnet inductance:
E dipole = 0.5 L dipole I 2dipole
Energy stored in one dipole is 7.6 MJoule
For all 1232 dipoles in the LHC: 9.4 GJ
Energy stored in twin dipole magnet: Estored 2Bdipole
2length rdipole
2
m0=
Rüdiger Schmidt 36
What does this mean?What does this mean?
10 GJoule……
corresponds to the energy of 1900 kg TNT corresponds to the energy of 400 kg Chocolate
corresponds to the energy for heating and melting 12000 kg of copper
corresponds to the energy produced by of one nuclear power plant during about 10 seconds
Could this damage equipment: How fast can this energy be released?
Rüdiger Schmidt 37
OutlineOutline
Energy stored in the LHC magnets and beams Charging the energy LHC dipole magnets - discharging the energy
• irregular discharge - magnet quenches
LHC Beams - discharging the energy• regular and irregular discharge
Magnets facing Beams Strategy for Protection of the LHC machine
Rüdiger Schmidt 38
0
2000
4000
6000
8000
10000
12000
-4000 -2000 0 2000 4000
time from start of injection (s)
dip
ole
cu
rre
nt (A
)
energy
ramp
preparation and access
beam dump
injection phase
coast
coast
LHC magnetic cycleLHC magnetic cycle
L.Bottura
450 GeV
7 TeV
start of the
ramp
Rüdiger Schmidt 39
0
2000
4000
6000
8000
10000
12000
-4000 -2000 0 2000 4000
time from start of injection (s)
dip
ole
cu
rre
nt (A
)
injection phase12 batches from the SPS (every 20 sec)
one batch 216 / 288 bunches
LHC magnetic cycle - Beam injectionLHC magnetic cycle - Beam injection
L.Bottura
450 GeV
7 TeV
Rüdiger Schmidt 40
Sector
1
5
DC Power feed
3 DC Power
2
4 6
8
7LHC
27 km Circumference
LHC Powering in 8 Sectors
Powering Subsectors allow for progressive Hardware Commissioning - starting two years before beam
P.Proudlock
Powering Sector
Powering Subsectors:
triplet cryostats cryostats in matching section long arc cryostats
Rüdiger Schmidt 41
Ramping the current in a string of dipole Ramping the current in a string of dipole magnetmagnet
Magnet 1 Magnet 2
Power Converter
Magnet 154Magnet i
LHC powered in eight sectors, each with 154 dipole magnets Time for the energy ramp is about 20-30 min (Energy from the grid) Time for discharge is about the same (Energy back to the grid)
Rüdiger Schmidt 42
OutlineOutline
Energy stored in the LHC magnets and beams Charging the energy LHC dipole magnets - discharging the energy
• irregular discharge - magnet quenches
LHC Beams - discharging the energy• regular and irregular discharge
Magnets facing Beams Strategy for Protection of the LHC machine
Rüdiger Schmidt 43
Operational margin of a superconducting magnetOperational margin of a superconducting magnet
Temperature [K]
App
lied
field
[T]
Superconductingstate
Normal state
Bc
Tc
9 K
Applied Magnetic Field [T]
Bc critical field
1.9 K
quench with fast loss of
~5 · 109 protons
quench with fast loss of ~5 · 106 protons
8.3 T
0.54 T
QUENCH
Tc critical
temperature
Rüdiger Schmidt 44
Power into superconductingPower into superconductingcable after a quenchcable after a quench
Cross section : Asc 10 mm2=
Current : Isc 10000 A=
Length of superconductor : Lsc 1 m=
Copper resistance at 300 C: cu 1.76 10 6 ohm cm=
Psc cu Isc2
Lsc
Asc= Psc 1.76 105 watt=
Specific temperature of copper at 300 C : cvcu 3.244joule
K cm3=
Temperature increase of copper TPsc
Asc Lsc cvcu=
Temperature increase within one second: T 5.425 103K
s=
Rüdiger Schmidt 45
Quench - transition from superconducting Quench - transition from superconducting state to normalconducting statestate to normalconducting state
Quenches are initiated by an energy in the order of mJ (corresponds to the energy of 1000 protons at 7 TeV)
Movement of the superconductor by several mm (friction and heat dissipation)
Beam losses
Failure in cooling
To limit the temperature increase after a quench
The quench has to be detected
The energy is distributed in the magnet by force-quenching the coils using quench heaters
The magnet current has to be switched off within << 1 second
Current after quench
0
2000
4000
6000
8000
10000
12000
-0.05 0.15 0.35 0.55
Time [seconds]
Cur
rent
[A]
Gaussian approximation
Current after quench
Current in a dipole magnets after a quench, when heaters are fired (7 TeV) - 7 MJ within 200 ms into magnet
Rüdiger Schmidt 47
Quench - Emergency discharge of energy …Quench - Emergency discharge of energy …
Magnet 1 Magnet 2
HTS leads 1 HTS leads 2
Power Converter
Magnet 154Magnet i
assume one magnet quenches assume the magnets in the string have to be discharged in, say, 200 ms
Discharge with about 1 MV: not possible
Udischarge_1Ldipole Idipole
0.2s= Udischarge_154
154Ldipole Idipole
0.2s=
Udischarge_1 6.426 103 V= Udischarge_154 9.896 10
5 V=
Rüdiger Schmidt 48
……..and how it being done in the LHC..and how it being done in the LHC
Magnet 1 Magnet 2
Power Converter
Magnet 154
Magnet i
when one magnet quenches, quench heaters are fired for this magnet the current in the quenched magnet decays in about 200 ms the current in all other magnets flows through the bypass diode that can stand the current for about 100-
200 seconds
Bypass Diode …
installed in 1.9 K system (not accessible)
needs to carry 12 kA during the exponential discharge for about 150 seconds
needs to be radiation tolerant
need to be very reliable (all diodes tested at cold before installation)
one diode for each dipole magnet
two diodes for each arc quadrupole magnets
F.Rodriguez-Mateos, D.Hagedorn
F.Rodriguez-Mateos, K.Dahlerup-Petersen
Energy extraction system in LHC tunnelEnergy extraction system in LHC tunnel
Resistors absorbing the energy
Switches - for switching the resistors into series with the magnets
Rüdiger Schmidt 51
OutlineOutline
Energy stored in the LHC magnets and beams Charging the energy LHC dipole magnets - discharging the energy
• irregular discharge - magnet quenches
LHC Beams - discharging the energy• regular and irregular discharge
Magnets facing Beams Strategy for Protection of the LHC machine
Rüdiger Schmidt 52
Regular (very healthy) operationRegular (very healthy) operation
Assuming that the beams are colliding at 7 TeV
Single beam lifetime larger than 100 hours…..• corresponds to a loss of about 1 kW / beam
• far below the cooling power of the cryogenic system, even if all particles would be lost at 1.9 K
• losses should be either distributed across the machine or captured in the warm cleaning insertions
Collision of beams with a luminosity of 1034 cm-2s-1 • lifetime of the beam can be be dominated by collisions
• 109 protons / second lost per beam / per experiment (in IR 1 and IR 5 - high luminosity insertions) - this is about 1.2 kW
• large heat load to close-by superconducting quadrupoles
• heavy shielding around the high luminosity IPs
Rüdiger Schmidt 53
Regular operation: some challengesRegular operation: some challenges
High radiation environment close to interaction point
Moderate radiation load in the arcs (in the order of 1 Gy / year)
Even less radiation dose in tunnel enlargements (about factor of 10 less compared to the tunnel - to be reviewed)
A large fraction of the electronics for quench protection, beam monitoring, vacuum monitoring, cryogenics and powering is located in areas with some radiation
Single Event Upsets (for example bit flips by radiation) introduce failures of the electronics
Development and qualification of radiation tolerant electronics since several years in many groups
Rüdiger Schmidt 54
End of data taking in normal operationEnd of data taking in normal operation
Luminosity lifetime estimated to be approximately 10 h (after 10 hours only 1/3 of initial luminosity)
Beam current somewhat reduced - but not much Energy per beam still about 200-300 MJ Beams are extracted in beam dump blocks
The only component that can stand a fast loss of the full beam at top energy is the beam dump block - all other components would be damaged
At 7 TeV, fast beam losses with an intensity of about 5% of a “nominal bunch” could damage superconducting coils
Rüdiger Schmidt 55
LHC ringLHC ring: 3 insertions for machine : 3 insertions for machine protection systems protection systems
Beam Cleaning IR3 (Momentum)
Beam Cleaning IR7 (Betatron)
Beam dump system IR6
RF+ Beam monitors IR4
Rüdiger Schmidt 56
Beam losses into materialBeam losses into material
Proton losses lead to particle cascades in materials The energy deposition leads to a temperature increase For the maximum energy deposition as a function of material there is no straightforward expression Programs such as FLUKA are being used for the calculation of the energy deposition
Magnets could quench…..• beam lost - re-establish condition will take hours
The material could be damaged…..• melting
• losing their performance (mechanical strength)
Repair could take several weeks
Rüdiger Schmidt 57
Damage of material for impact of a pencil beamDamage of material for impact of a pencil beam
Maximum energy deposition in the proton cascade (one proton): Emax_C 2.0 106
J
kg=
Specific heat of graphite is cC_spec 710.60001
kg
J
K=
To heat 1 kg graphite by, say, by T 1500K= , one needs: cC_spec T 1 kg 1.07 106 J=
Number of protons to deposit this energy is: cC_spec T
Emax_C5.33 10
11=
Maximum energy deposition in the proton cascade (one proton): Emax_Cu 1.5 105
J
kg=
Specific heat of copper is cCu_spec 384.56001
kg
J
K=
To heat 1 kg copper by, say, by T 500K= , one needs: cCu_spec T 1 kg 1.92 105 J=
Number of protons to deposit this energy is: cCu_spec T
Emax_Cu1.28 10
10= copper
graphite
Rüdiger Schmidt 58
Schematic layout of beam dump system in IR6Schematic layout of beam dump system in IR6
Q5R
Q4R
Q4L
Q5L
Beam 2
Beam 1
Beam Dump Block
Septum magnet deflecting the extracted beam H-V kicker
for painting the beam
about 700 m
AB - Beam Transfer Group
about 500 m
Fast kicker magnet
Rüdiger Schmidt 59
Beam Dump Block - LayoutBeam Dump Block - Layout
about 8 m
L.Bruno
concrete shielding
beam absorber (graphite)
Rüdiger Schmidt 60
Beam on Beam Dump BlockBeam on Beam Dump Block
about 35 cm
M.Gyr
initial transverse beam dimension in the LHC about 1 mm
beam is blown up due to long distance to beam dump block
additional blow up due to fast dilution kickers: painting of beam on beam dump block
beam impact within less than 0.1 ms
Rüdiger Schmidt 61
L.Bruno: Thermo-Mechanical Analysis with ANSYS
Temperature of beam dump block at 80 cm insideTemperature of beam dump block at 80 cm inside
up to 800 C
Rüdiger Schmidt 62
L.Bruno: Thermo-Mechanical Analysis with ANSYS
Hydrostatic stress after beam depositionHydrostatic stress after beam deposition
Rüdiger Schmidt 63
Beam dump must be synchronised with particle free gap
Strength of kicker and septum
magnets must match energy of the beam
« Particle free gap » must be free of
particles
Requirement for clean beam dumpRequirement for clean beam dump
particle free abort gapof 3 ms
Kicker magnets constant angle
Beam dump block
Time
Kicker strength
Illustration of kicker risetime
Rüdiger Schmidt 64
OutlineOutline
Energy stored in the LHC magnets and beams Charging the energy LHC dipole magnets - discharging the energy
• irregular discharge - magnet quenches
LHC Beams - discharging the energy• regular and irregular discharge
Magnets facing Beams Strategy for Protection of the LHC machine
Lifetime of the beam with nominal intensity at Lifetime of the beam with nominal intensity at 7 TeV7 TeV
Beam lifetime
Beam power into equipment (1 beam)
Comments
100 h 1 kW Healthy operation
10 h 10 kW Operation acceptable, collimation must absorb large fraction of beam energy
(approximately beam losses = cryogenic cooling power at 1.9 K)
0.2 h 500 kW Operation only possibly for short time, collimators must be very efficient
1 min 6 MW Equipment or operation failure - operation not possible - beam must be dumped
<< 1 min > 6 MW Beam must be dumped VERY FAST
Failures will be a part of the regular operation and MUST be
anticipated
Rüdiger Schmidt 66
+- 3 ~5 mm
Beam +/- 3 sigma
56.0 mm
Beam in vacuum chamber with beam screen at 450 GeVBeam in vacuum chamber with beam screen at 450 GeV
Rüdiger Schmidt 67
+- 3 ~1.3 mm
Beam +/- 3 sigma
56.0 mm
Beam in vacuum chamber with beam screen at 7 TeVBeam in vacuum chamber with beam screen at 7 TeV
Rüdiger Schmidt 68
Beam +/- 3 sigma
56.0 mm
1 mm
+/- 8 sigma = 4.0 mm
Example: Setting of collimators at 7 TeV - with luminosity opticsExample: Setting of collimators at 7 TeV - with luminosity optics Beam must always touch collimators first !Beam must always touch collimators first !
R.Assmanns EURO
Collimators at Collimators at 7 TeV, squeezed7 TeV, squeezedopticsoptics
Rüdiger Schmidt 69
Jaws (blocks of solid materials such as copper, graphite, ….) very close to the beam to absorb more than 99.9 % of protons that would be lost
Primary collimators: Intercept primary haloImpact parameter: ~ 1 Impact parameter: ~ 1 mmmmScatter protons of primary haloConvert primary halo to secondary off-momentum halo
Secondary collimators: Intercept secondary haloImpact parameter: ~ 200 Impact parameter: ~ 200 mmmmAbsorb most protonsLeak a small tertiary halo
Particles
Beam axis
Impactparameter
Collimator jaw
Basic concept of Basic concept of two stage two stage collimationcollimation
R.Assmann / J.B.Jeanneret
Rüdiger Schmidt 70
Accidental kick by the beam dump kicker at 7 TeVAccidental kick by the beam dump kicker at 7 TeV part of beam touches collimators (about 20 bunches from 2800)part of beam touches collimators (about 20 bunches from 2800)
P.Sievers / A.Ferrari / V.Vlachoudis
circulating beam
Rüdiger Schmidt 71
Accidental kick by the beam dump kicker at 7 TeVAccidental kick by the beam dump kicker at 7 TeV part of beam touches collimators (about 20 bunches from 2800)part of beam touches collimators (about 20 bunches from 2800)
P.Sievers / A.Ferrari / V. Vlachoudis
Beryllium
Rüdiger Schmidt 72Half gap b [m]
LHC impedance without collimators
Typical collimator half gap at 7 TeV: 1.5 mm
F.Ruggiero, L.Vos
Impedance for different materials as a Impedance for different materials as a function of collimator half gapfunction of collimator half gap
Rüdiger Schmidt 73
Optimisation of Cleaning systemOptimisation of Cleaning system
Requirements for collimation system take into account failure scenarios and imperfect operation
• Worst case is the impact of about 20 bunches on the collimator due to pre-firing of one dump kicker module
Material for collimator is being reconsidered - low Z material is favoured Impedance to be considered - conducting material is favoured more exotic materials are considered: copper loaded graphite,
beryllium, partially plated copper ….
Rüdiger Schmidt 74
OutlineOutline
Energy stored in the LHC magnets and beams Charging the energy LHC dipole magnets - discharging the energy
• irregular discharge - magnet quenches
LHC Beams - discharging the energy• regular and irregular discharge
Magnets facing Beams Strategy for Protection of the LHC machine
Multiple turn beam loss
due to many types of failures
Passive protection Avoid such failures (high reliability
systems - work is ongoing to better estimate reliability)
Rely on collimators and beam absorbers
Active Protection Failure detection (from beam monitors
and / or equipment monitoring) Issue beam abort signal Fire Beam Dump
Single turn beam loss
during injection and beam dump
In case ofIn case of any failureany failure oror unacceptable beam lifetimeunacceptable beam lifetime, , thethe beam beam must bemust be dumpeddumped immediately, immediately, safely into thesafely into the beam dump block beam dump block
Rüdiger Schmidt 76
Beam Loss MonitorsBeam Loss Monitors
Primary strategy for protection: Beam loss monitors at collimators and other aperture limitations continuously measure beam losses
Beam loss monitors indicate increased losses => MUST BE FAST
When beam losses exceed threshold:
Beam loss monitors break Beam Permit Loop Beam dump sees “No Beam Permit” => dump beams
Rüdiger Schmidt 77
B.Dehning
1.E+04
1.E+06
1.E+08
1.E+10
1.E+12
1.E+14
1.E+16
1.E-02 1.E-01 1.E+00 1.E+01 1.E+02 1.E+03 1.E+04 1.E+05 1.E+06
duration of loss [ms]
qu
ench
leve
ls [
pro
ton
/s]
total quench levels at 450 GeV
total quench levels at 7 TeV
max range
min range
max range
min range
DynamicRange of
108
Beam loss monitors: quench levels as function Beam loss monitors: quench levels as function of loss durationof loss duration
BLMCs at aperture limitations and
Collimator - 0.1 ms
BLMAs in arcs2.5 ms
450 GeV 7 GeV
Rüdiger Schmidt 78
Beam loss monitors: Ideas for realisationBeam loss monitors: Ideas for realisation
ionisation chamber
gas N2
normal pressure
800 to 1800 V
# of electron / ion pairs: 50 - 70 MIP / cm
Current to frequency converter
first stage (input cable length up to 400 m)
dynamics about 107
input current: 30 pA to 50 mA
output frequency: 0.05 Hz to several MHz
second stage (optical fibre length up 1.5 km)every channel with micro controller (FPGA)
several mean loss values
in parallel
energy tracking
chamber
B.Dehning
Rüdiger Schmidt 79
Architecture of the BEAM INTERLOCK SYSTEM Architecture of the BEAM INTERLOCK SYSTEM
Pt.1
Pt.2
Pt.3
Pt.4
Pt.5
Pt.6
Pt.7
Pt.8ATLAS
CMS
LHC-BALICE
Momentumcleaning
RF Beam Dump
Betatroncleaning
BEAM 1clockwise
BEAM 2counter-clockwise
InjectionBEAM II from SPS
InjectionBEAM I from SPS
BEAM DUMPCONTROLLERS
BPC
BIC
BPCBPC
BPCBPCBPC
BIC
BIC
BIC
BIC BIC
BIC
BIC
BIC
BIC
BIC
BIC
BICBIC
BIC
BIC
Beam Interlock Loopssignal transmitted viaoptical fibre at 10 MHz
Rüdiger Schmidt 80
Electron CloudElectron Cloud
81Rüdiger Schmidt
Electron cloud: bunch train coming inElectron cloud: bunch train coming in
T = t0 proton emits a photon (synchrotron radiation)
82Rüdiger Schmidt
Electron cloud: photon creates electronElectron cloud: photon creates electron
T = t1 photon hits vacuum chamber and creates electron
83Rüdiger Schmidt
Electron cloud: more secondary electronsElectron cloud: more secondary electrons
T = t2 electron accelerated by the potential of the next bunch, then hits vacuum chamber, and generates more electrons
84Rüdiger Schmidt
Electron cloud: many bunches to come...Electron cloud: many bunches to come...
T = t3 electrons accelerated by the potential of the next bunch,
hit vacuum chamber, and generates more electrons
Rüdiger Schmidt 85
Effects from the electron cloudEffects from the electron cloud Several nasty effects
• Vacuum degradation
• Heat load in cryogenics system
• Beam instability
Has been obseved at several accelerators with intense bunch trains• B-factories
• SPS as injector for LHC
Depends on many parameters• Bunch distance and intensity
• Surface of vacuum chamber (cleanliness, coefficient for desorption)
Cures• Special surface materials for vacuum chamber
• Avoid too close bunch distance (LHC: 75 ns should be ok)
• “Beam Scrubbing” to clean surfaces
Rüdiger Schmidt 86
LHC: From today to colliding beamsLHC: From today to colliding beams
2003 - Spring: Start of installation of general services
(electricity, ventilation, ....)
2003 – July: Start of installation of the cryogenic
distribution line
2004 – Spring: Start of magnet installation
2005: Hardware commissioning of first LHC sector
2006: First beam test – injection from SPS through 1/8 of
the LHC (to be confirmed soon)
2007: Finish installation and hardware commissioning
2007 : Commissioning with two beams and first proton
proton collision
From the summary of the Large Hadron Collider From the summary of the Large Hadron Collider Machine Advisory Committee in March 2002Machine Advisory Committee in March 2002
The LHC is a global project with the world-wide high-energy physics community devoted to its progress and results
As a project, it is much more complex and diversified than the SPS or LEP or any other large accelerator project constructed to date
The Status and the complexity of the LHC is documented in more than 80 papers at this conference (EPAC 2002) - this talk is considered as a very brief overview
Machine Advisory Committee, chaired by
Prof. M. Tigner, March 2002
Rüdiger Schmidt 88
Acknowledgement Acknowledgement
The LHC accelerator is being realised by CERN in collaboration with The LHC accelerator is being realised by CERN in collaboration with institutes from many countries over a period of more than 20 yearsinstitutes from many countries over a period of more than 20 years
Main contribution come from the USA, Russia, India, Canada, special Main contribution come from the USA, Russia, India, Canada, special contributions from France and Switzerland contributions from France and Switzerland
Industry plays a major role in the construction of the LHCIndustry plays a major role in the construction of the LHC
Thanks for the material from:
R.Assmann, L.Bottura, L.Bruno, R.Denz, A.Ferrari, B.Goddard, M.Gyr, D.Hagedorn, J.B.Jeanneret, P.Proudlock, B.Puccio, F.Rodriguez-Mateos, F.Ruggiero, L.Rossi, S.Russenschuck, P.Sievers, G.Stevenson, A.Verweij, V.Vlachoudis, L.Vos
Rüdiger Schmidt 89
…….and thanks to the organisers of SUSSP for inviting me giving this presentation
Rüdiger Schmidt 90
Some references (...more in write-up)Some references (...more in write-up)Accelerator physics Proceedings of CERN ACCELERATOR SCHOOL (CAS),
http://schools.web.cern.ch/Schools/CAS/CAS_Proceedings.html• In particular: 5th General CERN Accelerator School, CERN 94-01, 26
January 1994, 2 Volumes, edited by S.TurnerSuperconducting magnets / cryogenics Superconducting Accelerator Magnets, K.H.Mess, P.Schmüser, S.Wolff, World
Scientific 1996 Superconducting Magnets, M.Wilson, Oxford Press Superconducting Magnets for Accelerators and Detectors, L.Rossi, CERN-AT-
2003-002-MAS (2003)LHC Technological challenges for the LHC, CERN Academic Training, 5 Lectures,
March 2003 (CERN WEB site) Beam Physics at LHC, L.Evans, CERN-LHC Project Report 635, 2003 Status of LHC, R.Schmidt, CERN-LHC Project Report 569, 2003 ...collimation system.., R.Assmann et al., CERN-LHC Project Report 640, 2003 LHC Design Report 1995 LHC Design Report 2003 - in preparation