Accelerators LISHEP Lecture III Oliver Brning CERN - - PDF document
Accelerators LISHEP Lecture III Oliver Brning CERN http://bruening.home.cern.ch/bruening LHC Performance Goals collision energy: Higgs discovery requires: E > 1 TeV CM proton collisions (discovery potential) requires: E
http://bruening.home.cern.ch/bruening
collision energy: proton collisions (discovery potential) requires: requires strong magnetic fields instantaneous luminosity ´L´:
beam
L > 10 cm sec
−2 −1
σ = L(t) dt L
CM
´turn around time´ and operation efficiency depends on the beam life time, the LHC cycle, rare events: integrated luminosity: number of events in detector / sec = L
event 33
E > 5 TeV Higgs discovery requires: E > 1 TeV
luminosity lifetime and operation cycle field quality and resonances FODO lattice synchrotron radiation beam screen electron cloud dipole packing factor 2 in 1 magnet design 2808 bunches with 10 particles per bunch luminosity insertions super conducting magnet technology
11
ω Q m r = B γ v Q ω m = B γ =
injection magnet vacuum chamber extraction / target RF cavity
(LHC/LEP: 11.3kHz) Cyclotron:
Synchrotron: R = const. B = const.
2π Q c 2π B L p = E / c Q
high beam energy requires: for E >> E −different types of magnets −space for experiments etc −drift space for installation B−field is not uniform: −high magnetic field −large packing factor ’F’
R = const. uniform B−field: B d l E = realistic synchrotron:
F L[meter] B = 8.38 T
p = 7000 GeV/c F = 0.8 arcs: L = 22200 meter L = 27000 meter B[T] = 0.3 p[GeV/c] 2π
iron saturation: 2 Tesla
−4
required maximum dipole field:
earth: 0.3 * 10 Tesla
B γ Physics: LEP tunnel:
max
Amperes Law: this design principle was used for the LEP magnets field amplification with iron core field quality is determined by the pole face shape
h beam yoke vacuum chamber coil l >> 1 µ
H E H
H = I N B = H µ µ
Ferro magnetic material
B I P = R I
2
P > 78 MW / magnet B = 8.38 T
8.4 T is at the limit of available technology! (current density!)
LHC:
max
LEP:
P = 20 kW / magnet P = 10 MW I = 4500A; R = 1m Ω
superconducting technology!
B = 0.135 Tesla I = 280000 A
P > 39 GW
coil precision and stability is a major concern for superconducting magnets! cosine field distribution in the magnet dipole field cross section generates a uniform vertical amplification process does not work for fields above 2 Tesla! saturation field quality control via pole face shape does not work for the LHC magnets! use the coil design to determine the field quality
magnetic induction magnetic field
B H
y x
φ
r
B = µ 2 r π I [-sin( ), cos( ), 0] φ φ r > a: Overlap the two cylinders: φ
1 2 1
φ2 r sin( ) - r sin( ) = 0 B = 0
x y
B = const. in C j = 0 A r cos( ) - r cos( ) = d B C
r r
1 2
p y x
I I B
a a
r < a: B = [-sin( ), cos( ), 0] φ φ 2 µ0 j r φ
1 2 1
φ2
with time −no Ohmic losses −field quality given by geometry −magnets can quench −field quality changes −field quality given by pole face geometry −field amplified by ferromagnetic mat. −iron saturates at 2T −Ohmic losses
superconducting magnets:
Superconducting Magnets
conventional magnets:
sustaining high current densities sustaining high current densities small margins for temperature and mechanical stress! He at 2K is super fluid and has high therm. conductivity
2
LHC: B = 8.4 T; T = 1.9 K; j = 1−2 kA / mm parameterized by 3 parameters −high ambient magnetic field lowers the capability of −low temperatures increase the capability of
Super conducting Magnets
super conducting state:
= −c rot E Persistent Currents:
B
Δ
Ι Ι
Coil Winding:
vacuum pipe beam superconducting cable
Superconducting Cable:
cable NbTi + Cu
B t
cable and filiaments
Superconducting magnet design
cross section for inner coil
winding: coil
Superconducting magnet design
the magnet design requires a strong support structure! 30 winding layers for inner coil: equivalent weight of 150 limousines / m! I = 11 kA; B = 8.4 T F = l I B F = 92400 N / m equivalent to the weight of 5 limousines / m / winding
Force Acting on the Coils
−
* 2 * 0.5 * 4
− + + + + +
3.8 km; 2 rings; B = 3.5 T; T = 4 K HERA: e / p 1991 E = 0.9 TeV
Hamburg, Germany
6.3 km; 2 rings; B = 5.5 T; T = 4.4 K
Other Collider Synchrotrons
1989 E = 0.1 TeV LEP2:
CERN
e / e 27 km; B = 0.1 T E = 7 TeV Tevatron: p / p
Chicago, USA
1985 6.3 km; B = 4.5 T; T = 4.2 K E = 1 TeV LHC:
CERN
B = 8.4T T = 1.9 K L = 27 km RHIC:
New York, USA
E = 0.25 TeV 1999 Au/Au; p / p
Superconducting Magnet Types
reduction of integrated L Quench level:
lost −1 8
N < 7.0 10 m 0.0002% of beam machine protection at all times! minimize losses! remove stray particles before they reach cold magnets! magnet quench beam abort hours of recovery time!
1 MJ melts 2 kg Cu!! first storage ring that requires collimation at all operational phases!
beam energy:
ca. ca. ca.
PRIM SEC secondary halo tertiary halo primary halo beam core APERTURE
noise IBS can damage equipment generated by: primary beam halo: beam core: 2σ non−linearities (beam−beam) 2σ − 6σ 6σ − 8σ
primary collimator generated by: can quench cold equipment secondary beam halo: mechanical aperture margins! required collimator gap opening depends on
magnet quench limit = 20% total beam + + P(7TeV)!!!! magnet quench limit = 0.02% total beam beam losses not critical at injection beam losses not critical at injection + − +
Other Superconducting Machines
Tevatron: p / p
Chicago, USA
1985 E = 1 TeV L = 6.3km magnet range: 6 HERA: e / p 1991 E = 0.9 TeV
Hamburg, Germany
magnet range: 20 L = 6.3km RHIC:
New York, USA
E = 0.25 TeV 1999 Au/Au; p / p magnet range: 7 L = 3.8km magnet range: 16 L = 27km LHC:
CERN
E = 7 TeV
stability requires: l < f Δ f p[GeV] l > f Δ strong focusing requires many quadrupole magnets with short spacing reduction of f = 1 l k k = 0.3 g[T/m]
focal length: trajectory stability: B d l effective quadrupole strength:
large quadrupole diameter −> small gradient decreases with number of quadrupoles and number of interconnects peak field limited by quench behaiviour critical surface of a superconductor! limited by peak field at the coils large beam size! requires large magnet bore diameter increased dipole magnet cost reduced quadrupole strength maximize peak dipole field for each dipole maximize the area occupied by dipole magnets
B d l
maximum beam energy implies maximum quadrupole strength:
build curved dipole magnets ( ca 2cm sagitta) schematic layout of one LHC cell (23 cells per arc) dipole deflection angle
beam
14.4 meter long dipoles with a peak field of 8.4T 4 cm change of the trajectory along 1 dipole! compared to a vacuum chamber diameter of 4cm new design concept (does not exist in other machines)! stability of the dipole geometry!?!
MBA MBB MBB MBA MBB MQ MQ
106.90 m
MBA
installation in the tunnel: tolerances on geometry cryostated LHC magnet: 30 T of cold mass: difficult transportation and tight
collision regions collision point two separate rings
CM p
anti−particles: limited by anti−particle production collider ring design requires 2 beams: such a magnet design has never been done before design with only one aperture requires particles and 2−ring design implies twice the hardware LHC 2−in−1 design is a compromise between the two F = q v B LEP: e / e− + Tevatron: p / p− + limited by beam−beam interactions (# bunches)
E = 2 E
ALICE RF injection b1 collimation machine protection extraction injection b2 LHCb CMS TOTEM ATLAS > 4000Kg TnT
beam2 beam1 IP3 IP8 IP5 IP6 IP7 IP2 IP1
LHC Layout
2 Ring Layout:
2−in−1 magnet design powering in 8 independent octants more than 10GJ stored electromagnetic energy
IP4
(7 keV for the LHC)
accelerated charge emits electro−magnetic waves bending plane radiation fan in bending plane
particle trajectory light cone synchrotron
γ
4
P ρ2
radio signal X−rays 1
γ
LEP: γ = 200000 LHC: γ = 7000
<E >
γ
γ
3
ρ
also functions as a vacuum pump in the LHC! magnets from synchrotron radiation! protect the cold bore of the superconducting the LHC is the first super conducting machine with synchrotron radiation too expensive to absorb at 1.9 K!
P = 5 kW
UV light
synchrotron light hits vacuum chamber next to the bunch − Electrons are accelerated by the next bunch Electrons hit vacuum chamber and generate more e Electrons are accelerated by the next bunch Electron cloud Synchrotron light removes electrons from chamber instability and heat loss!
beam screen at 10K to 20K
field quality double bore; L = 15 m p−p and Ion Beams: (Pb; Ca) 7 TeV p−p discovery potential (Higgs) B = 8.4 T Collider: LEP Tunnel: Superconducting Magnets: T = 1.9 K I = 11700 A f(T, B, I) magnet quench! Cooling:
30 kTons coldmass; 90 Tons He superfluid He at 1.9K (2 R = 27 km)
1
N
area A interaction region
n N N f A
b 1 2 rev −2 −1
[ L ] = cm s σ
beam−beam interaction and resonances total beam current; machine protection
ev
many bunches high bunch current small beam size
hardware limitations
N / sec = L
N N
1 2
area A interaction region
n N N f A
b 1 2 rev
11 protons per bunch
bunch intensity:
watch out for total beam power!
A =
4π β ε
maximize the number of bunches avoid unwanted head on collisions! luminosity
Triplet
L = 116 meter IP
D1 D2 D1 D2 Triplet
Δ L < 4.9 10 cm sec
max
too small!
32
separate the two beams left and right from the IP with additional orbit bumps crossing angle:
IR layout: additional head on collisions for a maximum number of bunches: bunch separation of less than 232 meter C = 26.7 km b n < 115
−2 −1
head on
d
n Q + m Q + p Q = r
x s y
IP
long range beam−beam beam−beam
increases interacting cross section
crossing angle: breaks symmetry between x,y planes
pro’s: avoids additional head−on collisions couples longitudinal and transverse motion breaks the bunch symmetry con’s: generates additional tune shift requires larger triplet magnet aperture
radiation dose in detector and insertion regions!
Synchrotron Radiation Beam Power E = 300 MJ = 120 kg TnT P = 0.5 W/m Beam−Beam Interaction: + magnet quality aperture
b
N + long range beam−beam beam power
b
n = 2808
Beam Size: < 5 10
−3
N = 10
p 11
I = 0.5 A
beam
−6
beam losses must be smaller than 2 10 N − + + + +
tot b
n = 57 114; I = 13 A; range: 7 µ n = 2808
b
Other Superconducting Machines
Tevatron: p / p
Chicago, USA
1985 E = 1 TeV HERA: e / p 1991 E = 0.9 TeV
Hamburg, Germany
RHIC:
New York, USA
E = 0.25 TeV 1999 Au/Au; p / p beam losses are not critical at injection beam losses are not critical at injection magnet quench limit = 20% of total beam
b
n = 6 36; I = 2 mA; range: 6
beam
LHC: B = 8.4 T; T = 1.9 K; range = 16; I = 0.5 A
beam beam b
n = 180; I = 0.5 mA; range: 20
beam
A
b 1 2 rev
N
1 2
area A interaction region
ε
Luminosity: Limit: magnet strength aperture
A = π β ε LHC: <β>
arc= 80 meter
= 0.5 meter
IP
β σ = ε β β σ =
IP
QF QF QF QD QD QD (strength!)
ca 20 events per crossing! large aperture triplet quadrupoles quadrupole aperture small distance from the IP bunch luminosity:
11 11
N = 1.1 10 <−> 1.5 10 A =
2
4π σ
bunch
L = 4.25 10 cm sec
−1 −2 30
triplet assembly: LHC parameters: L = 23 m ∗ = 0.5 m ∗ β βmax= 4.7km σ ∗= 16 m µ limit:
and non−linear resonances luminosity descrease ca 10 hours beam−beam, resonances and rest gas collisions collective effects and instabilities, electron−cloud
e+
y
−t/ τ
I(t) = I e
−11
LHC: P < 10 Torr Beam Lifetime: I t beam size changes during operation Luminosity Lifetime: [atmosphere: P = 750 Torr]
(assume 10 hours for the LHC)
20min 30min 50 min dipole current time
avoid beam losses and magnet quenches! experience from HERA (after 10 years)
magnet cycle:
beam abort due to failure or beam losses each unscheduled abort implies at least 1 hour delay!
Total:ca 60 minutes + physics time Main Dipole Cycle
(no longer pursued)
lepton collider without synchrotron radiation (τ = 2.2 µ ) s muon lifetime Muon Collider: muon source VLHC: magnet technology 95 km; 2 ring; B = 12 T; n = 20800 520 km; 2 ring; B = 2 T; n = 130000 Linear Collider: 500 GeV / 3 TeV CERN NC; 2 beams USA / Japan / Germany SC USA NC
1.3 GHz
Beam Size: σ 1 / γ No Bending Field: reduced synchrotron radiation High Frequency: E = − A
t high frequency = c f λ small structure NLC: CLIC: 11.4 GHz 30 GHz alignment and wake fields
(no longer pursued)
ILC:
RF structure layout
anti−hydrogen
High Energy Physics solid state physics chemestry biology Synchrotron Radiation Sources: Hospitals: cancer treatment Industry: surface treatment sterilisation nuclear waste disposal Nuclear + Atomic Physics: LEAR:
medecin NCSL: deuterons for neutron therapy (Detroit) synchrotron light sources: