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Der LHC Proton-Proton Collider und Der LHC Proton-Proton Collider und seine supraleitende Magneteseine supraleitende Magnete
Rüdiger Schmidt - CERN
Universität Wien
Februar 2002
2
Mit dem LHC will man am CERN möglichst intensive Teilchenstrahlen bei einer Energie von 7 TeV auf kleinstem Raum zur Kollision bringen, um möglichstviele neue Teilchen zu erzeugen
3
LEP Event
4
108 events / sekunde
LHC Event
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29 Oktober 2002
Rüdiger Schmidt
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Was ist der LHC ?Was ist der LHC ?
Der nächste Beschleuniger, der in einen neuen Energiebereich vorstossen wird - 7 TeV/c => Neue Physik (Higgs Teilchen)
Proton-Proton Collider mit sehr hoher Luminosität und Energie Ablenkmagnetfeld in Bogen :
Schwerionen - Collider mit sehr hoher Energie
LHC und die CERN Infrastruktur
im LEP Tunnel, Länge etwa 27 km, 8 Sektionen mit 4 Experimenten Optimale Ausnutzung der existierenden CERN Beschleuniger für den LHC
(SPS, PS, Booster, LEAR, Linacs, Ionenquellen)
1982 : Erste Studien zum LHC Projekt
1994 : Genehmigung durch den CERN Council
1996 : Entscheidung zum Bau des Beschleunigers
2006/2007: Inbetriebnahme mit Strahl
7
Das CERN ist das führende europäische Forschungsinstitut für Teilchenforschung
Es liegt bei Genf im schweizerischen -französischen Grenzgebiet
Österreich ist eines der CERN Mitgliedsländer, und somit wesentlich am Bau des LHC beteiligt
LHCproton-protonCollider7 TeV/c imLEP Tunnel
LEP: e+e- 104 GeV/c (1989-2000)
Umfang26.8 km
Injectionfrom SPS at450 GeV/c
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8 arcs with a length of about 2.8 km
8 straight sections with a length of about 600 m
Straight sections are used for physics experiments, and for accelerator systems
Beam cleaning, beam dump, RF-acceleration, and beam instrumentation
10
ÜbersichtÜbersicht
LHC Parameter
Energie und Luminosität
LHC Layout
Supraleitende Magnete für den LHC
Machine Protection
•Elektromagnetismus und Relativitätstheorie•Thermodynamik•Mechanik•Quantenmechanik•Physik nichtlinearer Systeme•Festkörperphysik und Oberflächenphysik•Teilchenphysik und Strahlungsphysik
+ Ingenieurwissenschaften
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Energie Energie
LEP Ablenkfeld B = 0.123 tesla
Maximaler Impuls 103 GeV/c
Radius 2805 m
Elektromagnete teilweise aus Beton
LHC Ablenkfeld B = 8.33 tesla
Maximaler Impuls 7000 GeV/c
Radius 2805 m Magnetfeld mit Eisenmagneten maximal 2 tesla, daher werden
supraleitende Magnete benötigt
B = p / e0 • R
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Energy in the magnet system: 11 GJ
In case of failure, extract energy with a time constant of up to about 100 s
Drop 35 tons from 28 km
Energy stored in MagnetsEnergy stored in Magnets
The energy in the magnetscorresponds to an energy that melts 7500 kg of copper
29 Oktober 2002
Rüdiger Schmidt
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LuminositätLuminosität
L = N2 f n b / 4xy
mit N ......... Teilchen im Paket
f ......... Umlauffrequenz
nb......... Anzahl der Paket
xy ... Strahldimensionen am Wechselwirkungspunkt
Anzahl der „Neuen Teilchen“:
Das Ziel ist eine Luminosität von etwa 1034 [cm-1s-2] LEP (e+e-) : 3-4 1031 [cm-1s-2] Tevatron (p-pbar) : 3 1031 [cm-1s-2] B-Factories: > 1033 [cm-1s-2]
Wie lässt sich so eine hohe Luminosität erreichen ?
][][ 212 cmscmLtN
29 Oktober 2002
Rüdiger Schmidt
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Large number of bunchesLarge number of bunches
2835 bunches - spacing of about 25 ns
Minimum beam size at IP of 0.5 m
Bunch structure with 25 ns spacing Experiments: more than 1 event / collision Vacuum system: photo electrons
Crossing angle to avoid long range beam beam interaction Interaction Region quadrupoles with gradient of 250 T/m
and 70 mm aperture
29 Oktober 2002
Rüdiger Schmidt
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Beam current and energy stored in the beamBeam current and energy stored in the beam
Many bunches - Current in one beam about 0.5 A
Energy in one beam about 330 MJ
Dumping the beam in a safe way Beam induced quenches (when 10-7 of beam hits magnet at 7
TeV) Beam stability and Magnet Field quality Beam cleaning (Betatron and momentum cleaning) Synchrotron radiation - power to cryogenic system Radiation, in particular in experimental areas from beam
collisions (beam lifetime is dominated by this effect)
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Challenges:Challenges: Energy stored in the beam Energy stored in the beam
R.Assmann
One beam, nominal intensity(corresponds to an energy that melts 500 kg of copper)
Momentum [GeV/c]
Ene
rgy
stor
ed in
the
bea
m [
MJ]
x 200
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Energy in two LHC Beams: 700 MJ
Dump the beams in case of failure within 89 s after dump kicker fires
The beam dump is the onle element in the LHC that can stand the beam impact
Energy in Beams Energy in Beams
Drop it from 2 km
One beam, nominal intensitycorresponds to an energy that melts 500 kg of copper
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SummaryLHC Parameter
Momentum at collision 7 TeV/cMomentum at injection 450 GeV/cDipole field at 7 TeV 8.33 TeslaCircumference 26658 m
Luminosity 1034 cm-2s-1 Number of bunches 2808 Particles per bunch 1.1 1011 DC beam current 0.56 AStored energy per beam 350 MJ
Normalised emittance 3.75 µmBeam size at IP / 7 TeV 15.9 µmBeam size in arcs (rms) 300 µm
Arcs: Counter-rotating proton beams in two-in-one magnetsMagnet coil inner diameter 56 mmDistance between beams 194 mm
High beam energy in LEP tunnelsuperconducting NbTi magnets at 1.9 K
High luminosity at 7 TeV very high energy stored in the beam
beam power concentrated in small area
Limited investment small aperture for beams
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LHC Layout
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Layout of the LHC ringLayout of the LHC ring: 8 arcs, and 8 long : 8 arcs, and 8 long straight sections straight sections
Momentum Cleaning
Betatron Cleaning
Beam dump system
RF + Beam instrumentation
One sector
= 1/8
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Periodischer Aufbau: FODO ZellePeriodischer Aufbau: FODO Zelle
Dipol- und Quadrupol Magnete– Teilchenbahn stabil für Teilchen mit Sollimpuls
Sextupol Magnete– zur Korrektur von Teilchenbahnen für Teilchen mit Impulsabweichung
– Teilchenbahn stabil für kleine Amplituden (etwa 10 mm)
Multipol-Korrekturmagnete– Sextupol - und Dekapolkorrekturmagnete am Ende der Dipolmagnete
– Teilchenbahnen können instabil werden (selbst nach vielen Umläufen kann eine Teilchenbahn plötzlich instabil werden , z.B. 106)
QF QD QFdipolemagnets
small sextupolecorrector magnets
decapolemagnets
LHC Cell - Length about 110 m (schematic layout)
sextupolemagnets
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Bahnstabilität durch Supraleitende Magnete - Bahnstabilität durch Supraleitende Magnete - Quadrupol- und MultipolfelderQuadrupol- und Multipolfelder
LHC
Teilchenschwingungim Quadrupolfeld(kleine Amplitude)
Harmonische Schwingung(Koordinatentransformation)
Kreisbewegung im Phasenraum
z
y
y
y'
LHC
Teilchenschwingungbei nichlinearen Feldernund grosser Amplitude
Amplitude wächst bis zumTeilchenverlust
Keine Kreisbewegung im Phasenraum
z
y
y
y'
29 Oktober 2002
Rüdiger Schmidt
25
distance about 100 m
Interaction point
QD QD QF QD QF QD
Experiment
Crossing angle for multibunch operation
Focusing quadrupole for beam 1, defocusing for beam 2 High gradient quadrupole magnets with large aperture (US-JAPAN) Total crossing angle of 300 mrad Beam size at IP 16 m, in arcs about 1 mm
29 Oktober 2002
Rüdiger Schmidt
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Layout of insertion for ATLAS and Layout of insertion for ATLAS and CMS CMS
200 m
inner quadrupoletriplet
separationdipole (warm)
recombinationdipole
quadrupoleQ4
quadrupoleQ5
ATLAS or CMS
inner quadrupoletriplet
separationdipole
recombinationdipole
quadrupoleQ4
quadrupoleQ5
collision point
beam I
Example for an LHC insertion with ATLAS or CMS
24 m
beamdistance194 mm
beam II
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1232 main dipoles +
3700 multipole corrector magnets
392 main quadrupoles +
2500 corrector magnets
Regular arc:
Magnets
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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
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Insulation vacuum for the cryogenic distribution line
Regular arc:
Vacuum
Insulation vacuum for the magnet cryostats
Beam vacuum for
Beam 1 + Beam 2
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Vacuum Vacuum chamberchamber
Beam vacuum systemBeam vacuum system
Beam screen is required for most of the machine
Beam screen Beam screen with cooling with cooling channels and channels and pumping slotspumping slots
Ensures vacuum stability
Captures synchrotron radiation at 5-20 K
Beam stability => Low impedance: thin copper layer
Electron cloud effects:- Minimise reflectivity- Beam scrubbing (as in SPS)
31
One of 1800 interconnection between One of 1800 interconnection between two superconducting magnets: LHCtwo superconducting magnets: LHC
6 superconducting bus bars 13 kA for B, QD, QF quadrupole
20 superconducting bus bars 600 A for corrector magnets (minimise dipole field harmonics)
42 sc bus bars 600 A for corrector magnets (chromaticity, tune, etc….) + 12 sc bus bars for 6 kA (special quadrupoles)
13 kA Protection diodeTo be connected:
• Beam tubes• Pipes for helium• Cryostat• Thermal shields• Vacuum vessel• Superconducting cables
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Dipolmagnete für den LHC
1232 DipolmagneteLänge 15 mMagnetfeld 8.3 T2 Strahlrohre mit 56 mm Öffnung
29 Oktober 2002
Rüdiger Schmidt
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Spulenanordnung für DipolmagneteSpulenanordnung für Dipolmagnete
29 Oktober 2002
Rüdiger Schmidt
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Ansicht des Dipolmagnet im KryostatAnsicht des Dipolmagnet im Kryostat
Vakuumröhre für Strahlen
Supraleitende Spule
Nichtmagnetische Stahlklammern
Ferromagnetisches Eisen
Stahlzylinder für Helium
Isoliervakuum
Stützfüsse
Vakuumtank
Two - in One MagnetTwo - in One Magnet
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Die Entdeckung der Die Entdeckung der SupraleitungSupraleitung
1908 -- Kamerlingh Onnes verflüssigt Helium.
1911 -- R-T Messung für Quecksilber
?"…. Mercury has passed into a new state, which on account
of its extraordinary electrical properties may be called the superconductive state …."
Copyright A.Verweij
39
Magnetfeld - Stromdichte - TemperaturMagnetfeld - Stromdichte - Temperatur
Materialeigenschaften:
Tc kritische Temperatur
Bc kritisches Feld
Produktionsprozess:
Jc kritische Stromdichte
Temperature [K]A
pplie
d fie
ld [
T]
Superconductingstate
Normal state
Bc
TcNiedrigere Temperatur
grössere Stromdichte
Typisch: für NbTi:
2000 A/mm2
@ 4.2K, 6T
Für 10 T, Operation unterhalb 1.9 K erforderlichCopyright A.Verweij
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Typische SupraleiterTypische Supraleiter
Das hohe kritische Feld der Supraleiter Typ II lässt den Bau von Magneten mit hoher Feldstärke zu
1962 -- Entwicklung von kommerziellen
Niobium-Titan (NbTi) supraleitenden Drähten.
Charakterisierung von Supaleitern durch:TemperaturMagnetfeldStromdichte
Copyright A.Verweij
41
Helium:Helium:PhasendiagrammPhasendiagramm
T>T: HeI
T<T: HeII(superflüssiges Helium)
T=2.17 K
LHC: T=1.9 K
P1.2 bar
Copyright A.Verweij
42
Helium ParameterHelium Parameter
0
2
4
6
8
10
12
0 1 2 3 4 5 6 7Temperature (K)
Cp
(J
/g/K
)
T
Spezifische Wärme von Helium als Funktion von T
Phasenübergangbei 2.18 Kelvin
Superflüssiges 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
Temperature [K]
Fie
ld [
T]
SC
n
T
z.B durch Teilchenverluste Erwärmung If T > Tcritical Quench
T=temperaturemargin (1.4 K for LHC)
Tc
Bc
Quench = Übergang Supraleitung Quench = Übergang Supraleitung NormalleitungNormalleitung
T 5.425 103 K sec-1Temperaturanstieg pro Sekunde:
TPsc
Asc Lsc cvcuErwärmung von Kupfer:
cvcu 3.244joule
K cm3Specifische Temperatur von Kupfer bei 300 C :
Psc 1.76 105 wattPsc cu Isc2
Lsc
Asc
cu 1.76 10 6 ohm cmWiderstand von Kupfer bei 300 K:
Lsc 1 mLänge des Leiters :
Isc 10000 ampStrom :
Asc 10 mm2Querschnittsfläche :
Leistung im Falle eines Quenches im Supraleiters:
Spezifische Wärme
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QuenchQuench
Bewegung des Supraleiters um einige m kann einen Quench auslösen
Strahlverluste von etwa 10-6 können die Dipolmagnete bei 7 TeV zum Quenchen bringen
Der Supraleiter wird mit Kupfer stabilisiert - der Widerstand von Kupfer unterhalb einer Temperatur von 30 K ist etwa 1/100 im Vergleich zum Widerstand bei 300 K
Der Magnetstrom muss im Quenchfall schnell abgeschaltet werden (etwa 100 ms)
45
Ein supraleitender DrahtEin supraleitender Draht
1 mm6 m
Typischer Wert für maximalen Strom bei 8 T, 1.9 K: 800 A
Copyright A.Verweij
46
LHC: Superconducting MagnetsLHC: Superconducting Magnets
Dipole assembly in industry
Arc 15-m dipoles and quadrupoles
Insertion dipoles and quadrupoles
Corrector magnets
47
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
A.Rijllard
48
Sextupoles and decapoles to be installed at the extremities of the main dipoles
Delivery must precede dipole magnet fabrication (contribution from India and fabrication in industry)
Corrector magnet fabricationCorrector magnet fabrication - - construction for 11 types of magnets construction for 11 types of magnets startedstarted
L. Garcia-Tabares
49
Machine protection: Machine protection: Beam energyBeam energy
Beam Cleaning:Beam Cleaning: Capture particles in the warm sections of the LHC with an efficiency of better than 99.9% to avoid losses that could quench superconducting magnets
In case of equipment failure, beam instabilities etc:
• Capture initial beam losses that could damage LHC equipment
• Beam Loss Monitors close to collimators and other aperture restrictions produce a fast and reliable signal to dump the beam if beam losses become unacceptable
For 7 TeV: fast beam loss between 106 and 107 protons could quench a dipole magnet
The beam dump block The beam dump block isis the only system that can the only system that can stand the full 7 TeV beam - 3stand the full 7 TeV beam - 3··101014 14 protons
50
Beam Cleaning SystemBeam Cleaning System
Collimators close to the beam are required during all phases of operation
• Sophisticated beam cleaning system with many collimators has been designed limit aperture to about 6-10
• Together with the Beam Loss Monitors produce a fast and reliable signal to dump the beam if beam losses become unacceptable
51
+- 3 1.3 mm
Beam +/- 3 sigma
56.0 mm
Beam in vacuum chamber at 7 TeVBeam in vacuum chamber at 7 TeV
Example for Example for failure failure at 450 GeVat 450 GeV
Assume that the current inone orbit correctormagnet is off by 10% of maximum current (Imax = 60 A)
12.0 mm
16.0 mm
Beam +/- 3 sigma
Beam +/- 3 sigmaand orbit corrector10 % / 100 % of Imax
56.0 mm
Ralphs EURO
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 !Collimators might remain at injection position during the energy Collimators might remain at injection position during the energy rampramp
Ralphs EURO
Collimators at Collimators at 7 TeV, squeezed7 TeV, squeezed
54
Particles that touch collimator after failure of normal conducting D1 magnets
After about 13 turns 3·109 protons touch collimator, about 6 turns later 1011 protons touch collimator
V.Kain
“Dump beam” level
1011 protons at collimator
55
Beam Loss MonitorsBeam Loss Monitors
Primary strategy for protection: Beam loss monitors at collimators continuously measure beam losses
Beam loss monitors indicate increased losses => MUST BE FAST
After a failure: Beam loss monitors break Beam Permit Loop Beam dump sees “No Beam Permit” => dump beams
In case of equipment failure, enough time is available to dump the beam before damage of equipment - including all magnets and power converters - but issues such a General Power Cut etc. are still being addressed
56
Prototype LHC cell:Prototype LHC cell: the 110 m long String 2 the 110 m long String 2
Full size model of one LHC cell (six dipoles and two quadrupoles)
2001: 3 dipoles and 2 quadrupoles
Cooled down to 1.9 K and onedipole and two quadrupole circuits were powered to nominal current
Cell has been completed (now six dipoles) and is today being cooled down
Experiment were performed in 2001 and will continue soon
57
String 2:String 2: First Powering of dipole magnets First Powering of dipole magnets
58
760.00
760.40
760.80
761.20
761.60
0 2 4 6 8 10 12 14 16 18 20Seconds
Amps
Imeas
Iref
String 2:String 2: Start of the LHC dipole circuit Start of the LHC dipole circuit ramp (0-20s) simulates ramp after ramp (0-20s) simulates ramp after injection of beam at 450 GeVinjection of beam at 450 GeV
50 ppm of full current = 350 MeV
Q.King et al. ICALEPS 2001
59
String 2:String 2: LHC dipole circuit ramp (0- LHC dipole circuit ramp (0-4s)4s)
759.98
760.00
760.02
760.04
760.06
0 1 2 3 4Seconds
Amps
Imeas
Iref
2 ppm = 14 MeV
Results were achieved with a new method of digital regulation together withan ultra high precision current measurement system
60
Integration and InstallationIntegration and Installation
Space in tunnel and underground areas is limited Equipment for many systems need to be installed 3-D computer model for tunnel and underground areas
61
ConclusionsConclusions
The LHC is installed and commissioned in eight (rather)independent sectors - that allows for
activities to be performed in parallel
Installation of LHC started with “general services” March 2002
Civil engineering is nearly completed
Most contracts with industry for equipment supply have
been awarded
Fabrication of equipment under the responsibility of other labs goes well
Planning can now be based on deliveries and contractual documents
62
ConclusionsConclusions
Fabrication of equipment
Installation of completed components
Very thorough commissioning of the hardware systems starting in 2005, sector by sector, as key for successful fast start up with beam
From
now
to
2006
String 2 gave us a lot of confidence as we observed a smooth commissioning of the hardware systems
In 2006 - one beam injected and transported across two sectors (25% of the ring)
Start-up with two beams in spring 2007
29 Oktober 2002
Rüdiger Schmidt
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LHC injector complex - pre-accelerators existLHC injector complex - pre-accelerators exist
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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
65
Accelerator physics and operationAccelerator physics and operation Dynamic aperture of 11 sigma: for all magnets the maximum
tolerated multipoles were specified
Preparations based on very well controlled slow ramp with PELP function (parabolic, exponential, linear and parabolic)
Accurate modelling of beam dynamics through the cycle Magnetic multipoles Dynamic effects in superconducting magnets Beam beam effects - head on / parasitic crossings
Preparation of slow feedback for tune and orbit, and possibly chromaticity - prototyping at the SPS
Online magnetic measurements (multipole factory) for feed-forward to corrector circuits
66
Powering and Quench ProtectionPowering and Quench Protection
Almost 1800 circuits from 60 A to 24 kA distributed around the 27 km LHC accelerator => 1800 Power Converter
The eight sectors of the LHC are largely independent - accurate tracking of current is required
Very high performance is needed for the 24 main circuits with main dipole and quadrupole magnets at I = 12 kA
For the main circuits the current needs to be controlled at the ppm level (12 mA at 12 kA)
Protection of 8000 magnets, 1800 High Temperature Superconductor current leads, and a large number of superconducting bus bars
67
Machine protection: Machine protection: Magnet energy
Energy in dipole magnets: 10 GJoule
… per sector reduced to 1.3 GJoule
Uncontrolled release of energy is prevented:
Fire quench heaters
Current by-passes magnet via power diode
Extract energy by switching a resistor into the circuit - the resistor with a mass of eight tons is heated to 300 °C
All components of the system have been validated, and production started (part in collaboration with Russia and India)
13 kA switches from Protvino Russia
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