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The ITER Neutral Beam system: status of the project and review of the main technological issues

presented by

V. Antoni

Consorzio RFX, Euratom-ENEA Association, Padova, Italy

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M. Bigi, A. De Lorenzi, D.Marcuzzi, A. Masiello, V. Toigo, P.Zaccaria,P.Agostinetti, G. Anaclerio, S. Dal Bello, M. Dalla Palma, E.Gaio, L. Grando, F. Milani, R. Nocentini, L. Novello, S. Peruzzo, N. Pilan, N. Pomaro, R. Piovan, F.Sattin, G. Serianni, M. Spolaore, M. Valisa, B. Zaniol, L. Zanotto, G.RostagniConsorzio RFX, Padova, ItalyS. Sandri, M. PillonENEA, Frascati, ItalyM. Cavenago, P. SpolaoreINFN, Padova, ItalyR. Hemsworth, D. Boilson, J.J. Cordier, B. De Esch, L. Svensson,CEA,Cadarache, FranceM. Liniers, A. López-Fraguas, J. Alonso,CIEMAT, Madrid, SpainA.Antipenkov, , M.Dremel, C.Day,FZK, Karlsruhe, GermanyE. Speth,H.D.Falter, U. Fantz, P. Franzen, B.Heinemann, W. Kraus, C. Martens, R.Riedl,IPP, Garching, GermanyT. T. Jones, B Chuilon , S. J. Cox, A. Emmanoulidis, M. Gilber M Kovari, Cs Jones G. Lawrence, M.J. Loughlin, D. Martin, J Milnes, E. Surrey, Y. Xue , C. Waldon, M J WatsonUKAEA, Culham, United KingdomT. Bonicelli, I. Benfatto, P. Barabaschi, P.L. Mondino,EFDA,GarchingA.TangaITER Team

co-authors

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Neutral beam injection: principles

Ion source

NeutraliserResidual ion Dump (RID)

AcceleratorPlasma

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ITER NBI requirements

Neutral beam injection is required since the beginning of ITER operationThe NBI system consists of 2 (+1) beams for Auxiliary Heating and Current Drive

P=16.5MWI=40AV=1MV ( to heat the core plasma)t pulse=3600s

Beam parameters:

1MeV neutrals implies negative ions for efficient neutralisation (60%)

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NBI injectors in ITER

DNB

2+1 NBItangential injection

On/off axis injection by tilting the beam axis vertically

Plan view Vertical cross section view

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Existing systems: JT 60U and LHD

In JT-60U 1.6MW, 360 keV for pulses lasting 20 s.

In Large Helical Device (LHD) 5.7MW , 184 keV. Steady operation up to 120 s at 0.2–0.3MW.

Y. Takeiri, et al., Nucl. Fusion 46 (2006) S199

Y. Ikeda, et al., Nucl. Fusion 46 (2006) S211

Upgrade up to 100s foreseen in next future.

Y. Ikeda, et al., P3-B-336

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Project revision: EU activities

Since 2003 an extensive activity promoted and co-ordinated by EFDA and carried out by six EU Associations (CEA, CIEMAT, FZK, IPP, ENEA-RFX and UKAEA) has been performed in Europe aimed to:

a) revise and update the NBI design for ITER [1]

b) bring the design of the alternative concepts for ion source and accelerator to the same level of detail of the reference design

c) adapt the design to a generic Test Facility.

[1] “ITER Technical Basis”, edited by IAEA, Vienna 2002

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The NBI sub-systems

The NBI system can be separated in 4 subsystems:

a) The Injector

b) The Power Supply and Voltage Distribution System

c) The Control and Data Acquisition System

d) The Auxiliary System.

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The Injector can be separated in beam components (Ion Source, Accelerator, Neutralizer, Residual

Ion Dump and Calorimeter) other components (cryo-pump, vessels, fast shutter, duct, magnetic

shielding, and residual magnetic field compensating coils)

The injector

15m 5m

9m

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Beam formation

Four components (source, accelerator,neutraliser,RID) contribute to the beam formation

Elliptic beam size 0.6x0.8m

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Beam formation (acceleration and neutralisation)

RID Neutraliser

ElectrostaticAccelerator

IonSource

Additional electrons from a) Stripping losses ( p<0.3Pa)b) Secondary electrons

-1MV

Neutralisation of D- ions by chargeexchange collisions with D2 molecules:

neutralisationD- + D2 => D0 + D2 + e

re-ionisation (competing reaction)D0 + D2 => D+ + D2 + e

Injector plan view

Voltage spatial distribution

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POWER SUPPLY

BEAM SOURCE

BEAM LINE

TRANSMISSION LINE

POWER SUPPLY

0.05

2÷4

INPUTPOWER

4÷81

17÷20to PLASMA

55÷59

5

40

NEUTRALISER

CALORIMETER

RID

ION SOURCE

DUCT

0.6

POWER SUPPLY

BEAM BEAM LINE

OTHERCOMPONENTS

LINE

SUPPLY

0.05

2÷5

ACCELERATOR

INPUTPOWER

4÷81

16÷20to PLASMA

55÷59

5

40

0.25

SOURCE

17÷1817÷18

Power balance [MW] with 1MeV D Beam

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Beam formation: negative ion production

Surface production (attachment of surface electrons to incident atoms)Cs injection greatly increases negative ion yield as it decreases surface material working function

Negative Ion production

Volume production (attachment of low energy electrons to excited molecules)

plasma

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Ion source

H-

Ie- -

NS

e- -

- -

(magnets turned by 90º)

plasma grid (Up ~ -20 kV),pos. bias (10 – 20 V)

grounded grid

extraction grid (Ux ~-15 kV)Csevaporator

water cooled Faraday screen

Al2 O3 ceramic

gas feed

filter field

NS

Driver ExpansionRegion

ExtractionRegion

H-

Ie- -

NS

e- -

- -

(magnets turned by 90º)

Ie- -

NS

e- -

- -

(magnets turned by 90º)

- -

NS

e- -

- -

(magnets turned by 90º)

- -

NS

e- -

- -

(magnets turned by 90º)

- -

NS

e- -

- -

(magnets turned by 90º)

plasma grid (Up ~ -20 kV),pos. bias (10 – 20 V)

grounded grid

extraction grid (Ux ~-15 kV)Csevaporator

water cooled Faraday screen

Al2 O3 ceramic

gas feed

filter field

NSS

Driver ExpansionRegion

ExtractionRegion

FILAMENTS

H-

RF driven Arc driven

Extractionregion

Both sources have demonstrated to fulfil requirements on current density, pressure, power and low electron co-extraction. Recent progress have led to long pulses in RF sources (IPP, Garching) and improved spatial uniformity in arc driven source (JAERI,Naka)Still to be demonstrated stable long pulse with low Cs consumption

Extraction area 0.6x1.5mTotal extraction hole area 0.2m2

Current density 200A/m2

Uniformity 10%

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Ion source design

Support structure

SINGAP extractor

Magn shield

PG bus bar

Bias bus bar

Variable capacitors(C2)

Drivers

Source case

Fixed capacitors(C1)

Electrodepositedcopper(b)1 m

RF driven Arc driven

Front view

Both sources mechanically compatible with reference and alternative accelerator

8 RF drivers 72 filaments

Integrateddesign

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RF coil

Case

Faraday shield

(b)0.25 m

Cooling circuit inlet/outlet

Cooling circuit channels

Cuts

Water inlet

Water outlet

High heat load on Faraday Shield tobe removed bynarrow coolingchannels

Removal of wholecassette

Removal of single filament

G.Anaclerio et al. P3-B-444

Ion source design: issues

RF driven Arc driven

D. Marcuzzi et al., P3-B-339 or

Additional requirements due to filament holder cooling

Filamentsreplacementby remote handling

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Accelerator: two concepts

SINGAP

MAMuG

-990 kVPlasma grid

Extraction grid Pre-acceleration

grid

Electrode (grounded grid)

G1 G2 G3 G4

Plasma grid

Extraction grid

5 acceleration grids

JAERI, NakaV= 836 keV, j= 146 Am-2 in H for 0.2s

CEA, CadaracheV= 850 keV, j= 15 Am-2 in D

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Section view of Beamsource in SINGAP configuration Detail of plasma, extraction and pre-

acceleration grids

Plasma grid

Extraction grid

Pre-acceleration gridH- or

D-

beam

Grids design

5-14 MW/m2

due to stripped electrons

Extraction and acceleration grids are subjected to large power densities aroundthe apertures

Thermalstresses

Thermaldeformations Beam

Beam

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Optimization of grids design for SINGAP with conflicting requirements from:

thin gridsrelatively large magnets and apertureslimited grid bowing and apertures misalignments

beam optics

cooling needs relatively large channels close to the heated surface

Grids design

φ13 7

φ15 5 4

1 3

6

5

1 1

7

1 1

1

Horizontal cross section Vertical cross section

Sm2Co17magnets

Cooling channel

SINGAP extraction grid

Similar optimisation to be applied to MAMuG extraction and acceleration grids.

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Upstream side

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Neutraliser requirements

2500

3200

1875 O/ALL

720

H2 or D2inlet

Cooling water i/o

H- or D- Beam

• on channel walls 4.2 MW (max. 0.5 MW/m2)• on leading edges 0.4 MW (max. 2.2 MW/m2)• Total power 4.6 MW

Power deposition from ion beam interception:

• Beam on/off 5x104

• Breakdowns 4.5x105

Heating cycles during ITER lifetime:

Additional power deposition due to electrons(stripping losses in SINGAP):

• on leading edges 2.7 MW (max. 26-30 MW/m2)

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Electron power loads on leading edges(front view) in SINGAP configuration

Neutraliser : thermo-mechanical issues

Deviated and focusedelectrons lead to localpeaks of power density up to 25 - 33 MW/m2

Peak power densities cause large temperature gradients and bending stresses on leading edges .

Work is in progress to :a) assess optimization of cross section and cooling parameters to satisfy ITER fatigue lifetime requirements.b) design new systems to deflect and dump the electrons

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Residual Ion Dump

Function:

Deflecting by an electrostatic field and dumping on actively cooled panels the ions emerging fromthe neutraliser.

Coolingwater i/o

BeamA bias potential up to - 20 kV is applied and modulated (± 5 kV/50 Hz) to reduce the power densities on the channel walls.

Insulated panels-20 kV

2.7 m

3.2

m

1.3 m• Total power (for 7 mrad beam divergence) 18.5 MW• Peak power density on panels 6 MW/m2

• Beam on/off 5x104

• Breakdowns 4.5x105

Power deposition from ions and neutrals deposition:

Required heating cycles during ITER lifetime:

Work in progress to assessfatigue requirementsfatigue mitigation by

voltage sweeping shortening of breakdown recovery

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The Power Supply and Voltage Distribution System

The Power Supply (PS) and Voltage Distribution System provides the High Voltage (HV) to the accelerator grids (AGPS) and supplies the ion source (ISPS) and the auxiliary components.

The power is transmitted to the ion source and the acceleration grids via a HV transmission line, SF6 insulated for -1MV dc to ground.

PS for the ion source (IS) and pipes for IS and grids cooling are hosted inside the HVD insulated in SF6

An HV bushing provides the interface between the TL (in SF6) and the ion source and the acceleration grids in vacuum.

STEP UP TRANSFORMERS

POWER SUPPLY BUILDING

TRANSMISSION LINE

HV DECK

BUSHING \\70m

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Acceleration Grid Power Supplies

0 V

-1 MV

Ac/dc converter Dc/ac inverter

Step-up (isolation)Transformer

-800 kV

-600 kV

-400 kV

-200 kV

69 kV59 A

7 A

6 A

3 A

3 A

40 A

Step-down Transformer

MAMuG Configuration

< 200 µsResponse time of the load protection system

± 5 %Max. voltage ripple

40 ACurrent at ground level

-200 kV / 3 AGrid 4

-400 kV / 3 AGrid 3

-600 kV / 6 AGrid 2

-800 kV / 7 AGrid 1

-1000 kV / 59 AMain supply

ValueParameter

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The AGPS step-up transformers are the most challenging components:• very high insulating voltage (1 MV dc)• high value of the secondary voltage (about 160 kV ac) • square waveforms, 400 Hz operating frequency ( for inverters)

The ISPS transformers have lower turn ratio and power but same insulation structure as AGPS ones (the operation frequency is 1 kHz in the reference design)

(The closest industrial application is 600kV HVDC transmission)

Power Supplies:TechnologicalTechnological issuesissues

(For SINGAP, at least three stages are necessary as a single or two stage AGPS appears not feasible, due to the mix problematic of ac and dc insulation for the transformer winding)

Feasibility assessment made in collaboration with industry has concluded that AGPS and ISPS transformers are feasible for both accelerators

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Alternative design based on two Alternative design based on two HVDsHVDs

Reference design

Alternative design

No electric devices inside the High Voltage Deck (HVD) in SF6 ,which hosts only the cooling water and gas insulated feeding pipes for the beam source

All ISPS inside a new HVD ( HVD1) air insulated for -1MV to ground and placed at the beginning of the transmission line TL1

Reduction of number of transformers from 8 to 1, supplying all the ion source power supplies

Simplification of design and reduction of weight and size of HVD2

Better PS accessibility for testing and maintenance

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Transmission line: SINGAP accelerator

A new TL design has been designed for SINGAP (and arc drivensource) for the alternative PS design.

To the HVD1

HVD2

To the Bushing

Air-to SF6 feedthrough

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Transmission line: Open issues

• Cooling water for beam services

•Current leakage depending on temperature.

•Metal corrosion due to electrolysis.

•SF6-epoxy insulation [1]

•Surface charge accumulation on spacers.

•Radiation Induced Conductivity effects on spacers electric fielddistribution.

•Metal particles

•Effectiveness increase of manufacturing-installation procedures for particle control.

•Design adaptation of the spacer and screens to cope with the unavoidable presence of particles inside the TLs and HVD

[1] A. De Lorenzi, et al (P3-B-382).

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Bushing: reference design

High voltage feedthrough for all electrical and cooling services of the beam sourceInterface between the gas insulated (SF6 at 0.6MPa) transmission line and the ITER primary vacuum Barrier for tritium containment and vacuum confinement

SF6Vacuum

Double barrier obtained with two insulating rings (alumina on vacuum side and Fiber Reinforced Polymer (FRP) on gas side) and guard gas in the interspace (N2)

Large ceramic rings recently manufactured

(T. Inoue et al.,P3-B-362)

SF6

Vacuum

MAMuG 1MV bushing

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Bushing: SINGAP configuration

A new design for SINGAP has led to considerable simplification of the bushing :

intermediate voltage structures removed

source and pre-accelerator assembly sustained only from the HV bushing

Open issues for both designs:HV DC insulation in pressurized gas, vacuum and solid insulators in presence of ionizing radiations (γ and X rays) and residual magnetic field

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Main technological issues: summary

Thermo-mechanical

issues

Electric issues

Heat load and

components

Mechanical design constraints

Protection

Beamperformance

FatigueMelting,

OpticsNegative Ion J

Remote Handling full compatibility Vacuum and differential pressureAccurate beam alignment

HV electrical insulation

Arc control

Vacuum

Gas

Radiation (X-ray)ParticlesMagnetic fields

ElectrolysisLiquid/Solid

Radiation (γ-ray)Particle drift

ActiveprotectionPassive

protection

Fast detectionInterlock

Core-snubberInductanceresistance

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Test Facility

• As most of the issues are strongly coupled, those of them still open can be tackled and solved only by testing a full scale NBI at full performance in D and H.

• A Test Facility where to install and operate a NBI before operation in ITER is therefore mandatory in order to provide a reliable system.

• Such a Test Facility should also allow all the needed adjustments and modifications to be performed in order to optimise the system.

• In the framework of the EU activities a schematic design for a generic site has been prepared

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Power supplyMaintenance

Experiment

Auxiliary systems

Cooling towers

At present work is in progress to adapt the generic site to Padovasite, which has been proposed by EU as the Test Facility site

Test Facility for a generic site

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Test Facility Auxiliary Systems

Cryosystem

Forepumpingsystem

Top flange platform

60 MW cooling tower

Heat rejection system

Primary Heat

Transfer System

HV deck

TL2

TL1

HV deckplatform

Experiment ground

level

gas

100m

The auxiliary systems consist of

cryogenic plantcooling plantpumping and gas injection plant

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Conclusions

A thorough revision activity of the ITER NBI design promoted by EU has led to the identification of several technological issues.

Some of the issues have been solved, others are in the process of being solved, others remains open.

The complexity of the design suggests the construction of a Test Facilty to test the NBI before operation in ITER.

Several posters give more details

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Today POSTERS

Subject Author &content PosterNuclear safety M. Loughlin et al. “Tritium monitoring…” P3-B-105Sources P. Franzen et al. “ Status IPP RF Source….”P3-B-160

D. Marcuzzi et al., “RF source design…” P3-B-339G.Anaclerio et al. “Arc driven source…” P3-B-444M Froeschle et al.”Half size RF source…” P3-B-450

Bushing T. Inoue et al.,”Beam source and bushing” P3-B-362SINGAP B. de Esch “Post accelerated electrons…” P3-B-226

P. Agostinetti “SINGAP grids…” P3-B-406Diagnostics N. Pomaro et al. “Diagnostics design…” P3-B-329

I. Day et al. “Thermocouples analysis…” P3-B-356D. Homfray et al. “Electr. Energy distr.” P3-B-375

Electric insulation A. Masiello et al. “HV DC vacuum and gas…”P3-B-372A. DeLorenzi et al.”1MV Transmission line” P3-B-382

Injector C. Jones et al. “Absolute valve..” P3-B-434J. Milnes “High Heat Flux elements…” P3-B-442J Alonso et al. “Residual B coils…” P3-B-487JJ Cordier “NBI Remote Handling” P2-G-263

Power supply E. Gaio et al. “RF power supply…” P3-B-469M. Bigi et al. “grid breakdown protection…”P3-B-462

Existing NBI Y.Ikeda et al.”NBI for JT-60SA…” P3-B-336

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Spare slides

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• simplification of the high voltage transmission line and bushing

• less critical and smaller postinsulators forgrids support

• plane grids (plasma, extraction and pre-acceleration)

• easier horizontal and vertical beam steering by means of translations of the grounded grid

SINGAP accelerator

The SINGAP accelerator has been designed

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Cooling inletCooling outlet

Cooling inlet/outlet (lateral wall)

Design activity aimed to optimization of main chamber walls temperature control to minimize Cs consumption and maximize negative ion production

Ion source design: cooling

RF driven Arc driven

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Cooling inletCooling outlet

Cooling inlet/outlet (lateral wall)

Design activity aimed to optimization of main chamber walls temperature control to minimize Cs consumption and maximize negative ion production

Ion source design: cooling

RF driven Arc driven

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Essential Measurements - Control and Interlock

Diagnostic Measured quantity Thermocouples Surface temperature, water temperature IR Cameras Surface temperature Viewing Cameras Visible imaging Pressure probes Gas pressure Gas Flow probes Gas flow Water flow probes Water flow RF power meters RF transmitted power, RF reflected power, SWR Current probes Electrical current, arc discharges Voltage dividers Electrical voltage

Scientific Measurements – Beam Characterization

Diagnostic Measured quantity Fibre Optics arrays Tomographic imaging and Energy profile of the beam Laser telemetry Displacement and acceleration Langmuir probes Source plasma density and temperature Residual Gas analysers Residual gas composition Magnetic Probes Residual magnetic field

Safety and protection

Diagnostic Measured quantity Neutron detectors Neutron flux Gamma Detectors Gamma radiation

The control system provides control and interlock functions and manages data acquisition.

The Control and Data Acquisition System

Ref. N. Pomaro and S. Peruzzo, "Design Study of the diagnostics of the ITER Neutral Beam Injector and the Neutral Beam Test Facility", this Conference, P3-B-329

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Calorimeter / 1

Function:

• Dumping of the neutral beam emerging fromthe RID during commissioning and conditioning phases. (Non active component)

• Diagnostic of correct beam generation and aiming with thermocouples arrays.

Vertical cross section

∅ 20 mm STEs

• Max. total power 21.2 MW (for 3 mrad beamdivergence)

• Max. power density on STEs 25 MW/m2

Power deposition:

• Beam on/off 1x104

• Breakdowns 7x104

Required heating cyclesduring ITER lifetime:

Weight 2.5 t

Beam

2700

3300230

0Weight 2.5 t

BeamBeam

2700

3300230

0

Closed configuration

Work in progress to assessfatiue lifetime

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Upper flange (15 tons)

Vertical cryopumps (2 x 6 tons)

Calorimeter (2.5 tons)

HV Bushing (19 tons)

Gas baffle

RID (4 tons)

Neutraliser (14.5 tons)

Beam Source (26 tons)

BS Vessel (30 tons)

Beam Line Vessel -Beam Line Vessel -

Beam line vessel (54 tons)

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Changes by using two halves of ITER cryopump

neglectible influence on thethermohydraulic distribution of thecryogenic fluids and on thepressure drops.

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RID / 4

The Magnetic RID alternative

IPP and UKAEA courtesy

Advantages:• increased beam line transmission and hence

increased injected power (1.7 MW for a 3 mrad divergence beam)

• wide operation window regarding beamalignment, divergence and steering

• robustness against changes in the neutralizer target thickness, changing the balance of positive and negative residualions,

• no accelerated secondary electrons.

Disadvantages:• creates an additional stray field that has to

be compensated• the present design exceeds the allocated

length of the reference design by 0.2 to 0.3 m.

(Taken from IPP Final Report 2006)

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Essential Measurements - Control and Interlock

Diagnostic Measured quantity Thermocouples Surface temperature, water temperature IR Cameras Surface temperature Viewing Cameras Visible imaging Pressure probes Gas pressure Gas Flow probes Gas flow Water flow probes Water flow RF power meters RF transmitted power, RF reflected power, SWR Current probes Electrical current, arc discharges Voltage dividers Electrical voltage

Scientific Measurements – Beam Characterization

Diagnostic Measured quantity Fibre Optics arrays Tomographic imaging and Energy profile of the beam Laser telemetry Displacement and acceleration Langmuir probes Source plasma density and temperature Residual Gas analysers Residual gas composition Magnetic Probes Residual magnetic field

Safety and protection

Diagnostic Measured quantity Neutron detectors Neutron flux Gamma Detectors Gamma radiation

The control system provides all control function and interlock protection.

thermocouples and relative cabling on the Calorimeter Panels

The Control System and the diagnostics

Ref. N. Pomaro and S. Peruzzo, "Design Study of the diagnostics of the ITER Neutral Beam Injector and the Neutral Beam Test Facility", this Conference, P3-B-329

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NBI in ITER:Gas flow

Gas in: source, neutraliser

0.3Pa

<0.001Pa

Gas out: Cryo-pump (Pumping surface ~50 m2 )

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Test Facility for NBI: planning proposed by EU

time

Operation in ITER

t=0t =-7yt =-10y

OperationConstructionDesign

Decision on Source and accelerator

Work in progress (EU and JA) to optimise procurement and operation planning, in particular Source operation in parallel to full injector construction

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The Power Supply System of the ITER NB InjectorLoad protection in case of grid breakdownLoad protection in case of grid breakdown

In case of grid breakdown (a routine events) the energy stored in the filter and stray capacitance is discharged and can damage the grids.

Protection by DC breakers is not feasible due to the high voltagePassive protections (core snubbers) plus fast switch-off of the inverters is foreseen

Status of the workStatus of the workRevision of the analyses of the reference designImprovement of the model simulated (unprotected stray capacitances, rectifier diodes)Analysis of the core snubber modeling and design (concentrated or distributed )Assessment of the passive and active protections for the SINGAP case [3]

[3 M. Bigi, V. Toigo, L. Zanotto, “Protections Against Grid Breakdowns in the ITER Neutral Beam Injector Power Supplies”, ID469 this conference

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Thermomechanical issues

1)Heat load and effect on componentscomponents protection ( localised enhanced heat load and surface

damages , coolant leakage, outgassing, sputtering) fatigue and thermal cycles and sweeping

beam performance ( source wall temperature and current density (negative ion production), optics and deformation of the grids

2) Mechanical design and constraintsRemote Handling full compatibility vacuum and differential pressure requirementsaccurate beam alignment

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Electric issues

1) HV electrical insulation in different mediavacuum ( radiation: X rays, particles emitted by thermal emission, sputtering, arcs , effect of magnetic fields both residual and applied)gas (radiation: gamma rays, drift of chargesliquid or solid vacuum. (electrolysis)

2) Arc controlmaximum energy tolerable to avoid de-conditioning

passive (core snubber , resistance, inductance)Protection

active (fast detection and intervention system)

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5 accelerationgrids

Plasma and extraction grids

-200

-400

-600

-800

-1 M

V

0 kV

Multi Aperture Multi GridMAMuG (7 grids)(ITER reference design)

H- or D-

Beam

Single Gap Single ApertureSINGAP (4 grids)(alternative EU proposal)

350 mm

H- or D-

Beam

The accelerator: two alternative concepts

Plasma,extraction andpre-acceleration grids

Groundedgrid

0 kV

-930

kV

-1 M

VAr

cch

ambe

r

Arc

cham

ber

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TRANSMISSION LINE: reference design

• In the reference design the Transmission Line is a multipolar one (9 electrodes), insulated in pressurized SF6.

1500 mm

250 mm

The reference design review has highlighted some issues:

•The required 1 MV insulation under dc voltage is two times the insulation obtained by the ultimate industrial realization for unipolar lines: the realization of a multipolar line with sufficient reliability against voltage breakdown requires further R&D.

•The Multipolar Structure requires great complexity for the connection to the AGPS.