Ion Beam Sources for Neutral Beam Injectors: studies and design for components active cooling and caesium ovens Andrea Rizzolo Consorzio RFX, Padova, Italy andrea.rizzolo@igi.cnr.it Advanced Physics Courses, 1 st October 2009 International Doctorate in Fusion Science and Engineering
Introduction Andrea Rizzolo Advanced Physics Courses 1 st October 2009 2
PRIMA PRIMA Padova Research on Injector Megavolt Accelerated PRIMA is the ITER Neutral Beam Test Facility to be built in Padova. It will house to experiments: SPIDER and MITICA. Andrea Rizzolo Advanced Physics Courses 1 st October 2009 3
SPIDER SPIDER Source for Production of Ion SPIDER is the ITER full size ion source experimental device. of Deuterium Extracted from Rf plasma It is characterised by the same extracted current density but lower acceleration voltage (100 kv) then required by ITER NBIs (1 MV). The aim of SPIDER is to face the main problems concerning the ion source and the optimization of its functional parameters. REFERENCES: P. Sonato et al., Fusion Eng. Des. 84 (2009) 269 SPIDER Andrea Rizzolo Advanced Physics Courses 1 st October 2009 4
MITICA MITICA is the ITER Neutral Beam Injector prototype, with whom shares the same components and MITICA parameters P = 16.7 MW I = 40 A (D - ) V = 1 MV T = 3600 s operat challenging parameters: Ion source 40 A negative ion 1.6 MW current 1 MV acceleration voltage 16.7 MW D 0 Beam 40 MW D - Beam total neutral beam Extractor power of 17 MW at the injector exit Calorimeter 17.0 MW ERID 19.6 MW Neutralizer 7.3 MW Accelerator 9.0 MW 0.7 MW Andrea Rizzolo Advanced Physics Courses 1 st October 2009 5
PLASMA RF SOURCE Plasma RF coil SPIDER and MITICA share the same ION SOURCE with the same extracted ion current and main functional parameters. The source is a negative source and deuterium ions are extracted from a radio frequency plasma. driver plate Plasma chamber Cs oven The negative ion production is caesium enhanced RF driver Water connections Capacitor Andrea Rizzolo Advanced Physics Courses 1 st October 2009 6
SPIDER electrostatic accelerator The accelerator grids are copper plates with machined cooling channels closed by means of copper electrodeposition. The cooling water and the bias are supplied trough stainless steel tubes connected to each grid. The grids have also 1280 holes for ion extraction and acceleration. Andrea Rizzolo Advanced Physics Courses 1 st October 2009 7
Ph.D Activity Plan Andrea Rizzolo Advanced Physics Courses 1 st October 2009 8
Ph.D. activity plan The PhD activities will be focused on research and design optimization of components for Negative Ion Beam Sources, and in particular for the ITER Neutral Beam Injectors. CFD and thermo-hydraulic analyses Grid prototypes development Water cooling experimental campaigns Caesium ovens design Andrea Rizzolo Advanced Physics Courses 1 st October 2009 9
CFD and thermo-hydraulic analyses The Beam Source is composed of many actively cooled components subjected to very high and localised heat loads (given by co-extracted Water flow streamlines electrons and back streaming positive ions). Copper plate The design of cooling circuits has to be carried out finding a compromise among heat removal efficiency, pressure drops and uniformity of Cooling channels water flow distribution. Nucleate boiling of cooling water has to be avoided. Andrea Rizzolo Advanced Physics Courses 1 st October 2009 10
Grid prototype development Several engineering issues have to be faced and unusual technologies have to be investigated to demonstrate the feasibility of the proposed design Stainless Steel to Copper welding Small dimensions of tubes and grid Many tubes very close each other Embedding of magnets and thermocouples during copper electrodeposition Andrea Rizzolo Advanced Physics Courses 1 st October 2009 11
Water cooling experimental campaigns Cooling channels characteristics: Few millimeters typical dimension Rectangular cross section Motivation: No clear indication of suitable correlations to be applied Experimental data that can validate CFD simulation are required Andrea Rizzolo Advanced Physics Courses 1 st October 2009 12
Caesium ovens design A Cs oven design for SPIDER beam source has to be developed starting from existing Cs ovens. Main issue: in vacuum operation CEA IPP Andrea Rizzolo Advanced Physics Courses 1 st October 2009 13
The work done so far Andrea Rizzolo Advanced Physics Courses 1 st October 2009 14
CFD analyses Water flow distribution analyses have been dedicated to verify the flow uniformity in the accelerator grid cooling channels and pressure drops. Maximum water flow rate difference : 5% Andrea Rizzolo Advanced Physics Courses 1 st October 2009 15
CFD analyses Grounded grid cooling channels Range% = 2.0 Pressure drop = 1.5 bar Extraction grid cooling channels Range% = 1.2 Pressure drop = 1.5 bar Plasma grid cooling channels Range% = 1.2 Pressure drop = 0.4 bar Andrea Rizzolo Advanced Physics Courses 1 st October 2009 16
Single Channel Prototypes (SCPs) Grid prototype Cooling experiments Heat exchange measurements Engineering issues solving Design verification in SPIDER-like conditions Cooling channel verification Benchmark of CFD code Single channel prototypes design and construction To build a grid-like prototype To be tested in a proper test-bed Andrea Rizzolo Advanced Physics Courses 1 st October 2009 17
Single Channel Prototypes (SCPs) 200 mm 3 SCPs for each grid type arranged in a 9 Channel plate having the same 270 mm extraction grid issues: Small tubes Tubes welded on plate side Tight inter-axial distance Andrea Rizzolo Advanced Physics Courses 1 st October 2009 18
Single Channel Prototypes (SCPs) Single channel prototypes of different grid cooling channels are being built to: Demonstrate design feasibility (SS-Cu welding, electro deposition ) Validate CFD models by testing the in SCPs a specific test-bed called Insulation Cooling Experiment (ICE) Grounded grid cooling channel Extraction grid cooling channel Plasma grid cooling channel Andrea Rizzolo Advanced Physics Courses 1 st October 2009 19
SCPs development Stainless Steel (SS) tubes to Copper plate welding Literature research (few data) Comparison of different techniques (Friction Welding, Electron Beam Welding, Explosion Bonding) Friction Welding R&D activity carried out with supplier collaboration to improve the grid design Machining of the 9 Chanel plate FW of 18 SS tubes Cooling channel machining (close milling tolerances, thin walls) Grinding (adequate surface roughness before electrodeposition) Embedding of thermocouples during copper electrodeposition Andrea Rizzolo Advanced Physics Courses 1 st October 2009 20
Friction welding R&D Friction welding: Technique to weld dissimilar metals No fusion of the base metal Preparation Welding Drilling Friction welding samples to develop the welded connection Andrea Rizzolo Advanced Physics Courses 1 st October 2009 21
Friction welding R&D Welding parameter definition Friction welding process Andrea Rizzolo Advanced Physics Courses 1 st October 2009 22
Friction welding R&D Helium leak test: Helium gas at 25 bar Vacuum Pressure test Vacuum test Sample # High Pressure Test Reference value Vacuum Test Reference value 10 <4.8. 10-8 mbar. l/s. 4. 10-8 mbar. l/s. 13 <2.. 10-8 mbar. l/s. 1.8. 10-8 mbar. l/s 14 <2.. 10-8 mbar. l/s. 1.6. 10-8 mbar. l/s. <3. 10-9 mbar. l/s. 2.9.10-9 mbar.l/s. <2.8. 10-9 mbar. l/s 2.5. 10-9 mbar. l/s <1.2 10-9 mbar. l/s 1.1. 10-9 mbar. l/s OK! 16 <2.8. 10-8 mbar. l/s. 2. 10-8 mbar. l/s. <2.4. 10-9 mbar. l/s 2.3. 10-9 mbar. l/s Andrea Rizzolo Advanced Physics Courses 1 st October 2009 23
Friction welding R&D Tensile test Tensile test 16000 14000 12000 Force [N] 10000 8000 6000 4000 2000 0 #13 #10 0 0,2 0,4 0,6 0,8 1 1,2 1,4 Displacement [mm] Welding interface Pure copper MTS 810 tensile test machine OK! OK! σ ~150 200 MPa σ ~25 MPa (250 kn axial force). yield yield σ ~350 MPa σ ~70 MPa ultimate ultimate Andrea Rizzolo Advanced Physics Courses 1 st October 2009 24
9 Channels plate realization Friction Welding Chanel machining Electrodeposition Andrea Rizzolo Advanced Physics Courses 1 st October 2009 25
Future work Andrea Rizzolo Advanced Physics Courses 1 st October 2009 26
Water cooling experimental campaigns ICE: Insulation Cooling Experiment Aim: to verify the heat removal capability of the cooling circuits reproducing the SPIDER grid working conditions. Vacuum condition: < 0.3 Pa Heat flux: up to 1 MW/m 2 Water resistivity: Water flow: Water pressure: > 10 MΩ m up to 10 m/s 2 MPa Water temperature: up to 180 C Andrea Rizzolo Advanced Physics Courses 1 st October 2009 27
Water cooling experimental campaigns CFD models ICE Water cooling experimental Crosscheck campaign results CFD model validation to verify SPIDER grid design Andrea Rizzolo Advanced Physics Courses 1 st October 2009 28
Caesium ovens design Design activity is ongoing in strong collaboration with ITER India Key points: Compatibility with SPIDER beam source To be operated in vacuum Development of refurbishment procedure Caesium level indicator to be developed Andrea Rizzolo Advanced Physics Courses 1 st October 2009 29
Summary CFD analyses on water flow distribution in acceleration grid channels Single Channel Prototype construction: Friction Welding R&D and samples production 9 Channel plate in realization o ICE plant design ongoing o Caesium oven design ongoing Andrea Rizzolo Advanced Physics Courses 1 st October 2009 30
Thank you for the attention! Andrea Rizzolo Advanced Physics Courses 1 st October 2009 31