Operation of large RF sources (H, D ) for fusion Lessons learned at ELISE

Transcription

1 Max-Planck-Institut für Plasmaphysik Operation of large RF sources (H, D ) for fusion Lessons learned at ELISE Ursel Fantz for the IPP-NNBI Team 1 m IR camera 13 C 1 C m 1.8 m Grid system Tungsten wire calorimeter 3.5 m 8 A H on the calorimeter 5 th NIBS, Oxford, UK September 1 16,16

2 Modular source concept for size scaling From the prototype source via a ½ size ITER source (ELISE) to the ITER source RF driven source, f = 1 MHz, 8 kw/driver Neg. ions (H, D ) at.3 Pa using Cs Co-extracted electrons: e/ions < 1 Beam homogeneity: D < 1% Stable up to one hour 1.5 A Prototype source ELISE source A 4 A SPIDER, MITICA, HNB & DNB Ursel Fantz, p. 5 th NIBS, September 1 16, 16

3 The ELISE test facility Parameter and targets Tank Isotope H -, D - RF power = x 18 kw in 4 drivers A ex = 1 cm, uniformity > 9% I ion,acc = A, U tot = 6 kv, I e /I ion < 1 at.3 Pa U ex < 1 kv Plasma: 36 s Beam : 1 s every 15 s (HV) As part of the EU roadmap for ITER NBI First plasma in Feb. 13 Initial experiments w/o Cs Initial experiments with Cs Increase of RF power and pulse length Source inspection in 15 Towards ITER relevant RF power Talk: Dirk Wünderlich Gate Valve Ø 1.5m Main insulator 1 m Extraction system Ion source Beam Diagnostic calorimeter Cryopumps OUTLINE: Operation Inspection Consequences for ITER source Ursel Fantz, p. 3 5 th NIBS, September 1 16, 16

4 SWR, Cos phi Frequency [khz] Operation: RF issues Matching and breakdowns One generator feeds two drivers in series breakdowns at higher RF power Free-oscillator vs. solid-state amplifier less efficient & water cooling frequency flips occur 3 Frequency flip.5 Frequency (Oscillator) MHz 18 kw series config. changed into parallel config. (less RF voltage) higher C1, C.5nF 6.5nF Transformer C1 Ground C1 Variable C: -1.5nF 1nF C -6 kv 4nF Ion source Variable C: -1.5nF C Ion source 1 86 SWR (Amplifier).5 84 cos ϕ (Oscillator) Capacitance C (in series) [nf] Automatic power control and frequency matching developed with industry MonO7: Werner Kraus Solid state generators for MITICA / ITER NBI 15 kw amplifiers purchased for AUG and W7-X Successfully tested at BATMAN Ursel Fantz, p. 4 5 th NIBS, September 1 16, 16

5 Operation: RF issues Mutual coupling and breakdowns Introduction of electromagnetic shields (EMS) lifetime of Faraday screen () Sufficient cooling of EMS water cooled support rod RF coil Faraday shield Necessity of EMS with active cooling Melting traces at Mo coated Faraday screen in RADI EMS quadrant Increase safety margin for breakdowns distances, triple-points Open issue Breakdowns Driver cylinder Electric field strength [V/m] 4x1 7 3x1 7 x1 7 1x1 7 Al O 3 Quartz Gap between coil and driver cylinder [m] Ursel Fantz, p. 5 5 th NIBS, September 1 16, 16

6 Operation: Cs consumption Reduced Cs consumption due to improved oven and improved conditioning scenarios Well controlled Cs evaporation (DT < 1 C) SID for measuring and controlling evaporation Air Vacuum Heating sleeves Insulation bag Surface ionization detector Nozzle Cs consumption remarkably reduced approx. factor of (minimum) in prototype source Oven nozzle Full metal bellow valve ELISE with two ovens has similar consumption as prototype source (despite larger size) More consumption causes breakdowns between grids Liquid Cs reservoir, exchangable against Cs dispenser Lower Cs consumption in ITER sources reduced oven maintenance reduced source contamination with fine-adjustable Cs oven and walls at 35 C Ursel Fantz, p. 6 5 th NIBS, September 1 16, 16

7 Operation: Cs (re-)distribution Plasma redistributes efficiently Cs ThuO4: Christian Wimmer source MonP19: Eleni Aza beam Prototype source: vacuum plasma; one vs. two Cs ovens; different nozzle geometries Ratio of Cs densities top/bottom day Vacuum (before pulse) BATMAN 3 ELISE: back-streaming positive ions p [Pa], Intensity [a.u.] Cs 85 Filling Pressure Time [s] 1 Plasma Pulse number WedO3: Alessandro Mimo Position of Cs oven less relevant Open issue: Cs dynamics due to back-streaming ions Ursel Fantz, p. 7 5 th NIBS, September 1 16, 16

8 Operation: Magnetic filter field Filter field generated by easy adjustable PG current ( 1 ka 1 mt at PG, x-y centred) About 1 mt sufficient to cool electrons down Pronounced plasma drift not observed H vs. D: adjustable strength (and topology) needed Extr. current density [A/m ] Extr. current density [A/m ] j ion j e operating point Deuterium,.6 Pa 3 kw/driver j ion j e Hydrogen,.6 Pa 3 kw/driver w/o add. field B strengthened Magnetic field at PG [mt] OES data Ursel Fantz, p. 8 5 th NIBS, September 1 16, 16 T e [ev] Electron temperature Top Bottom Electron density 1 3 PG current [ka] External magnets for electron suppression To be optimized!! Installed PG current of 5 ka sufficient (for ELISE config. of return conductors) Adjustment of PG current independent from accelerator field highly advisable n e [1 17 m -3 ]

9 Operation: Magnetic filter field Filter field generated by easy adjustable PG current ( 1 ka 1 mt at PG, x-y centred) Beam deflection due to fringe field in accelerator Beamlet groups Two segments distinguishable with both Calorimeter at 3.5 m distance BES at about m distance Beam homogeneity influenced by field strength Homogeneity of beamlet groups or individual apertures not accessible Homogeneity above 9% for the segments achievable Ursel Fantz, p. 9 5 th NIBS, September 1 16, 16 Power density [kw/m ] BES intensity [Ctsnm] IR calorimetry I PG.6 ka bottom 4. ka top 5 16 horizontal LOS Beam emission spectroscopy Vertical position [m]

10 Operation: Co-extracted electrons Electron suppression by interplay of FF, bias and Cs Spatial variation accessible: I e for top and bottom segment measured separately at ELISE j ex [ma/cm ] I EG [A] j ion Bottom Top I e. ka Bias current [A] j ex [ma/cm ] I EG [A] j ion I e Hydrogen, kw,.3 Pa s RF, 1 s beam Top 4 Bottom 55 A PG current [ka] Pronounced asymmetry! Temporal stability depends strongly on Cs conditioning Better electron suppression at slightly higher pressure Talk: Dirk Wünderlich Replace strict global limit I e / I H - < 1 by power density limit Open issue: Spatial variation of I e Ursel Fantz, p. 1 5 th NIBS, September 1 16, 16

11 Operation: Stripping in the accelerator Stripping ( H + H H + ) dominantly in the first gap Obtained and quantified via BES Stripping below 1%, p tank = 1-5 mbar (as in MANITU; both cryopump) Stripping fraction [%] Hydrogen U ex =8 kv LOS #1 #7 #5 Deuterium U ex =6 kv LOS #7 #5 # Pressure [Pa] Very low stripping and lower I e suggests to relax lower pressure limit to.4 Pa Intensity [counts] Intensity [a.u.] MonP7 Marco Barbisan, RFX U ex =6 kv, U acc = kv Doppler peak Unshifted H div = Pa Stripping peak Wavelength [nm] Doppler peak.3 Pa Broad comp. Deuterium Fitted curve Wavelength [nm] Broad component detected Ursel Fantz, p th NIBS, September 1 16, 16

12 j ex [A/m ] Electron / ion ratio j ex [A/m ] Operation: Source performance Short pulses: comparison of source performance at.3 Pa ITER req. Hydrogen,.3 Pa ITER req. ELISE. mt BATMAN RF power per driver [kw] Electron / ion ratio ITER req. Deuterium,.3 Pa ITER req. ELISE 3.8 mt BATMAN RF power per driver [kw] 8 kw/driver of the installed 1 kw should be sufficient Long pulses: source performance limited by co-extracted electrons Talk: Dirk Wünderlich Relax lower pressure limit to.4 Pa Open issue: Operation at high RF power Ursel Fantz, p. 1 5 th NIBS, September 1 16, 16

13 Maintenance after years of operation: Source Inspection of source vessel Faraday screens OK Traces of back-streaming ions Driver with Faraday screen Driver with Faraday screen Grid pattern b.s. ions Grid pattern b.s. ions Cs coating Low Cs contamination (reduced Cs consumption) Elements found by EDX: Cs, Mo, Ni Diagnostic windows Open issue: Ni release from back plate Ursel Fantz, p th NIBS, September 1 16, 16

14 Maintenance after years of operation: Grid system No damages but some discoveries PG: Cu traces at back side Cu sputtering between grids PG back side EG: black rings around apertures EG GG EG PG Plasma Extraction Grounded Grid BP Bias Plate GG: strong sputtering around apertures GG Deposition of Cu on GHB and some removal by beam halo or re-ionized particles Open issue: Origin and consequences Ursel Fantz, p th NIBS, September 1 16, 16

15 Open issues Operation at high RF power Broad beam component and Ursel Fantz, p th NIBS, September 1 16, 16

16 Conclusions: Towards A acc. (8 A ex.) D beams for up to 1 hour Lessons learned with ELISE (and BATMAN, MANITU, RADI) RF issues Caesium Filter field 8 kw RF power/ driver could be sufficient Solid state RF generators Breakdowns Lower Cs consumption Position of Cs oven unproblematic Conditioning for long pulses Installed PG current sufficient Need to adjust PG current Beam Global beam homogeneity of > 9 % Currents Stable ion currents Global I e /I H - limit vs. power density limit Relax pressure to.4 Pa Spatial and temporal control of electrons More input expected from long pulse operation at high RF power Test of MITICA field at ELISE Ursel Fantz, p th NIBS, September 1 16, 16

17 Vertical position [cm] Conclusions: Towards A acc. (8 A ex.) D beams for up to 1 hour Lessons learned with ELISE (and BATMAN, MANITU, RADI) RF issues Caesium Filter field 8 kw RF power/ driver could be sufficient Solid state RF generators Breakdowns Lower Cs consumption Position of Cs oven unproblematic Conditioning for long pulses Installed PG current sufficient Need to adjust PG current Beam Global beam homogeneity of > 9 % Currents Stable ion currents Global I e /I H - limit vs. power density limit Relax pressure to.4 Pa Test of MITICA field at ELISE Spatial and temporal control of electrons divergence IR camera 13 C 1 C DENSB 9 More input expected from long pulse operation at high RF power Ursel Fantz, p th NIBS, September 1 16, Horizontal position [cm]