Development of a Multi-Purpose, Multi-Frequency Gyrotron for DEMO at KIT

Transcription

1 KSTAR Conference 2015 February 25-27, 2015, Daejeon, Korea Development of a Multi-Purpose, Multi-Frequency Gyrotron for DEMO at KIT M. Thumm a,b, K.A. Avramidis a, J. Franck a, G. Gantenbein a, S. Illy a, P.C. Kalaria a, I.G. Pagonakis a, C. Wu a, J. Zhang a and J. Jelonnek a,b Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany a Institute for Pulsed Power and Microwave Technology (IHM) b Institute of High Frequency Techniques and Electronics (IHE) manfred.thumm@kit.edu KIT University of the State of Baden-Württemberg and National Large-scale Research Center of the Helmholtz Association

2 Overview Requirements for DEMO Gyrotrons Targets of DEMO Gyrotron Development at KIT MW, CW Coaxial-Cavity Gyrotron - Multi-Purpose, Multi-Frequency Gyrotron ( GHz, f = 33.8 GHz) - Step-Frequency Tuning ( GHz, f = 2 GHz) 1 MW, CW Conventional-Cavity Gyrotron - Multi-Purpose, Multi-Frequency Gyrotron ( GHz, f = 33.0 GHz) Summary and Acknowledgments 2 M. Thumm et al.; Development of a Multi-Purpose, Multi-Frequency Gyrotron for DEMO at KIT

3 Requirements for DEMO Gyrotrons (I) Current design studies on Electron Cyclotron Heating & Current Drive (ECH&CD) systems for the demonstration fusion power tokamak plant DEMO demand gyrotron frequencies of above 200 GHz for efficient CD and a total gyrotron efficiency above 60 % to achieve a sufficient fusion gain factor. (E. Poli, et al. Nuclear Fusion, 53, (10pp) (2013)) Required gyrotron frequency depends on the Aspect Ratio A of DEMO and on the relevance of CD in plasma operation. Indicative frequencies for different Aspect Ratio A A = R/a B t [T] f_heating f_current Drive γ [Am -2 /MW] (Top Launch) M. Thumm et al.; Development of a Multi-Purpose, Multi-Frequency Gyrotron for DEMO at KIT

4 Requirements for DEMO Gyrotrons (II) Gyrotron flexibility could compensate the rigidity of a DEMO reactor: Multiple Frequencies: distance between two frequency ~ 34 GHz. Selection between pulses. 3-4 frequencies possible. Single disk gyrotron window sufficient. Step Tunability: 2-3 GHz between step: max. span 10 GHz for NTM stabilization. During the pulse (but not very fast). Broadband gyrotron window required. Output mm-wave Beam Quality: 95 % demonstrated for ITER gyrotrons Reliability: ITER gyrotron (GYCOM) demonstrated 95% > 98% could be reasonable for DEMO (demonstrated for 140 GHz W7-X gyrotron (Thales)) Unit Power: 1 2 MW (coaxial-cavity/backup: conventional cavity), Efficiency: up to 60 % Requirements for high gyrotron efficiency: Excellent quality of electron beam Excellent alignment of tube components and magnetic field Multi-stage depressed collector 4 M. Thumm et al.; Development of a Multi-Purpose, Multi-Frequency Gyrotron for DEMO at KIT

5 Towards DEMO: 240 GHz Coaxial-Cavity Gyrotron Development Targets of KIT development f = GHz, P = MW, η > 60 % Frequency step-tunability ( f 2 GHz, +/-10 GHz tunability) Classic technical limitations Emitter radius 65 mm Electric field at emitter surface 7 kv/mm Emitter current density 4 A/cm² Magnetic compression B 0 /B gun 40 Spread of electron guiding centers λ/5 Ohmic loading on resonator wall 2 kw/cm² Results in Beam radius R b 10 mm, cavity radius R cav 31 mm χ M. Thumm et al.; Development of a Multi-Purpose, Multi-Frequency Gyrotron for DEMO at KIT

6 Typical Spectra for Very-High-Order Modes R b = 9.60 mm R cav = mm R b = mm Spectra around the modes TE 47,31 and TE 51,27 from f 0 12 GHz to f GHz 6 M. Thumm et al.; Development of a Multi-Purpose, Multi-Frequency Gyrotron for DEMO at KIT

7 Ohmic Losses at High Frequencies Ohmic loading on cavity surface C c, C c = R c /R cav TE 49,29 (χ = 158): Ohmic loading would allow 2 MW! Power limitations: frequency emitter radius / bore-hole diameter electron gun design emitter current density 7 M. Thumm et al.; Development of a Multi-Purpose, Multi-Frequency Gyrotron for DEMO at KIT

8 Towards DEMO: Fundamental Studies of a 240 GHz Coaxial-Cavity Gyrotron p m 1 2 p/m ~ 0.57 (R c /R cav ~ 0.31) 3 X m,p = TE +(m-3),p+1 very small caustic radius (too) large caustic radius (conventional gyrotrons) TE +(m-2),p+1 TE +(m-3),p+1 TE -m,p TE +(m-2),p+1 m = ; p = TE 28,16 140/1.5 [Piosczyk et al. 1997] 2. TE 31,17 165/1.5 [Piosczyk et al. 1999] 3. TE 34,19 170/1.5 [Rześnicki et al. 2007] 4. TE 52,31 170/4.0 [Beringer et al. 2010, Design] 8 M. Thumm et al.; Development of a Multi-Purpose, Multi-Frequency Gyrotron for DEMO at KIT

9 Optimum Features of Multi-Frequency Gyrotrons Cavity Radius: R cav Bessel Zero of Cavity Mode TE m,p : X m,p Caustic Radius of Cavity Mode TE m,p : R c = (m/x m,p )R cav = C c R cav Relative Caustic Radius: C c = R c /R cav = (m/x m,p ) Electron Beam Radius: Radius of Q.O. Launcher: R b 1.05 R c R L Brillouin Angle: θ B = arccos[1-(r cav /R L ) 2 ] 1/2 Azimuthal Spread Angle: 2ϕ = 2arccos(C c ) Length of Straight Launcher Cut: L = 2πR L sinϕ/(ϕtanθ B ) If m/x m,p of the modes is the same, R b, 2ϕ and L are also the same and the mm-wave output beam hits the same point at the tube gyrotron output window! 9 M. Thumm et al.; Development of a Multi-Purpose, Multi-Frequency Gyrotron for DEMO at KIT

10 Multi-Purpose Multi-Frequency Coaxial-Cavity Gyrotron for DEMO with Different A=R/a CVD-Diamond Window: t = mm, - 20 db Reflection Bandwidth = 2.2 GHz Frequency [GHz] Application CD, A=2.6 W7-X UG H, A=3.1 ITER UG H, A=3.6 CD, A=3.1 H, A=4.0 CD, A=3.6 CD, A=4.0 Cavity Mode TE 28,17 TE 35,21 TE 42,25 TE 49,29 TE 56,33 Bessel Zero Relative Caustic Radius C c Normalized Window Thickness [λ] Window Center Frequency [GHz] 4/2 5/2 6/2 7/2 8/ Max. deviation of C c is 0.27%, therefor max. horizontal output beam shift of only 50µm 10 M. Thumm et al.; Development of a Multi-Purpose, Multi-Frequency Gyrotron for DEMO at KIT

11 Step-Frequency Tunable Coaxial-Cavity Gyrotron GHz < GHz < GHz Freq. [GHz] f [GHz] Cavity Mode TE 46,28 TE 47,28 TE 48,28 TE 49,28 TE 47,29 TE 48,29 TE 49,29 TE 50,29 TE 51,29 TE 49,30 TE 50,30 TE 51,30 TE 52,30 Rel. Caust Rad. C c f 0 11 GHz f 0 f GHz Max. deviation of C c is 2.8 %, therefore horizontal output beam shift of max. 2 mm 11 M. Thumm et al.; Development of a Multi-Purpose, Multi-Frequency Gyrotron for DEMO at KIT

12 TE 49,29 -Mode Coaxial Cavity f = GHz R cav = mm (loading: 2.0 kw/cm²) R coax = 8.55 mm (loading: 0.2 kw/cm²) n=91 longitudinal corrugations (0.3/0.3 mm) Q D 2700 (L cyl = 15 mm) R beam = mm Preliminary cavity design for a coaxial gyrotron operating in the TE 49,29 mode. Outer wall is shown in blue (upper edge), the tapered coaxial insert in red (lower edge) and the electron beam in brown. 12 M. Thumm et al.; Development of a Multi-Purpose, Multi-Frequency Gyrotron for DEMO at KIT

13 Startup Scenario for the TE 49,29 Mode > 2 MW output power η el = 34 % with margins (EURIDICE) Initial operating point: 9.58 T, 85.6 kev, 69.3 A, velocity ratio α = 1.22 Assumptions 16 % spread in velocity ratio infinitely thin beam axial B-field not tapered 13 M. Thumm et al.; Development of a Multi-Purpose, Multi-Frequency Gyrotron for DEMO at KIT

14 First Magnet Design Difficulty: 10 Tesla at Ø 270 mm warm bore-hole! 9 Main Coils Gun Coil (subject to discussion) Coil Currents: ~ 150 A (ARIADNE) 14 M. Thumm et al.; Development of a Multi-Purpose, Multi-Frequency Gyrotron for DEMO at KIT

15 Coaxial Magnetron Injection Gun (MIG) Triode-Type MIG Emitter radius: 65 mm Modulation Anode (-10 kv) Body (0 kv) Emitter width: 4.3 mm Laminar beam (at boundary to nonlaminar) Guiding Magnetic Field Line Cathode (-86 kv) Electron Beam Velocity ratio (α) spread: 3.1 % (Emitter roughness not yet considered) Coaxial Insert (0 kv) (ARIADNE) 15 M. Thumm et al.; Development of a Multi-Purpose, Multi-Frequency Gyrotron for DEMO at KIT

16 Multi-Frequency Conventional Cylindrical-Cavity Gyrotron (JAEA Mode Series) CVD-Diamond Window: t = mm, - 20 db Reflection Bandwidth = 2.2 GHz Frequency [GHz] Application CD, A=2.6 W7-X UG H, A=3.1 ITER UG H, A=3.6 CD, A=3.1 H, A=4.0 CD, A=3.6 CD, A=4.0 Cavity Mode TE 25,9 TE 31,11 TE 37,13 TE 43,15 TE 49,17 Bessel Zero Relative Caustic Radius C c Normalized Window Thickness [λ] Window Center Frequency [GHz] /2 5/2 6/2 7/2 8/ Max. deviation of C c is 0.22%, therefor max. horizontal output beam shift of only 50µm 16 M. Thumm et al.; Development of a Multi-Purpose, Multi-Frequency Gyrotron for DEMO at KIT

17 17 M. Thumm et al.; Development of a Multi-Purpose, Multi-Frequency Gyrotron for DEMO at KIT

18 Cold Cavity Design Parameter Values Frequency (GHz) 170 / 203 / 236 / 269 Cavity Mode TE 31,11 TE 37,13 TE 43,15 TE 49,17 Cavity Radius R 0 (mm) Beam Radius R e (mm) / 9.10 / 9.06 / 9.04 L1 (mm) 16 L2 (mm) 12 L3 (mm) 16 D1 (mm) 2 D2 (mm) / 1175 / 1443 / M. Thumm et al.; Development of a Multi-Purpose, Multi-Frequency Gyrotron for DEMO at KIT

19 Conventional Cavity TE 43,15 -Mode Gyrotron Multi-Mode Calculations f 0 = GHz (λ 0 = 1.27 mm) Cavity radius mm (loading: 2 kw/cm 2 ) Beam radius 9.06 mm Operating parameters: T, 58 kev, 39 A, velocity ratio α = MW output power (η el = 36 %; with margins) 19 M. Thumm et al.; Development of a Multi-Purpose, Multi-Frequency Gyrotron for DEMO at KIT

20 Gyrotron Simulations with Realistic Beam Parameters With consideration of the perpendicular velocity spread (Gaussian Spread) α spread (rms) (%) With consideration of the radial beam width (Thick beam) (Linear Spread) Radial width (RL = Larmor Radius) Radial Width/λ 0 2*RL *RL *RL *RL *RL Unstable mode M. Thumm et al.; Development of a Multi-Purpose, Multi-Frequency Gyrotron for DEMO at KIT

21 Output Power and Operating Parameters of Conventional Cavity Gyrotron with Wall Loading > 2 kw/cm² Maximum Wall Loading (kw/cm 2 ) Output Power (kw) Beam Energy (kev) Beam Current (A) M. Thumm et al.; Development of a Multi-Purpose, Multi-Frequency Gyrotron for DEMO at KIT

22 Summary & Acknowledgments Conclusions DEMO-compatible 1 2 MW, CW gyrotrons at an operating frequency of GHz are under investigation at KIT. Mode selection strategy including aspects of multi-frequency and steptuning operation has been shown in this presentation. Design of the other gyrotron components (MIG, quasi-optical converter) is currently progressing. Acknowledgements This project has received funding from the European Union s Horizon 2020 Research and Innovation Program under Grant Agreement No The views and opinions expressed herein do not necessarily reflect those of the European Commission. 22 M. Thumm et al.; Development of a Multi-Purpose, Multi-Frequency Gyrotron for DEMO at KIT