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Runaway Electron Mitigation Collaboration on J-TEXT

Runaway Electron Mitigation Collaboration on J-TEXT. Collaborating Institutions:. David Q. Hwang UC Davis Sixth US-PRC Magnetic Fusion Collaboration Workshop. Application of accelerated CT for Runaway Electron (RE) mitigation. RE Simulation**.

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Runaway Electron Mitigation Collaboration on J-TEXT

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  1. Runaway Electron Mitigation Collaboration on J-TEXT Collaborating Institutions: David Q. Hwang UC Davis Sixth US-PRC Magnetic Fusion Collaboration Workshop

  2. Application of accelerated CT for Runaway Electron (RE) mitigation RE Simulation** ** Smith, H.M. et al. Plasma Phys & Control Fusion 51(2009) 124008

  3. Theoretical Comparison of Bremsstrahlung vs. Collision* Comparison of stopping power of RE in various noble gas media by collisional (dashed lines) and bremsstrahlung cooling (solid lines) * Bakhtiari, M., G.J. Kramer, M. Takechi, H. Tamai, Y. Miura, Y. Kusama, and Y. Kamada, Role of Bremsstrahlung Radiation in Limiting the Energy of Runaway Electrons in Tokamaks. Physical Review Letters, 2005. 94(21): p. 215003.

  4. Experimental setup for Present CT Injector

  5. Formation Circuit Injector Acceleration Circuit Saturable core inductor. The CTIX injector is unique: (1) the injector operates repetitively, (2) breakdown and formation are initiated by fast gas injection, and (3) the acceleration bank is delayed and switched with saturable core inductors. 100 ohm Power supply 20 kV, 8 kW 50 micro F 40 kV 720 kA 0.15 micro F 50 kV 500 ohm 100 ohm Power supply 20 kV, 8 kW 50 micro F 40 kV 720 kA 0.15 micro F 50 kV 500 ohm

  6. CT Penetration of Vacuum Magnetic Field * Hwang et.al , Nucl. Fusion 40,#5 (2000)

  7. Ratio of Magnetic Field to Wave Forces * Fwave/ Ffield Plasma-beta * Newcomb MHD model Phys. : Of Fluids B3 (1991)

  8. Curves of constant magnetic field corresponding to kinetic energy density equaling magnetic energy density show tokamak fueling/impurity injection requirements in this plot of CT velocity vs. mass density.

  9. Additional Magnetic Perturbation Effects by CTs • Compressibility of CT leads to increase of internal magnetic field at stopping location • Condition of stopping is equilibrium of the internal and external magnetic pressure • CT resistivity leads to reconnection of the CT field and remaining tokamak field. • The reconnection will spoil the tokamak field and limit the RE energy (similar to edge magnetic resonance RE mitigation)

  10. Accelerator He Injection No Gas Injection He Injection

  11. Rutherford Backscattering (RBS) spectrum after 20-shot run with Kr puff Si-28 Au-197 Cu-63 Fe-56 Cl-35 Cr-52 Kr-84

  12. New Collaborative Investigation in Runway Electron Mitigation (REM) on J-TEXT Relativistic theory shows RE stopping force by bremsstrahlung cooling can be more effective than collisional stopping of RE. The effect is more efficient at higher RE energy found in larger tokamaks such as EAST, ITER Mitigation most effective by delivery of high-Z ions on the magnetic axis Compact Toroid can deliver noble gas ions to magnetic axis in msec time scale. Collaborative project of high-Z CT injection of J-TEXT disruption studies HEEM Test facility for diagnostics calibration and simulation code benchmark

  13. Characteristics of JCT injector Conical Electrodes Initial inner diameter 0.4 m Initial outer diameter 0.5 m Final inner diameter 0.2 m Final outer diameter 0.4 m Straight length 0.5 m Taper length 2 m Stored capacitor energy 250 kJ (formation) 500 kJ (acceleration) Peak current 500 kA (formation) 2 MA (acceleration) CT composition H2 + (Ne, Ar, Kr, Xe) JCT pulsed-power (PFN, switches) JCT injector on J-TEXT JCT injector

  14. High Energy Electron Magnetized (HEEM) test facility for X-ray diagnostics calibration and simulation code benchmarking • Specifications: • Transverse magnetic field: 0.5 T to 1 T • Energetic pulsed electron beam: ~1 MeV at a current of 1 A • HEEM e-beam pulse length: ~10 μs • High-Z CT electron density: ~1015 cm-3 • High-Z CT velocity: ~100 km/s • High-Z CT noble gas species: He, Ne, Ar, Kr, Xe • Purpose: • High-Z CT penetration of a transverse magnetic field • High-Z CT interaction with an energetic electron beam • Testing and calibration of JCT injector, X-ray diagnostics and data acquisition system • Simulation code benchmarking

  15. J-TEXT Collaboration in REM • RE dominated on magnetic axis profile • CT penetration to tokamak center • CT penetration model determined • Internal CT field can spoil the RE acceleration path via reconnection • CT deliver high-Z noble ions in msec time scale • New REM method via Bremsstrahlung cooling • International collaborative experiment on J-TEXT using US JCT injector at RE up to 5 MeV • HEEM test stand for injector, diagnostic calibration and Code benchmark at 1 MeV

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