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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**. - PowerPoint PPT Presentation
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Runaway Electron Mitigation Collaboration on
J-TEXT
David Q. HwangUC Davis
Sixth US-PRC Magnetic Fusion Collaboration Workshop
Collaborating Institutions:
Application of accelerated CT for Runaway Electron (RE) mitigation
RE Simulation**
** Smith, H.M. et al. Plasma Phys & Control Fusion 51(2009) 124008
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.
Theoretical Comparison of Bremsstrahlung vs. Collision*
Experimental setup for Present CT Injector
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.Formation Circuit
Saturable coreinductor.
Acceleration Circuit
Injector
0.15 micro F50 kV
50 micro F40 kV720 kA
50 micro F40 kV720 kA
0.15 micro F50 kV
100 ohm
100 ohm
500 ohm
500 ohm
Power supply20 kV, 8 kW
Power supply20 kV, 8 kW
CT Penetration of Vacuum Magnetic Field
0
0.2
0.4
0.6
0.8
1
1.2
0.01 0.1
Vf /
Vo
1
target field in Teslas
0
0.2
0.4
0.6
0.8
1
1.2
0.01 0.1 1
rigid body theory
Internal compressional CT Energy
* Hwang et.al , Nucl. Fusion 40,#5 (2000)
Ratio of Magnetic Field to Wave Forces Fwave
Ffield 4
pct
Plasma-beta
Fwave/ Ffield
*
* Newcomb MHD model Phys. : Of Fluids B3 (1991)
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.
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)
Accelerator He Injection
No Gas Injection
He Injection
1.2x1015
1.0
0.8
0.6
0.4
0.2
0.0
-0.2
elec
trons
/cm
^3
35302520151050µsec
Interferometer at z=142 cm
60304
1.2x1015
1.0
0.8
0.6
0.4
0.2
0.0
-0.2
elec
trons
/cm
^3
35302520151050µsec
Interferometer at z=142 cm
60323
Rutherford Backscattering (RBS)spectrum after 20-shot run with Kr puff
Si-28
Cl-35Cr-52
Fe-56
Cu-63
Kr-84
Au-197
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
JCT injector on J-TEXTCharacteristics of JCT injectorConical 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
High Energy Electron Magnetized (HEEM) test facility for X-ray diagnostics calibration
and simulation code benchmarking
• Specifications:1. Transverse magnetic field: 0.5 T to 1 T2. Energetic pulsed electron beam: ~1
MeV at a current of 1 A3. HEEM e-beam pulse length: ~10 μs4. High-Z CT electron density: ~1015 cm-3
5. High-Z CT velocity: ~100 km/s6. High-Z CT noble gas species: He, Ne,
Ar, Kr, Xe
• Purpose:1. High-Z CT penetration of a
transverse magnetic field2. High-Z CT interaction with an
energetic electron beam3. Testing and calibration of JCT
injector, X-ray diagnostics and data acquisition system
4. Simulation code benchmarking
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