Destruction of a Magnetic Mirror-Trapped Hot Electron Ring by a - - PowerPoint PPT Presentation
Destruction of a Magnetic Mirror-Trapped Hot Electron Ring by a shear Alfven Wave Y. Wang 1 , W. Gekelman 1 , P. Pribyl 1 , D. Papadopoulos 2 1 University of California, Los Angeles 2 University of Maryland, College Park Work supported by ONR MURI
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Work supported by ONR MURI award (Fundamental Physics Issues on Radiation Belt Dynamics and Remediation), performed at the Basic Plasma Science Facility which is supported by DOE and NSF
1 University of California, Los Angeles 2 University of Maryland, College Park
Destruction of a magnetic mirror-trapped hot electron ring by a shear Alfvén wave
} Radiation Belt Remediation – Artificial
* Image from NASA website
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Destruction of a magnetic mirror-trapped hot electron ring by a shear Alfvén wave
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Destruction of a magnetic mirror-trapped hot electron ring by a shear Alfvén wave
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Fast electrons are generated by Electron Cyclotron Resonant Heating (ECRH) at fmicrowave = 2fce. (Peak Power = 15 kW, pulse duration = 30 ~ 50 ms)
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X-rays are measured outside the 3/8’’ stainless steel vacuum chamber, which cut off x-ray transmission below 100keV.
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The perpendicular E field generates a hot electron population with large perpendicular energies, which grad-B and curvature drift in the θ-direction and form a hot electron ring in the magnetic mirror.
Destruction of a magnetic mirror-trapped hot electron ring by a shear Alfvén wave
5 } The size and position of the hot electron
° = 47
cone loss
θ
° = ! ! " # $ $ % & − =
−
56 1 ) ( 1 tan
min max 1 min
B z B θ
} The axial extension of the ring is
Destruction of a magnetic mirror-trapped hot electron ring by a shear Alfvén wave
6 } The RMF antenna is composed of 2
} Driven by 2 independent RF drivers,
} The shear Alfvén wave dispersion relation
Measured BAlfven vectors 2 m away from antenna
Destruction of a magnetic mirror-trapped hot electron ring by a shear Alfvén wave
} The shear Alfvén wave significantly
} The x-ray signal is modulated at the
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Destruction of a magnetic mirror-trapped hot electron ring by a shear Alfvén wave
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Destruction of a magnetic mirror-trapped hot electron ring by a shear Alfvén wave
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Electrons lost axially travel ~ 11m along the magnetic field line to the anode. X-rays are generated on the mesh anode.
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Electrons lost radially are most likely to strike the waveguide, which is the closest metallic
* Graph normalization: Parallel loss is about 2% of radial loss
Destruction of a magnetic mirror-trapped hot electron ring by a shear Alfvén wave
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Destruction of a magnetic mirror-trapped hot electron ring by a shear Alfvén wave
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} The ring becomes asymmetric in the
} The deformation of the ring gives
Destruction of a magnetic mirror-trapped hot electron ring by a shear Alfvén wave
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} The ring becomes asymmetric in the
} The deformation of the ring gives
Destruction of a magnetic mirror-trapped hot electron ring by a shear Alfvén wave
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} The ring becomes asymmetric in the
} The deformation of the ring gives
Destruction of a magnetic mirror-trapped hot electron ring by a shear Alfvén wave
14 } LH and RH waves of arbitrary
} The x-ray intensity is only related to
} LH and RH waves of same amplitude
and arbitrary phases are mixed.
} The x-ray oscillation is phase locked
to the RH component.
Destruction of a magnetic mirror-trapped hot electron ring by a shear Alfvén wave
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} X-ray spectrum is measured by analyzing pulse heights from the
Destruction of a magnetic mirror-trapped hot electron ring by a shear Alfvén wave
16 } The hot electron ring is deformed in the non-uniform Alfvén wave field,
} Collective modes of the ring, with three dimensional spatial distortion, can
Destruction of a magnetic mirror-trapped hot electron ring by a shear Alfvén wave
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The enhanced loss of fast electrons trapped in a magnetic mirror geometry irradiated by shear Alfvén waves is studied by laboratory experiments.
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Magnetic mirror trapped fast electrons with energies up to 3 MeV are generated by 2nd harmonic Electron Cyclotron Resonance Heating
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Shear Alfvén waves are launched by a Rotating Magnetic Field antenna with arbitrary polarity
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Irradiated by a right-handed circularly polarized shear Alfvén wave, the electrons are lost in both the radial and axial direction with a modulated at fAlfvén. The loss continues even after the termination the wave. }
Test particle simulation confirms that the single particle motion of the trapped fast electrons in presence of a shear Alfvén wave is not adequate to explain the experimental observation.
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No axial loss is observed in the test particle simulation with a wave amplitude measured in the experiment
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It is proposed that the deformation of the hot electron ring drives a collective mode of the ring that leads to electron losses from the magnetic mirror.
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Experimental evidence indicates deformation of the hot electron ring, most likely due to the Ewave×B0 drift in the Alfvén wave field. The deformation grows when the electron azimuthal (grad-B and curvature) drift matches the rotation of the RH shear Alfvén wave. The non-uniform 3D charge distribution in the deformation builds up a large scale global electric field and leads to electron loss.
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