Generation of Suprathermal Electrons During Plasma Current Startup by Lower Hybrid Waves in a Tokamak PDF Download
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Category :
Languages : en
Pages : 8
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Author:
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Category :
Languages : en
Pages : 8
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Author:
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Category :
Languages : en
Pages :
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Lower hybrid waves have been used on the PLT tokamak both to start the plasma current and to ramp it up from pre-existing levels. The waves, at 800 MHz, were launched from a 6-waveguide grill. The phasing between adjacent guides could be selected electronically, and thus the launched spectrum could be set and changed at will. For start-up, the waveguide phase difference was initially set at 0° in order to create a plasma, then switched to 90° to drive the current. Over 100 kA of plasma current, at a density of 0.5 to 1 x 1012 cm−3, was generated in this manner. Ramp-up experiments were performed under a wide variety of conditions. The most efficient ramp-up was found at the lowest plasma densities and with the fastest launched spectrum (n/sub e/ approx. 2 x 1012 cm−3, N/sub parallel/ approx. 1.6 peak); approx. 20% of the launched RF power was converted to (increased) poloidal field energy. All of the ramp-up results are in excellent agreement with a theory which determines the efficiency of ramp-up from the consideration of the relative energy losses of the superthermal current-carrying electrons to collisions and to the opposing inductive E-field.
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Category : Aeronautics
Languages : en
Pages : 1126
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Lists citations with abstracts for aerospace related reports obtained from world wide sources and announces documents that have recently been entered into the NASA Scientific and Technical Information Database.
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Category : Controlled fusion
Languages : en
Pages : 160
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Category : Power resources
Languages : en
Pages : 526
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ISBN:
Category : Science
Languages : en
Pages : 724
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Author: Junji Fujita
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Category : Laser plasmas
Languages : en
Pages : 156
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Category : Electron distribution
Languages : en
Pages : 36
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Author:
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Category :
Languages : en
Pages :
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The circuit equations for current-drive in a start-up or ramp-up plasma are derived by finding appropriate response functions in the presence of an electric field. The effect of arbitrary wave-induced fluxes on runaway production and current generation can then be determined. An interpretation of the rather remarkable PLT ramp-up efficiencies, difficult to explain using the steady-state efficiency, is now possible. A parameter regime, available also on reactor-grade devices, is identified wherein quick ramp-up by lower-hybrid waves may be efficient.
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Languages : en
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Lower hybrid waves with a narrow high velocity wave spectrum have been used to achieve high central electron temperatures in a tokamak plasma. Waves with a frequency of 2.45 GHz launched by a 16-waveguide grill at a power level less than 600 kW were used to increase the central electron temperature of the PLT plasma from 2.2 keV to 5 keV. The magnitude of the temperature increase depends strongly on the phase difference between the waveguides and on the direction of the launched wave. A reduction in the central electron thermal diffusivity is associated with the peaked electron temperature profiles of lower hybrid current-driven plasmas. 16 refs.
