Lower Hybrid Current Drive Experiments in Alcator C-Mod

Conference · Tue Oct 09 04:00:00 EDT 2007 · AIP Conference Proceedings

OSTI ID:961751

A Lower Hybrid Current Drive (LHCD) system has been installed on the Alcator C-MOD tokamak at MIT. Twelve klystrons at 4.6 GHz feed a 4x22 waveguide array. This system was designed for maximum flexibility in the launched parallel wave-number spectrum. This flexibility allows tailoring of the lower hybrid deposition under a variety of plasma conditions. Power levels up to 900 kW have been injected into the tokomak. The parallel wave number has been varied over a wide range, n|| ~ 1.6–4. Driven currents have been inferred from magnetic measurements by extrapolating to zero loop voltage and by direct comparison to Fisch-Karney theory, yielding an efficiency of n20IR/P ~ 0.3. Modeling using the CQL3D code supports these efficiencies. Sawtooth oscillations vanish, accompanied with peaking of the electron temperature (Te0 rises from 2.8 to 3.8 keV). Central q is inferred to rise above unity from the collapse of the sawtooth inversion radius, indicating off-axis cd as expected. Measurements of non-thermal x-ray and electron cyclotron emission confirm the presence of a significant fast electron population that varies with phase and plasma density. The x-ray emission is observed to be radialy broader than that predicted by simple ray tracing codes. Possible explanations for this broader emission include fast electron diffusion or broader deposition than simple ray tracing predictions (perhaps due to diffractive effects).

• Research Organization: Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States)
• Sponsoring Organization: USDOE Office of Science (SC)
• OSTI ID: 961751
• Report Number(s): PPPL-4263
• Conference Information: Journal Name: AIP Conference Proceedings Journal Volume: 933
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
CYCLOTRONS
DEPOSITION
DIFFUSION
EFFICIENCY
ELECTRON TEMPERATURE
ELECTRONS
FLEXIBILITY
KLYSTRONS
LOWER HYBRID CURRENT DRIVE
Lower Hybrid Current Drive
PLASMA
PLASMA DENSITY
SAWTOOTH OSCILLATIONS
WAVEGUIDES
tokamak
rf heating