Current-drive and plasma formation experiments on the Versator-II tokamak using lower-hybrid and electron-cyclotron waves
During lower-hybrid current-driven (LHCD) tokamak discharges with thermal electron temperature T[sub e] [approx] 150 eV, a two-parallel-temperature tail is observed in the electron distribution function. The cold tail extends to parallel energy E[sub [parallel]] [approx] 4.5 keV with temperature T[sup cold][sub tail] [approx] 1.5 keV, and the hot tail extends to E[sub [parallel]] > 150 keV with T[sup hot][sub tail] > 40 keV. Fokker-Planck computer simulations suggest the cold tail is created by low power, high-N[sub [parallel]] sidelobes in the lower-hybrid antenna spectrum, and that these sidelobes bridge the spectral gap, enabling current drive on small tokamaks such as Versator. During plasma-formation experiments using 28 GHz electroncyclotron (EC) waves, the plasma is born near the EC layer, then moves toward the upper-hybrid (UH) layer within 100-200[mu]s. Wave power is detected in the plasma with frequency f = 300 MHz. Measured turbulent plasma fluctuations are correlated with decay-wave amplitude. Electron-cyclotron current-drive (ECCD) is observed with loop voltage V[sub loop] [le] 0 and fully sustained plasma current I[sub p] [approx lt] 15 kA at densities up to [n[sub e]] = 2 x 10[sup 12] cm [sup [minus]3]. The efficiency falls rapidly to zero as the density is raised, suggesting the ECCD depends on low collisonality. The EC waves enhance magnetic turbulence in the frequency range 50 kHz [approx lt] f [approx lt] 400 kHz by up to an order of magnitude. The time-of-arrival of the turbulence to probes at the plasma boundary is longer when the EC layer is farther from the probes.
- Research Organization:
- Massachusetts Inst. of Tech., Cambridge, MA (United States)
- OSTI ID:
- 6921746
- Resource Relation:
- Other Information: Thesis (Ph.D.)
- Country of Publication:
- United States
- Language:
- English
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Current-drive and plasma-formation experiments on the Versator-II tokamak using lower-hybrid and electron-cyclotron waves
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Related Subjects
VERSATOR TOKAMAK
ECR HEATING
LOWER HYBRID CURRENT DRIVE
COMPUTERIZED SIMULATION
DISTRIBUTION FUNCTIONS
FOKKER-PLANCK EQUATION
CLOSED PLASMA DEVICES
DIFFERENTIAL EQUATIONS
EQUATIONS
FUNCTIONS
HEATING
HIGH-FREQUENCY HEATING
NON-INDUCTIVE CURRENT DRIVE
PARTIAL DIFFERENTIAL EQUATIONS
PLASMA HEATING
SIMULATION
THERMONUCLEAR DEVICES
TOKAMAK DEVICES
700350* - Plasma Production
Heating
Current Drive
& Interactions- (1992-)