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[parallel] [approx] 4.5 keV with temperature T [approx] 1.5 keV, and the hot tail extends to E[parallel] [approx] 4.5 keV with T > 40 keV. Fokker-Planck computer simulations suggest the cold tail is created by low power, high N[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 electron-cyclotron (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, indicating the EC waves decay into ion modes and electron Bernstein waves during plasma formation. Measured turbulent plasma fluctuations are correlated with decay-wave amplitude. Toroidal currents up to I[sub p] [approx] 1 kA are generated, consistent with theory, which predicts asymmetric electron confinement. 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 [l angle]n[sub e][r angle] = 2 [times] 10[sup 12] cm[sup [minus]3]. The ECCD efficiency [eta] [equivalent to] [l angle]n[sub e][r angle]I[sub p]R[sub 0]/P[sub rf] = 0.003, which is 30%--40% of the maximum achievable LHCD efficiency on Versator. The efficiency falls rapidly to zero as the density is raised above [l angle]n[sub e][r angle] = 3 [times] 10[sup 12] cm[sup [minus]3], suggesting the ECCD depends on low collisionality. X-ray measurements indicate the current is carried primarily by electrons with energies 1 keV [approx lt] E [approx lt] 10 keV.
- Research Organization:
- Massachusetts Inst. of Tech., Cambridge, MA (United States). Plasma Fusion Center
- Sponsoring Organization:
- USDOE; USDOE, Washington, DC (United States)
- DOE Contract Number:
- AC02-78ET51013
- OSTI ID:
- 7154324
- Report Number(s):
- PFC/RR-92-13; ON: DE93002333
- Resource Relation:
- Other Information: Thesis (Ph.D.)
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
VERSATOR TOKAMAK
NON-INDUCTIVE CURRENT DRIVE
ANTENNAS
COMPUTERIZED SIMULATION
DISTRIBUTION FUNCTIONS
ECR HEATING
ELECTRON CYCLOTRON-RESONANCE
ELECTRON TEMPERATURE
EXPERIMENTAL DATA
FOKKER-PLANCK EQUATION
LOWER HYBRID CURRENT DRIVE
PLASMA DIAGNOSTICS
CLOSED PLASMA DEVICES
CYCLOTRON RESONANCE
DATA
DIFFERENTIAL EQUATIONS
ELECTRICAL EQUIPMENT
EQUATIONS
EQUIPMENT
FUNCTIONS
HEATING
HIGH-FREQUENCY HEATING
INFORMATION
NUMERICAL DATA
PARTIAL DIFFERENTIAL EQUATIONS
PLASMA HEATING
RESONANCE
SIMULATION
THERMONUCLEAR DEVICES
TOKAMAK DEVICES
700350* - Plasma Production
Heating
Current Drive
& Interactions- (1992-)