A plasma current is initiated and raised to a quasistationary level of about 20 kA by injection of the lower hybrid wave into a cold and low-density plasma produced by electron cyclotron resonance. The plasma current rises more slowly than the experimentally obtained L p /Rp magnetic diffusion time of the bulk plasma. The current rise time is inversely proportional to the bulk electron density, and agrees well with the collision time of the currentcarrying high-energy electrons with the bulk plasma.PACS numbers: 52.40.Db, 52.55.Gb A plasma current generated by an Ohmic heating electric field is maintained by injecting lower hybrid waves (LHW) in many tokamaks. 1 "" 6 These experimental results demonstrate the possibility of a steady-state operation in a future large tokamak.The startup of plasma current by a noninductive method is attractive for the further saving of the volt-seconds of the Ohmic heating transformer.Recently, experiments on current-startup by LHW have been tried in a target plasma produced by LHW alone 7 or by electron cyclotron resonance (ECR). 8 In the WT-2 tokamak, the plasma current increases linearly in time. However, the quasisteady state is not attained since the pulse duration of LHW is relatively short. The realization of the quasisteady state in the plasma current initiated by rf is necessary to clarify the mechanisms of the startup and quasistationary drive and to establish the startup scenario in a future large tokamak.In this Letter, we report on the startup and quasistationary drive of the plasma current by LHW in which the pulse width (=170 ms) is much longer than the experimentally obtained L p /R p time, where L p and R p are the total inductance and resistance of the bulk plasma. The experiments are carried out on the Japanese Institute of Plasma Physics T-IIU tokamak (major radius R 0 = 0.93 m and minor radius a L = 0.25 m). First, a cold and lowdensity target plasma is produced by the electron cyclotron wave of an ordinary mode (/=35.5 GHz) which is injected from the low-field side. 9 The electron cyclotron-resonance layer (ECR layer) is located at R =0.91 m where the toroidal field B t is L27 T. The initial filling-gas pressure P is 5x 10" 5 Torr for hydrogen. The electron temperature and density of the ECR plasma are about 20 eV and 2x 10 12 cm" 3 , which are measured by a movable floating double probe. Next, the LHW is injected into the ECR plasma via the launcher of a pair of C-shaped waveguides. 4 The calculated spectrum of the power emitted from the waveguides has a wide spread of parallel refractive index (n\\) from 4 to 1.4, which corresponds to a critical value of the accessibility condition for n e = 2x 10 12 cm -3 . In the current startup by rf alone, it is particularly essential to control the vertical field carefully. A quasistationary vertical field of about 10 G is always applied at the beginning of the LHW pulse to bring the Larmor radius of a high-energy electron beam inside the vacuum vessel, 10 where the stray field is estimated at below 2 G under this exper...

For any s ∈ [−∞, 0] and oriented homology 3-sphere Y , we introduce a homology cobordism invariant rs(Y ) whose value is in (0, ∞]. The values {rs(Y )} are contained in the critical values of the SU (2)-Chern-Simons functional of Y , and we have a negative definite cobordism inequality and a connected sum formula. As applications, we have several new results on the homology cobordism group. As one of such results, we give infinitely many homology 3-spheres which cannot bound any definite 4-manifold. As another result, we show that if the 1-surgery of a knot has the Frøyshov invariant negative, then all positive 1/n-surgeries of the knot are linearly independent in the homology cobordism group. In another direction, we use {rs} to define a filtration on the homology cobordism group which is parametrized by [0, ∞]. Moreover, as a hyperbolic example, we compute an approximate value of rs for the 1/2-surgery along the mirror of the knot 52 in Rolfsen's knot table. Z 6.2. A pseudometric on Ker h 1

A nearly-cylindrical column of laser-produced plasma has been generated successfully in a uniform magnetic field. The radius of the column initially increases and then decreases (bouncing motion). In the vicinity of the outer surface of this plasma column, where there is a steep density gradient with scale length shorter than the local ion Larmor radius, an azimuthal modulation appears in the plasma luminosity. This is indicative of flute-like instability with the azimuthal wave number k ⊥∼4×103 B 0.8 (in MKSA units). The dispersion equation based upon the linearized Vlasov equation with the local approsimation is derived and the occurrence of the lower-hybrid-drift instability is predicted. Fairly good agreement is found between theory and experiment.

No abstract