|dc.description.abstract||Experiments on the STaR-1M tokamak have addressed the following
problems in magnetic confinement fusion research: 1) the attainment of
quasi-continuous operation in a fusion reactor by inductively driving a
current which alternates polarity; 2) plasma heating by inducing
turbulence to enhance the Ohmic dissipation; and, 3) the stability of
tokamak plasmas carrying large currents.
STOR-1M plasmas have major and minor radii of 22 cm and 3.5 cm,
respectively, and are produced with hydrogen at a pressure of 0.9 mTorr.
Typical discharges carry a current of 5 kA with a toroidal field of 1 T.
Around the current peak, electrons at a density of 1 x
heated to a temperature of 80 eV. The ions, with an effective charge
number of 2, reach a temperature of 30 eV. Input energy is confined for
almost 0.1 ms at the current peak, and the total discharge length is
usually 4.5 ms.
To simulate the current reversal phase in an ac tokamak reactor, a
sinusoidal plasma current has been sustained for one cycle. Peak currents
of 8 kA and electron densities of 1.8 x
1013 cm-3have been attained.
The electron density at the reversal is always at least 2 x
The unexpected equilibrium when the toroidal current goes through zero may
be due to vertical plasma currents closing through the limiter or chamber
To induce turbulence for plasma heating, an electric field pulse
of amplitude up to 360 Vim and width 20 µs drives up to 10 kA of current.
on top of a normal discharge. After the pulse, electron temperatures of
300 eV and ion temperatures of 200 eV have been recorded. About 200 µs
after the pulse, the electron density and temperature reach a peak,
implying that containment of energy is enhanced.
The safety factor at the plasma surface during the pulse can be as
low as 1.5. Disruptive behaviour, in the form of current interruption and
loop voltage spikes, is observed when the safety factor is between 1.85
and 2.1. Outside this range, the plasma is grossly stable.||en_US