1 - Nuclear Sciences and Applications - IAEA

218 JET TEAM
0.1
5 10
Input Power (MW)
FIG. 2. Neutron rate as function of input power for RF heating only. Solid squares: enhanced phase.
Open squares: later phase (t > 4.4 s).
peaked than n, within the plasma core. Such behaviour is expected from neoclassical
transport 17,18]. Outside the core, the usual broad n, profiles are observed.
The ratio nI(0)/nI(a/2)=2. As a result, central Zofr is some 30% higher and n/n,
somewhat lower than the average value. Depending on the mix of heating power
applied and the resulting range of O, C and Ni levels obtained, central Zeff after 1 s
varies from 2.5 to 4 and nyn. from 0.75 to 0.5. The core power balance is little
affected by radiated power losses. In the best cases, the period of enhancement
terminates as shown with an abrupt loss of central temperature, density and
accumulation. Sawtooth oscillations do not appear prior to, or during, the times
of interest.
Enhanced core temperatures are obtained only in cases where a strong perturbation
of the density and electron temperature is produced, and for which the RF
resonance was located within the plasma core. The effect is not dependent on a
particular \ spectrum, and has been obtained using either monopole (k,, = 0) or
dipole (ku=7m 1 ) antenna phasing. The enhancement is obtained with H or He 3
minority heating, indicating the effect is not associated simply with a nonmaxwellian
tail produced by second harmonic heating of the backround deuterium.
Neutron emission is predominantly thermal in origin. Enhanced temperatures
and neutron yield are not obtained when the resonance location (resonance
half width 0.3m) is shifted 0.5m from the magnetic axis, to the region outside the