Analysis of collective Thomson scattering for alpha particles diagnostics on tokamaks
An analysis is carried out of the alpha particles feature of the scattering dynamic form factor in a tokamak configuration. It is shown that the magnetic field in general causes two main effects: (1) a frequency roll-off (i.e. a decrement) affects the form factor for small values of the angle between the scattering wavevector and the plane perpendicular to the magnetic field, because the electron mobility depends on this angle and (2) the form factor exhibits a frequency modulation due to the ion cyclotron motion. A constraint is derived on the geometry of the experiment in order to avoid these effects. The ratio between the alpha and electron signal depends on the Salpeter parameter alpha and on the angle. Another constraint on the geometry results from the condition that this ratio be greater than unity. The presence of the magnetic field also gives a resonant enhancement of the alpha particles dynamic form factor at the lower hybrid frequency; the role of the resonance is outlined and its connection with the electronic roll-off is discussed. Finally, a survey is made of the power and geometry required for experiments using CO(2) laser and 140 GHz gyrotrons as sources, in order to achieve useful signal to noise ratio for the measurement of the alpha particles in the D-T phase of JET.
Bibliographic Reference: Report: RT/FUS/88/30 EN (1988)
Availability: Available from Servizio Studi e Documentazione - ENEA, Centro Ricerche Energia Frascati, C.P. 65 - 00044 Frascati, Roma (IT)
Record Number: 199010505 / Last updated on: 1994-12-01
Original language: en
Available languages: en