We describe measurements of non-linear interactions between drift waves and law-frequency flute-like modes in the UMIST quadrupole. We present experimental measurements of the bispectrum, and a l s ~ results from a technique of "amplitude correlation" which we believe provides a more direct way of determining the direction of the energy flow. On the basis of the results we propose a model olenergy flaw in the drift-wave spectrum: the observed spectrum contains regions af growth at high frequency and damping at low frequency, with flow dawn the spectrum via a cascade mediated by the flute-like modes.

We have extended the theory for density fluctuations in collisional plasmas by including effects due to the presence of an electromagnetic pump wave, and derived some new and comparatively simple results.

This paper considers the anomalous growth of the radiation intensity, which is caused by an EM wave incident on an inhomogeneous nonstationary plasma. The amplitude of the reflected signal can thus during relatively short time intervals be larger than that of the incident wave. The reason is that the plasma parameters can pass through values, for which linear resonance of leaking surface waves exist. An analytical expression is obtained for the maximum value of the intensity of the reflected wave for two different plasma density profiles, interacting with waves of different polarization. It is shown that the effect can occur repeatedly in a nonstationary plasma with a nonmonotonous density profile, if the region, where the inhomogeneity gradient changes sign, increases.* Below we consider only the case where the planes defined by the vectors k , , E and k, , 6 , ( 6 , is the unit vector along the z-axis) are identical.

A linear thcor) is dcielopcd for drift iiitvcs Bith frequencies betiiecn the electron and ion bouncc frequencics in a collisionless plasma confined to a magnetic quadrupole. A n integro-direreniial cifcntaluc equation U hich allot+s for large ion-Larmor-radius cffccts. temperature gradients. and radial \nri;ition of the eigenrunction is dcriied from the linearized Viasot equation. The fundamental drift mode obscrtcd in the L'MIST stcadj-state quadrupole has one full ttaielength around a closed magnctic field line nith the electrostatic w a t e potential antisJmmciric about the maximum field points. BJ numsrical mitition or the cigcnialue equation. the theoretical dispersion curie for this mode IS extended t o short t i a i c l e n g t h ~ and the \ariation of the corrtsponding potential along a field line 1s determined. I . I S T R O D L ' C T I O SESPERISlEsTAL studies of electrostatic wives in a plasma confined to a magnetic quadrupole are current13 being carried out at the Lnii,ersity of Jlanchester Institute of Science and Technology (UMIST). Drift ivaves x i t h one full u.a\elength around a closed magnetic field line ha\,e been observed to occur spontaneously. C.ARTER et d. (1951 ) ha1.e made a theoretical and experimental study of these drift Lvaves in the UMIST quadrupole. Their theoretical and experimental dispersion curves are in good agreement throughout the entire axial \vave number range from k, 2 0 . 6 cmi to k , 2 1.6 cm-'. The general shape of the theoretical curws shoiving ~a v e amplitude variation along a field iine is also ~vc.11 reproduced b! the experimental results in this k , range. This mode is belicxd to be excited b! . a dissipati\,e trappcdclcctron mechanism \vhich \vas in\,cstigated recently by NI'ILLETT. i ~i tri. ( 19S6)..Although the obsei\'ed spectrum of spontaneous drift \\'a\ es in the ChI!ST

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