We demonstrate that guided resonant modes can be readily observed in asymmetrical photonic crystal slabs on high-index substrates. In spite of the high radiative loss associated with all optical modes in these cases, the guided resonant modes are found to give rise to strong high-Q features in the transmission spectra. Since these photonic crystal structures are far more robust and easier to fabricate than the free-standing photonic crystal membranes used in previous studies of guided resonant modes, detailed studies of relevant optical phenomena and the implementation of proposed applications are greatly simplified.

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Focused ion beam ͑FIB͒ methodologies for successfully milling copper ͑U.S. Patent No. 6,322,672 B1͒ have been demonstrated. Approaches to milling copper ͑Cu͒ are required because standard FIB mill procedures produce rough, uneven cuts that are unsuitable for circuit edits, a principal FIB function. Efforts to develop gas assisted etching ͑GAE͒ processes which would smoothly mill Cu failed because Cu halides are not volatile and remain on the substrate as corrosive electrically conductive debris. Single crystal studies show that Cu grains with different crystal orientations vary in mill rate by as much as 4ϫ. Moreover, the ͑110͒ crystal orientation, which mills most slowly, forms a Cu 3 Ga phase when milled with a focused Ga ion beam. This phase is particularly resistant to milling and, in polycrystalline Cu, propagates during the milling operation, contributing to the uneven trench profiles. CoppeRx, a novel scan strategy, cleanly and uniformly removes polycrystalline Cu with minimal damage to the underlying dielectric. CoppeRx minimizes the formation and propagation of the Cu 3 Ga phase and equalizes the etch rates of the Cu crystal orientations. The CoppeRx strategy includes the milling of an ''egg crate'' topography to minimize the propagation of the Cu 3 Ga phase and the creation of a heavy atom sacrificial layer of the Cu surface ͑U.S. Patent Application No. 20010053605͒ which scatters the incident Ga ion beam, thereby reducing the channeling influence on Cu milling rates. This heavy atom layer is created by flowing W͑CO͒ 6 vapor during the FIB milling process. The CoppeRx scan strategy is especially beneficial for milling thick ͑Ͼ0.8 m͒ Cu structures with large, prominent grains. Because Cu interconnect lines are relatively thin ͑Ͻ0.4 -0.5 m͒, grain-related milling roughness is less of a problem. The CoppeRx egg crate topography and W scattering layer are not required. Instead, the successful cutting of 40 ohm Cu interconnect lines to produce Ͼ20 M ohm open circuits is achieved by flowing O 2 or H 2 O during the milling process ͑U.S. Patent No. 6,322,672B1͒. The O 2 /H 2 O flow smoothes the Cu milling by producing an amorphous surface oxide, thereby reducing channeling, and by enhancing the etch selectivity for Cu relative to the surrounding and underlying SiO 2 based dielectric. These interconnect cuts have been routinely done at the bottom of high aspect ratio holes ͑e.g., 1ϫ1ϫ9 m͒.

A divertor coil set has been installed on the Tara tandem mirror for stabilization of m = 1 flute-like modes. We discuss the effectiveness of divertor stabilization in experiments where m = 1 modes are driven to instability by plug electron cyclotron heating (ECH) in an ion cyclotron heated (ICH) plasma. The instability onset is characterized by thresholds in ECH power, fueling rate, ICH power and mapping radius of the divertor null. In general, the stability is enhanced by mapping the null radially inwards into the plasma.The interdependence of these parameters and their effect on equilibrium profiles and stability boundaries are discussed. ii I -INTRODUCTIONRecent designs for mirror confinement devices have attempted to obtain as much axisymmetry as possible within the constraint of stability to interchange modes", 2 . Tara 3 ', and other tandem mirror experiments (TMX-U', Phaedrus 6 , Gamma-10 7 ) have used non-axisymmetric minimum-B field configurations to provide MHD stability at the expense of power consumption, access to the plasma, and transport due to ion drifts across flux surfaces 8 .We have installed a magnetic divertor coil set in the Tara central cell for halo fueling 9 1 0 and axisymmetric stabilization of interchange modes", 2 . In this paper we report on the stabilization of rigid flutelike modes during divertor operation in an axisymmetric field configuration. This instability occurs in these experiments during fundamental electron cyclotron heating (ECH) in one of the axisymmetric plug cells adjacent to the central cell, although it can also be initiated by other power sources or adjustment of input gas pressure or central cell IonCyclotron Heating (ICH) power. We find that the threshold for instability occurs at higher ECH power levels during divertor operation.When driven to instability, the plasma is best described by a rigid gaussian profile rotating azimuthally around the machine axis1 3 . The 1 transition between this behavior and quiescent operation is quite sudden. We describe here the parameterization of the thresholds for loss of stability. The range of conditions for which stable operation is possible is enhanced significantly by operation of the divertor, and scales with the strength of the divertor field.The structure of this paper is as follows: In section II we briefly describe the divertor coil set and operation. In section III we discuss the theoretical reasons which motivated the installation of the magnetic divertor. In section IV we review the nature of the mode under consideration as seen in Tara. In section V we discuss the dependence of stability on key operating parameters. In section VI we discuss the qualitative agreement of results with theory, and several alternative mechanisms which may explain the stabilization. In section VII we summarize our conclusions. II -Divertor Construction and Operation