A. Sykes R. J. Akers L. C. Appel P. G. Carolan J.W. Connor N. J. Conway G. F. Counsell A. Dnestrovskij Yu.N. Dnestrovskij M. Gryaznevich P. Helander M. P. S. Nightingale C. Ribeiro C. M. Roach M. Tournianski M. J. Walsh H. R. Wilson The S
H -mode operation has been achieved in high current I p . 200 kA plasmas in the START spherical tokamak for both neutral-beam-injection-heated and Ohmic discharges. The transition to H mode features the development of well-defined edge pedestals in density and temperature, which signifies the formation of an edge-transport barrier, and associated e…
PublishedN. J. Conway P. G. Carolan M. R. Tournianski
A 20-chord Doppler spectrometer is used on the START spherical tokamak to record charge-exchange recombination (CXR) spectra. ‘‘Passive’’ radiation, mostly from near the plasma edge, is also present, and comes from electron-impact excitation of C5+ as well as C6+ CXR due to thermal neutrals. The relatively wide neutral beam, together with t…
PublishedD. A. Gates R. Akers L. Appel P. G. Carolan N. Conway et al.
The Small Tight Aspect Ratio Tokamak (START) [A. Sykes et al., Nucl. Fusion 32, 769 (1994)] spherical tokamak has recently achieved the record value of toroidal beta~30% in a tokamak-like configuration. The improvements that have made these results possible are presented along with a description of the global equilibrium parameters of the discharge…
PublishedP. G. Carolan N. J. Conway C. A. Bunting P. Leahy R. O’Connell et al.
Fast charge-coupled device (CCD) detector arrays placed at the output of visible spectrometers are used for multichord Doppler shift analyses on the COMPASS-D and START tokamaks. Unequal magnification in the horizontal and vertical axes allows for optimal matching of throughput and spectral resolution at the CCD detector. This involves cylindrical …
PublishedP. G. Carolan R. O’Connell
A multianode photomultiplier (8X8 anodes of 2.5X2.5 mm2) is used to detect a collection of spectra in a high dispersion echelle spectrometer. A cylindrical lens is placed at the output slit to increase the dispersion at the photomultiplier. The cross talk between adjacent spectra is non-negligible (although
PublishedR. J. Colchin P. G. Carolan R. Duck T. Edlington S. K. Erents et al.
Low-aspect-ratio tokamaks offer both the economic advantage of smaller size and a number of physics advantages which are not available at conventional aspect ratio. The Small Tight Aspect Ratio Tokamak (START) [Fusion Technology 1990, edited by B. E. Keen, M. Huguet, and R. Hemsworth (North-Holland, Amsterdam, 1991), Vol. 1, p. 353] was conceived a…
PublishedP. G. Carolan A. C. Selden C. A. Bunting P. Nielson
The superior etendu available from a Fabry-Perot spectrometer is also accessible when used in reflective mode in producing a narrow bandwidth rejection, or “notch,” filter. We consider the instrumental defects and the practical effects involved in realizing a useful device. A simple figure of merit is obtained which allows the Fabry-Perot chara…
PublishedA. W. Morris P. G. Carolan Fl Fitzpatrick T. C. Hender T. N. Todd
The question of the influence of nonaxisymmetric field perturbations on tokamaks is investigated. Recent experiments in the COMPASS-C tokamak [in Proceedings of the 15th Symposium on Fusion Technology, Utrecht (North-Holland, Amsterdam, 1989), Vol. 1, p. 3611 with externally applied helical fields reveal that magnetic islands do not appear until th…
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