A synchrotron radiation source emits coherent infrared (IR) radiation when the electron bunch length is comparable to the wavelength of the emitted radiation (see for example [1,2]). To generate coherent radiation in the far IR (THz) region, a 'low alpha mode' has been devised at the ANKA storage ring operating at 1.3 GeV. The corresponding lattice has a significantly reduced momentum compaction factor. The spectral dependence of the emitted radiation is recorded at the ANKA-IR beam line, where the synchrotron light is produced in the fringe field of a bending magnet [3]. This edge radiation has the advantage of being more collimated than constant field radiation. This allows the observation of frequencies down to 1 cm −1 through a modest vertical aperture, which would not be possible with classical constant field emission due to the increasing beam divergence with decreasing frequency. The onset of coherent emission is found at a synchrotron frequency of about 10 kHz. At 5 kHz, an intensity enhancement of up to 5 orders of magnitude, with respect to the incoherent emission, is observed in the spectral range between 1 and 65 cm −1 .

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The electron storage ring at ANKA is designed as a variation of an eightfold DBA structure. Since its commissioning the facility has been operated with zero dispersion in the long straight sections resulting in an emittance of about 100 nmrad. Since mid 2004 ANKA is operated with dispersion distributed over the complete ring thus reducing the emittance to 50 nmrad. Optics calculations and measurements as well as operational experience will be discussed. In order to reduce the losses due to Touschek scattering, a lengthening of the bunches was done by modulation of the main frequency with twice the synchroton frequency. An increase of the lifetime by 5 h could be achieved. EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH CERN -AB Department AbstractThe electron storage ring at ANKA is designed as a variation of an eightfold DBA structure. Since its commissioning the facility has been operated with zero dispersion in the long straight sections resulting in an emittance of about 100 nmrad. Since mid 2004 ANKA is operated with dispersion distributed over the complete ring thus reducing the emittance to 50 nmrad. Optics calculations and measurements as well as operational experience will be discussed. In order to reduce the losses due to Touschek scattering, a lengthening of the bunches was done by modulation of the main frequency with twice the synchrotron frequency. An increase of the lifetime by 5 h could be achieved.

A synchrotron radiation source emits coherent infrared (IR) radiation when the electron bunch length is comparable to the wavelength of the emitted radiation (see for example [1, 2]). To generate coherent radiation in the far IR (THz) region, a 'low alpha mode' has been devised at the ANKA storage ring operating at 1.3 GeV. The corresponding lattice has a significantly reduced momentum compaction factor. The spectral dependence of the emitted radiation is recorded at the ANKA-IR beam line, where the synchrotron light is produced in the fringe field of a bending magnet [3]. This edge radiation has the advantage of being more collimated than constant field radiation. This allows the observation of frequencies down to 1 cm −1 through a modest vertical aperture, which would not be possible with classical constant field emission due to the increasing beam divergence with decreasing frequency. The onset of coherent emission is found at a synchrotron frequency of about 10 kHz. At 5 kHz, an intensity enhancement of up to 5 orders of magnitude, with respect to the incoherent emission, is observed in the spectral range between 1 and 65 cm −1 .

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