SVET : SLS Vertical Emittance Tuning

The main objective of SVET is to upgrade the Swiss Light Source (SLS) at PSI to enable R&D on ultra-low emittances.

The CLIC damping ring aims at delivering an e+/e- beam with ultra-low vertical normalized emittance of 5 nm for achieving the required collider luminosity. This corresponds to a geometrical emittance of less than 1 pm at 2.86 GeV, which has never been reached in any lepton storage ring, especially for bunch currents equivalent to the ones of the CLIC DR, i.e. in a regime where collective effects and especially intra-beam scattering (IBS) are predominant. The SuperB e+e- factory aims at comparable vertical emittances of down to 4 pm at 7 GeV at bunch currents in the order of 2 A, i.e. again in IBS dominated regime. These ultra-low emittances are also extremely important for present and future light sources such as the Swiss Light Source storage ring (SLS) at PSI and MAX-IV at Maxlab in Sweden.

In order to obtain and control these ultra-low emittances, not only low magnetic error tolerances and extremely good control of the geometric alignment of the magnets are required, but also a combination of diagnostics for precise beam size, position and emittance measurement as well as on-line correction techniques. The suppression of betatron coupling and controlled excitation of vertical dispersion in order to adjust the vertical emittance to an optimum value with respect to brightness and lifetime are necessary. All these issues will have to be addressed in a dedicated R&D program, which will comprise three fields of activity:

    a) Suppression of betatron coupling and vertical dispersion by utilizing skew quadrupoles,

    b) Measurement of small vertical beam size and emittance by means of high resolution
         beam profile monitors,

    c) Measurements of IBS contributions to emittance and of the particle distribution in the
         IBS-halo.

SLS has achieved a vertical geometric emittance of around 3 pm at 2.4 GeV, one of the smallest vertical emittances ever obtained and only a factor 5 larger than the ultimate vertical emittance limit given by the quantum nature of synchrotron radiation. In this respect, SLS represents the ideal test-bed for deploying diagnostics and testing experimental approaches with a goal of reaching sub-pm vertical emittance beams. Recognizing this unique opportunity, PSI has agreed to allocate machine time to this important R&D program, making the SLS - a user facility by nature - an important R&D infrastructure.

Image of vertically polarized synchrotron radiation at SLS