Scientific Highlights from the Department "Large Research Facilities" (GFA)
Minimum emittance coupling in the SLS
Recent measurements of the vertical beam size in the SLS have shown that the value of the vertical emittance is ~ 3.2 pm-rad, close to the fundamental limit set by the quantum nature of synchrotron radiation (~ 0.5 pm-rad). The vertical beam size was determined using an optical imaging device especially built for this purpose. In this device the images are formed from vertically polarised light emitted by the electron beam in the visible to UV part of the spectrum. The new monitor allows determination of vertical beam sizes below 10 microns with sub-micron accuracy. The emittance is determined from the measured beam size and prior knowledge of the betatron and dispersion functions at the source point, determined by other means. This extremely small vertical emittance testifies to the careful reduction of transverse emittance coupling (0.05%) obtained in the SLS by virtue of carefully adjusting the settings of the ring lattice. To the best of our knowledge, this is the lowest reported coupling in an electron storage ring.
Increased beam power in the proton cyclotron
As part of the proton cyclotron up-grade it is planned to gradually increase the beam current from 2 mA to 3 mA over the next three years. This up-grade would allow the cyclotron beam power to be increased from its present value of 1.2 MW (already a world record) to a value of 1.8 MW. This up-grade is essentially achieved by improving the high power RF system responsible for accelerating the protons. New 50 MHz copper cavities have recently been installed in the main cyclotron ring to deliver a higher acceleration voltage per turn. The injector cyclotron will also be equipped with new resonators in coming years. An important element in the injection process will be the installation of a “bunching cavity” at the 10th harmonic of the main ring frequency, 500 MHz. This “super-buncher”, recently installed between the injector and main cyclotron, will “prepare” the protons for a more efficient injection into the main ring. Access to the cyclotron during maintenance and repair periods must not be limited by excessive activiation of components. In order to limit the effects of activiation in the accelerator it is important to maintain particle losses at their present value while the current is increased. The challenge therefore is to decrease the the relative losses. Authorisation to perform test runs (one per week) at higher beam power was received from the BAG on the 19th of Septemeber 2007. The latest test resulted in a record maximum current of 2.15 mA at 590 MeV, corresponding to a beam power of 1.27 MW.
The Scientific Reports – containing accounts of research topics from all the different areas – provide an impression of the variety of subjects researched at PSI.
