Pick-up Electrode System for the Cr Stochastic Cooling System

The collector ring (CR) of the FAIR project will include a fast stochastic cooling system for rare isotope beams ( β = 0.83) and antiprotons ( β = 0.97). To reach a good signal to noise ratio of the pick-up even with a low number of particles, a cryogenic movable pick-up electrode system based on slotlines is under development. The sensitivity and noise properties of an electrode array has been calculated using field-simulation and equivalent circuits. For three-dimensional field measurements, an electric nearfield probe moved by a computer controlled mapper has been used. SLOTLINE PICK-UPS FOR THE CR The pick-ups must have a large bandwidth, a high S/N ratio and a large aperture. A new planar electrode is developed [1] to meet these requirements. The electrodes consist of a slotline perpendicular to the beam and a microstrip circuit on the rear side of a planar Al 2 O 3 substrate (Fig. 1, top, left). The mirror currents induce traveling waves in both directions of the slotline. At approx. λ /4 from the end of the slotline, the signal is coupled out to the microstrip line. The λ /4-section at the beginning of the microstrip is a virtual short to one of the two conductors of the slotline. The exact length of these sections has been used to optimize the frequency response. The two signals are coupled out to 110 Ω microstrip lines and are combined in a 100 Ω to 50 Ω Wilkinson combiner. The position of the 110 Ω to 100 Ω transition has also been optimized. The figure 1 (top, left) shows the layout of an eight slot pick-up board on a scale of 1:3. A pick-up tank will consist of two times eight modules. The modules will be cooled down to 30 K using cold heads and will be movable. The two figures below show a simplified design of a module. The right figure shows a cut across the first module prototype. Beside the PU board, the module also contains vertical connection boards. On these Al 2 O 3 boards, a cryogenic low noise amplifier is foreseen. A small antenna can be used to test all connections and amplifiers of the module PICK-UP ELECTRODE SYSTEM FOR THE CR STOCHASTIC COOLING SYSTEM * C. Peschke, F. Nolden, GSI, Darmstadt, Germany Figure 1: Layout of eight slot pick-up module prototype on a scale of 1:3. Wilkinsoncombiner (100Ω/50Ω) slotline/ micro-striptransition Au contact socket to ampl. board 6mm slots milled thru Cu and Al2O3 Al2O3 bridge metalized holes (vias) impedance transformer (110Ω-line) open end (L=8mm) Cu top module side Al2O3 1.9mm without Cu Cu bottom beam side