1. Target Specifications & History (to avoid reinventing a broken wheel!) 2 nd December 2009 Chris Booth The University of Sheffield

2. Enter last 1-2 ms of beam Not disturb next injection Variable dip depth –Required entry into beam unknown, but ~5 mm –Beam shrinkage 17.8 mm –Travel  25 mm –Reproducibility ~0.2 mm Accurately synchronised to ISIS, drift/jitter < 0.2 ms Frequency 1 Hz or faster Target titanium 1 mm across beam, 10 mm along Slit across beam pipe 2 mm wide max. Radiation hard, UHV materials Resonant system disfavoured. On-demand actuation preferred. Original Specification (2003) 2

3. Axis  beam (motion // beam) –Single arm (plus counterweight) –5 mm and 2 ms entry into beam –  = 12.6 mrad –  = 2  (1 Hz) –Arm length R = 63 m (!) –Target velocity 396 ms -1 (!) –Multiple spokes makes R even greater –Target position & adjustability – see next slide Considered solutions 1) Rotating arm A 3 R  5 mm

4. Axis // beam (motion across beam) –1 (or n) spokes –Cross ~ 30 mm in 2 ms –V = 15 ms -1 ;  = 2  /n; R = 2.4 n m –N.B. Slot across beam-pipe (not allowed!) –Source of particles moves significantly –Axis of rotation must be adjustable vertically (to control depth) –Rotary motion – bearings in vacuum Considered solutions 2) Rotating arm B 4 R 30 mm

5. Fixed coils, moving magnet –Brushless, easier to cool coils,... Bearing-free design – shaft supported on diaphragm springs –Required travel  large springs (~150 mm diameter) –Designed fatigue-free –Tests: unstable. Did not align shaft when extended. Non-lubricated bearings –Ceramic on titanium –Brass on titanium –Leaded bronze –DLC on DLC Considered solutions 3) Linear motor options 5

6. External linear drive –Transmission through diaphragm/bellows to vacuum region –Caburn designers/engineers could not guarantee lifetime Linear drive + lever –Smaller amplitude drive + mechanical advantage –Fail-safe (falls out of beam) –Possibly combined with diaphragm? –Stiff enough lever ( I -beam)  too much inertia for required acceleration –Bearing again (with lateral forces) Considered solutions 4) Linear motor variations 6 drive target