Target Specifications & History

(to avoid reinventing a broken wheel!)

2nd December 2009

Chris Booth

The University of Sheffield

• 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

• 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 solutions1) Rotating arm A

3

R

5 mm

• 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 solutions2) Rotating arm B

4

R

30 mm

• 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 solutions3) Linear motor options

5

• 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 solutions4) Linear motor variations

6

drive target