1. Alternative Targets I. Bailey University of Liverpool / Cockcroft Institute Cockcroft Institute RAL 27 th Sepember 2006

2. Alternative Target Concepts  Gas-cooled –Initial study from LLNL - W. Stein  Radiatively-cooled –BINP high-density graphite target  Liquid metal –BINP - liquid Pb (not suitable for baseline) –Cornell - Hg  Crystallized W –KEK (not suitable for baseline?)  Application of baseline target to alternative positron source designs

3. Compton Source Requirements  Total gamma flux power –100kW  Average heat load on the target – 1.9 kW (error factor ~ 1.5)  Gamma-ray energy –30 MeV (monochromated)  Target material –Tungsten (Z=74) is proposed for Compton source. –Pair creation cross-section ~Z 2 –Ionization loss ~ Z –Long time duration for production  smaller stresses  W okay?  Gamma-ray energy –Factor 2 increase in pair creation cross-section. – Ionization loss has very small energy dependence. –Small thermal stress per a positron produced. Kuriki - KEK

4. High Z metals planned to use, such as BiPb, Mercury. BiPb has melting temperature 154 o C. Hg has boiling temperature 354 o C BiPb has melting temperature 154 o C. Hg has boiling temperature 354 o C Hg or BiPb Jet velocity~10m/s Profile of jet~ 1.5x4 mm 2 Calculations show absolute feasibility of this approach LIQUID METAL TARGET Flange diameter 2¾”Hg jet uses latent heat of vaporization

5. Lens with shield Hg or BiPb target unit Collimator Cryo plumbing Flange diameter 2 ¾ in FULLY ASSEMBLED UNIT

6. As soon as the temperature profile is known, the thermal pressure p T can be expressed where characterizing the ratio of the thermal pressure to the specific thermal energy called Grüneisen coefficient. Instant position of the bunch moving in the target, at the left (one frame from movie) Isotherms after the bunch passage, at the right. MODELING OF PULSED HEATING

7. Discussion  Cross-overs between target designs  Are there alternative designs we should be investing more / less effort in?  Is the community large enough to sustain so many alternatives?  Which target designs apply to which source concepts (conventional / Compton / baseline)?