Tungsten Powder Test at HiRadMat Scientific Motivation

1. Tungsten Powder Test at HiRadMatScientific Motivation P. Loveridge, T. Davenne, O. Caretta, C. Densham, J. O’Dell, N. Charitonidis 23 April 2011

2. Motivation • Designing targets for new accelerator based facilities is becoming more and more challenging due to increasing accelerator beam power and the associated power deposition in the target. • Targets must sometimes accommodate significant power deposition in continuous form or sometimes as an intense pulse followed by an interval of cooling. • Maintaining the target temperature and stress levels within safe limits is the main design driver and results in increasingly elaborate designs as time averaged and pulse power deposition are increased Solid peripherally cooled targets Segmented Targets Flowing or rotating Targets Increasing Power Deposition

3. Solid targets T2K target designed for 750kW beam Prefer small diameter to conduct heat to surface Helium cooling Titanium target body Graphite(ToyoTanso IG-43) Ti-6Al-4V tube and windows (0.3 mm thick) Limit of approximately 1MW for peripherally cooled solid targets Graphite to titanium diffusion bond Prefer large beam sigma to reduce dynamic stress due to pulsed beam ~940 mm

4. Segmented targets ISIS Euronusuperbeam Packed bed Concept for 4MW beam Increased surface area. Coolant reaching maximum energy deposition region. Reduced static and dynamic stresses. Increased beam power possible with thinner plates

5. Flowing and rotating targets SNS mercury target Continuously refresh target material to accommodate multi-MW power deposition 5MW ESS target wheel concept Gap of 2mm

6. Limitations of target technologies Flowing or rotating targets Segmented Peripherally cooled monolith

7. Thermal Shock in liquid targets Merit, Flowing mercury jet 14GeV proton beam Kirk et al. Pulsed proton irradiation of mercury target. Cavitation of mecury causing damage to annealed stainless steel containment LANSCE-WNR Riemer et al.

8. Is there a ‘missing link’ target technology? LIQUIDS SOLIDS Contained liquids Open jets Flowing powder Monolithic Segmented Some potential advantages of a flowing powder: Resistant to shock waves Quasi-liquid: can be conveyed in a pipe Offline cooling Few moving parts Mature technology Areas of concern can be tested off-line

9. Potential Multi-MW Powder Target Applications Open jet: Contained discontinuous dense phase: Powder target integrated with magnetic horn for superbeam Contained continuous dense phase: Powder target integrated with solenoid for Neutrino factory

10. Tungsten Powder Test Programme Low Velocity 2 1 3 High Velocity 4 1. Suction / Lift 2. Load Hopper 3. Pressurise Hopper 4. Powder Ejection and Observation • Plant at RAL developed to do offline testing • Dense phase and lean phase transport • Erosion studies • Heat transfer and cooling of powder

11. Motivation for in-beam powder test • Splash and cavitation in a liquid (mercury) is a result of propagation and reflection of pressure waves through a continuous medium. • It has been asserted that powder will not be subject to splashing or violent events because of its discrete nature. Individual powder grains do not easily transmit pressure waves to neighbouring grains and as such pressure waves tend to be contained within the grains. • A mechanism for a powder eruption has been identified as a result of a beam induced pressure rise in the carrier gas. The expansion of the carrier gas may be violent enough to aerodynamically lift some powder. While this is a potentially interesting threshold to find we expect that it will confirm that eruption velocities are small compare to the splashing velocities observed with mercury. • In order to confirm these assertions the response of a powder target to the proton beam must be tested to definitively answer the following two questions • Will a powder target splash/erupt? • Can you propagate a pressure wave through a powder target to its container?

12. Mercury Thimble In-beam test