1. Present status of production target and Room design Takashi Hashimoto, IBS/RISP 2015, February

2. Production target

3. Production target at KOBRA We are planning two production target system. 1.Solid state target 2.Cryogenic gas target Requirements - for solid state target high beam intensity capability (Example: beam condition: 238 U, 20 MeV/u, 100 pnA, target: 9 Be, 0.1 mm → heat deposit in target: 174 W) - for cryogenic gas target Heat deposit of exit window is limited about 2W. (ref. CRIB cryogenic gas target) Are there methods of heat reduction? (direct cooling etc…)

4. Production target at KOBRA Solid state target There are three candidates. Water cooling target cooling target using cold head rotating target cooling water Liq. N2 reserver The consideration is start from a water cooling target, since the structure is simple and handling is easy. Conceptual models

5. Production target at KOBRA Conceptual design of a water cooling target270 mm 100 mm Target size 30 x 30 mm 100 mm 50 mm Target : Be Target holder : Cu Target ladder : Cu

6. Simulation of target temperature (ANSYS) Beam spot size: 1mm , target material and thickness: Be, 0.1 mm Start temperature: 22 ℃, flow rate of cooling water: 120 ml/sec Malting point of Be Maximum heat loss on the target: 50 W Maximum beam intensity 238 U, 20MeV/u case: ~ 29 pnA 96 Zr with 20 MeV/u case: ~85 pnA 12 C with 20 MeV /ucase : ~3500 pnA Typical simulated result (50W deposit) Production target at KOBRA

7. Parameter dependence of maximum temperature of the production target - Most effective parameter: Thermal conductivity of target (green line). - Effect of temperature of target ladder (red line) is small The advantage of “Cold head” type target is small

8. Production target at KOBRA Other problem of “Cold head” type target Target ladder is shrinking in cooling process. Since Thermal shrinking rate of ladder (Cu) and target (Be) is different, the target becomes bend. (In the calculated case, the target is bended about 0.2 mm. ) There is possibility that the target is broken in cooling process. Position displacement of Cold head type target A water cooling target is better from this point of view

9. Production target at KOBRA 170 mm 10 mm  (upstream & downstream) Standard design upstream hole size dependence Realistic design - Optimize of the hole size of target holder - Downsizing If the hole size is smaller, we can get better cooling effect. 2 mm 5 mm 8 mm 10 mm 15 & 20 mm The maximum heat deposit is increased to 98 W from 76 W by changing the upstream hole size from 10mm to 5 mm. If the both of hole sizes are 5 mm, The acceptable heat deposit become 110 W

10. Production target at KOBRA Beam,  = 2 mm Target holder cover, t = 0.3 mm Target, t = 0.1 mm Target holder base, t = 1.0 mm Target holder support on ladder, t = 5.0 mm Hole  = 5 mm Maximum heat loss on the target: 110 W Maximum beam intensity 238 U, 20MeV case: ~ 63 pnA 96 Zr with 20 MeV case: ~187 pnA 12 C with 20 MeV case : ~7700 pnA Swung Beam,  = 2 mm, 5 degs Picture of beam swinger @ RCNP EN course

11. Production target at KOBRA We need more high power target: Rotating target Measured results of Ar + C case Same structure of Big-RIPS target except for a water cooling system. It is start point of consideration.

12. Production target at KOBRA Cryogenic target The structure is as same as the CRIB cryogenic gas target We just made a conceptual design. We should optimize window material and window size

13. Production target at KOBRA Summary of production target ・ A water cooling target can accept about 50W heat deposit. If the hole size of the target retainer can be made smaller, it is available for higher heat deposit. → In order to fix the hole size, I want to know the final geometrical setup of KOBRA 1 st stage. ・ Maximum energy deposit in target of present design is about 110 W Although this result is not reached our request, the designed target can use on some light to medium mass beam. ・ We will start a simulation of maximum beam intensity on realistic case (for example, 86 Kr + 124 Sn) ・ We are starting the consideration of a rotating target for much higher heat deposit case. (For example, SHE experiment) Start point of consideration is as same the structure of Big-RIPS rotating target. ・ Consideration of a cryogenic target was started. Start point of consideration is as same the structure of CRIB cryogenic target.

14. Room design

15. KOBRA experimental hall - In order to perform a measurement of  -ray with a good S/N ratio, we should make a low-background condition. - Especially, neutron is not only background source but also making radiation damage of Ge crystal. - The main source of backgrounds is production target and beam dump in D1. - These source points should separate from the experimental hall. - We made a conceptual design of experimental hall based on GEANT4 simulation

16. Target chamber Beam dump 238 U KOBRA experimental hall Simulation of neutron shielding efficiency as a function of wall thickness. Simple geometry model ･ A Be target with the thickness of 0.1 mm is inside the target chamber ･ Inside of beam duct and chamber are vacuum ･ A 238 U beam with the energy of 20MeV/u is irradiated the target, and stopped at beam dump. ･ All model surrounded by concrete walls Physics List: QGPS_BERT_HP Shielding efficiency = Number of generated neutrons Number of neutrons out side the wall

17. KOBRA experimental hall Calculation shielding efficiency of generated neutrons at target and beam dump as a function of thickness of concrete wall Efficiency is reached 90 % at 2.5 m and saturated at 3 m. 2.5 – 3 m thick is one of criteria

18. More precise model constructed in GEANT4. KOBRA experimental hall Simulated conditions: ･ 238 U, 20MeV/u ･ Number of injected particles: 10 8 ･ Detector volume set at the hole of beam duct Measured point Measured point

19. KOBRA experimental hall Energy spectra of neutron, proton, electron, and photon at F2 neutron proton electron photon Main component is neutron, especially, low-energy neutron (less than 20 keV component is about 89%) In order to shield low-energy neutron, we can use water tanks, Boron-Nitride, Cd plates etc.. If you need shielding, we can set these materials at around detector. Rough estimation of neutron rate at around F3 Distance between F2 and F3 is about 7200 mm The point like neutron source is assumed at F2 -> 3.4 x 10 4 /m 2 /10 9 Uranium beam Super Clove case: about 15 pps/crystal -> much lower than background from the secondary target!

20. KOBRA experimental hall This design still not fixed because KOBRA design work is not fixed. After fixed the KOBRA design, I will make more realistic one.

21. KOBRA experimental hall Summary of design of experimental hall ・ To decrease neutron background from the production target and beam dump, a thickness of concrete wall must be at least 2.5 m. ・ The realistic model constricted in GEANT4 model space. Simulation results: The main background in the experimental area is low-energy neutron. Estimated background of super clover crystal at F3 is about 15 pps. It is enough lower than the background from secondary target. ・ More precise model will construct after the all design works are fixed.