1. Present status of the target and beam dump system at BigRIPS fragment separator Koichi Yoshida RIKEN High Power Targetry Workshop April 11 – 15, Oxford

2. RI Beam Factory (RIBF) at RIKEN year Beam Intensity From Dr. Kamigaito ・ Operation of RIBF started in 2007. ・ Various ions from p to 238 U can be accelerated. ・ Maximum energy is 345MeV/n for heavy ions up to 238 U ・ Goal intensity is 1 pμA for all ions. Max. Power = 82 kW Goal 49 pnA => 4.0 kW 689 pnA => 11.4 kW 486 pnA * => 12.7 kW 123 pnA => 3.1 kW *fixed-energy mode with single-stage charge stripping SC-ECRIS(28GHz)+RILAC2 K700 fRC SRC

3. RI beam produced (400) for 115 experiments Production yield measured (1404) New isotope 2007, 2008 New isotope 2011 New isotope 2012 New isotope 2013 New isotope 2014 New isotope 2015 RI beam produced at BigRIPS (May 2007 – Dec 2015) Max. intensity 18 O1000 pnA 48 Ca689 pnA 70 Zn123 pnA 78 Kr486 pnA 124 Xe38 pnA 238 U49 pnA 238 U 124 Xe 78 Kr As of Dec. 2015 A total of ~140 new isotopes identified so far. 70 Zn 48 Ca BigRIPS Fragment Separator From SRC Production & separation Particle identification & two-stage separation 1 st stage Wedg e Two-stage separator 2 nd stage Major features of BigRIPS 18O18O Production of RI beams ・ Projectile fragmentation ・ In-flight fission of 238 U beam Photo of 2 nd stage  Large acceptances ±50 mr, ±3%  Superconducting quadrupoles  Pole-tip radius = 17 cm, pole tip field = 2.4—2.5 T  Two-stage separator scheme  2 nd stage with high resolution  Max. Rigidity B  = 9 Tm

4. →2.9MW/m 2 10MW/m 2 154MW/m 2 109MW/m 2 →156MW/m 2 201MW/m 2 12MW/m 2 →1.7MW/m 2 18MW/m 2 39MW/m 2 A/Z=3.5 A/Z=2 238 U→ 100 Sn Target and Beam Dump: Beam Spot and Power Density Beam Power in Target (Be 1/3 Range) Prim.Beam 238 U ~ 48 Ca ~ 12 C 1p  A Trg.Thick 4.4 ~ 17.2 ~ 47.9 [mm] Be Trg.  E 19.7 ~ 3.2 ~ 0.9 [kW/1p  A] in  1mm 25.1 ~ 4.1 ~ 1.1 [kW/mm 2 ] in volume 5.7 ~ 0.2 ~ 0.02 [kW/mm 3 ] ・ Target Beam Spot Size: Small  ~1mm (fwhm) Target Thickness : various thicknesses necessary Optimum thickness ~ 1/3 of the Range. but depends on the experimental request. Material: Be, C, W, Pb, etc. Melt. Point 1284, 3600, 3382, 328 o C ・ Beam Dump placed inside and exit portion of D1 magnet Beam Spot Size, Power Density varied as RI beam setting. R= B  beam / B  separator for the case of 238 U 345MeV/n with 4.4mm Be target, Rotating wheel target with water cooling Stationary system with highly efficient water cooling Beam Power( 238 U 345MeV/n,1p  A=82kW) is dissipated in a target and a beam dump. A/Z=3 R=0.5 R=0.75 R=0.8 R=0.9 R=1.1 R=1.25 R=1.5

5. Design of the target system Made by Dr. Atsushi Yoshida, Toshiyuki Kubo, 2002 – 2006 Nucl. Instr. Meth. A521(2004)65 Nucl. Instr. Meth. A590(2008)204 Nucl. Instr. Meth. A655(2011)10 Sustainable for a 238 U beam at 345 MeV/n, 1p  A Heat Load for 4mm Be target: 17.8 kW  1 mm beam spot : 22.7 kW/mm 2 5.67 kW/mm 3 ANSYS Simulation ->  300 mm rotating disk with water cooling Step-shape disk target: various thicknesses Thin disk Thick disk Beam Air-press. Box Target vacuum chamber double-piped shaft water-cooled disk ANSYS (FEM code) simulation T(water ch.)=25C

6. 6 BigRIPS Target System with maintenance cart target chamber Beam 1m access tunnel *Size : φ30cm *Material : Be, W *Step shaped edge 20,15,10 mm thick for N, Ca, Ar beams 10, 7, 5 mm thick for Kr, Xe, U beams 4, 3,, 2 mm thick for U beam Disk target : for High-power beam  Be : 20,15,10 mm thick Ladder target : for Low-power beam Target ladder (fixed target) *Diameter : ~ 20 mm *Thickness : 1 ~ 20, ~ 60 mm The water way is cut in the ladder. Rotating Target

7. Design of Beam Dump 6.2MW/m 2 4.4MW/m 2 7.9MW/m 2 22.5MW/m 2 20MW/m 2 1.8MW/m 2 45.6MW/m 2 Surface: 242 ℃ Water side:160 ℃ Surface: 369 ℃ Water side:154 ℃ T max = 248 ℃ T max = 394 ℃ T max = 192 ℃ T max = 126 ℃ Reduces Power density Prolongs effective length by 1/sinθ sin 20°= 0.34 sin 6° = 0.1 A Cu-Ag swirl tube with a INCONEL swirl ribbon A Cu screw tube M8 Twist Ratio=3 (24mm) ・ Cooling tubes with high heat transfer coefficient ・ Tilted Wall By N. Fukuda, H. Mizoi, K. Yoshida, and T. Kubo Beam stops in a wall of cooling channel High pressure 1 MPa High Velocity 10 m/s Critical Heat Flux. ~55 MW/m 2 NIM B317(2013)373

8. T max = 350 ℃ （ Rad. Damage) Critical Heat Flux (Strong vaporization of cooling water, 55 MW/m 2 ) BigRIPS Beam Dump Acceptable Beam Power (kW) BigRIPS Acceptance 136 Xe 124 Xe 238 U 86 Kr 78 Kr 48 Ca 40 Ca 238 U(effective) R = Bρ_beam / Bρ_RI beam Operation Limit: a) Critical Heat Flux at cooling channel b) Radiation Damage : T > 350 deg. effect is large. Beam dump accept most of the beam except for 238 U. charge state distribution of 238 U 89,90,91+ after the target helps to reduce the heat density. A special exit beam dump for an intense 238 U beam 1 mm Wall thickness to improve the cooling power (design only) Inner dump Exit dump Wall thickness: 3 mm (can stop 18 O beam) Cu-Cr-Zr Of-Cu Cu-Ag

9. Current Status of the target and beam dump system Construction and Installation was finished at 2006, and operation was started at 2007. (beam intensity is low) Designs of target and beam dump system were based on thermal model simulation. Tests for the cooling power were performed by monitoring the beam spot temperature in parallel with operations. Up to 2014, fixed targets (ladder) were used for experiments. In 2015, rotating targets started for using for experiments. From 2014, effective tests of cooling power became possible. (beam intensity) year Beam Intensity Goal 49 pnA => 4.0 kW, 1.6kW(Be 7mm) 689 pnA => 11.4 kW, 2.2kW(rot Be 15mm) 486 pnA => 12.7 kW, 3.4kW(rot Be 10mm) 123 pnA => 3.1 kW, 1.4kW(Be 12mm) SC-ECRIS(28GHz)+RILAC2 K700 fRC

10. Beam-spot temperature measurement Beam Target chamber (upper view) (1) Fiber (2) CCD (3) IR, Telescope Sapphire view port & Lenz unit mounted on the Target chamber Temperature ( ℃ ) 200-500deg (1) Infrared Fiber Scope (2) IR thermal image camera 12m distance Spot (φ5mm) temperature only Used as on-line monitor 2m up IR camera: Very weak for radiation Can be used only for a short time. IR-FAIX43 200 ~ 500 ℃ InGaAs(1.55μm) TVS-8500 AVIO (Japan) Temp. Calib. Heater+Be plate, TC Spatial resolution (1px =0.5mm) 0.5mm slit -> 2mm(H), 3mm(V)

11. Ladder target (fixed target) Rotating target Be 30mm 、 283pnA 、 1.9kW 234 ℃ Be 15mm 、 280pnA 、 0.88kW 282 ℃ Be 15mm, 420pnA, 100rpm 1.3kW Beam spot 84 ℃ Beam spot temperatures for 48 Ca 345MeV/n Beam

12. Beam spot temperatures for various beam 238 U +Be 124 Xe +Be 78 Kr +Be 48 Ca +Be Be MP (1278 ℃ ) 238 U +W 124 Xe +W 78 Kr +W 48 Ca +W W MP (3387 ℃ ) rot W (ANSYS) rot Be (ANSYS) 345 MeV/n, 1 p  A Beam Be fixed (Cylindrical Model, Beam spot  1 mm) Deposited Power/target thickness is relatively well measure. Various combination of beams and target thicknesses  Tr1 : Beam Spot Temp. = Tr2 + Qin*Ln(r2/r1) /(2πκLtg ) Qin = Ibeam * dE ∝ dE / Ltg (( Cylindrical model )) analytical model Fixed Target: agree with a simple cylindrical model -> heat transfer coeff. Is not important? some data are higher -> thermal contact between target and ladder is bad? ANSYS calc. -> Zeren Korkulu’s talk Rotating Target: higher temperature than the initial estimation -> need detailed simulations Extensive simulations with ANSYS are now undergoing.

13. Beam spot size 4.5x141 8.8x28.1 1.9x23.6 Heat density (MW/m 2 ) 3.88 10.1 53.5 Cooling water speed (m/s) 10 10 10 Max. Temp ( ℃ ) ： 68.7 182 394 Max. Temp at cooling channel( ℃ ) ： 44.2 129 179 Thermocouple Temp.( ℃ ) ： 37.43 96 168 Max heat flux at cooling channel(MW/m 2 ): 2.99 9.32 23.2 Temperature measurement with 48 Ca 345MeV/n 500pnA (8.3kW) Thermo-couples mounted on the exit beam dump Beam 2 mm behind the surface fixed Dump: Position change Change the beam optics -> various beam spots, Heat densities : good agreements

14. Beam Spot size 3.0x 27.2 3.0 x 27.2 3.0x27.2 Heat Density(MW/m2) 29.9 29.9 29.9 Cooling water speed(m/s) 10 5 2.8 Max temp.( ℃ ) ： 301 332 358 Max temp. at cooling channel( ℃ ) : 154 195 224 Thermocouple Temp.( ℃ ) ： 140 157 175 Max. Heat flow at cooling cha.(MW/m2):17.1 14.7 14.4 Water velocity dependence 3-10 m/s Good agreements -> estimation of heat transfer coefficients is appropriate.

15. Summary & Outlook BigRIPS target system and beam dump system is overviewed. Validation of the design is on going by using intense beams available at RIBF. – For target Temperature of fixed target : Scattered Observed temperatures of rotating target are higher than expected. Further simulations are necessary. Need to figure out the reasons – For Beam dump good agreements of measurements with thermocouples and simulations were obtained. Suggest the estimation of heat transfer coefficients are correct. Highest temperature (surface) have not yet be measured. Accuracy of the estimation of beam spot is not well. Thermal camera to monitor the dump surface is highly desired. Thermal stresses and fatigues for the target and beam dump need to be considered.