p2n Converter Geneva Meeting TRIUMF Report Geneva, October 16, 2017 Luca Egoriti Alexander Gottberg Tom Day Goodacre

Content UCx 100 µA license amendment Past design overview + updated concepts Target Converter p2n offline tests Future tasks

UCx 100 µA License Amendment Meeting with TRIUMF radiation protection group (Mon, Oct 2nd): 2-step process: Internal (TRIUMF accelerator division) safety review CNSC safety approval, ~12 weeks processing time Proton beam tails could increase α-emitting inventory: to be quantified Beam tails and halo known and characterized Now: retrieving data and evaluate impact on radioisotope inventory Ongoing: benchmarking set limits of halo monitor and discussion with beam physics group for reducing tails Fr isotopes online production as a benchmark for α-inventory Schedule FLUKA inventory simulation and data analysis (Nov 30th) Internal safety review (December 2017) Submit application for safety review by TRIUMF EH&S (Jan 2018)

Past overview Target

Initial Connection, Target Legs, Target Body Thermal gradients top-down always present in any simulation Lateral thickness 0.2 mm seemed the only option, but high risk of failure

Thermal Optimization Study Changed current leads geometry Better temperature distribution Cold spot in the center without beam interaction Temperature: Max on legs = 3500 °C (can be optimized by changing profile) Max on container = 2700 °C (can be optimized but will lower average temperature)

Iterations

Latest target – “Smiley heart” target Tmax [°C] Tmin [°C] Legs 2750 1870 Container 2521 1575 Graphite boat 1950 1860 Increases by 200 °C during 50 kW beam irradiation (~30 W deposited in 0.15mm Ta window) At max converter temperature: container T@ cap is still <2000 °C Length = 30 mm Diameter = 40 mm Lateral thickness = 0.38 mm (TRIUMF targets, sustainable when TaC coated) Legs: two different thicknesses (2.5 mm; 1.5 mm) before and after splitting Legs and end-caps EDM out of one single tantalum piece Machining challenge: 40 mm diameter 3.7 V voltage drop across target (leg to leg)

Hot converter scenario If entire converter surface is at 2300 °C: Radiation from Converter to Target: 430 W Max T on target cap: Emissivity 0.2  Tmax=1925 °C T-dependent emissivity  Tmax = 1930 °C Consequence: target affected positively, T more homogeneous Next steps: Optimizing tantalum profile Experimental verification Experimental optimization through heat shields

Past overview Converter

First TRIUMF concept Brings converter close/inside annular UCx Run converter as moderate in temperature as possible. copper tungsten Parameters N-induced fiss @100µA 9.49 E12 [fiss/sec] %p-induced fiss 4.65% [(p-ind fiss)/(tot fiss)] Tot Pow Dep [W] 6659 W Max Temperature in W 1652 °C Max Temperature in Cu 638 °C Graphite boat Tantalum container and windows UCx Clamping issue over beam cycles Target heating not properly addressed Target: machining challanging Ta beam windows machining/assembly not addressed

Ta + Cu, Radiation included Entire converter Cu only Water path Beam Heating = 7730 W Tmax tungsten = 1800 °C Tmax copper = 290 °C Tmax WaterLine = 200°C Max Cu plastic strain = 0.007 Max W plastic strain = 0.0055

Previous Converter Geometry Tmax in tungsten ~1860 °C Tmax in copper ~350 °C Tmax water pipes ~160 °C 2 cm 7 cm 2 Issues: Tungsten 6 mm away from Copper surface  lower solid angle for neutrons to UCx Two contact surfaces: different thermal contact due to machining tolerances

Latest converter - Geometry 6mm 10mm 4mm p-beam 14 mm 13mm Tungsten in line with copper – minimizes distance W-UCx Minimizes distance W-UCx Asymmetries in Copper: more thermal mass in the rear one  can take more power Tungsten asymmetry to distribute power differently front-rear Additionally, front one takes ~300 W thermal radiation from target Run thermal-electric on target only, computed radiation power from front surfaces Applied temperature boundary condition so that emits the same power, run thermal simulation on the entire geometry to assess converter temperature Assumption: copper emissivity/”absorptivity“ = 0.1, while polished copper <0.07 (conservative, if stays polished) 1 mm distance between copper brackets Different copper bracket thickness to distribute heat flow more evenly over the pipe cooling interface Copper fillets

Latest Converter – Simulation Results Different Tmax in the two copper brackets Tmax (tungsten) = 2137 °C Different Tmax in the two cooling lines [Tmax (front)=140°C; Tmax (rear)=180 °C] Water temperature from simulations = 60 °C  colder water could go first in the rear bracket to avoid boiling [Tsat (@7.5 bar) ~165 °C] Tmax1 = 385 C Tmax2 = 361 C Comparison with previous simulation: W symmetrical, Cu asymmetrical Tmax (W) = 2250 °C Tmax (Cu) = 440 °C

Test Stand Target

p2n Target Heating Tests in ATTS Two optical lines of sight for pyrometer (P) measurements 4 K-type and 4 C-type thermocouples First p2n target machined with AETE material Tests to be fitted in AETE-target test schedule Schedule ATTS modifications available to fit p2n target tests: (Fri, Nov 10th) First target machined with AETE material (Thu, Nov 30th) First full heated test with 1500A (Christmas 2017) Tests to be fitted in AETE-target test schedule (P) (P) Test aim Benchmark simulations with pyrometer temperature data Prove target integrity after 1 cycle Prove target integrity for long continuous operation (ideally 3 weeks)

Implementation Heat balance: Ohmic heating (1500 A; 3.7 V) = 5550 W Beam power deposition = 7300 W Total power deposited = 12850 W Max allowed power deposition = 12 kW → More simulation and validation work required Power supplies proposal: Three parallel power supplies (600 A; 16V) Short them while entering two power lines (target heater + FEBIAD magnet coil) Distribute current evenly until they are merged together at the connectors AC/DC transformer station to be checked with Franco Target + Converter mass I talked to Franco via email to arrange a meeting this past week, he seemed into it but I still haven’t got any reply after I sent 2 email reminders. Will tackle him in person next week.

Test Stand Converter

p2n Converter Test Stand 1 Thermocouple- out (water) Thermocouple- in (water) Similar geometry to the online converter Contact temperatures much lower than online converter Table-top: converter and TIG welder hold in place with equipment present in Remote Handling shop Thermocouples attached with wire Power: 1000 W Cooling: 1000 [W/m2 K] T@ central TC= 220-300 °C T@ lateral TC = 80 °C Thermocouple holes Argon flow to prevent oxidation T@Cu TC1 = 70°C T@Cu TC2 = 67°C TIG welder tip TIG welder ceramic support

p2n Converter Test Stand 2 – Asymmetric (new proposal) Scenario h[W m^-2 C^-1] Power [W] Tmin W [°C] Tmax W [°C] Tmin Cu [°C] Tmax Cu [°C] 1 1000 750 337.6 2051.1 147.8 535.1 2 2000 263.1 1976.4 78.8 460.2 3 4000 224.4 1937.5 47.7 421.3 4 6000 210.6 1923.7 39.0 407.6 5 500 235.1 1377.4 108.5 366.7 6 185.4 1327.6 62.5 316.8 7 159.6 1301.7 41.8 290.9 8 150.4 1292.5 36.0 281.7

p2n Converter Test Stand - Schedule Fri, Oct 29th: Standard copper pieces ready Mon, Nov 13th: Joao Pedro arrives at TRIUMF with W piece(s) Wed, Nov 15th: Copper brackets + W converter(s) assembled by TRIUMF machine shop Thu, Nov 16th: Setup and troubleshooting Fri, Nov 17th – Tue, Nov 24th: Copper conductance + thermal cycling tests: Ramp-up 0  1000W in ~10 mins Ramp down 1000W  0 W in ~10 mins As many cycles as possible in the Deformation/damage assessment on Cu and W All W parts duplicated for future CuCrZr tests if needed (CuCrZr has yield stress higher than copper by a factor 100) Kth copper Kth CuCrZr

Future tasks Cooling system Max outlet temperature: Heat exchanger (rated for 120 kW for the whole system) could be enough Plastic pipes limit water temperature. Check for changing material/replacement frequency Pressure drops calculation: additional heat shield pipes + converter water path might affect too much water flow Write EEC proposal (Start now) ISAC infrastructure Check for AC/DC conversion capabilities (Franco). Fri, Oct 20th Order 2 (600 A, 16V) power supplies in parallel to the same already existing one (Nov, 15th) Simulate thermal load to the target and FEBIAD connectors ISAC test stand: (Dec 2017) Water-cooled connector test up to 1000 A Temperature measurement (previous thermocouple implementation) ISAC target module connector test (During shutdown, Jan-Apr 2018) Water-cooled connector test up to ~1800 A Thermocouple implementation) On average, there is a 3-month mismatch between initial test plan and current situation

Suggested Geometry Only one step because of potential bad/no contact while expanding and because of machining tolerances