Vacuum gas dynamics investigation and experimental results on the TRASCO-ADS Windowless Interface P. Michelato, E. Bari, E. Cavaliere, L. Monaco, D. Sertore; INFN Milano - LASA - Italy A. Bonucci, R. Giannantonio, SAES Getters S.p.A - Italy L. Cinotti; ANSALDO - Italy P. Turroni; ENEA Bologna Italy
XADS Ansaldo beam line configuration
XADS Ansaldo Beam line windowless configuration Beam line: at the reactor exit: 4x5 cm 2 9 m Beam line has a tapered section Beam line: at the interaction ti point is 12x5 cm 2
TRASCO - WINDOWLESS Proton beam Released gases Source LBE H 2 and isotopes Noble gases Po, Hg Evaporation (T = 460 C) Nuclear reaction, degassing Nuclear reaction Nuclear reaction
Windowless target vacuum system design LBE Evaporation experimental data, vapor composition Not condensable e Gases: H 2, Ar, He etc Q source terms High activity vapors (Po, Hg) Evaporation data & vapor composition ν flux & ε sticking BEAM TUBE geometry Conductance calculation ν flux & ε sticking View factor calculation Fluxes calculation l & Deposition distribution Pump choice P=Q/S eff Pressure is negligible Condensation? View factor calculation Fluxes calculation & Deposition distribution!radioactive!
LBE vapors Flux measure PARTIAL PRESSURE APPROACH FLUX MEASURE APPROACH Using the P=Q/S equation Using a proper tools of measure we cannot measure the partial pressure of LBE vapors with usual BA gauge for vapor condensation on it Our system is not in thermodynamics equilibrium we cannot calculate S because the sticking on the pipe wall is not known we can measure the deposition rate at several different temperature we can evaluate the sticking coefficient by a proper numerical method based on angular coefficient we can calculate the evaporation rate at the emitting surface NO! YES!
ν = ν + (1 ε ) ν i 0i n i Numerical Approach inci method of angular coefficients (j) has been chosen in according to Saksagaski theory of vacuum gas dynamics view factor calculated using Ansys. ν inc i = ϕ i > j ν j ε keep into account: reflection, desorption, ν ads i j= 1 = ε i n j= 1 ϕ i > j ν j sticking, condensation and has to be evaluated by experiment. Solving the entire system of equation Original Evaporation rate can be reconstructed. i j1 j2 j3
LBE evaporation 1/2 log10 0 (evaporat tion rate) [g/cm 2 s] -3-4 -5-6 -7 Raoult Law Gravimetric experimental data new data (Knudsen cond) -8 0.001 0.0011 0.0012 0.0013 0.0014 0.0015 1/T (K -1 ) 460 C ANSYS view factor calculation Measured specific evaporation rate vs. temperature
LBE evaporation 2/2 Evaporating surface: 60 cm 2 LBE Operative temperature: 435 C, for conservative evaluation calculation done at 460 C LBE Evaporation Mass Massive Flux Estimated Rate evaporated at at beam tube partial pressure (g cm -2 s -1 ) tapered tube outlet at the Temperature ( C) inlet (reactor exit) (g/y) (mg/y) (mbar) interaction point (mbar) 435 4.7 10-8 89 8.5 1.3 10-6 460 1.1 10-7 212 20 3.3 10-6 550 * 4.7 10-6 8890 845 1.6 10-4 550 C is not an operative condition
LBE Evaporation Oven up to 600 C, 3 kw heater 3 thermocouples for the temperature control loop Ceramic fiber and aluminum insulation Turbo molecular pump vacuum system (p<10-5 Pa) UHV connection (CF flanges with soft iron Gasket) About 1liter LBE, 31cm 2 evaporation surface (63 mm diameter) 2/ 3m long analysis pipe with thickness deposition monitors Window for direct view of the LBE during measurement Possibility to inject gas over and under the LBE level
Experimental apparatus: sensors Quartz Oscillator thickness monitor Sensor can be exposed to direct view of the LBE vapors and hidden in UHV condition Active area 0.5 cm 2 Sensitivity is 1 Å 50 ng Sensor dimension (Φ=30mm) Sensor Temperature control by water flow
LBE measurements
Not condensable gases: hydrogen isotopes and noble gases Molecular regime gm S eff = 1 S p + C 1 C T M (*) 1 cost p = eq Q S eff * Conductance calculation: 7 m tube at 400 C, 2 m at room temperature
Not condensable gases 1/2 : Hydrogen isotopes Isotope Yield: Production Q Beam pipe Pressure Activity it atoms/ in 1 year (mbarl/s) Conductance S pump = in 3 years proton (normal l) (l/s) (mbar) (Bq) H 2 1.75 64.2 2.0 10-3 16.0 1.3 10-4 D 2 3.2 10-1 11.6 3.7 10-4 11.4 3.2 10-5 T 2 9.6H10-2 3.5 1.1 10-4 9.3 1.2 10-5 5.2 10 15 Total 79.3 2.5 10-3 1.7 10-4 5.2 10 15 Data are relative to 600 MeV, 5 ma beam Hydrogen will come also from metal degassing but the gas load will be reduced rapidly due to high temperature operation.! Data relative to T91 not available!
Not condensable gases 2/2 : Noble gases Isotope Production in Q Conductance Pressure Activity in 3 1 year (normal l) (mbarl/s) (l/s) S pump = years (mbar) (Bq) (*) He 96 9.6 3.1 10 1-4 11.4 2.7 10-5 0 Ar 0.023 7.2 10-7 3.8 1.9 10-7 3.2 10 12 Kr 0.53 1.7 10 10-5 2.6 6.6 10-6 7.7 10 13 Xe 0.21 6.7 10-6 2.1 3.3 10-6 2.6 10 13 Total 10.4 34 10 3.4 10-4 36 10 3.6 10-5 11 10 1.1 10 14 Amount of noble gases produced with a 6 ma beam E P = 600 MeV (*)Activities data are relative to a 5 ma beam Total pressure: Hydrogen isotopes + noble gases 2 10-4 mbar
Pump performances vs. gas Gas to Refrigerator L He Ion TMP Diff. NEG be cooled cooled pump pump pump pumped cryopump cryopump H 2, D 2, Y Y Y Y Y Y T 2 He P Y P Y Y N Noble gases Y Y P Y Y N Compatibility and efficiency of the different pumping system relative to the gases to be pumped. Y: satisfactory, N: can not be used, P: poor pumping efficiency.
NEG pumps Base on chemisorption and physisorption properties of metal alloys Pump ONLY reactive gases (do not pump noble gases) Excellent pumping speed and sorption capacity for hydrogen and its isotopes (20 scc of H 2 in 1 g of alloy) No moving parts No need of power supply after activation i No reemission of gas (if not heated)
NEG pumps
High activity vapors: mercury and polonium Limited it amount: negligible ibl influence on total t pressure Main responsible of the activity of the vapor and condensed phase Diluted in LBE: evaporation process in not well known (few data) Mercury experiments are under study Polonium experiment: not possible For Polonium we choose a SIMULATOR: Te Why? Same chemical group, similar elemental vaporization enthalpies, similar oxidation states, similar electronic affinities. We set up two apparatus for evaporation measurement of Te traces (100 ppm) in LBE: 1. cold finger with chemical analysis (ICP) 2. thickness monitor in Knudsen conditions (deposit vs. time and ICP).
Te evaporation: cold finger method
Apparatus for Te evaporation: thickness monitor Viewport To vacuum pump Thickness monitor Diaphragm Bellow Heathers LBE (Te) oven Thermocouple
LBE + Tellurium evaporation at 400 C 2 nm of deposited Te 0.8 mg evaporated from the source Deposition (nm) 8.0 7.0 6.0 5.0 4.0 3.0 20 2.0 1.0 0.0 τ = 5 10 4 LBE+Te LBE only Te deposition 0E+0 0.E+0 1E+5 1.E+5 2E+5 2.E+5 3E+5 3.E+5 4E+5 4.E+5 5E+5 5.E+5 Time (s) If Te is a good simulator for Po Only 1 % of the total amount of Te is evaporating (total is 100 mg) Only 1 1.5% of Po will leave the LBE (total Po is 37g/y)
LBE + Tellurium evaporation: other measurements 2.5 2.3 De eposition (nm m) 2.1 1.9 1.7 1.5 1.3 1.1 0.9 τ = 4 10 4 s T= 450 C Tellurium deposition at 450 C: 2.1 nm Source evaporation: at o about 1% 0.7 0 50000 100000 150000 200000 250000 Time (s) Chemical analysis (cold finger method) confirm the data at 400 C Deposition measurements at 500 C: deposition is close to the one of LBE? Not clean surface?, PbTe?
Beam line vacuum system? High capacity NEG pump Po Hg traps Ion pump Turbo MP? Cryogenic pump?? 2 m, t: room temp. High Hgh capacity capacty NEG pump Po Hg traps Lead bismuth condensation 7 m, t: 400 C
Beam line vacuum system? High capacity NEG pump Po Hg traps Ion pump Turbo MP? Cryogenic pump?? Are the colored boxes In the correct position? 2 m, t: room temp. 7 m, t: 400 C High Hgh capacity capacty NEG pump Po Hg traps Lead bismuth condensation
Conclusion LBE evaporation rate: measured Model and view factor tools: validated The same model can be used for any geometry Not condensable gases: source terms investigated Po and Hg evaluation Te simulator for Po Te: experiments with Te trace in LBE indicates that only 1% of the Te concentration left LBE
TRASCO ADS The Italian TRASCO program (INFN, ENEA and italian industries) aims to study the physics and to develop the technologies needed d to design an Accelerator Driven System (ADS) for nuclear waste transmutation and secondly to produce energy. The main objectives of the research program are: Conceptual design of a 600 MeV - 6 ma proton LINAC. Design and construction of main accelerator components (proton source, RFQ, SC cavities). Development of methods and criteria for neutronics, thermal-hydraulics hd li and plant tdesign for an EA(E (Energy Amplifier)-like sub-critical system Materials technologies and development of components to be used in a plant in which lead or LBE (Pb 44.5 %, Bi 55.5 %) acts as a primary target and as the coolant (e.g. the interface accelerator / reactor) 80 kev 5 MeV 100 MeV 600 MeV Preaccelerator High Energy Superconducting Linac (3 sections) Proton Injector Low Energy Superconducting Linac (ISCL) 6 ma Proton Beam Windowless interface LBE target Sub Critical Reactor GRIPPER TRACK DRIVE
100 Vapor pre essure (T Torr) P PoCRC ( x) P TeCRC ( x) P PoIPPE ( x) P Te.mpbp ( x) P PoCRC ( x) P Te.mpbp ( x) P PoCRC ( x) P TeCRC ( x) 10 1 0.1 Ratio Pvap Po / Pvap Te Te Po 0.01 400 420 440 460 480 500 520 540 560 580 600 Temperature ( C) x Vapor pressure of pure Te,Po and vapor pressure ratio 1 and 2