Norbert Tesch , A. Leuschner, M. Schmitz, A. Schwarz

1. Design Studies for an 18 MW Beam Dump at the future e+e- Linear Collider TESLA Norbert Tesch, A. Leuschner, M. Schmitz, A. Schwarz Deutsches Elektronen-Synchrotron (DESY), Hamburg, Germany ICRS 10 / RPS 2004 – Madeira – 13th May 2004 A. Introduction B. Thermal Aspects C. Radiolysis and Pressure Waves D. Shielding and Activation E. New Idea: Gas Dump

2. A.1 TESLA Linear Collider

3. A.2 Water Beam Dump • Problem: How to dump 18 MW? Solid, fluid or gas based beam dump? • Solid dump: graphite-copper-water dump with heat conduction from copper to water • Even with a fast sweeping system (needed to distribute the energy) the solid option was not practicable for the given beam power in terms of heat extraction • Therefore the base line design was the fluid (water) dump option ! The basic parameters of the water beam dump • Cylindrical H2O volume with L=10 m, Ø=1.5 m and p=10 bar  Tboil=180°C • Fast (within bunch train) circular sweep with Rfast= 8 cm needed to avoid local boiling • Not considered here: beam window (vacuum/water, huge design effort!!!) and beam pipe Problems to be addressed: • Radiation Handling • Shielding • Activation • Dismantling and disposal of activated material@ final shut down Other Processes  Radiolysis  Pressure waves Thermal Aspects  Heat extraction external / internal

4. A.3 Schematic Layout of Water Beam Dump exhaust / chimney general cooling water sand containment shielding hall air treatment water-system water-dump vessel basin dump shielding commissioning beam spent beam

5. B.1 External Heat Extraction general cooling water 60°C 30°C Heat Exchanger B  Two-loop system with pB  pA Static Pressure 10bar 70°C 40°C  Main piping DN 350mm Secondary Loop Pump B  Water flow of 140 kg/s neededto remove 18 MW 70°C 40°C Heat Exchanger A Static Pressure 10bar 80°C 50°C 1% to 10% of total water flow  Recombination system should be directly in return pipe ! Primary Loop 18MW / T=30K  140kg/s Hydrogen Recombiner Water Filtering (ion exchanger, resin filter) Pump A Water Dump 18m3, 10bar Storage Container Scheme of Water System

6. B.2.1 Internal Heat Extraction - Introduction Heating Process temperature Tinst Teq 1/rep time T0 Tinst :instantaneous temperature rise caused by energy deposition of 1 bunch train, dE/dV(r,z) = c    Tinst(r,z), thermal diffusion within 1ms only 10m in water Teq :temperature rise assuming a time independent heat source S, with average power and spatial distribution given by subsequent bunch trains, S(r,z) = 4Hz  dE/dV(r,z)  conservative estimation for the temperature at a given position ŝ=(r,,z): T(ŝ)  T0 +Teq(ŝ) + Tinst(ŝ); with T0 = water inlet temp. (50°C) Task under the given external water mass flow of 140kg/s, create a suitable water velocity field inside the dump vessel, in order to: keep T(ŝ) well below boiling point (180°C) at any position, i.e minimize Teq(ŝ)

7. B.2.2 Internal Heat Extraction - Heat Source Tinst(r,z) = 1/(c  )  dE/dV(r,z)  (Tinst)max = 40K @r = 8cm, z  200cm  Tinst = 28K @r = 8cm, z  300cm 1 bunch train in water, 6.8  1013 e- @ 400GeV x= y= 0.55mm and fast sweep Rfast= 8cm e- 4Hz bunch train repetition:  (dP/dz)max 50kW/cm @ z  300cm dP/(dzdr) dr = 50kW/cm dP/dz dz = 18MW z=300cm radial power density @ z=300cm longitudinal power density

8. in: 140kg/s, 50°C out: 140kg/s, 80°C 260 kg/s 130kg/s 130kg/s T0=54°C 120kg/s e- 130kg/s 130kg/s 82°C 59°C 10kg/s z=3m B.2.3 Internal Heat Extraction – Fichtner* * calculations done by Fichtner GmbH & Co KG velocity (r, ) [m/s] 2 1 1.5m 0  vortex flow, velocity  f(z), CFD-ACE 6.6 code  front / rear part split and water mixing internal flow140 to 280 kg/s,here 260 kg/s  water velocity at inlet nozzle  30 m/s ! p (in-out)  5 bar 130 kW pump power !  2d (r, ) stationary simulation at z=3m : T0+max(Teq+Tinst) = 54°C+47K+28K = 125°C well below 180°C boiling point ! T0 + Teq(r, ) @ z=3m [°C] 101 91 81 max(Teq) = 47K 71 61 T0=54

9. B.2.4 Internal Heat Extraction – Framatome* * calculations done by Framatome ANP GmbH in: =140kg/s, 50°C out: =140kg/s, 80°C velocity (r, z) [m/s] r 125 mm e- v  2.8 – 2.4 m/s z tube 1 tube 2 0 0 50mm 10m T0 + Teq(r, z)  longitud./radial flow, 3d, PHOENIX 3.4 code internal flow = external flow =140kg/s tube 1/2: 0.1/0.02% porosity  15% radial flow max. tube 2 temp., 50°C+45K+0K = 95°C max. water temp.between tube 1 & 2 T0+max(Teq+Tinst) = 50°C+58K+0K = 108°C max. tube 1 temp.is at z  4m, r=130mm T0+max(Teq+Tinst) = 50°C+34K+7K = 101°C [°C] tube 2 108 r max(Teq) = 58 K 125mm z 0 3.3m 5m 6.7m tube 1 T0=50

10. C.1 Pressure Waves - TÜV-Nord* Assumptions r 75cm  consider 1 bunch train 860s long as dc-beam source: S = 1/860s  dE/dV for 0  t  860s and S = 0 otherwise  CFD code Fluent 6.0 without handling of phase transition 10bar, 50°C vsound1.5km/s e- 10m z 400GeV, =0.55mm, 8cm fast sweep p [bar] Results p(r) @ z=2.5m 0  t  800s • in water:pmax  3.7bar near z-axis @ 100s pmin  -1.6bar near z-axis @ 950s  reduces boiling temp. & solubility of gases !!! • at vessel cylinder: pmax  1.8bar @ 650s • at front/rear face (windows): pmax  0.5bar • pressure wave decay to 0 after  3ms (<<250ms) 3 t [s] 2 600 800 700 500 1 400 300 10 50 100 150 200 0 r [cm] 0 10 20 30 40 50 60 70 75 p [bar] p(r) @ z=2.5m 0.8  t  1.6ms Pressure if close to boiling temperature (imperfect beam with   6mm, no sweep, after 325s) • in water: pmax  9bar, pmin  -6bar • at vessel cylinder: pmax  2.7bar • at front/rear face (windows): pmax  0.5bar • pressure wave decay to 0 after  20ms 2 1.2 1 1.1 0.8 1.4 1.3 1.6 0 1.5 1.0 t [ms] 0.9 -1 r [cm] 0.95 75 0 10 20 30 40 50 60 70 * calculations done by TÜV-Nord Gruppe -2

11. C.2 Radiolysis Fundamentals  H2O cracked by shower of high energy primary electron  net production rate at 20°C and 10 bar:30 ml/MJ H2and15 ml/MJ O2corresponding to 0.27 g/MJ H2Owith spatial distribution according to dE/dV profile  solubility in water at 60°C: H2: 16 ml/l and O2:19.4 ml/l Our Case  18 MW:4.8 g/s H2O cracked whole primary water (30m3) would be radiolysed in 72 days ! recombination needed with 0.54 l/s H2 + 0.27 l/s O2  4.8 g/s H2O + 58 kW (0.3%  Pbeam)  solubility limit during 1 bunch train at 10 bar dE/dV 530 J/cm3 for H2& dE/dV 1300 J/cm3 for O2; our case (dE/dV)max= 160 J/cm3 So far it looks almost good, BUTH2-control is a critical thing: solubility during bunch train passage can be exceeded locally due tolocal pressure drops with negative p or rise of Tinst danger of H2 gas bubblescomparable to local boiling  if not all H2 is recombined, H2can accumulate atspecial locations (local pockets)  danger of explosion (e.g. nuclear power plant Brunsbüttel) • recombination in gas-phase without expansion doubtful • recombination should happen directly in return pipe of dump vessel to ensure that 100% of the water will reach the decompress-compress stage  Framatome proposal  Fichtner proposal

12. surface 7m sand 3m normal concrete dump 3m normal concrete soil & groundwater D.1 Radiation Handling Shielding of water vessel towards soil, groundwater and surface* soil & groundwater : 3m normal concrete or equivalent to reach planning goal of 30 Sv/a due to incorporation surface: 3m normal concrete or equivalent + 7m sand or equivalent to reach planning goal of 100 Sv/a due to direct radiation * calculations done with FLUKAcode Activation of primary circuit* 18MW, 30m3 water Main contribution of activation in watercomes from 3H and 7Be 3H: 20keV -, t1/2=12a, Asat=250TBq, A(5000h)=8TBq,A(10a)=110TBq - no direct dose rate, but problem if released due to accident or maintenance ! 7Be: 478keV , t1/2=54d, Asat=108TBq, A(5000h)=102TBq - main contributor to local dose rate, assume equal distribution in water system  300mSv/h at surface of component and 50mSv/h in 50cm distance ! (after 5000h) - accumulation in resin filters, but also adsorption on circuit surfaces (esp. heat exchanger)  local shielding needed !  2cm thick stainless steel dump vessel gives400mSv/h on its axis (5000h and 1 month cooling)  regular inspection of vessel (welds, ...) seems to be problematic !

13. exhaust r 5m containment air 5m 5m 2m 2m 2m z 10m 20cm steel + 1.8m concrete dump D.2 Radiation Handling Activation of containment air* 18MW, 3000m3 air  necessity of closed containment,„closed“  under-pressure by continuous exchange rate of1vol/h and controlled exhaust  looks fine except forshort lived isotopes: need „delay line“ of about 1 hour ! Scheduled opening of primary circuit 30m3 water, 100TBq of 3H flush water into storage tank,  100l remain (0.1mm on 1000m2), vent system with dry gas via 95% efficient condenser 5l  10GBq tritium have to be released to outside air • meeting the limit of 1kBq/m3 needs venting with 107m3 air  this takes 1000h=42days with 104 m3/husing a chimney is necessary (acceptance!) Dismantling of activated system after final shut down after 20 years, 200TBq of 3H primary water solidifying as concrete  5000 barrels (200l, 40GBq) steel components (150t, 106Bq/g) & concrete shielding (1500t, 200Bq/g)  = a lot of M€ * calculations done with FLUKAcode

14. E.1 New Idea: Gas Dump Problems and disadvantages of water dump: • High tritium production (to reduce: larger atomic number of dump material) • Critical window design, 10 bar static + 0.5 bar dynamic (reduce pressure) • Radiolysis, local and instantaneous effects represent a severe risk (to avoid: one-atomic gas) • Handling of water during maintenance and final shutdown (less tritium) • Disposal costs not negligible (less tritium) • To overcome most of the problems and disadvantages the following gas beam dump was proposed: • Material: Noble gas (first attempt: Argon @ 1 bar) in inner tube (r=4 cm) acts as scattering target, (energy deposition of 0.5 %) and distributes the beam energy longitudinally (no sweeping) • Main part of the energy is dumped in Iron shell of radius 52 cm (average power loss 18 kW/m) • Surrounded by 4 cm thick Water cooling system • Dump system has diameter of 1.20 m and length of 1000 m • Can be used as- dump as well tunnel gas dump

15. E.2 Gas Dump: Energy Density  Energy density in GeV/cm3 in r-z view for one 400 GeV electron* * calculations done with FLUKAcode

16. E.3 Gas Dump: Comparison Advantages of gas dump: • Tritium production • Beam window • Radiolysis • Maintenance and disposal • Cases of emergency • Acceptance and permission !!! Disadvantages of gas dump: • Length of dump inside collider tunnel • Space for additional shielding needed adopted tunnel design necessary • Not easy to reach constant energy density of18 kW/m over whole length Conclusion: • The fluid (water) beam dump seems to be feasible, but with severe disadvantages !!! • The gas (argon) beam dump option seems to be a very attractive alternative and will surely be considered in an early design stage of the next linear collider !!!