Approaches to a High Power BEAM DUMP for an (TESLA like) ILC

Transcription

1 Approaches to a High Power BEAM DUMP for an (TESLA 8 --like) ILC DESY : IHEP Protvino : M. Schmitz, A. Leuschner, N. Tesch, A. Schwarz M. Maslov, V. Sytchev ILC-BDIR Workshop, Royal Holloway, London, 22nd June 25 A. Introduction A. Introduction heat extraction limit Focus of this Talk B. Solid Dump (Graphite based) B. Solid Dump (Graphite based) C. Liquid Dump (Water) C. Liquid Dump (Water) new crazy idea? D. Gas Dump (Argon) D. Gas Dump (Argon) E. Comparative Summary E. Comparative Summary Approaches to a High Power Beam Dump for an (Tesla8-like) ILC, michael.schmitz@desy.de, ILC-BDIR-Workshop, Royal Holloway, London, Wed. 22. June 25 1

2 bunch train with N t particles Introduction e- or e+ with E T t BEAM SWEEPING WINDOW ABSORBER repitition time 1/ν rep Distribution of Beam on Absorber intra bunch train (fast sweep) average power (slow sweep) Separation of beam vacuum and absorber Beam to be dumped (TESLA 8 parameters) E =4GeV, N t = e-, T t 1ms, ν rep =4Hz pulsed power source with W t =4.4MJ per train P ave =17.5MW in average Thermal and Mechanical Issues heating and heat extraction stresses and pressure Radiochemical Aspects radiolysis, dissociation Radiological Issues handling of induced radioactivity shielding of direct radiation Approaches to a High Power Beam Dump for an (Tesla8-like) ILC, michael.schmitz@desy.de, ILC-BDIR-Workshop, Royal Holloway, London, Wed. 22. June 25 2

3 C-based absorber embedded in Cu C-based absorber embedded in Cu Solid Dump: Heat Extraction Solid Dump: Heat Extraction capture 4 GeV shower longitudinal: 5m, transversal: 1R m (C)+3R m (Cu)=7cm+5cm E =4GeV, P ave =17.5MW I ave =44µA (dp/dz) max 75kW/cm! How to get rid of? Heat extraction by transverse heat conduction and sweeping Heat extraction by transverse heat conduction and sweeping z α tot.12w/(cm 2 K) and (dp/dz) max = α tot w ( T eq ) max allow ( T eq ) max 4K (prevent oxidation of C) w 2cm / (kw/cm) (dp/dz) max 5cm Cu 7cm C 7cm C 5cm Cu w heat flow T eq T eq cooled surfaces 75kW/cm 15m! slow sweep 8 sandwiches of 25cm = 2m beam 2m 5m beam, linear sweep of length w Discussion huge and heavy absorber huge vacuum system complicated slow beam sweeping C-Cu Approach not suitable only reasonable for (dp/dz) max kw/cm P ave 1kW level Approaches to a High Power Beam Dump for an (Tesla8-like) ILC, michael.schmitz@desy.de, ILC-BDIR-Workshop, Royal Holloway, London, Wed. 22. June 25 3

4 4 Water Dump: Introduction Water Dump: Introduction Motivation heat extraction in solid absorbers limited by heat conductivity improve heat extraction by flow of a liquid absorber material water Own Investigations supported by 3 Companies Own Investigations supported by 3 Companies Feasibility study of water dump 1.) Framatome (Erlangen): branch of Siemens / KWU, construction of nuclear power plants 2.) Fichtner (Stuttgart): worldwide operating engineering office, technical consulting, Calculations on transient pressure dynamics in the water dump 3.) TÜV-Nord (Hamburg): technical consulting, supervision of technical facilities and cars Assumptions for the Water Dump Studies Assumptions for the Water Dump Studies beam: 4GeV, e-, 4Hz, 4.4MJ per train resp. 17.5MW in average σ x =σ y =.55mm and fast (within train) circular sweep with R fast =8cm water dump: cylindrical H 2 O volume ( 18m 3 ) L=1m (shower capture), Ø=1.5m (shower capture + off axis tilted beam from both ends) 1bar=1 6 Pa T boil =18 C not considered here: window, beam sweeping, beamstrahlungsdump

5 5 Water Dump: Overall Scheme Water Dump: Overall Scheme normal cooling water sand exhaust / chimney? enclosure air treatment hall water-system basin emergency/comm. beam tilted 15mrad water-dump vessel spent beam, tilted 15mrad dump shielding back

6 6 Water Dump: External Water System Water Dump: External Water System Fichtner Fichtnerand and Framatome Framatomemainly mainly agree agree in in layout layout of of external external water water system system Generals two loop system with p B > p A main piping DN 35mm Primary Loop Primary Loop fully He gas-tight system 14kg/s between 5 C / 8 C 1bar static T boil =18 C 3m 3 water content water filtering hydrogen recombination Static Pressure >1bar Static Pressure 1bar Hydrogen Recombiner normal cooling water 6 C Heat 3 C Exchanger B 7 C 4 C 7 C 8 C Secondary Loop Heat Exchanger A Primary Loop 17.5MW / T=3K 14kg/s Pump B 4 C 5 C Pump A 1% to 1% of total water flow Water Filtering (ion exchanger, resin filter) Scheme of Water System Water Dump 18m 3, 1bar Storage Container

7 7 Water Dump: Internal Heat Extraction introduction Water Dump: Internal Heat Extraction introduction Heating Process Heating Process temperature T inst 1/ν rep T inst : instantaneous temp. rise caused by energy deposition of 1 bunch train, de/dv(r,z) = c ρ T inst (r,z), thermal diffusion within 1ms only 1µm in water T eq : temperature rise assuming a time independent heat source S, with average power time T eq 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,φ): T(ŝ) T + T eq (ŝ) + T inst (ŝ) ; wheret = water inlet temp. (5 C) Task Task T under the given external water mass flow of 14kg/s, create a suitable water velocity field inside the dump vessel, in order to: keep T(ŝ) well below boiling point (18 C) at any position, i.e minimize T eq (ŝ)

8 8 Water Dump: Internal Heat Extraction the heat source Water Dump: Internal Heat Extraction the heat source T inst (r,z) = 1/(c ρ) de/dv(r,z) ( T inst ) max = = 8cm, z 2cm T inst = = 8cm, z 3cm 1 bunch train in water, GeV σ x = σ y =.55mm and fast sweep R fast =8cm 4Hz bunch train repetition: (dp/dz) max z 3cm Energy Density (1 bunch train), de/dv [J/cm 3 ] dv=4.4mj e z [cm] r [cm] dp/(dr*dz) [kw/cm²] dr=5kw/cm radial power z=3cm r [cm] dp/dz [kw/cm] z=3cm dz=17.5mw longitudinal power density z [cm]

9 9 Water Dump: Internal Heat Extraction Fichtner scheme Water Dump: Internal Heat Extraction Fichtner scheme out: 14kg/s, 8 C e- 13kg/s 82 C 13kg/s z=3m 26 kg/s T =54 C in: 14kg/s, 5 C 13kg/s 12kg/s 13kg/s 59 C 1kg/s velocity (r, φ) velocity (r, φ) [m/s] m vortex-like flow, velocity f(z), CFD code front / rear part split and water mixing internal flow 14 to 28 kg/s, here 26 kg/s water velocity at inlet nozzle 3 m/s! p (in-out) 5 bar 13 kw pump power! 2d (r, φ) stationary simulation at z=3m : T +max( T eq + T inst ) = 54 C+47K+28K = 125 C well below 18 C boiling point T + T eq (r, z=3m T + T eq (r, z=3m T =54 [ C] max( T eq ) = 47K

10 1 Water Dump: Internal Heat Extraction Framatome scheme Water Dump: Internal Heat Extraction Framatome scheme in: =14kg/s, 5 C out: =14kg/s, 8 C velocity (r, z) velocity (r, z) r [m/s] e- tube 1 tube mm v m/s z 5mm 1m long. + radial flow, 3d-sim., PHOENIX code internal flow = external flow = 14kg/s tube 1/2:.1/.2% porosity 15% radial flow max. tube 2 temp., 5 C+45K+K = 95 C max. water temp. between tube 1 & 2 T +max( T eq + T inst ) = 5 C+58K+K = 18 C max. tube 1 temp. is at z 4m, r=13mm T +max( T eq + T inst ) = 5 C+34K+7K = 11 C T + T eq (r, z) T + T eq (r, z) r 125mm 3.3m tube 2 18 max( T eq ) = 58 K 5m 6.7m tube 1 T =5 z [ C]

11 Assumptions Assumptions Water Dump: Pressure Waves (TÜV-Nord) Water Dump: Pressure Waves (TÜV-Nord) consider 1 bunch train 86µs long as dc-beam source: S = 1/86µs de/dv for t 86µs and S = otherwise CFD code, no handling of phase transition: fluid vapour 75cm r 1bar, 5 C e- v sound 1.5km/s 1m z 4GeV, σ=.55mm, 8cm fast sweep Results Results in water: p max 3.7bar near 1 µs p min -1.6bar near 95 µs reduces boiling point & solubility of gases! at vessel cylinder: p max 65 µs at front/rear face (windows): p max.5bar pressure wave decay to after 3ms if heating gets near boiling temperature (simulated σ 6mm, no sweep, stop beam after 325µs) in water: p max 9bar, p min -6bar! at vessel cylinder: p max 2.7bar at front/rear face (windows): p max.5bar pressure wave decay to after 2ms p [bar] Approaches to a High Power Beam Dump for an (Tesla8-like) ILC, michael.schmitz@desy.de, ILC-BDIR-Workshop, Royal Holloway, London, Wed. 22. June p [bar] p(r) z=2.5m z=2.5m t t 8µs 8µs 3 t [µs] t [ms] r [cm] p(r) z=2.5m z=2.5m.8.8 t t 1.6ms 1.6ms r [cm] 11

12 12 Fundamentals Fundamentals Water Dump: Radiolysis Water Dump: Radiolysis H 2 O cracked by shower of high energy primary electron net production rate at 2 C / 1 atm (n.c.):.3 l/mj H 2 and.15 l/mj O 2.27 g/mj H 2 O spatial distribution according to de/dv profile solubility in 6 C water: H 2 : 16 ml/l and O 2 : 19.4 ml/l Our Case Our Case at 2 MW: 4.82 g/s H 2 O whole primary water (3m 3 ) would be radiolysed in 72 days! thus recombination: 6 l/s (n.c.) H l/s (n.c.) O 4.82 g/s H 2 2 O + 58 kw (.3% P beam ) solubility limit during 1 bunch train at 1 bar de/dv 53 J/cm 3 for H 2 & de/dv 13 J/cm 3 for O 2 ; our case (de/dv) max = 16J/ cm 3 So far it looks almost good, BUT H 2 control is critical: So far it looks almost good, BUT H 2 control is critical: solubility during bunch train passage can be exceeded locally due to local pressure drops (negative p), rise of T inst and amount of solved H 2 danger of H 2 gas bubbles and induced pressure waves comparable to local boiling if not all H 2 is recombined, H 2 can accumulate at prominent locations (local pockets) danger of explosion (e.g. nuclear power plant Brunsbüttel) need 1% recombination, i.e. out gassing at low pressure + recombiners in return pipe

13 13 scheme Water Dump: Radiation Handling (1) Water Dump: Radiation Handling (1) Shielding of direct radiation neutrons: ~ isotropic distribution shielding to protect surface, soil, groundwater & air muons: range in soil 7m surface protected by 15mrad tilt + 12m sand 4GeV e- surface: <.1mSv/year 7m sand 12m sand 3m normal concrete dump muons 3m normal concrete groundwater: incorporation <.3mSv/year Activation of primary circuit, 18MW, 3m 3 water in water besides short lived isotopes also 7 Be, 3 H=T,... A(t)=p (1-e -λ t ) p production rate = A sat λ ln2/t 1/2 3 H: 2keV β -, t 1/2 =12a, A sat =28TBq (.76g, 2.8l T 2 or 5g HTO), A(5h)=9TBq, A(1a)=12TBq - no outside dose rate, but incorporation risk if released due to accident or maintenance! 7 Be: 478keV γ, t 1/2 =54d, A sat =12TBq, main contributor to dose rate - equal distribution in primary loop 3mSv/h! at surface of components - accumulation in resin filters, but also adsorption on circuit surfaces (esp. heat exchanger) local shielding, remote handling procedures Legal limit of draining 3 H & 7 Be: 5MBq/m 3 <<TBq/m 3 dilution is not the solution to pollution 2mm thick stainless steel dump vessel gives 4mSv/h on its axis (5h op., 1month wait) regular inspection of vessel (welds,...) seems to be problematic

14 14 scheme Water Dump: Radiation Handling (2) Water Dump: Radiation Handling (2) Activation of air in enclosure, 18MW, 3m 3 air necessity of enclosure, closed keep under lower pressure by continuous exchange rate of 1/h and controlled exhaust A sat A(5h) specific saturation [Bq/m 3 ] w/o air exchange with exchange 1/h legal limit 3 H 1.4GBq 43MBq 47k 3 1k 7 Be 39MBq 37MBq 12k 7 6k enclosure air O.k., except for: a) short lived need delay line of 1h, b) opening of primary circuit r 5m 5m dump 2m 2m 1m exhaust 2m 5m z 2cm steel + 1.8m concrete Scheduled opening of primary circuit, 3m 3, 1TBq of 3 H after 1years flush water in storage tank, 1l remain (.1mm on 1m 2 ), vent system with dry gas via 95% efficiency condenser 5l 1GBq tritium have to be released to outside air meet the limit of 1kBq/m 3 needs dilution in 1 7 m 3 and takes 1h=42days! with 1 4 m 3 /h extrememly strong recommendation to use a chimney 2m Dismantling of activated system after final shut down, 2 years 2TBq of 3 H primary water solidifying as concrete 5 barrels (2l, 4GBq) steel components (15t, 1 6 Bq/g) & concrete shielding (15t, 2Bq/g) Σ 5M

15 15 Water Dump: Discussion Water Dump: Discussion Compared to the solid C-Cu dump, the water dump looked quite attractive at first sight, BUT Except for the answer to the heat extraction issue other critical aspects showed up at a closer look: additionally quite similar (not calc.) to C-Cu approach: Radiolysis and Hydrogen Gas Transient Pressure Window handling of highly activated (cooling) system, esp. High Tritium Content in cooling water requires huge effort in radiation protection even scheduled opening for maintenance reasons is complicated enclosure and 2m high chimney dismantling costs not negligible Inherent Potential of Destruction / Explosion of a Highly Activated Water System Difficult to get permission and antis of the LC-project will find here good arguments Motivation for a new idea

16 16 Gas Dump: First Thoughts Gas Dump: First Thoughts One atomic noble gas core (Ar, Xe) is surrounded by solid material (Fe) Basic Idea Basic Idea gas core acts as scattering target (only small amount of energy deposition) and distributes energy longitudinally over ~ 1km into surrounding material low energy densities, no sweeping, small spot size possible, no radiolysis surrounding material takes main part of energy Z > 2 reduced tritium production tunnel r [cm] First Attempt (not optimized) First Attempt (not optimized) gas dump 1.2m, ~1km air water, 4cm Energy density (1 electron 4GeV), de/dv [GeV/cm 3 ] r-bin=1cm, z-bin=1m Fe, 52cm thick Ar core, normal conditions z [m]

17 17 Gas Dump: Rough Results 1km long dump, (compared to water dump) Gas Dump: Rough Results 1km long dump, (compared to water dump) Thermal & Mechanical Issues Thermal & Mechanical Issues Argon: 8kg, takes only.5% primary energy, i.e. 22kJ per train resp. 9kW 22kJ T inst 1K (total volume) p.3bar, i.e. low transient pressure on window (.5bar) Iron: m=8tons, takes all primary energy, (de/dm) max per train=3j/g T inst 1K (4K) 18MW over 4m (dp/dz) max 5kW/m (5kW/cm) T eq (heat conduction in iron) 42K and T eq (heat transfer iron/water) 3K Argon core and inner iron area will reach temperatures of about 5 C Argon pressure will go up to 2-3 bar Radiological Aspects, 18MW, (no extra shielding around iron assumed) Radiological Aspects, 18MW, (no extra shielding around iron assumed) neutron dose at surface: 1m sand shielding gives.1msv/year (3m concrete + 7m sand) muon dose at surface: dump longer than muon range, 5cm iron of the dump itself is equivalent to 2m sand shield depth of dump tunnel relaxed tritium sat.: 3 TBq in Fe (solid),.7 TBq in Ar,.2 TBq in cooling water (3TBq) tunnel air activation (tritium sat.): 8.4GBq in 2m 3 = 42kBq/m 3 (47kBq/m 3 ) dose levels at the dump and in tunnel: few msv/h (1mSv/h at shielding, but 1mSv/h at components)

18 18 Gas Dump: Rough Results cont d, (compared to water dump) Gas Dump: Rough Results cont d, (compared to water dump) Maintenance Maintenance Water System: lower activated (1-4 of water dump), no hydrogen Opening of Argon core: 5l,.3TBq of 3 H after 1years (12TBq in water) activated gas is rinsed out and pressed into a vessel n.c.) how much is released to air during this process?.1%.3gbq (1GBq) Discussion, Open Questions Discussion, Open Questions 1m of tunnel is activated to dose rate levels of few msv/h optimization of dump & additional shielding to reach.1msv/h an adapted or extra tunnel design is desirable (crossing angle preferred) high gas and iron temperature flatten dp/dz profile via Ar pressure by sectioning the dump spot size limit of this dump? need no fast sweep, applicable as dump for γ/γ-collider study thermal effects in Ar core: convection, change in density profile is the (angular) beam stability compatible with the long axis of the dump? (4cm/1km=4µrad) make it suitable to dump beamstrahlung as well. Consequences? (e.g. wider gas core,..) The gas dump approach seems to be an attractive alternative, it should be considered in an early design stage of the ILC.

19 19 Comparative Summary Comparative Summary Graphite-Copper Dump Water Dump Noble Gas Dump 2m x 2m, 5m long 1.5m, 1m long 1.2m, 1km long (extra? tunnel) heat conductivity & immense slow sweep radiation degradation of heat conductivity of graphite? adequate water flow no slow sweep explosive radiolysis gases in a highly activated system need increased spot size (fast sweep) to limit energy density total tritium inventory 3TBq 3% in water, rest in C-Cu all in water maintenance complicated high activated components, dismantling costs not negligible heat conductivity no slow sweep no dissociation of one atomic gas cyclic stress in C tolerable transient pressure in water gas buffers transient expansion window 2m unless not put upstream of sweeping Technically not practicable for high power applications vac./water window 2cm challenging design Principally feasible, but inherent risks will make it difficult to sell it as reliable, safe and robust. vacuum/gas window 8cm design ~exists applicable for smaller spot sizes and therefore as γ/γ-dump tritium inventory factor 1 less and 98% bound in a solid easier maintenance activation of 1km tunnel Attractive new idea, which should be investigated in more detail