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lh 2 target for an 11 GeV Møller experiment @jlab - prospect - S. Covrig hall c, jlab 14 august 2008 hp lh 2 targets for pv q weak target design cooling power remarks

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basic design principle: minimize density reduction and fluctuations high luminosity ( ~ 10 38 cm -2 s -1 ), ℒ ~ 1.867e36·ℑℓ ρ (ℑ in µA, ℓ in cm, ρ in g/cm 2 ) closed loop re-circulating unpolarized targets essential loop components: –pump (highly turbulent flow, Re ~ 10 5-6 ) –high power heat exchanger (counterflow with he) –high power heater –Al cell with thin windows (<0.25 mm) overpressure (>1 atm) and sub-cooled liquid (few K) all used until now are < 1kW density reduction requirement was accomplished within experimental specs density fluctuations were controlled at a few % level Al windows backgrounds contamination were manageable q w will break the 2 kW barrier –acceptable target density fluctuations ~ 50 ppm –first target @jlab designed with cfd simulations –caveats: beam raster motion not included in simulations, no idea what the δρ⁄ρ will be

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p / T / psia / K / kg/s L cm P / I W / µA beam spot mm Δρ⁄ρ % δρ⁄ρ ppm E GeV sample25 / 20 / 0.640700 / 402110000.2 happex26 / 19 / 0.120500 / 35-55 4.8 x 4.8 6 x 3 ?1003 pva425 / 17 / 0.1310250 / 200.1 3920.854 e15821 / 20 / 1.81501000 / 11-121<1.56545/48 g025 / 19 / 0.320500 / 40-602 x 21.52383 qwqw 35 / 19 / 1352500 / 1804 x 4???<501 e2e? / ? / ?1506000 / 100? x ??????<511 high power lh 2 targets for pv used and future design parameters and results

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parameters that affect target density in beam - bulk - (T,p) (T), isobaric conditions, 1 K -> 1.5 % density change for rastered beams (d = intrinsic beam diameter ~100µm, a = raster size ~ mm, f = raster frequency ~ 25kHz @jlab, I = beam current), after filling a full raster pattern (in time ), static liquid for laminar motion the average temperature of the fluid after passing the raster volume in g0 –raster from 2 to 3 mm dropped ⁄ from 240 to 100 ppm –pump head from 0.5 to 1 psid dropped ⁄ from 240 to 68 ppm + turbulence ΔT(g0) = 0.27 K in 0.4 ms ΔT(qw) = 0.55 K in 0.8 ms ΔT(g0) = 2.7 K for 0.5 m/s ΔT(qw) = 1.4 K for 2 m/s

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liquid flow limitations due to viscous heating

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parameters that affect target density in beam - @ windows - typically Al made, 75 – 250 µm thickness in beam – still pressure vessel heat generation in windows – a few W, but sources high heat fluxes into the fluid g0 3 mils exit window q = 43 W/cm 2 (2x2 raster), 18 W/cm 2 into the fluid covering the beam raster area q w 5 mils exit window 78 W/cm 2 (4x4 raster), 33 W/cm 2 into the fluid covering the beam raster area e2e 5 mils window 47 W/cm 2 (4x4 raster) cfd simulations in fluent (without phase transition) show ΔT w ~ 10-30 K at the wall this is a problem since chf correlations argue that the chf for lh 2 at a wall is about 10 W/cm 2 in conjunction with ΔT > 10 K all these targets seem to boil at the windows parameters of interest: turbulence, flow pattern, raster size, sub-cooling (a bit)

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sub-cooled nucleation bubble models for q w in a 3” pipe Unal model (1975) Kolev model both models were originally developed for water for slugs to film transition Taylor instability would apply

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q w models simulated in fluent 400 are g0-type longitudinal flow 600 are new type, transverse flow 8 liters cell 606-6 will be used in q w q w is a 15 MJ reservoir

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fluent summary tables for models prior to 606-6 606-6 ΔT bv = 0.44 K

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g0-type cell for q w model 400, internal flow diverter off the cell central axis to induce higher turbulence in the bv and mitigate the “dead” flow spot at the exit window

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q w transverse flow designs

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e158 target loop design 1.5 m long, 3” id cell, 55 liters 1000 W design power, ~700 W from 11 µA beam 65 ppm density fluctuations on helicity flip scale

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q w He hx design is a hybrid one coil 15 K (designed for 500 W @17 g/s) two coils 4.5 K (designed for 2500 W @25 g/s) fluent simulation of the 2.5 kW, 30 liters hx flow pattern -> the fins are not included in the cfd simulation <- lowest temperature on the h 2 side 16.4 K (above freezing)

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a new phase space for an e2e h 2 target @200 psi h2 has a liquid excursion of 13 K between 20 K and the critical Tc = 33 K not the first high pressure target on-site happexII ran a 20 cm race-tack cell @200- 212 psi He target (the cell had 7 and 8 mils Al windows in beam), target power 200 W, density fluctuations 2% of asymmetry width

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remarks q w is the first target on-site designed using cfd simulations (cell, hph, crude hx check), has 4x the g0 flow, 5x the power for 8x the volume @twice the raster -> goal to get 10x better density fluctuations (we’ll know when we’ll measure it) cfd is a tremendous design help -> for now limited to the steady-state uniform heating in the raster volume (meaning density reduction) -> a realistic model for density fluctuations could be developed based on q w experience e2e is 2.6x the q w target power in beam volume -> density reduction could be a problem e2e cell windows heating should be no worse than g0 viscous heating could limit the flow in the loop to no more than 1 kg/s cooling power has to be investigated carefully, 6 kW needs about 50 g/s CHL helium 10x better than q w density fluctuations will be a challenge, a clear picture of this if q w achieves its goal here

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