Slide 1

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

Slide 2

basic design principle: minimize density reduction and fluctuations high luminosity ( ~ 10 38 cm -2 s -1 ), ~ 1.867e36 ( in A, in cm, 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 (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 will be

Slide 3

p / T / psia / K / kg/s L cm P / I W / A beam spot mm % 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

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 ~100m, 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 T(g0) = 0.27 K in 0.4 ms T(qw) = 0.55 K in 0.8 ms T(g0) = 2.7 K for 0.5 m/s T(qw) = 1.4 K for 2 m/s

Slide 5

liquid flow limitations due to viscous heating

Slide 6

parameters that affect target density in beam - @ windows - typically Al made, 75 250 m 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 T 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 T > 10 K all these targets seem to boil at the windows parameters of interest: turbulence, flow pattern, raster size, sub-cooling (a bit)

Slide 7

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

Slide 8

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

Slide 9

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

Slide 10

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

Slide 11

q w transverse flow designs

Slide 12

Slide 13

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

Slide 14

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

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 (well know when well 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