lh2 target for an 11 GeV Møller experiment @jlab
- prospect -
S. Covrig
hall c, jlab
14 august 2008
hp lh2 targets for pv
qweak target design
cooling power
remarks
basic design principle: minimize density reduction and fluctuations
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high luminosity ( ~ 1038 cm-2s-1), ℒ ~ 1.867e36·ℑℓρ (ℑ in µA, ℓ in cm, ρ in g/cm2)
closed loop re-circulating unpolarized targets
essential loop components:
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pump (highly turbulent flow, Re ~ 105-6)
high power heat exchanger (counterflow with he)
high power heater
Al cell with thin windows (<0.25 mm)
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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
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qw will break the 2 kW barrier
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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
high power lh2 targets for pv
used and future
design parameters and results
p/T/ m

psia / K / kg/s
L
cm
P/I
W / µA
beam spot
mm
Δρ⁄ρ
%
δρ⁄ρ
ppm
E
GeV
sample
25 / 20 / 0.6
40
700 / 40
2
1
1000
0.2
happex
26 / 19 / 0.1
20
500 / 35-55
4.8 x 4.8
6x3
?
100
3
pva4
25 / 17 / 0.13
10
250 / 20
0.1
0.1
392
0.854
e158
21 / 20 / 1.8
150
1000 / 11-12
1
<1.5
65
45/48
g0
25 / 19 / 0.3
20
500 / 40-60
2x2
1.5
238
3
qw
35 / 19 / 1
35
2500 / 180
4x4
???
<50
1
e2e
? / ? / ?
150
6000 / 100
? x ?
?????
<5
11
parameters that affect target density in beam
- bulk •
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(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
T 
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2c pl fda
ΔT(qw) = 0.55 K in 0.8 ms
E t I
2c pl va
ΔT(g0) = 2.7 K for 0.5 m/s
ΔT(qw) = 1.4 K for 2 m/s
in g0
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ΔT(g0) = 0.27 K in 0.4 ms
for laminar motion the average temperature of the fluid after passing the raster volume
T 
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E t I
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
liquid flow limitations due to viscous heating
parameters that affect target density in beam
- @ windows •
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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
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g0 3 mils exit window q = 43 W/cm2 (2x2 raster), 18 W/cm2 into the fluid
covering the beam raster area
qw 5 mils exit window 78 W/cm2 (4x4 raster), 33 W/cm2 into the fluid covering
the beam raster area
e2e 5 mils window 47 W/cm2 (4x4 raster)
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cfd simulations in fluent (without phase transition) show ΔTw ~ 10-30 K at the
wall
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this is a problem since chf correlations argue that the chf for lh2 at a wall is
about 10 W/cm2 in conjunction with ΔT > 10 K
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all these targets seem to boil at the windows
parameters of interest: turbulence, flow pattern, raster size, sub-cooling (a bit)
sub-cooled nucleation bubble models for qw in a 3” pipe
Unal model (1975)
D B1

 A1D
t
t
Kolev model
D B

A
t
t
both models were originally developed for water
for slugs to film transition Taylor instability would apply
qw 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 qw
qw is a 15 MJ reservoir
fluent summary
tables for models
prior to 606-6
606-6
ΔTbv = 0.44 K
g0-type cell for qw
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
qw transverse flow designs
qw transverse flow designs
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e158 target loop design
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1.5 m long, 3” id cell, 55
liters
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1000 W design power, ~700
W from 11 µA beam
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65 ppm density fluctuations
on helicity flip scale
qw 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 h2
side 16.4 K (above freezing)
a new phase space for an e2e h2 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 @200212 psi He target (the
cell had 7 and 8 mils Al
windows in beam),
target power 200 W,
density fluctuations 2%
of asymmetry width
remarks
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qw 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 qw experience
e2e is 2.6x the qw 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 qw density fluctuations will be a challenge, a clear picture of this
if qw achieves its goal here