Transcript Pion production in high Z targets (experiment vs. simulation)

1 cm diameter tungsten target
Goran Skoro
University of Sheffield
Potential problems with the high
temperature, 1cm diameter,
tungsten target(s)
Shock:
it seems to be too high for
4MW beam power (50 Hz);
unexplored territory.
Cooling:
peak temperature rise
~ 600 K per pulse;
cooling by radiation –
equilibrium temperature too high
for 4MW beam power (50 Hz).
Forced cooling has to be included (this could be difficult) but the problem of high
stress persists (could be even worse).
Next pages show a few late-night thoughts (with a little help from MARS and
ANSYS) about the possibility to use the target(s) at the room temperature.
This would (almost) eliminate the fear of shock effects (material is ‘stronger’) so the
cooling scheme becomes the main concern.
Goran Skoro
Neutrino Factory target
Tungsten; 1cm diameter, 25 cm length
Beam energy = 10 GeV
Parabolic beam, r_beam = r_target
Optimal beam pulse length
3 x 2 ns bunches
energy deposition from MARS
B = 20 T
“MERIT”
- Energy deposition density –
(for 3 different target-beam scenarios)
“Study II”
Goran Skoro
“Best yield”
Neutrino Factory target
Tungsten; 1cm diameter, 25 cm length
Beam energy = 10 GeV
Parabolic beam, r_beam = r_target
Optimal beam pulse length
3 x 2 ns bunches
energy deposition from MARS
B = 20 T
“MERIT”
- Temperature rise per pulse –
(for 4 MW beam power, 50 Hz frequency)
“Study II”
~ 600 K
at the centreline
~ 200 K
at the surface
Goran Skoro
“Best yield”
Minimal value of the heat transfer coefficient needed to remove heat from the
target between the pulses as a function of the cooling time (number of targets)
Heat transfer coefficient [W/cm2K]
ANSYS result for the
“Best yield” scenario
For cooling schemes such as natural
convection (air, water), forced convection
(air, water, perfluorocarbons), spray cooling
(perfluorocarbons) the heat transfer
coefficients are well below 1 W/cm2K.
Only solution: impinging liquid jet(s).
Candidates:
FC77 (poor thermal properties),
glycol-water mixture
or ‘pure’ water.
The question is: Can we reach the heat
transfer coefficient of 8 W/cm2K needed
for the scenario of 200 x 1cm diameter
target by using the impinging water jet(s)?
25
Goran Skoro
50
100
200
Cooling
time [s]
300
400
Number of
targets
In order to reach 8 W/cm2K we need:
Mass flow rate > 20 grams/s;
Jet velocity, v > 10 m/s (more important);
Nozzle diameter (d) and nozzle-to-target
separation (S) should be carefully chosen
in order to have the core of the jet as
bigger as possible (4 < S/d < 10);
Higher number of jets instead of single jet
How to enhance heat transfer:
Jet pulsations,
Surface enhancements.
Problem:
How to construct such a complicated
cooling system (inside an already
non-trivial target concept)?
Goran Skoro
Other (non-negligible) reasons for concern
in the case of high velocity water jets:
- Instability of jet(s);
- Geometry of the target (cylinder) – positions
of the nozzles (number of jets);
- Corrosion (should be small for tungsten);
- Additional ‘stress’;
- Erosion (for high velocity jets, v > 5 m/s).
Erosion, for example
Data: scarce, but there are few short duration
tests with aluminium and copper (haven’t found
data for tungsten)
material
Jet
freq.
[Hz]
V
[m/s]
Dur.
[h]
Erosion rate
[nm/impact]
Al
33
5
5
~ 0.1
Cu
4.2
125
4
~ 5
Even if the the erosion rate for tungsten is 100
smaller than for aluminium, the projected erosion
after (let’s say) 1 Million beam pulses is at the level
of 0.5 mm (10% of the target radius). And the long
term erosion effect is much worse.