Yury Sobolev - Petersburg Nuclear Physics Institute

Status of the UCN sources
at the TRIGA Mainz reactor
Institut für Physik, University of Mainz:
W.Heil, A.Kraft,Th. Lauer, Yu. S., Th. Zechlau
Institut für Kernchemie, University of Mainz:
K.Eberhardt, G.Hampel, Ch.Plonka-Spehr, N.Trautmann
Petersburg Nuclear Physics Institute, Gatchina, Russia
Yu.Borisov
2011
Yury Sobolev
TRIGA Mark II - The last TRIGA in Germany
two operation modes:
steady state:
100 kWth , 1012 n/cm2s
pulse mode
250 MWth (30 ms), 1015 n/cm2s
every 5 min
“UCN C” - Prototype at the tangetial beamport
~ 200cm³ sD2
2006-2009: Investigation of working parameters
First UCN produced in Mainz (Jun.2006)
A.Frei, et.al, Eur. Phys. J. A 34, 119-127 (2007)
Investigation of solid deuterium
2007: Starting Time of flight investigations
Reactor operating at 100kW
Countrate in beam 1500 cts/s
I.Altarev, et.al, Eur. Phys. J. A 37,9-14 (2008)
Investigation of source parameters from 2008-2009 (see diss. Th.Lauer)
“How to prepare a good sD2 crystal?”
Freezing the UCN converter from gas phase
Procedure is important for quality
7
new freezing technique
UCN yield [a.u.]
6
old freezing technique
5
4
3
2
Polycrystal with bad thermal conductivity
1
0
0
2
4
sD2 quantity [mol]
6
8
•
Keep the converter temperature constant at 6K (+/- 0.1K)
•
Growing speed < 4mm/h
Results of the prototype (end 2009)
- Proof of principle sucessfully demonstrated
- Optimal crystal parameters exists now (for Mainz!)
- UCN mean free path in sD2 (23 +/- 5) mm (in Mainz!)
140
120
intensity [a.u.]
PF2 Testbeam
Countrate in 2009:
100
UCN C Triga
Mainz
80
60
40
Factor 7
20
0
3
8
13
velocity [m/s]
18
~ 3300 cts/s
Results of the prototype (end 2009)
9.5l stainless steel volume
Distance to converter 6m
4 UCN/cm³ confirmed in a storage experiment (beamport C)
UCN D (a UCN source for beamport D)
x 1013
10
radial beam tube D
neutrons/cm 2
total
thermal neutrons
1
radial beam tube D
 thermal neutron fluence
 total neutron fluence
0.1
tangential beam tube C
0
10
20
30
40
50
60
70
80
90 100 110
distance cm
Factor 3 - 4 higher neutron fluence per reactor pulse in beam tube D
Future plans in Mainz ( UCN user facility!)
„UCN C“
Pulsed :
~ 10-15 UCN/cm³
Continous:
PF2 testbeam
Improved source concept
„UCN D“
Only Pulsed
~ 30-40 UCN/cm³
A new UCN D source concept
Only liquid helium
Screenshot of LabView Source Program
Improvements
Think about an efficient premoderator!
premod
Solid deuterium
15 mm solid para hydrogen
Gain
2.5
6 mm solid methane
Gain
4
Some pictures: alu nose variant and gas system
Control center of the TRIGA Mainz UCN source
1. Test: growth of a sD2 cryo-crystal with simultaneous
freezing of hydrogen premoderator:
Dewars
Completion
exchange of the freezing
Nose temperature during H2/D2 freezing
and pulsed operation of TRIGA after
Dewars
exchange
Completion
of the freezing
H2/D2 pressure during freezing and
Pulsed operation of TRIGA after
Conclusion:
1. freezing H2/D2 simultaneously results in a non perfect sD2 crystal
2. Hydrogen premoderator decrease sD2 crystal from heat load from
reactor core (observed)
Problem: freezing of hydrogen premoderator needs about 12h
First ucn storage measurement at UCN D
UCN D: results of ucn storage experiment I
TOF comparison
UCN D, nocado 45° bend
UCN C, glass 45° bend
UCN C, nocado 45° bend
Comparison of TOF measurements for UCN D and UCN C sources: Setup for
storage experiment is 1m higher than beam axis, both shutters where opened.
One can see approx. same temporal behaviour for ucn/vcn arrival time, slightly
faster arrival for UCN C can be explained with a shorter distance to sD2 converter.
UCN D: results of ucn storage experiment II
UCN storage curve (red points, stat. error bar are too small to be visible) with two
exponents fit: p0*exp(-t/p1)+p2*exp(-t/p3), fit errors are statistical, ucn density extrapolated
to t=0:
ρ(0) = 7.44 ( 9.51) ucn/cm^3 – - for nocado(glass) bend 45°
Conclusion and outlook:
• construction of UCN D is completed and source currently
can be operated in test regime
• UCN density of 10 cm-3 achieved in storage volume of
10 liters (preliminary) with clear understanding on how to
improve it up to 30-40 ucn/cm3
• Steps towards a UCN user facility at TRIGA Mainz
- on-site He-liquifier for long-term runs with ucn sources,
- an experimental platform
- additional reactor stuff (operateurs ) to provide continuous reactor
operation for at least 30 days
Thank you
for your attention !