Takeyasu ItoUniversity of Tennessee
EDM Collaboration meeting August 19-20, 2004
Nature of a Separate Production Cell
• What dimensions are appropriate and what UCN density can be achieved?
• What fill time for the production cell (4 liter) will be required with a 1” aperture connecting pipe?
• What should be the time for the ultra-pure helium to become contaminated with 3He?
Takeyasu Ito 2
ModelMeasurement cell
Production cell
Connecting tube
Beam
Parameters•Measurement cell volume: Vm= 7cm x 10cm x 50cm = 3500cm3
•Connecting tube cross sectional area: Atube = (2.5/2)2 = 5cm2
•Production volume length: Lp=100 cm•Production volume cross sectional area: Ap=20cm x 20cm = 400 cm2
•Beam cross sectional area: Abeam= 10cm x 10cm = 100 cm2
•UCN production rate: Rp= 1 ucn/cm3/sec•UCN velocity: vucn= 600 cm/sec•Cell lifetime: cell = 1200 sec•Neutron lifetime: beta = 886 sec
Takeyasu Ito 3
EquationsWhen the valve is closed:
ddtVmnm
1
1
cell
Vmnm
ddtApLpnp AbeamLpRp
1
1
cell
ApLpnp
When the valve is open:
ddtVmnm
1
1
cell
Vmnm vucnAtube
4np nm
ddtApLpnp AbeamLpRp
1
1
cell
ApLpnp vucnAtube4
np nm
Takeyasu Ito 4
ResultsU
CN
den
sity
nm
np
Valve opens at t=2500 s
Time (s)
np0 Rp p
tot AbeamAp
nm0 np
0 VpVp Vm
pfill p
tot
Takeyasu Ito 5
ResultsU
CN
den
sity
nm
np
Valve opens at t=2500 s
Time (s)
mfill
4VmvucnAtube
Takeyasu Ito 6
Summary• UCN density in production cell
• Production cell fill time
• UCN density in measurement cell
• Measurement cell fill time
• In order for nmsep~nm
combined, Vp»Vm
• If pcell > m
cell, then perhaps nmsep > nm
combined possible
np0 Rp p
tot AbeamAp
pfill p
tot ~ 500s
nm0 np
0 VpVp Vm
mfill
4VmvucnAtube
~ 5s