Ametek ORTEC MOBIUS-B, User Manual, Page: 7 / 28

1
ORTEC MÖBIUS
™
RECYCLER
CONDENSING LIQUID NITROGEN HPGE DETECTOR COOLING SYSTEM
1. INTRODUCTION
The ORTEC MÖBIUS Recycler integrates a Sunpower® CryoTel® Stirling-cycle cryocooler with a specially designed
28 liter liquid nitrogen (LN2) dewar to yield a high-reliability HPGe detector cooling system. This is especially useful for
counting laboratories that have periodic power failures. The MÖBIUS fits easily under standard lead shields with the
same footprint as a regular dewar. The remote status display can be mounted outside the lead shield for easy
visibility.
A continuously operating MÖBIUS requires refilling only once every two (2) years — a major savings in worry, time,
money, and exposure to LN2 handling risks. During a power failure, the MÖBIUS performs as a standard dewar. After
power is restored, check the LN2 level and top it off if necessary — that’s all it takes to return the system to maximum
performance.
The MÖBIUS supports our Streamline and PopTop® detector lines, and horizontal as well as vertical dipstick-type
cryostats. In addition, a number of non-ORTEC cryostats and detectors are supported; contact your ORTEC
representative for more information. If you have purchased a detector in addition to a MÖBIUS, all detector-specific
information is included in the detector’s data sheet and user manual.
1.1. HOW MÖBIUS WORKS
The MÖBIUS has a computer-controlled pressure system that maintains a
constant and stable 0.5 psi (3.5 kPa) in the vapor space of the dewar. A
pressure transducer feeds the pressure in the dewar to the onboard
computer, which controls the rate at which the Sunpower cryocooler re-
condenses the nitrogen vapor to liquid. The cryocooler operates only when a
cryostat is installed and the two fill/vent valves are closed (i.e., when the
system is pressurized). This evaporation/re-condensation process is
illustrated in Figure 1.
The fill collar has redundant pressure relief valves designed to open if the
pressure exceeds 1 psi (6.9 kPa). In the event of power loss the cryocooler
stops, the pressure inside the vapor space starts increasing, and nitrogen
vapor slowly begins escaping into the atmosphere via the pressure relief
valves. However, if power remains on and the system is operating in an
uninterrupted steady state, there is no LN2 loss and the system can operate
indefinitely without an LN2 refill.
The LN2 level monitor calculates the level of liquid nitrogen in the dewar,
giving you ample opportunity to schedule maintenance.
1.2. UPS INTEROPERABILITY
The MÖBIUS is designed to run on ac mains power. However, during a power
failure it acts as a conventional dewar and can keep a detector cold for
200 hours or more, depending on the level of LN2 in the dewar. When power is restored, the unit’s cryocooler restarts
and it resumes recycling nitrogen gas boil-off as before.
Figure 1.