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PPMS family of instruments
April 2014
outline • PPMS family
– wet: PPMS, EverCool, EverCool-‐II (SQUID also) – dry: Dynacool, VersaLab
• Temperature control – all but VL: He gas flow – VL: thermal switch
• Field control – persistent switch – no pers. switch
• Chamber control – states: vented, flooding, purged, sealed... – valves – pumps
3 kinds of messages we will have
• educaSon – How does it work?
• seUng the course – How do I use it?
• ensuring arrival – What can go wrong?
look for these icons throughout talks...
family tree branch #1: MPMS and progeny
2007 1995 1984
MPMS 3 EverCool
MPMS 3
RSO
A.C.
oven
MPMS options
2008 available
today:
MPMS MPMS-XL (MultiVu)
1998
MPMS EverCool
transport
fiber probe
EDC
EDR high pressure low field
rotator
PPMS (branch #2)
1994
Helium-3
family tree branch #2: PPMS and progeny
EverCool-2
2007 2010 2000 1994
VersaLab
PPMS
DynaCool
PPMS EverCool
ACMS
Resistivity
ACT Heat Capacity VSM TTO
Helium-3 Torque VSM oven
Dil. Fridge
ETO
PPMS options
Reliquefier for PPMS
2008 available
today:
high pressure
SPM
PPMS
Hi Vac
PPMS family: our focus here
VersaLab
DYNACOOL
PPMS PPMS EverCool-‐II
Unique Cryostat Design
• Vacuum Space
• Cooling Annulus
• Sample InserSon Tool
• Sample “Puck”
• Sealed Sample Chamber
• 12-‐pin Connector
PPMS Sample Puck™
Heat Capacity Microcalorimeter
AC Transport Puck
12-pin connector
PPMS inside
Cooling flow
Liquid Helium 4.2 K, 1 atm
Sample 1.9 – 400 K
Probe isolaSon vacuum
SuperconducSng magnet
Dewar isolaSon vacuum
Sample chamber
Pump
ATL or Goodbye! Dewar boiloff
Shield
Cooling annulus
ATL or Goodbye!
PPMS EverCool inside
• EverCool-‐II improves – uses more efficient gas cooling
– gas-‐only cooldown – more efficient QD-‐made compressor Liquid Helium
4.2 K, 1 atm
Pump
G-‐M Cryocooler
Condenser
DynaCool inside • pulse tube Cryocooler in gas
– Efficient use of available cooling
– Inherently vibraSon isolated • Large, solid copper links to
magnet – Large A/L, simple
• Helium flow cooled by direct contact with cryocooler – Large gas flows without
affecSng magnet temperature
Pump
4 K plate
Shield
Bucket
vacuum!
VersaLab inside
• smaller 0.1 W G-‐M cooler – runs on 1-‐phase 220 V
• 1st stage (40 K) cools – radiaSon shield – chamber via thermal switch
• 2nd stage (4 K) cools – SC magnet – cryopump charcoal
vacuum!
40 K
4 K
PPMS probe: closer look
Temp. control: PPMS and Dynacool
• He gas flow cools chamber • heaters in chamber block & neck • dual impedance
– main (ON/OFF): 0 – 5 gas liters/min. – low temp (“CLT”): 0.7 liters/min.
• range: 1.8 – 400 K (1.9 K for PPMS)
PPMS probe
Temp. control Sps
• use sinter filter on transfer line to clean L-‐He • change scroll pump Sp seals
– EverCool, Dynacool – 3-‐6 months interval, as needed
• low-‐T “bump” on pre-‐2013 PPMS systems – wait at 20 K to ensure monotonic cooling – app note 1070-‐300
Magnet control: PPMS
• persistent mode (top) – saves LHe – very quiet field
• driven mode (bokom) • takes ~20 sec to change modes
magnet control: Dynacool and VersaLab
• magnet always driven • filter removes noise in B-‐field
• magnet is solid conducSon-‐cooled – magnet temp. monitored
magnet power supply
filter (~ 100 ohms)
SC magnet
magnet control Sps
• reported field based only on current in magnet power supply – no field sensor in chamber
• accuracy issue for B < 1 T • app note 1070-‐207
chamber control • Seal: isolate chamber from outside • Purge/Seal: 3x flush and pump from
– dewar boiloff (PPMS) – gas bokle (DC, VL)
• Vent/Seal: leaves at 1 atm • Pump Cont.: keep pumping w/
mechanical pump, gets to ~1 torr – rotary vane (PPMS) – diaphragm (VL) – scroll (DC, PPMS EC-‐II)
• Vent Cont.: keep flooding w/ gas • HiVac: cryopump acSvely pumping
chamber control Sps
• maintain clean oil in rotary vane pump • regenerate cryopump charcoal as needed • “upper neck” region can stay cold aoer block warms to 300 K – ices up if vented: wait 1 extra hour at 300 K
• pressure gauge calibraSon is coarse, tells: – vented – purged – HiVac
wiring on sample chamber
• twisted pairs of low resistance Cu alloy – running in annulus à thermal exchange w/ He gas – roundtrip resistance from Lemo connector ~1.1 ohm
• each wire – 1m of length – 0.32mm diameter – approx. 100 pF capacitance to ground
• raSngs – 50 V DC max – 500 mA max conSnuous
End
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