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