Janis Physicist Presenting 
Three Abstracts at LT-23

1. UHV He-3 Cryostats for SPM Application Near 300 mK
2. Cryogen-free Two Stage Adiabatic Demagnetization Refrigerator
3. Single Stage Cryogen-free He-3 Cryostat

ID number : LT2586
Program number: 25EP10 - To be displayed August 25, 2002 from 12:00 to 19:00.

UHV He-3 cryostats for SPM application near 300 mK

Authors: Z. Zhao, M. Jirmanus, E. Bobb

Various types of He-3 cryostats have been developed for Scanning Probe Microscopy application in a UHV environment.  These systems provide base temperatures between 280 mK to 340 mK, with hold time of 24 hours to several days.  A variety of designs have been developed including:

• A top-loading system into an UHV sample chamber, with a fixed He-3 stage.
• A He-3 insert that can be translated through a linear motion manipulator with the sample bottom or side loaded into the high field region of a superconducting magnet (solenoid or split coil).
• He-3 systems that either share the UHV space with the dewar, or have their own separate UHV space.
• He-3 inserts with a high field superconducting magnet and an integrated ESR modulation coil.

Design and performance details will be discussed.

ID number : LT2709
Program number: 26EP31 - To be displayed August 26, 2002 from 12:00 to 19:00.

Cryogen-free Two Stage Adiabatic Demagnetization Refrigerator

Authors: M. Jirmanus, Z. Zhao, L. Bobb

A cryogen-free adiabatic demagnetization refrigerator (ADR) has been developed using a 4 K pulse tube cryocooler.  Gallium Gadolinium Garnet (GGG) and the Ferric Ammonium Alum (FAA) were used for the first and second stage of the ADR, with Kevlar string supports for each stage.  The FAA stage reaches a base temperature below 50 mK, and remains below 100 mK for more than two days.  Special highly conductive flexible thermal links are employed to intercept any vibration generated by the pulse tube cryocooler and its compressor.  The performance of this cryo-cooled ADR is better (lower base temperature and longer hold time below 100 mK) than the equivalent liquid helium-based system.  A gold-plated 0.25” diameter OFHC copper rod serves as the cold finger sample mount, and ports are included in the system for adding windows or cold finger extensions as needed.  Design and performance details of the systems will be discussed. 

ID Number : LT2710
Program number: 26EP32 - To be displayed August 26, 2002 from 12:00 to 19:00.

Single Stage Cryogen-free He-3 Cryostat

Authors: Z. Zhao, M. Jirmanus, L. Bobb

We have developed a cryogen-free He-3 cryostat, which uses a two stage G-M cryo-cooler for He-3 condensation.  After the He-3 gas is condensed, an internal charcoal sorption pump is used to pump the He-3 pot down to near 300 mK.  Details of the design, fabrication, operation, and performance are presented.  

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