Janis CCS-150 User manual

PART 1: System Instructions

TABLE OF CONTENTS
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I.
Section 1
SAFETY:

1.1 
Safety Summary
II.
Section 2
INTRODUCTION:

2.1 
General Description

2.2 
System Components

2.3 
System Configurations and Options
III.
Section 3
INSTALLATION:
3.1 Mounting
3.2 
Power Requirements
3.3 
Compressor Cooling Requirements
3.4 Interconnections
IV.
Section 4
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OPERATION:
4.1 
Removing the Vacuum Shroud
4.2 
Sample Mounting
4.3 Evacuation
4.4 
Start-up Sequence/Cooldown
4.5 
Temperature Control
4.6 
Changing Samples
4.7 Shutdown
V.
Section 5
MAINTENANCE:
5.1 
Scheduled Maintenance
5.2 
Unscheduled Maintenance
5.3 
Maintenance Supplies
VI.
Appendix
Connector Wiring Diagrams
Test Results
Cryostat Engineering Drawing
CTI Refrigerator & Components Manual
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SECTION 1
SAFETY
1.1 SUMMARY
All safety pressure reliefs are installed to provide protection to the equipment and
operating personnel. Do not tamper with any pressure relief.
High voltage is present within the system components, and can cause serious injury from
electric shock. Follow these instructions to ensure operator safety:
1.
Disconnect all components from the electrical power source before making
component interconnections.
2.
Shut off the compressor power switch before connecting it to a power source.
3.
Do not connect the cold head power cable to the cold head while the compressor is
running.
High gas pressure is present within the system, and can cause serious injury if suddenly
vented. Follow specified procedures when assembling and disassembling the self-sealing
gas couplings on the flexible gas lines. Use caution to avoid puncturing the flexible gas
lines.
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SECTION 2
INTRODUCTION
2.1 GENERAL DESCRIPTION
Janis closed cycle refrigerator (CCR) systems provide a convenient means of cooling
samples to temperatures below 10 K, and can be used to perform a wide variety of optical
and electrical experiments between —8 K and 325 K (475 K optional). CCR systems
require no liquid helium or liquid nitrogen as a source of cooling. Instead, a closed loop
of helium gas is compressed and expanded, based on the Gifford-McMahon (G-M)
thermodynamic cycle. During the expansion phase of each cycle, heat is removed from
the cold finger, on which the sample is mounted. (A detailed description of the G-M
cycle can be found on page C-3 in the refrigerator manual). A heater and thermometer
are installed on the cold finger and are used to precisely control the sample temperature.
2.2 SYSTEM COMPONENTS
Janis CCR systems include the following components:
1.
Compressor: This provides a supply of high-pressure helium gas to the cold head. It
can be either air cooled or water cooled, and can be configured to match the available
AC voltage and frequency.
2. Cold Head: This expands the helium gas to cool the sample. It includes two cold
stations, the first stage (radiation shield mount) and the second stage (sample mount).
3.
Gas Lines: These lines are connected between the compressor and cold head supply
and return fittings, and transfer the helium gas between the two components. The gas
lines are flexible stainless steel and include quick disconnect fittings on both ends.
4.
Vacuum Jacket: This is bolted to the cold head. It includes an evacuation valve,
safety pressure relief, electrical feedthroughs, and a clamped vacuum seal for easy
access to the sample space.
5. Radiation Shield: This bolts to the cold head first stage. It is used to intercept room
temperature radiation before it reaches the sample, allowing the lowest possible
sample temperature to be achieved.
6.
Optional Temperature Controller: This may be provided for use in monitoring and
controlling the sample temperature. Detailed operating procedures can be found in
the accompanying temperature controller manual.

2.3 JANIS CCR MODELS
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Janis offers CCRs in a variety of configurations to match different experimental
requirements. The supplied system configuration is indicated on the system manual data
page. Standard configurations include:
CCS-150 
A general purpose configuration that includes four optical windows and a
3" inner diameter vacuum jacket.
CCS-250 
Intended for non-optical measurements, it includes a cylindrical stainless
steel vacuum jacket.
CCS-350 
This is compact optical configuration, suitable for use when available
space is limited. It can be supplied in a rotatable (CCR-350R) or a non-
optical (CCS-350T) configuration.
CCS-350S This sub-compact configuration is suitable for narrow gap magnets, or
optical geometries with very limited space. A non-optical version (CCS-
350ST) is also available.
A high temperature optical model with operating range from 12K - 475 K.
A very high temperature (CCS-450H) version is also available with an
operating range of up to 600 K.
CCS-450
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SECTION 3
INSTALLATION
BEFORE BEGINNING THE SYSTEM INSTALLATION, REVIEW THE CTI
COMPRESSOR AND COLD HEAD INSTRUCTIONS FOUND IN THE
REFRIGERATOR MANUAL.
3.1 MOUNTING
The Janis CCR cold head can be mounted and operated in any convenient orientation. A
mounting base with four 1/4" (M6) clearance holes is provided for mounting to a table or
manipulator. Most systems include four tapped holes on the vacuum jacket bottom
flange for mounting to an optical table with cold finger oriented downwards. The
separate compressor assembly must remain upright to all times.
3.2 POWER REQUIREMENTS
The model 8200 compressor front panel includes switches used to select system voltage
and frequency. Before connecting the compressor to any power source, be sure the
switch configuration matches the available power source. (Refer to page 3-5 in the
compressor manual for additional details).
Most temperature controllers also include selectable voltage settings. Choose the
appropriate voltage by rotating the selection wheel located at the main power connector.
Refer to the controller manual (if applicable) for additional information.
3.3 COMPRESSOR COOLING REQUIREMENTS
Model 8200 compressors are available in either air or water cooled configurations. Air
cooled compressors must be located with free access to the front and rear panels, to avoid
restriction of the air flow. Water cooled compressors require a continuous flow of
cooling water for operation. (Refer to the compressor manual pages 3-3 through 3-5 for
complete details).
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3.4 SYSTEM INTERCONNECTIONS (SEE FIGURE 3.1)
Gas Lines - Interconnecting helium supply and return gas lines should be installed in the
sequence described on page
3-1
of the compressor manual. Use two wrenches when
tightening the fittings and support the gas lines to prevent gas leakage during assembly.
Cold Head Power - Connect the supplied cable from the compressor "cold head power"
outlet to the matching connector on the cold head motor. Be sure the compressor power
is off when making this connection.
Temperature Controller (when applicable) - Connect the supplied thermometry cable
from the cold head 10-pin electrical feedthrough to the automatic temperature controller.
The dual "banana plug" should be connected to the heater output and low terminals. (If
no temperature controller is supplied with the system, a 10-pin mating connector is
provided for attaching to a user supplied controller and cable).
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SECTION 4
OPERATION
4.1 REMOVING THE VACUUM SHROUD (SEE FIGURE 4.1)
1.
Before removing the vacuum shroud, vent the vacuum space by turning the shroud
evacuation valve knob counter-clockwise.
2.
Remove the clamp located just above the evacuation valve, and carefully lift the
shroud off the refrigerator.
3.
Remove the four 6-32 screws that hold the radiation shield to the cold head, and lift
the radiation shield off the refrigerator. The cold head sample mount and sample
holder are now accessible.
4.2 SAMPLE MOUNTING
Most CCR systems are supplied with a sample holder. If the sample holder is removed, a
thin film of thermal grease (such as Crycon) or thin indium foil should be used to
enhance thermal contact when reinstalled. Grease or indium can also be used to improve
the thermal contact between the sample and sample holder.
Janis CCR systems include provisions for additional electrical feedthroughs for customer
wiring of the samples. Small gauge wires (32 AWG, 35 SWG) should be used to
minimize heat leak into the sample, and the wires should be thermally anchored in
several spots to the cold head using Stycast epoxy, GE 7031 varnish, by tying with nylon
string or floss, or by using mylar or aluminum tape (See figure 4.2). Once the sample is
mounted to the cold head, install the radiation shield and vacuum shroud. Any visible
dirt or lint on the sealing gasket is sufficient to cause a vacuum leak, so be sure the gasket
and flanges are clean and lightly greased before mounting the vacuum shroud.
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VACUUM FLANGE
ACUATION VALVE
ERATOR KNOB
1/4-20 TAPPED MOUNTING HOLES
VACUUM SHROUD
,Z Z--
VACUUM FLANGE
RADIATION SHIELD
RADIATION SHIELD MOUNTING SCREWS
SAMPLE MOUNT
SAMPLE HOLDER
SYSTEM ACCESS
FIGURE 4.1
S
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TO SAMPLE
THERMOMETER 
SUGGESTED SAMPLE
WIRING THERMAL
ANCHOR LOCATION
TO CONTROL
THERMOMETE
AND HEATER
SAMPLE WIRING
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SYSTEM WIRING
FIGURE 4.2
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4.3 EVACUATION
Janis CCR systems are equipped with a bellows sealed evacuation valve, which allows
evacuation and sealing of the insulating vacuum jacket. Prior to cooldown, connect a
turbomolecular or diffusion pump to the valve and evacuate the shroud to a pressure of
1.0 x 
torr or less. Better vacuum levels provide greater insulation, resulting in
shorter cooldown times and lower final temperatures. A cold-trapped mechanical
vacuum pump can be used instead; however, this may limit the lowest temperature
attainable.
The evacuation valve can remain open during the initial phase of the system cooldown.
However, it should be closed before the sample temperature reaches 200 K to avoid
backstreaming of oil from the vacuum pump into the cryostat. Outgassing and o-ring
permeation will cause the pressure to rise slowly over time, therefore periodic re-
evacuation may be necessary. Re-evacuation is required whenever a new sample is
installed, or when the minimum temperature obtained begins to increase.
The CCS-450 high temperature model is equipped for operation to 475 K. When
operating above 325 K, the system should be evacuated continuously to prevent
contamination due to heater outgassing.
4.4 CRYOSTAT COOLDOWN
Switch on the automatic temperature controller and observe the temperature readings.
Temperature values of —290 K to 300 K should be displayed.
Review Section 3 of the CTI compressor manual before beginning the cooldown.
Establish a flow of cooling water as described in the CTI manual, then switch on the
compressor. The temperature should begin to drop within a few seconds, and the system
will achieve 10 K in about 1 hour.
Occasionally, time constraints will not permit thorough evacuation before the cooldown
begins. In this case, water vapor and other condensables can freeze out and contaminate
the sample. To avoid this problem, the cold finger can be kept at 300 K (using the
automatic temperature controller) during the first 40 minutes of operation, which will
cause the contaminants to settle on the cold radiation shield rather than on the sample.
An additional 20 - 30 minutes will be needed for the sample to reach the base
temperature. (This technique only needs to be used if initial system pressure is greater
than 5 x 10 -3 ton).
4.5 TEMPERATURE CONTROL
Most systems are supplied with an automatic temperature controller, silicon diode
thermometer, and 25 ohm control heater. Options include other diode or resistance
thermometers, thermocouples, and different heater resistance. The actual configuration
of your system can be found on the data sheet contained in this manual.
Most Janis CCR models operate from <10 K to 325 K. (The CCS-450 operates from —12
K to 475 K). Choose a temperature setpoint from within the appropriate range, and enter
values from Proportional (P), Integral (I), and Derivative (D) parameters. Some