OPERATING INSTRUCTIONS FOR THE JANIS RESEARCH ST
Contents
1.2. Once the sample is mounted to the system reinstall 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 4 3 EVACUATION Janis ST systems must be evacuated for proper performance The system includes two independent vacuum spaces One vacuum space is used to insulate the high efficiency transfer line while the other vacuum space surrounds the sample region Both spaces are evacuated prior to shipment from Janis but it is recommended that both be re evacuated prior to use Both vacuum spaces utilize a low leak rate evacuation valve which allows evacuation and sealing Prior to operation connect a turbomolecular or diffusion pump to the transfer line evacuation valve located just above the flow regulator valve and evacuate to a pressure of 1 0 x 107 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 reduce the transfer efficiency The rigid leg of the transfer line incorporates an activated charcoal getter to help maintain good vacuum levels when the leg is inserted into a cryogen storage dewar For this reason it is preferable to maintain vacuum in the transfer line at all times and to never allow helium gas or moist air to
3. flow valve completely and wait until the sample temperature stabilizes or begins to increase As in step 6 above open the flow regulator just enough to reach 77 K Too large a flow will cause liquid to collect inside the sample mount making temperature control at higher temperatures difficult or impossible 4 6 OPERATION For operation at 4 2 K or 78 K with LN gt the flow regulator valve should be opened just enough to maintain this temperature at the sample mount The flow rate required is a function of the heat load into the cold finger and will vary depending on configuration and experimental application For operation above 4 2 K or 78 K with use an automatic temperature controller as described in section 4 7 below Once the temperature is above 20 K the flow regulator valve can be partially closed reducing the LHe consumption significantly Adjustments in the flow regulator setting can be made at any time either to increase the cooling power or reduce the cryogen consumption In general the smallest flow rate should be chosen that will cool the sample to the desired temperature For elevated temperatures choose a setpoint using the automatic temperature controller The temperature controller will supply power to the contro heater and will stabilize the system at the selected temperature setpoint Continuous operation below 4 2 K is achieved by reducing the pressure at the helium vent port with a mechanical vacuum pump T
4. system that interfaces with samples It includes a copper cold finger with tapped mounting holes heater and thermometer for monitoring and regulating the temperature The system is designed to operate with either LN gt or LHe as the working cryogen High efficiency transfer line The ST transfer line combines vacuum insulation with multilayer superinsulation to provide low cryogen losses during transfer A needle valve flow regulator is built in to the transfer line One end of the transfer line is inserted into the cryogen storage container while the other end is inserted into the cold finger cryostat Radiation shield This shield usually fabricated from polished aluminum tubing is mounted to a thermal anchor on the cold finger cryostat It intercepts room temperature radiation thereby reducing the heat load on the sample This helps the system achieve lower sample temperatures Vacuum jacket Most ST systems include a vacuum jacket that surrounds the cold finger cryostat Vacuum Jackets are available in a variety of configurations including optical compact and tubular The ST 400 cryostat for UHV is generally not equipped with a vacuum jacket Optional temperature controller Many types of automatic temperature controllers are available for use with the ST system These controllers allow the user to select a desired control temperature while adjusting several other control parameters including proportional and integral values The t
5. where the heat capacities are smallest the P value should be low and the 1 value should be high Derivative D control can usually remain zero throughout the operating range As the control temperature is increased larger proportional and smaller integral values can improve temperature stability and response time Some controllers include an autotuning function that selects appropriate PID values automatically This function is most useful only for temperatures above 50 K For complete discussion of this feature as well as comprehensive controller operating procedures and specifications refer to the temperature controller manual 4 8 CHANGING SAMPLES Before changing samples the cold finger should be warmed to room temperature This can be accomplished in either of two ways 1 The flow regulator valve can be closed and the system allowed to warm up for several hours Use the control thermometer to determine when the system is approaching room temperature 2 The flow regulator valve can be closed and the temperature controller set for 295 K Once the thermometer reaches 295 K wait until the heater power approaches 0 The evacuation valve can now be opened and the sample changed as described in sections 4 1 and 4 2 Dry nitrogen or argon gas can be used to break the vacuum if the sample is particularly sensitive to water vapor WARNING The radiation shield will remain cold even after the sample has warmed to room tempera
6. ION BAYONET VITON O RING SAFETY VALVE CONNEC TION oo SEALED 8 PIN PRESSURE FEEDTHROUGH RELIEF T FORCE NG ER GENERATOR J 7 HIGH NW 25 NW 25 A Rn FLOW VALVE gt FLANGE CRYOGEN A REGULATOR N ER zen ma Y 0 0 4 5 NOMINALROTATABLE T Sl CONFLAT 63CF NIN 1 7 PIN UHV 74 5 NOMINAL CONFLAT FEEDTHROUGH 2 4 DOUBLE SIDED _ CONCENTRICITY SPACER 48 0 NW 25 0 75 OD CRYOGEN VENTING 50 OD AT GUIDE TUBE DETACHABLE RADIATION SHIELD ANCHOR FEEDTHROUGH 0 50 0 D P50 REDUCER STORAGE 38 1mm 2 75 TO 1 33 DEWAR LES 5 00 FEEDTHRORGH NOMINAL 50 OHM CARTRIDGE HEATER amp PROVISION FOR SENSOR INTERNAL 1 00 DIA COPPER SAMPLE MOUNT WITH PROVISION FOR SENSOR GOLD PLATED CRYOGEN ENTRY 1 00 DIA COPPER AND NEEDLE VALVE SAMPLE MOUNT W 4 M3 TAPPED HOLES ON 75 19 1mm DBC NOTE ALL DIMENSIONS ARE IN INCHES JANIS RESEARCH CO WILMINGTON MA CONFIDENTIAL AND PROPRIETARY THIS DRAWING AND OR INFORMATION CONTAINED HEREIN IS THE SOLE PROPERTY OF RESEARCH COMPANY ANO iS NOT TO BE RELEASED OR DIVULGED TO THIRD PARTIES WITHOUT THE EXPRESSED WRITTEN CONSENT OF THE JANIS RESEARCH COMPANY INC M6 TAPPED CENTER HOLE HELICOIL VIEW CUST APPROVAL A a PN sat 1781
7. OPERATING INSTRUCTIONS FOR THE JANIS RESEARCH ST 400 UHV SUPERTRAN SYSTEM Janis Research Company 2 Jewel Drive P O Box 696 Wilmington MA 01887 0696 978 657 8750 CAUTION The ST 400 cryostat contains components that should not be operated in excess of 475 K approx 200 C Care should be taken not to heat the exterior portion of the cryostat above 200 C for extended periods of time as this will degrade the o ring seals which seal the inner cryostat s insulation vacuum space from the room environment NOTE The cryostat helium introduction vent space is entirely separate from user s UHV space In the event of a failure of the seals mentioned above the UHV chamber will NOT be contaminated TABLE OF CONTENTS Section 1 SAFETY 1 1 Safety Summary Section 2 INTRODUCTION 2 1 General Description 2 2 System Components Section 3 INSTALLATION 3 1 Mounting 3 2 Electrical Connections Section 4 OPERATION 4 1 Removing the Vacuum Shroud 4 2 Sample Mounting 4 3 Evacuation 4 4 Initial Cooldown with LHe 4 5 Initial Cooldown with LN 4 6 Operation 4 7 Temperature Control 4 8 Changing Samples 4 9 System Shutdown Section 5 MAINTENANCE 5 1 Scheduled Maintenance 5 2 Unscheduled Maintenance 5 3 Vacuum Leaks 5 4 Wiring WIRING DIAGRAM ASSEMBLY DRAWING SECTION 1 SAFETY 1 1 SUMMARY All safety pressure relief valves are installed to provide protection to the equipment and operati
8. agram at the end of this manual for specific sensor and wiring details If no temperature controller has been supplied with the system refer to the appendix for pin assignments of all feedthroughs installed on the dewar Mating connectors are supplied which allow the user to attach cables as needed SECTION 4 OPERATION 4 1 REMOVING THE VACUUM SHROUD Before removing the vacuum shroud vent the vacuum space by turning the shroud evacuation valve knob counter clockwise Next remove the clamp located just below the evacuation valve and carefully lift the cryostat out of the vacuum shroud Finally remove the radiation shield mounting screws and lift the radiation shield off the cold finger The sample mount and sample holder are now accessible 4 2 SAMPLE MOUNTING Most ST 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 ST systems include provisions for additional electrical feedthroughs for customer wiring of the samples Small gauge wires 32AWG should be used to minimize heat leak into the sample and the wires should be thermally anchored in several spots to the cold finger by using Stycast epoxy varnish by tying with nylon string or floss or by using mylar or aluminum tape
9. emperature controller then maintains the desired temperature by applying power to the control heater Controllers purchased through Janis Research include cabling and are tested with the cryostat SECTION 3 INSTALLATION 3 1 MOUNTING The ST system is designed to operate in any orientation Greatest efficiency is achieved when operated in the vertical position Most ST systems include tapped holes on the base of the vacuum jacket which can be used for mounting to an optical table Compact systems such as the ST 300 and ST 300T include additional mounting holes on the instrumentation skirt 3 2 ELECTRICAL CONNECTIONS If an optional automatic temperature controller has been supplied with the ST system refer to the accompanying controller manual and connect to the appropriate AC outlet Automatic temperature controllers operate by using a feedback control loop in which the controller sends output to the control heater based upon the signal from the control thermometer For this reason it is important that the control heater and thermometer both be attached to the same copper block to prevent temperature oscillations When thermometers are supplied at both the cold finger for control and the sample holder for monitoring the sample temperature be sure the cold finger thermometer is designated as the control channel In most cases the control thermometer will be assigned to Channel A of the controller Refer to the accompanying wiring di
10. enter this vacuum space In the event moisture or helium gas accidentally contaminates the transfer line vacuum space re evacuate the line for several days before operating again The transfer line vacuum valve should be closed prior to the beginning of cooldown Next connect the vacuum pump to the cryostat evacuation valve and pump out the cryostat insulating vacuum space The cryostat evacuation valve should also be closed once evacuation is complete 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 will be necessary Re evacuation of the cryostat is required whenever a new sample is installed or when the minimum temperature obtained begins to increase NOTE Some ST systems are equipped for operation at high temperatures When operating above 325 K these cryostats should be evacuated continuously to prevent contamination due to heater outgassing 4 4 INITIAL COOLDOWN with liquid helium 1 For quickest cooldown and best results attach a mechanical vacuum pump to the LHe venting port of the cryostat and evacuate this space continuously during the first phase of cooldown This removes any air or moisture remaining in the line from a previous run and shortens the cooldown time by several minutes 2 Close the flow regulator valve at the transfer line storage dewar leg by turning the knurled bra
11. he flow regulator valve can be partially opened continuously replenishing the LHe inside the cold finger and resulting in a constant temperature of 2 5 K or less In order to reach the lowest possible temperature the flow valve should be opened several turns and should remain open for about 5 minutes This will allow LHe to fill the space inside the cold finger Next the flow regulator valve should be completely closed and the pressure inside the cold finger region reduced using a vacuum pump on the LHe vent port The minimum temperature typically about 1 5 K will be maintained until all the LHe is depleted from inside the cold finger about 8 minutes The process can be repeated as desired 4 7 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 thermometry can be found on the wiring diagram at the end of this manual Most Janis ST systems operate from 1 5 K to 325 K though an optional 500 K upper limit is available Choose a temperature setpoint from within the appropriate range and enter values for Proportional P Integral I and Derivative D parameters Some experimentation may be required to optimize these settings for a particular application In general when operating at the lowest temperatures
12. m gas will need to be added to maintain constant pressure in the storage dewar 5 After a short wait typically 5 10 minutes the sample mount will begin to cool rapidly At this time the vacuum pump should be disconnected from the system and the escaping helium vapor vented into the atmosphere or gas collection system Be sure to allow the pump to reach atmospheric pressure before disconnecting to avoid introducing air and moisture into the line 6 Once the sample mount temperature reaches about 5 K the flow regulator can be closed until the sample temperature begins to increase Open the regulator just enough to cool the sample mount to 4 2 K For best operating efficiency it is best to open the regulator valve just enough to maintain the desired minimum temperature 4 5 INITIAL COOLDOWN with liquid nitrogen Cooldown with LN is very similar to operation with LHe and the procedure above can be used with the following exceptions l Because LN will freeze when it is pumped it is best not to initiate transfer with a vacuum pump Instead use a storage dewar pressure of about 5 psi and open the flow regulator valve about 3 turns It will take 5 10 minutes before the sample mount temperature begins to drop 2 Itis often necessary to add gas pressure to the storage dewar to maintain constant pressure of 5 psi Either helium or nitrogen gas can be used for this purpose 3 Once the temperature reaches about 100 K close the
13. ng personnel Do not tamper with any pressure relief valve During sample change it is possible for the radiation shield to remain cold even after the sample has warmed to room temperature Use gloves when handling a cold radiation shield to avoid low temperature burns During system shutdown the transfer line leg will be extremely cold upon removal from the storage dewar Do not touch the transfer line with bare hands Always wear insulating gloves when handling the transfer line after use Do not bend the transfer line to a radius of less than 8 inches to prevent possible damage to the inner line Do not close the flow regulator valve on the transfer line more than hand tight Never use a wrench or any tool on the flow regulator knob to prevent damage to the needle valve and seat SECTION INTRODUCTION 2 1 GENERAL DESCRIPTION The Janis Research SuperTran ST System is a continuous flow research cryostat that can be used to perform a wide variety of experiments in the temperature range from 1 5 to 325 K 500 K or 700 K optional Liquid helium or nitrogen is continuously transferred through a high efficiency superinsulated line to a copper sample mount inside the cryostat vacuum jacket A needle valve is incorporated in the transfer line and is used to regulate the cryogen flow to the sample mount 2 2 SYSTEM COMPONENTS The Janis ST system includes the following components l Cold finger cryostat This is the part of the
14. ss operator knob counter clockwise Insert the transfer line cryostat leg into the cryostat o ring sealed port and tighten the brass o ring seal nut to form a gas tight seal 3 Slowly insert the storage dewar leg of the transfer line into the LHe storage dewar For easiest adjustment of the transfer rate the storage dewar should be equipped with a 0 5 psi pressure gauge a venting valve and a hose adapter for adding helium gas pressure if necessary As the leg enters the storage dewar open the flow regulator valve about 2 3 turns and monitor the pump pressure or exhaust for a few seconds to confirm that the flow is not restricted The pump pressure should increase slightly and the exhaust of the vacuum pump will typically show traces of oil vapor The flow rate is quite small during the initial phase of the transfer until the entire inner line becomes cooled Close and open the valve several times during the first few minutes of transfer to be sure the valve does not freeze shut during cooldown and that the flow is not restricted Once the leg is fully inserted into the storage dewar raise the leg about 1 cm from the storage dewar bottom to minimize the chance of frozen debris entering the line 4 In general heat introduced by conduction down the transfer line leg is sufficient to maintain positive pressure in the storage dewar Adjust the storage dewar vent valve to maintain a storage dewar pressure of 2 psi In some cases heliu
15. to reach 4 are indications of a vacuum problem Ifthese symptoms appear re evacuate the shroud as described in paragraph 4 3 If the symptoms disappear no further action should be required If the symptoms remain or reappear quickly a vacuum leak may be present Contact Janis Research to obtain further direction in this case 5 4 WIRING Occasionally a heater or thermometer wire may be broken during sample removal or installation If this occurs reconnect the broken wire using 60 40 rosin core solder Be sure to insulate the joint with shrinkable PVC tubing or Teflon insulation The heater located at the sample mount is designed to accept the normal output of most temperature controllers Occasionally however a heater may burn out Replacement heater kits are available from Janis and include all materials and instructions necessary for replacement 12 CRYOSTAT SERIAL NUMBER 11452 8 PIN FEEDTHROUGH LOCATION GUIDE TUBE PIN A POS CURRENT I PINB POS VOLTAGE V DT 670B SD DIODE D6008395 PINC NEG CURRENT 1 ON INTERNAL HEATER POST CONTROL SENSOR CURVE 02 PIN D NEG VOLTAGE V PINE PIN F PING 50 OHM CARTRIDGE HEATER ON INTERNAL HEATER POST PIN H 72 LONG FLEXIBLE TRANSFER LINE CRYOGEN REVISIONS ERJ 7 DESCRIPTION A RADAIN SELD FROM 1 75 00 10 0 OD a aca wei N i sd EVACUAT
16. ture Use gloves when handling a cold radiation shield to avoid low temperature burns or wait until it warms to room temperature before handling 4 9 SYSTEM SHUTDOWN To shut down the system simply close the flow regulator valve and turn off the temperature controller If possible mount a pressure relief valve on the helium venting port This will permit any cryogen remaining in the inner line to vent safely to atmosphere while preventing any air or moisture from entering the cryostat The storage dewar should then be vented to atmospheric pressure and the transfer line storage dewar leg removed from the storage dewar WARNING The transfer line leg will be extremely cold upon removal from the storage dewar Do not touch the leg with bare hands Always wear insulating gloves when handling the transfer line after use 11 SECTION 5 MAINTENANCE 5 1 SCHEDULED MAINTENANCE The Janis SuperTran system requires no regularly scheduled maintenance The exterior surfaces of the vacuum jacket can be cleaned with a spray household cleaner periodically as necessary The transfer line should be evacuated periodically as discussed in section 4 3 5 2 UNSCHEDULED MAINTENANCE Unscheduled maintenance may be occas onally required to repair problems arising during the course of operation These problems may be related to vacuum leaks or wiring failure 5 3 VACUUM LEAKS Condensation on the outside of the vacuum jacket and inability
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