Universal thermoregulating cryostat system icon

Universal thermoregulating cryostat system




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1. /onuuks.docUniversal thermoregulating cryostat system

UDC 53.082.6; 536.5

UNIVERSAL THERMOREGULATING CRYOSTAT SYSTEM



Zharkov I.P., Ermakov V.M., Safronov V.V., Tchmul A.G.

Institute of physics NAS of Ukraine, Science av., 46, 03037 Kiev, Ukraine

zharkov@iop.kiev.ua tel. +380-(44)-2651630


The search of perspective semi-conductor materials for their broad application in an engineering causes a necessitivity of a knowledge of a full picture of a phenomena, occurring in this materials. Breadth of knowledge requires a universality of used methods of measurements for a want of reasonable and economical approach to researches. Practically it is impossible to determine all physical characteristics of an object without investigations of its properties in a broad spectral range, their change under effect of the various external factors (electrical, magnetic fields, mechanical effects, etc.).

The determination of temperature dependence of its properties in a broad spectral interval is one from a methods of a study of an object. A cryosystems are the tool ensuring such researches.

The earlier offered cryostatting method /1/ was realized in cryostat systems of the UTRECS series and has ensured the high characteristic of maintenance of temperature in ranges 77,0 -300,0 (the liquid nitrogen is a work cryoagent) and 4,2-300 K (liquid helium) at minimum consumptions of cryoagents. As defects of these systems it is necessary to consider rather narrow range of their application (use in particular spectral range, limitation of application in commercial spectral instrumentation because of their dimensions etc.). Besides it is necessary to note, that cryosystem with using of a liquid helium as cryoagent only can ensure a most broad band of temperature measurements. This system by virtue of its design and technological features could not work with use of liquid nitrogen as the work cryoagent. Naturally, cryosystem, using a nitrogen as the work cryoagent the can not work with a helium. Moreover, any from the indicated models can not work with other work cryoagents, as: liquid neon, crypton etc.

It was developed the universal cryostat system, in which the indicated above defects are eliminated. The design of the cryostat, which is included in structure of a cryosystem, is shown on Fig.1.

Helium can inside a demountable outer case is surrounded by a copper shield cooled by the liquid nitrogen which fills in a nitrogen can. The helium and nitrogen cans are supported on low-thermal-conductivity thin-wall tubes attached to the top cover of the cryostat. The helium can suspension tubes are used, respectively: 1) for initial filling by the liquid helium, 2) for placing a floating the liquid helium level indicator and 3) for inserting needle valves. Valves are mounted in the tube telescopely ("one in other"). The valve of the gaseous helium supply (controlled by upper handweel) is teamed up with another needle valve of the liquid helium supply (controlled by the handwheel, too). In the upper part the helium can suspension tubes are interconnected by a collector to ensure exit of the evaporated helium into a recovery line through the exhaust pipe union. Suspension tubes and of the nitrogen can are used for the nitrogen filling in and gaseous nitrogen exit. The space between the helium can, the nitrogen can and the outer case is evacuated through a vacuum cock. High vacuum is produced by a cryopump mounted on a outside surface of the cryostat helium tank. The load-in column is centered in the outer case and has the thermostatting chamber as its bottom part. Electric heater (R=100 Ohms ± 20%, Umax=30 V ) is wound on the outer surface of the chamber. Heater leads are soldered to a connector placed on the top cover of the cryostat. A heat exchanger soldered to the bottom of the thermostatting chamber is connected to the tube of helium supply. Gaseous helium flows away from the thermostatting chamber through the column and exit pipe union. The load-in column is mounted in a gland seal and, if necessary, can be pulled down through it provided the leads of the electric heater are disconnected from the connector and capillary tube of the heat exchanger is unsoldered. The position of the column is fixed by the three screws. A slide gate is placed on top of the column. It blocks the inner channel thus making the sluice when changing the samples. To enable optical studies windows (their quantity, material and placement depends from conditions of a physical experiment) are mounted, respectively, on the case, the shield and the thermostatting chamber. To avoid the breakup of the cryostat under uncontrollable pressure increase the vacuum space, the helium can and the load-in column are protected by safety valves with bursting membranes which are pre-calibrated for the operation pressure 5-7·104Pa.

The functional scheme of the device for automatic pressure maintenance of nitrogen vapour is indicated on Fig.2. In this case in a cryosystem the device for a creation of an excess pressure in the tank with the worker cryoagent is entered. In it the pressure transducer has a set-up with specific initial pressure, for want of which thepower, bringed to the evaporator, is minimum. The schedule of dependence of voltage on the evaporator from the pressure of nitrogen vapor in a tank is shown in a Fig. 3. For a want of reduction of pressure the maximum potency is adjusted by regulation in the amplifier.

Thus this cryosystem provides:

- application of the cryostat in a serial commercial spectral instrumentation due to the small tail dimensions, easily placed in the object branch of the device;

- broad spectral range of researches due to replaceable mines with built-in cold windows from various optical materials (fused silica, quartz, selenide of zinc, , mylar etc.);

- use of one model of the cryostat at an activity with the work cryoagents of a different nature (nitrogen, neon, crypton, helium etc.);

- fast change of an object understudy without a stop of an experiment;

It is necessary especially to say about the new method of an obtaining of temperatures below 4,2 К. If in the old cryostat versions these temperatures were achieved by simultaneous pumping of the helium vapors from the mine and helium cavity of a cryostat, in the given design pumping is conducted only from the cryostat mine. Due to this were essentially reduced a liquid cryoagent consumption and time of an achievement of the lowest temperature (1,4 К) at using of the liquid helium. For an orientation of a researcher about a superfluid helium level (SHL) in a cryostat mine during an experiment the SHL level meter is established on the manipulator.

The cryostat at the choice of a researcher can be supplied with a set of manipulators ensuring:

- turn of a sample round a horizontal axis on 360 degrees, movement it upwards - downwards, turn of a sample of a rather vertical axis with simultaneous supply to a sample of the additional factors of physical effect (electrical fields etc.);

- mechanical effects on a sample;

- supply to a sample of a microwave - radiation.

The application of the temperature controller of a microprocessor type with realization of the PID-law regulation provides the smooth approach to specific temperature exponentially with high precision. The regulation can implement by a setting of a temperature manually from the forward panel of the temperature controller or under the specific program from the computer.

The following characteristics of the cryosystem are received:


Characteristics

Work cryoagent

Helium

Nitrogen

Control range of temperatures, K

1,4 - 300

70-300

Instability of temperature, K/hour, less

0,1

0,1

Stabilization of temperature, K

0,01

0,02

Cost of the liquid work cryoagent, Ltr/hour

0,08

0,15

Time of continuous activity without refilling by the work cryoagent, hour, not less

12

8



The literature

/1/ Medvedev V.S., Ermakov V.M., Vodolazskiy P.V., et all. Thermoregulating cryostat device. Invent. of USSR № 436334, MCI G 05d 23/30, G 05d 16/06, is published 15.07.74.- Reports of the inventions of USSR № 26, 27.02.75


Universal thermoregulating cryostat

Fig. 1 -

Electrical

heater

Heater exchanger

Thermostatting chamber

Changeable external and

screen windows


Needle valve

Vacuum valve

Work cryoagent can

Nitrogen can

Work cryoagent

filling

Nitrogen filling

Level indicator

sluice

Changeable column-in




Pressure

transducer


Gas exist


Amplifier


­­­­­­


Nitrogen

Evaporator

Fig.2 -

The functional scheme of the device for automatic maintenance of pressure of nitrogen vapour.


Uevap., V


40


30

20


10


P, pa


1000 2000 3000 4000 5000


Fig. 3 -

The dependence of the evaporator voltage on a gas pressure.


АННОТАЦИЯ


Разработана универсальная терморегулируемая криостатная система, обеспечивающая возможность работы практически с любым видом рабочего криоагента без изменения конструкции криостата. При применении жидкого гелия в качестве рабочего криоагента система обеспечивает регулирование температуры в диапазоне 1,4 – 4,2 - 300 К со стабильностью не хуже 0,1 К и расходе жидкого гелия не более 0,08 л/час. В случае использования жидкого азота система обеспечивает терморегулирование в диапазоне 77 ; 80 – 300 К со стабильностью не хуже 0,1 К и расходе жидкого азота не более 0,15 л/час.


АННОТАЦІЯ


Розроблена універсальна терморегульована кріостатна система, яка забезпечує можливість роботи практично з любим типом робочого кріоагента без зміни конструкції кріостата. При застосуванні рідкого гелія в якості робочого кріоагента система забезпечує регуляцію температури в діапазоні 1,4 – 4,2 - 300 К із стабільністю не гірше 0,1 К і витратами рідкого гелію не більше 0,08 л/год. У випадку використання рідкого азота система забезпечує терморегулювання в діапазоні 77 ; 80 – 300 К із стабільністю не гірше 0,1 К і витратами рідкого азота не більше 0,15 л/год.


THE SUMMARY


The universal thermoregulatting cryosystem ensuring a possibility of a work practically with any kind working cryoagent without a modification of a construction of the cryostat is developed. For a want of application of liquid helium as the work cryoagent the system ensures regulation of temperature in a range 1,4 - 4,2 - 300 K with the stability not worse 0,1 K and the consumption of liquid helium not more 0,08 Ltr/hour. In a case of use of liquid nitrogen the system ensures a thermal control in a range 77; 80 - 300 K with the stability not worse 0,1 K and the consumption of liquid nitrogen not more 0,15 Ltr/hour.

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