FIELD OF INVENTION
[001] The present invention relates to the development of a helium gas based closed cycle
cryogenic test system for characterization of high temperature superconducting (HTS)
coils. In particular, the present system comprises of a helium gas chamber containing the
5 high temperature superconducting coil to be tested, a vacuum chamber over helium
chamber, a cryo-cooler or cryo-refrigerator to facilitate closed cycle flow of helium gas
and an interface arrangement connecting helium and vacuum chamber to cryo-cooler.
BACKGROUND OF THE INVENTION
[002] The high temperature superconducting coils are key element of superconducting
10 system where they are employed. These coils have to undergo various checks and tests
before they are fitted on to the applications. These checks and tests range from trivial
physical inspection to highly sophisticated critical current measurement test. Therefore,
there has been a demand for developing a test facility which can enable the testing and
characterization of manufactured high temperature superconducting coils at 20K
15 temperature.
[003] DE112018000241T5 titled ‘A device for evaluating the performance of a
superconducting coil for a high-temperature superconducting rotary machine and method
for evaluating the performance of a superconducting coil using the device’ relates to a
device for evaluating the performance of a superconducting coil for a high-temperature
20 superconducting rotary machine and a method for evaluating the performance of a
superconducting coil using the device. It provides evaluation of the stability of a
superconducting coil and verifying its reliability, assessing whether or not it can be

commercialized, and the threshold current strength of a superconducting wire for
producing a superconducting coil or to evaluate the upper limit of the operating current
thereof, and is characterized in that the electromagnetic, thermal and mechanical
performance of a superconducting coil for a second generation high temperature
5 superconducting rotary machine can be evaluated.
[004] CN102735964A titled ‘High-temperature-superconductivity strip material multi-
field characteristic measuring device’ discloses a high-temperature-superconductivity strip
material multi-field characteristic measuring device, wherein one end of a measured
superconductivity strip material current lead is pressed and connected to two ends of the
10 measured superconductivity strip material, and the other end of the measured
superconductivity strip material current lead penetrates through the upper cover plate of
the dewar container; and one end of a measured superconductivity strip material measuring
lead is welded on the surface of the measured superconductivity strip material at intervals,
and the other end of the measured superconductivity strip material measuring lead entrants
15 through the upper cover plate of the dewar container.
[005] WO2017067511A1 titled ‘Superconducting coil defect location detection system’
discloses a superconducting coil defect location detection system, comprising a magnetic
circuit, a moving platform with multiple degrees of freedom, a detection device, an exciter
coil and a power source. The detection device is used to detect the magnetic field or
20 temperature of the surface of the superconducting coil, and on the basis of changes in the
magnetic field or temperature of the surface of the superconducting coil, to determine
whether there is a defect in the superconducting coil, and the location of the defect,
realizing defect location detection in the superconducting coil.

[006] CN1580803A titled ‘Method for measuring critical current homogenity of every
portion for super conducting strip’ discloses a method for measuring critical current
uniformity of all the portions of superconducting tape material characterized by that
energizing back field magnet with direct current to produce stable-constant PC magnetic
5 field used as background magnetic field. The space in which the superconducting tape
material is placed has no background magnetic field; the ratio value of residual magnetic
fields of all the portions of superconducting tape material is equal to the ratio value of
critical currents of all the portions of superconducting tape material, i.e. it is uniformity of
critical current of superconducting tape material.
10 [007] JP3704549B2 titled ‘Method and apparatus for evaluating superconducting critical
current characteristics of superconducting film’ relates to a method for evaluating the
superconducting properties of a superconducting film with high sensitivity, simplicity, and
low cost.
[008] JP3486173B2 titled ‘Method for measuring the critical current of a conductor
15 containing a superconducting material and an apparatus for implementing the method’
relates to a method for measuring the critical current of a conductor containing a
superconducting material and to an apparatus for carrying out this method. Conductors
containing superconducting materials include, magnets, used in various ways as conductors
for transformers and power distribution. Superconducting materials are advantageously
20 used as conductors.
[009] CN105301093B titled ‘A kind of superconducting coil defective locations detection
system’ discloses a kind of superconducting coil defective locations detection system
including magnetic circuit, multiple degrees of freedom mobile platform, detection device,

magnet exciting coil and power supply, magnetic circuit offers magnetic circuit window,
superconducting coil. Detection device, for detecting magnetic field or the temperature on
the superconducting coil surface to be measured, realizes the detection of superconducting
coil defective locations according to the variation in the magnetic field on the
5 superconducting coil surface to be measured or temperature.
OBJECTIVE OF THE INVENTION
[010] Therefore the object of the present invention is to develop a closed cycle cryogenic
test arrangement for characterization of high temperature superconducting (HTS) coils.
10 [011] Another object of the invention is to obtain temperature up to 20 K at HTS coil to be
tested and to maintain minimum helium leak rate (better than 10-6 mbar-litre/sec) inside the
test arrangement.
[012] Another object of the invention is to obtain and maintain vacuum of magnitude 10-6
mbar in the intended spaces in test arrangement.
15 [013] Further object of the invention is to maintain minimum heat leak from atmosphere to
helium gas pipes and helium gas chamber for maintaining temperature of cold and warm
gas piping and helium gas chamber because of external atmosphere.
[014] Further object of the invention is to maintain absolute mechanical integrity with
minimum permissible helium leak rate during all temperature transient and steady state
20 conditions.

[015] Yet another object of the invention is to capture accurate electromagnetic flux profile
near high temperature superconducting coil for various excitation currents by employing
non-magnetic material in test arrangement near coil to be tested.
[016] Yet another object of the invention is to maintain non-freezing conditions at O-rings
5 of vacuum chamber and interfacing flange during all temperature transient and steady state
conditions.
SUMMARY OF THIS INVENTION
[017] The present invention discloses development of a helium gas based closed cycle
cryogenic test arrangement for characterization of high temperature superconducting
10 (HTS) coils. The helium gas chamber and the helium gas flow circuit maintain helium leak
rate not more than 10-6 mbar-litre/sec to atmosphere. The helium gas chamber contains the
high temperature superconducting coil to be tested and hence, is configured with the
provision for excitation current and instrumentation therein.
[018] In an aspect, as the helium gas chamber is at very low cryogenic temperature (20K),
15 it is protected from external heat-in-leak for all three modes of heat transfer from external
environment.
[019] In an aspect, the vacuum chamber encloses the helium chamber completely. An
interface flange allows the connection of helium gas chamber and vacuum chamber to cryo-
cooler or cryo-refrigerator. The vacuum in vacuum chamber is maintained at magnitude
20 10-6 mbar or lesser. Minimum heat leak from atmosphere to helium gas pipes and helium
gas chamber is ensured during the operation.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
[020] It is to be noted, however, that the appended drawings illustrate only typical
embodiments of the present subject matter and are therefore not to be considered for
limiting of its scope, for the invention may admit to other equally effective embodiments.
5 The detailed description is described with reference to the accompanying figures. In the
figures, a reference number identifies the figure in which the reference number first
appears. The same numbers are used throughout the figures to reference like features and
components. Some embodiments of system or methods or structure in accordance with
embodiments of the present subject matter are now described, by way of example, and with
10 reference to the accompanying figures, in which:
[021] Figure 1 shows the system of closed cycle cryogenic testing to characterize high
temperature superconducting (HTS) coils
[022] Figure 2 shows the (a) Front view; (b) Side view; (c) Top view of Helium Gas
Chamber (101)
15 [023] Figure 3 shows the configuration of Helium gas chamber top plate (201)
[024] Figure 4 shows the configuration of Vacuum chamber (301)
[025] Figure 5 shows the configuration of Vacuum chamber top plate (401)
[026] Figure 6 shows the Cryo-refrigerator interfacing flange (302) arrangement
[027] With the following figure references:
20 101- Helium gas chamber
102- Cold cryogen flexible inlet pipe
103- Warm cryogen flexible outlet pipe

104- Inlet male nut
105- Outlet male nut
106- Front L shape horizontal stiffener
107- Front L shape vertical stiffener
5 108- Side L shape horizontal stiffener
109- Side L shape vertical stiffener
112- Support collar for helium gas chamber top plate
113- Cryogenic space for HTS coils to be tested
114- Front wall of helium gas chamber
10 115- Side wall of helium gas chamber
116- Bottom of helium gas chamber
201- Helium gas chamber top plate
202- Helium gas chamber port for excitation current IN
203- Helium gas chamber port for excitation current OUT
15 204- Helium gas chamber instrumentation port 1

205- Helium gas chamber instrumentation port 2
206- Helium gas chamber top plate lifting arrangement-1
207- Helium gas chamber top plate lifting arrangement-2
301- Vacuum chamber
20 302- Cryo-refrigerator interface flange
303- Interface flange extension pipe
304- Front L shape horizontal upper stiffener

305- Front L shape horizontal lower stiffener
306- Front L shape vertical stiffener
307- Bottom of vacuum chamber
308- Front wall of vacuum chamber
5 309- Support collar for vacuum chamber top plate
310- Side L shape horizontal upper stiffener
311- Side L shape horizontal lower stiffener
312- Side L shape vertical stiffener
313- Side wall of vacuum chamber
10 314- Vacuum port

315- Through holes to bolt tighten vacuum chamber top plate
316- Groove for O-ring

401- Vacuum chamber top plate
402- Vacuum chamber port for excitation current IN
15 403- Vacuum chamber port for excitation current OUT

404- Vacuum chamber instrumentation port 1
405- Vacuum chamber instrumentation port 2
406- Vacuum chamber top plate lifting arrangement 1
407- Vacuum chamber top plate lifting arrangement 2
20 503- Hole for mounting vacuum connecting sliding chamber
505- Extension pipe weld joint
603- HTS coil to be tested

604- Cryo-refrigerator
605- Cryo-refrigerator vacuum jacketed line
606- Vacuum connecting sliding chamber
607- Cryo-refrigerator cold outlet
5 608- Cryo-refrigerator warm inlet
[028] The figures depict embodiments of the present subject matter for the purposes of
illustration only. A person skilled in the art will easily recognize from the following
description that alternative embodiments of the structures and methods illustrated herein
10 may be employed without departing from the principles of the disclosure described herein.
DETAIL DESCRIPTION OF THE PRESENT INVENTION WITH REFERENCE
TO THE ACCOMPANYING DRAWINGS OF PREFERRED EMBODIMENTS
[029] While the embodiments of the disclosure are subject to various modifications and
15 alternative forms, specific embodiment thereof has been shown by way of example in the
figures and will be described below. It should be understood, however, that it is not
intended to limit the disclosure to the particular forms disclosed, but on the contrary, the
disclosure is to cover all modifications, equivalents, and alternative falling within the scope
of the disclosure.
20 [030] It should be noted that the description merely illustrates the principles of the present
subject matter. It will thus be appreciated that those skilled in the art will be able to devise
various arrangements that, although not explicitly described herein, embody the principles

of the present subject matter and are included within its scope. The present invention will
now be described more specifically with reference to the following specification.
[031] Figure 1 represents the system of complete closed cycle cryogenic testing configured
with a vacuum chamber (301) enclosing a helium gas chamber (101) with high temperature
5 superconducting (HTS) coil (603) to be tested therewithin. The said vacuum chamber (301)
encloses the said helium chamber (101) completely. The present invention is configured
with a helium gas chamber (101) of closed cycle cryogenic test arrangement kept at the
cryogen temperature upto 20 K and helps in maintaining the temperature of
superconducting coil under test. The vacuum jacketed line (605) is connected to a cryo-
10 cooler (604) engaging a pair of flexible pipes: cryo-cooler cold outlet pipe (607) delivering
the cold helium gas to helium gas chamber (101) through helium gas chamber cold inlet
(102) and cryo-cooler warm inlet pipe (608) bringing back the warm helium gas to cryo-
refrigerator (604) through helium gas chamber warm outlet (103).
[032] The configuration of the helium gas chamber (101) is shown in Figure 2. A pair of
15 flexible pipes are attached to said chamber (101) as cold cryogen flexible inlet pipe (102)
which enables the inlet of cold helium gas into helium gas chamber (101) and warm
cryogen flexible outlet pipe (103) (Figure 2a) which enables the outlet of warm helium
gas from helium gas chamber (101). The side and top view of said chamber (101) with cold
cryogen inlet (102) and warm cryogen outlet (103) is shown in Figure 2(b) and Figure
20 2(c) respectively.
[033] A pair of male nuts (104, 105) (Figure 2a, 2c) are attached to each of cold and warm
flexible pipes (102, 103) for connecting these pipes to Sterling cycle based cryo-cooler or
refrigerator. The said helium gas chamber (101) is cuboidal in shape which has a pair of

front walls (114), a pair of side walls (115) and one bottom rectangular base (116). A
support collar (112) is welded for welding the top plate of helium gas chamber on top of
all four walls of helium gas chamber (101). The space (113) created inside the helium gas
chamber is utilized for keeping the superconducting coil for its characterization (Figure
5 2c). On outside of the walls of helium gas chamber (101), multiple L shaped stiffeners are
configured to maintain its mechanical integrity under pressurized conditions. These are
front L shape horizontal and vertical stiffeners (106, 107) and side L shape horizontal and
vertical stiffeners (108, 109).
[034] Figure 3 shows the helium gas chamber top plate (201). A pair of ports, one ‘IN’
10 (202) and other ‘OUT’ (203) enable the excitation of superconducting coil under test by
passing excitation current to it. Second pair of ports (204, 205), provide instrumentation
inside the helium gas chamber (101) to monitor the temperature and current within the
chamber (101). A pair of lifting plates with eye holes (206, 207) embedded on each side of
helium gas chamber top plate (201) performs the lifting of the helium gas chamber (101)
15 and placing it inside the vacuum chamber (301) (Figure 4).
[035] The vacuum chamber (301) of closed cycle cryogenic test arrangement as shown in
Figure 4, is configured with a cryo-cooler interface flange (302) and interface flange
extension pipe (303) to connect the said vacuum chamber (301) and helium gas chamber
(101) to cryo-cooler (604). On outside of the walls of vacuum chamber (301), multiple L
20 shaped stiffeners are configured to maintain its mechanical integrity under vacuum
conditions. These are front L shape horizontal upper (304), lower (305) and vertical (306)
stiffeners and side L shape horizontal upper (310), lower (311) and vertical (312) stiffeners
(Figure 4). The said vacuum chamber (301) is cuboidal in shape which has a pair of front

walls (308) and side walls (313) and one bottom (307) rectangular base. A support collar
(309) is welded on top of all four walls of vacuum chamber (301) for bolt tightening (315)
the top plate of vacuum chamber (301), through various holes. On this said collar (309), a
rectangular groove (316) is provided for placing O-ring. A vacuum port (314) is provided
5 on front wall for connecting it to an external vacuum pump. The space created thereafter
inside the vacuum chamber is utilized for creating a vacuum envelop over cryogenically
cooled helium gas chamber (101) to maintain cryogenic temperature inside helium gas
chamber (101). The plurality of thermally insulating spacers of cuboidal shape made of
thermally insulating media (like bakelite, Teflon etc.) are placed at the bottom of helium
10 gas chamber (101) while keeping it in vacuum chamber (301). Application of this reduces
the conduction heat transfer from atmosphere to cryogenically cooled helium gas chamber.
[036] Figure 5 shows vacuum chamber top plate (401). A pair of ports, one ‘IN’ (402) and
other ‘OUT’ (403), are embedded for enabling the excitation of superconducting coil under
test. Another pair of instrumentation ports (404, 405), provides instrumentation inside the
15 helium gas chamber (101). A pair of lifting plates with eye holes (406, 407) provided on
each side of top plate (401) for lifting or placing in required place.
[037] The cryo-cooler interfacing flange (302) welded on interface flange extension pipe
(303) which is welded with Extension pipe weld joint (505) to vacuum chamber (301) as
illustrated in Figure 6. On top of interfacing flange (302) on radial side, there is a groove
20 (316) for placing O-ring and various holes (503) to mount vacuum connecting sliding
chamber (606) (referring Figure 1).
[038] The top plate (201) is placed onto helium gas chamber (101) and as a whole it is
placed inside the vacuum chamber (301) and covered with vacuum chamber top plate (401)

providing essential electrical and instrumentation connections thereupon. There is a
physical space or gap between helium gas top plate (201) and vacuum chamber top plate
(401).
[039] The inlet and outlet pipes (102, 103) of helium gas chamber (101) are routed inside
5 the interface flange extension pipe (303) with the aid of interface flange (302). The
interface flange (302) enables the disclosed process of closed cycle cryogenic flow. The
vacuum jacketed line (605) is connected to a cryo-cooler (604) engaging the pair of flexible
pipes: cryo-cooler cold outlet pipe (607) and cryo-cooler warm inlet pipe (608) which in-
turn are connected to the helium gas chamber cold inlet (102) and helium gas chamber
10 warm outlet (103) respectively of the helium chamber (101) for delivering the cold helium
gas to helium gas chamber (101) and bringing back the warm helium gas to cryo-
refrigerator (604).
[040] The said flange (302) also enables a single point vacuum connection for complete
test arrangement through vacuum connecting sliding chamber (606) routing essential
15 electrical/excitation current connections and instrumentation connections thereafter for
monitoring temperature and vacuum level in test setup. In the present invention, the
interfacing flange (302) when assembled with sliding chamber (606) enables the
continuous vacuum space with vacuum chamber (301), sliding chamber (606), vacuum
jacketed line (605) and cryo-cooler (604), thereby eliminating requirement of multiple
20 vacuum pumps. The configuration of interface flange and sliding chamber disclosed herein
makes only one vacuum pump sufficient to create vacuum in specified spaces. The vacuum
chamber gets evacuated with the help of external vacuum pump through port (314).

[041] In the preferred embodiment, a pair of neoprene based O rings are placed, one at the
groove (316) provided on the collar (309) of vacuum chamber (301) and another at the
groove (316) provided with the interface flange (302). The O rings are placed at these
locations for assembling the complete configuration.
5 [042] There is a necessity of characterization of coils before fitting them onto application
and also the cryogenic testing at operating temperature for estimation of its critical current.
The HTS coil (603) is excited with external current connected through (202, 203) of helium
chamber top plate (201) and through (402, 403) of vacuum chamber top plate (401). The
monitoring of temperature and current of the HTS coil (603) is performed through the first
10 pair of ports (204, 205) of helium chamber top plate (201) and the second pair of ports
(404, 405) of vacuum chamber top plate (401).
[043] The helium gas chamber (101) and the helium gas flow arrangement maintain helium
leak rate not more than 10-6 mbar-litre/sec to atmosphere. As the helium gas chamber (101)
is at very low cryogenic temperature (20K), it is protected from external heat-in-leak for
15 all three modes of heat transfer from external environment. An interface flange (302)
allows the connection of helium gas chamber (101) and vacuum chamber (301) to cryo-
cooler (604). The vacuum in vacuum chamber (301) is maintained at magnitude 10-6 mbar
or lesser. Minimum heat leak from atmosphere to helium gas pipes (102, 103) and helium
gas chamber (101) is ensured during the operation. The preferred embodiment maintains
20 non-freezing conditions at O-rings of the said vacuum chamber (301) and interfacing flange
(302) during all temperature transient and steady state conditions and does not have any
heat and mass transfer between in-going cold (102) and out-coming warm cryogen pipes
(103).

[044] The preferred embodiment captures accurate electromagnetic flux profile near high
temperature superconducting coil for various excitation currents by employing non-
magnetic material in test arrangement near coil (603) to be tested. The superconducting
coils are preferred in electrical systems and devices for carrying extremely high current
5 densities along with no resistive losses. Because of extremely high current densities,
generally superconducting coils are air cored, i.e. they are operated in a non-magnetic
environment (with the help of materials which are non-magnetic). When current is passed
in superconducting coil, it produces a strong magnetic field. For electromagnetic
characterization of superconducting coil, there must not be any magnetic material around
10 it, otherwise the magnetic field profile will get distorted. Following this, the present
invention involves the materials and processes which help in maintaining the non-magnetic
nature of components surrounding the superconducting coil (603) under test.
[045] It should be appreciated by those skilled in the art that conception and specific
embodiment disclosed may be readily utilized as a basis for modifying or designing other
15 structures for carrying out the same purposes of the present subject matter. It should also
be appreciated by those skilled in the art that by devising various arrangements that,
although not explicitly described or shown herein, embody the principles of the present
subject matter. Furthermore, all examples recited herein are principally intended expressly
to be for pedagogical purposes to aid the reader in understanding the principles of the
20 present subject matter and the concepts contributed by the inventor(s) to furthering the art
and are to be construed as being without limitation to such specifically recited examples
and conditions. The novel features which are believed to be characteristic of the present
subject matter, both as to its organization and method of operation, together with further

objects and advantages will be better understood from the following description when
considered in connection with the accompanying figures.
[046] It will be understood by those within the art that, in general, terms used herein, and
5 especially in the appended claims (e.g., bodies of the appended claims) are generally
intended as “open” terms (e.g., the term “including” should be interpreted as “including
but not limited to,” the term “having” should be interpreted as “having at least,” the term
“includes” should be interpreted as “includes but is not limited to,” etc.). It will be further
understood by those within the art that if a specific number of an introduced claim recitation
10 is intended, such an intent will be explicitly recited in the claim, and in the absence of such
recitation no such intent is present. For example, as an aid to understanding, the following
appended claims may contain usage of the introductory phrases “at least one” and “one or
more” to introduce claim recitations. However, the use of such phrases should not be
construed to imply that the introduction of a claim recitation by the indefinite articles “a”
15 or “an” limits any particular claim containing such introduced claim recitation to inventions
containing only one such recitation, even when the same claim includes the introductory
phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a”
and/or “an” should typically be interpreted to mean “at least one” or “one or more”); the
same holds true for the use of definite articles used to introduce claim recitations. In
20 addition, even if a specific number of an introduced claim recitation is explicitly recited,
those skilled in the art will recognize that such recitation should typically be interpreted to
mean at least the recited number (e.g., the bare recitation of “two recitations,” without other
modifiers, typically means at least two recitations, or two or more recitations).
Furthermore, in those instances where a convention analogous to “at least one of A, B, and

C, etc.” is used, in general such a construction is intended in the sense one having skill in
the art would understand the convention (e.g., “a system having at least one of A, B, and
C” would include but not be limited to systems that have A alone, B alone, C alone, A and
B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those
5 instances where a convention analogous to “at least one of A, B, or C, etc.” is used, in
general such a construction is intended in the sense one having skill in the art would
understand the convention (e.g., “a system having at least one of A, B, or C” would include
but not be limited to systems that have A alone, B alone, C alone, A and B together, A and
C together, B and C together, and/or A, B, and C together, etc.). It will be further
10 understood by those within the art that virtually any disjunctive word and/or phrase
presenting two or more alternative terms, whether in the description, claims, or drawings,
should be understood to contemplate the possibilities of including one of the terms, either
of the terms, or both terms. For example, the phrase “A or B” will be understood to include
the possibilities of “A” or “B” or “A and B.”
15 [047] It will be further appreciated that functions or structures of a plurality of components
or steps may be combined into a single component or step, or the functions or structures of
one-step or component may be split among plural steps or components. The present
invention contemplates all of these combinations. Unless stated otherwise, dimensions and
geometries of the various structures depicted herein are not intended to be restrictive of the
20 invention, and other dimensions or geometries are possible. In addition, while a feature of
the present invention may have been described in the context of only one of the illustrated
embodiments, such feature may be combined with one or more other features of other
embodiments, for any given application. It will also be appreciated from the above that the
fabrication of the unique structures herein and the operation thereof also constitute methods

in accordance with the present invention. The present invention also encompasses
intermediate and end products resulting from the practice of the methods herein. The use
of “comprising” or “including” also contemplates embodiments that “consist essentially
of” or “consist of” the recited feature.
5 [048] Although embodiments for the present subject matter have been described in
language specific to package features, it is to be understood that the present subject matter
is not necessarily limited to the specific features described. Rather, the specific features
and methods are disclosed as embodiments for the present subject matter. Numerous
modifications and adaptations of the system/device of the present invention will be
10 apparent to those skilled in the art, and thus it is intended by the appended claims to cover
all such modifications and adaptations which fall within the scope of the present subject
matter.
ADVANTAGE OF THE INVENTION
15 [049] The advantage of the present invention is that it obtains temperature up to 20 K at
HTS coil to be tested and maintains minimum helium leak rate (better than 10-6 mbar-
litre/sec) inside the test arrangement.
[050] Another advantage of the present invention is that it maintains vacuum of magnitude
10-6 mbar in the intended spaces in test arrangement.
20 [051] Further advantage of the present invention is that it maintains minimum heat leak
from atmosphere to helium gas pipes and helium gas chamber for maintaining temperature
of cold and warm gas piping and helium gas chamber.

[052] Further advantage of the present invention is that it maintains absolute mechanical
integrity with minimum permissible helium leak rate during all temperature transient and
steady state conditions.
[053] Yet another advantage of the present invention is that it captures accurate
5 electromagnetic flux profile near high temperature superconducting coil for various
excitation currents by employing non-magnetic material in test arrangement near coil to be
tested.
[054] Yet another advantage of the present invention is that it maintains non-freezing
conditions at O-rings of vacuum chamber and interfacing flange during all temperature
10 transient and steady state conditions.

We Claim:
1. A system for closed cycle cryogenic testing to characterize high temperature
superconducting (HTS) coils comprising:
- a cryo-cooler (604) to exchange heat via a pair of pipes, one each for
5 communicating cold gas (607) and warm gas (608) engaged in a vacuum
jacketed line (605) connected to the cryo-cooler (604);
- a helium gas chamber (101), configured to engage a plurality of
superconducting (HTS) coils (603) in space (113) therewithin, wherein the
helium gas chamber (101) allows communication of cold helium gas from the
10 cryo-cooler (604) into the helium gas chamber (101) through an inlet pipe (102)
connected to the pipe (607) and warm helium gas from the helium gas chamber
(101) to the cryo-cooler (604) through an outlet pipe (103) connected to the pipe
(608);
- a vacuum chamber (301) enclosing said helium gas chamber (101) with the HTS
15 coil (603) therewithin, wherein the vacuum chamber (301) connects said helium
gas chamber (101) with said cryo-cooler (604) routing the inlet and outlet pipes
(102, 103) of the helium gas chamber (101) inside an interface flange extension
pipe (303) of the vacuum chamber (301) with the aid of a cryo-cooler interface
flange (302) to enable a closed cycle cryogenic flow;
20 - a sliding chamber (606) connected to the interfacing flange (302) to enable
continuous vacuum space within the vacuum chamber (301), the vacuum
jacketed line (605) and the cryo-cooler (604) with a vacuum pump attached to
a port (314) and to enable essential excitation current connections and

instrumentation connections to the coil (603) for monitoring temperature and
vacuum level therein.
2. The system as claimed in claim 1, wherein the helium chamber (101) embedded
with the HTS coil (603) enclosed in the vacuum chamber (301) at 10-6 mbar defines
5 a closed cycle flow of helium gas by delivering cold helium gas from the cryo-
cooler (604) to the HTS coils (603) and warm gas from the HTS coils (603) back
to the cryo-cooler (604).
3. The system as claimed in claim 1, wherein the helium gas chamber (101) kept at
cryogenic temperature upto 20K ensures steady temperature in cold and warm gas
10 piping (102, 103) attached to the helium gas chamber (101) including said chamber
(101) with protection of external heat-in-leak by all modes of heat transfer from
external environment.
4. The system as claimed in claim 1, wherein the helium gas chamber (101) containing
the HTS coil (603) under test maintains helium leak rate better than 10-6 mbar-
15 litre/sec therewithin.
5. The system as claimed in claim 1, wherein the vacuum chamber (301) configures a
pair of ‘O-ring’, one each on a support collar (309) and on the interface flange (302)
of the vacuum chamber (301) attached with the aid of a groove (316) for restricting
heat and mass transfer between the cryogen pipes (102, 103) during temperature
20 transient and steady state conditions by ensuring proper assembly of the pipes (102,
103) and the sliding camber (606) with the flange (302).
6. The system as claimed in claim 1, wherein the helium gas chamber (101) and the
vacuum chamber (301) configure a plurality of horizontal (106, 108, 304, 305, 310,

311) and vertical (107, 109, 306, 312) stiffeners to maintain the mechanical
integrity of said chambers (101, 301) under pressurized conditions.
7. The system as claimed in claim 1, wherein the helium gas chamber (101) configures
a plurality of thermally insulating units at the bottom to reduce the conduction heat
5 transfer from atmosphere to cryogenically cooled helium gas chamber (101) placed
within the vacuum chamber (301).
8. The method for configuring closed cycle cryogenic test arrangement with HTS coil,
said method comprising the steps of:
placing a helium gas chamber (101) embedded with a HTS coil (603) inside
10 a vacuum chamber (301) covering with a vacuum chamber top plate (401) atop a
helium chamber top plate (201) maintaining a gap therebetween;
routing an inlet and outlet pipes (102, 103) of the helium gas chamber (101)
inside an interface flange extension pipe (303) with the aid of an interface flange
(302);
15 connecting a vacuum jacketed line (605) to a cryo-cooler (604) engaging a
flexible cryo-cooler outlet pipe (607) connected to the helium chamber inlet (102)
pipe and a cryo-cooler inlet pipe (608) connected to the helium chamber outlet pipe
(103);
connecting a sliding chamber (606) with the interface flange (302) attached
20 to the vacuum chamber (301) to enable the continuous vacuum space within the
vacuum chamber (301), the vacuum jacketed line (605) and the cryo-cooler (604)
including the sliding chamber (606) by external vacuum pump through a port (314);

exciting the HTS coil (603) with external current connecting through a pair
of ports (202, 203) of the helium chamber top plate (201) and through a pair of ports
(402, 403) of the vacuum chamber top plate (401);
monitoring temperature and current of the HTS coil (603) through a pair of
5 ports (204, 205) of the helium chamber top plate (201) and through a pair of ports
(404, 405) of the vacuum chamber top plate (401);
providing connection between the cryo-cooler (604) and the helium gas
chamber (101) with the pipe (607) communicating the cold helium gas to helium
gas chamber (101) through the helium gas chamber cold inlet (102) and bringing
10 back the warm helium gas from the helium chamber (101) to the cryo-cooler (604)
through the helium gas chamber warm outlet (103) connected to the pipe (608).
9. The method as claimed in claim 8, wherein electromagnetic flux profile is
maintained near high temperature superconducting coil (603) for various excitation
currents with non-magnetic material involved in test arrangement near the
15 superconducting coil (603).