Shielding characteristics of the hight-Tc ceramic hollow cylinders

Applied Superconductivity Printed in Great Britain.

Vol.1, Nor 7-9, pp. 1133 - 1138, All rights reserved

1993

0964-1807/93 $6.00 + 0.00 @ 1993 Pcrgmnan Prssr Ltd

Copyright

SHIELDING CHARACTERISTICS OF THE HIGH-Tc CERAMIC HOLLOW CYLINDERS V. Veselago,

V. Rubtsov,

Yu. Yakovets

and V. Stepankin

General Physics Institute, Academy of Sciences of Russia, 38 Vavilov St., Moscow

117942,

Russia

The results of shielding characteristics measurements of superconducting shields in the form of hollow cylinders based on YBazCuaOT high-T, superconducting ceramics are reported. Shields provided ac shielding coefficient up to 72 dB at 89 K. It was shown that spectrum analysis of magnetic flux inside cylindrical shield can be a tool to distinguish a mechanisms of field penetration into shielded volume.

INTRODUCTION

1.

Magnetic nological tion

fields

realization

area.

can

united

field

penetration

main

disadvantage

analysis,

since

field

hand,

pick-up method in

sample

hole,

is

So,

studying

the

the

practical in

junctions

ac

field

for

studies based

sample of

coil.

sample

When

behaves

harmonics

a

such the

such as a ceramic

hole.

by

of

additional

superconductor.

are a

other

simple

in

inserting

a

the

of

signal

into

the

electromagnetic

shielding.

of

results

An advantage

penetrates

measurements

1133

more

nonlinear

field

The

In the

analysis

provide

properties

be

be studied

a

a dc

mechanisms

creep.

to

flux

can

magnetic

importance, of

field

like

analysis

of

seems

harmonics

shielding

the

different

cylindrical

the

the

of

the flux

can

applica-

SQUID sensorsi21.

difficulty

due to

tech-

on measuring

distinguishing

behavior

the

of

and

is

to a wide

superconductivity

shielding

possibility

investigations network

allow

shielding

mechanism

the closest

techniques

example,

pick-up the

of

of

high-T,

methods

do not

inside

the

the

element. obvious

coil

the

methods

this

of

one

galvano-magneticl’l

for

because

induced

value

they

penetration;

realization,

this

of

is

in

a group

using

measurements

small

tasks proposed

Some

properties

of

shielding

data Besides

of

multiple

when an

fundamental Josephson

1134

World

Congress

on Superconductivity

2. ExPERIl4ENTALSETUP To carry a special

out

the

effective

experimental

of

this

system

of

the

signal

is

equipment

on

determination

of

signal

changing

coil

fed

is

to

match

the

impedance. frequency, working

the

temperature

a commercial

are

spectrum

K range.

than

coil

design

0.8%.

process perimental

of

of

the

field

We used the

field

cylinder

and

was used

the

preamplifier

of

0.3

for

input at

1 kHz

10 Ohm in

is

selectivity

device

dB

about

signal

measured tunable

was studied

an ac

nitrogen.

in

sample

by the

Its in

the by

a

within by means

field

dc

Thus,

fields

one the

affect

the

into

mutual

of

field

volume to

coil

of

study In

the

generates of

a

sections.

a shield.

and dc

by

The magnetic three

shield

oc-

stability

magnetic

geometry ac

volume

created

superposition

solenoidal

the

is

cell.

uniform

in

penetration

described

system

consisting

deviation

whole

features

temperature

the

the

measurements

specific

the

containing

coil

produce

and

doesn’t

field

field

the

to

shielding

and maintaining

magnitude

being

coil

30 dB transformer

signal

temperature

ensured

components. the

The pick-up bandwidth

coil

by liquid

Magnetic

magnetic

system

the

shield

was calculated

magnetic

ratio.

is

stabilization

with

being

octave

allows

analyzer.

surrounding

homogeneity

in

pick-up

a homogeneous

78-115

results

the

cooled

within

This

an

basis

cylindrical

resistance

with of

coil,

and

a

factor

noise

The preamplified

by the

solenoidal

a

region.

cupied

field

in

spectrum

system

conditions.

with

coil

a cryostat

managing

impedance

pick-up

The cryogenic comprises

pick-up

experimental

feature

temperature

acquisition

20 dB. A wide-band

nanovoltmeter

frequency

controlled

in the

parameters

The main

MOS-FET preamplifier

coil

O-54 dB. The spectrum of

the

a

results

with

selective

of

pick-up

This

of

shielding

a full

and

induced

into

O-200 kHz and a gain

well

reading

of

developed.

analyze

in

Data

the

was

to

pick-up-coil

and programmable signal

for

the possibility

environment.

magnetic

measurements

the

field

and less the exboth

shielding components

World

Congress

1135

on Superconductivity

RESULTS AND DISCDSSION

3.

The experimental rameters The

of

superconducting

shields

were

height,

about

shields

were

with

will

in

described shields

the

form

16 mm external prepared

a pressure

tails

setup

of

be published

based

of

used

cylinders and

cold-pressing and further

was

to

study

on YBa$Zu30, ceramic

hollow

diameter

using

15 kbar

above

with

4 mm wall

along thermal

the

pa-

system.

up to

40 mm

thickness.

The

longitudinal

processing.

axis

Further

de-

elsewhere.

1.0

0.2

88

89

87

85

‘I’ (K) Fig. coil

1. First-harmonic inside the screen.

Fig.1

shows

nal U1 in the dc magnetic operating more 0.1 of

than Oe.

temperature

pick-up field.

of

0.03%).

The

the dc magnetic

coil

inside

curves field

the

solenoidal of

the

the

first

shield

to

measure

coil

driver

the

Fig. 1 have

noted

of

on

a cylindrical used

amplitude in

induced

dependencies

The frequency

frequency

Different

signal

applied been

in the picture.

this

pick-up

harmonic

in superimposed signal

was

(1 kHz with ac

obtained

sig-

field with

THD not

was the

the

about values

1136

World Congress on Superconductivity

In coil

Fig.1

(and

shield

thus

the

hole)

shielding the

of

critical

versus

the

inter-grain

ing

of

an external

shield

(which

state

and

So,

current,

it

of

implies

links

network.

featuresIs],

external

the

of

this

creation

high

the

to

these

are

temperature took

above

typical

the

coherent

current

affects

the as

is

critical

well.

corresponds

Here to

the

transition. structure

of

a ceramic

intergrain

weak

electromagnetic

enrichment

of

discussion,

the penetrating

such

area.

a

strong

is

whole

non-linear

of

the

shielding

the transition means

to

It

a non-linear is

possible

analysis

spectrum

to

of

the

flux. this

of

the

the

nonlinearity

can

pick-up

voltage

It

place.

be is

We point

harmonic

region

coil

can

shielding

observed.

higher

in

to-

multiconnected

exhibit

the

shifts

cylindrical

current

harmonics

by

effectiveneess.

temperature

coefficient

in higher

of

spectrum

enrichment where

sys terns

be

region

attains

granular

can

less

which

such a paracoherent of

It

(much

temperature

critical

due to

the

field

onset

a complex

be observed

An example

shielding

of

of

Such

magnetic

the

shielding

the

The shield-

system)

magnetic

is,

behavior.

superconducting

shielding

nonlinearity

penetrating

shows

the

when

network

inter-grain

According

should

starts

dc

the

resulting

spectrum.

study

the

current

the

fields

corresponds

dependence,

critical

links

the temperature

shield

behavior

field

macroscopic

of

Mechanism

flux

magnetic

flux

magnetic

into

occurs

density.

transition

phenomenon

pick-up

that

This

current

the

the

penetrating

increases.

dc

material)

a

flux

in

decreases,

This

weak

influences

reduction

decrease

a

as

fields

external

magnetic

induced

magnetic

critical

weak links

is

hence

present.

the

grain

voltage

temperature

small

temperatures.

for

the

when

due to

current

of

the

inter-grain

YBa$us07

lower

of

ac magnetic

the

that

than H,r for ward

magnitude

external of

seen

magnitude

decreases

increase

easily

the

where

were the

easily

be

seen

in

Fig.2,

for

the

case

of

low

because

of

too

seen

that

improper

and

a

out

the

temperature

that

noticeably major

higher

present, increase

harmonics region,

coincided of

the

which

with

shielding

World

Congress

1137

on Superconductivity

0

ii

-10

f

-20

H ac= 0.7 Oe

= l.OkHz

T

- 90.3 K

p -30 -40 :: xi -50 a bo ;i; -60 -70 -NO

1 15 17 19 21 23 25 27 29

Frequency

(kHz)

Fig. 2. Frequency spectrum of the pick-up coil inside the screen. We have

apply

the

finding

ments of

the detailed

temperature

coefficient

measured

at the base

88.5

89.0

of

signal

spectrum

dependence signal

89.5

induced

on the

enrichment

to

of

the

frequency

is

90.5

90.0

ac field

3. AC shielding

coefficient

versus

shielding

shown in Fig.3.

91.0

T W)

Fig.

measure-

temperature.

91.5

1138

World Congress on Superconductivity

This dependence was measured with help of registration oh higher proper

harmonics

value

these

data

of

in the

the shielding

seems to

traditional

case

the shielding

spectrum.

In this

effectiveness

be more precise

of

one-frequency

properties

occurs

case

measurements.

the absence

we can define

at given

and reliable

within

of

an

temperature

and

than ones in

the

The major change

of

91-89 K and reached almost con-

stant value of 72 dB below 89 K. It

is

worthwhile

penetrating

flux

able

the noise

above

harmonics enables

were

to

note

that

the

spectrum

below 89 K showed no higher level

observed

us to think

with

that

(and hence the highest

(while

the residual

shielding

harmonics

above this

flux

value)

inside

the

notice-

the higher

experimental

magnetic

coefficient

of

signal

temperature

This

certainty).

analysis

evidence the shield

can be attributed

to a magnetic field

leakage through the ends of

the cylindrical

shield

of a finite

This mechanism can allow for

the presence

magnetic

field

length.

inside

spectrum,

the shield

Finally, hollow

flux

adding higher

which would be inevitable

through the shield netic

without

inside

magnetic field

the case

of

flux

penetration

walls.

it

cylinder

in

harmonics to the signal

is clear

that

a ceramic is

superconducting

a valuable

penetration

the spectrum analysis

into

method for

shield studying

of an ac mag-

in the form of

a

the mechanisms of

such shields.

References 1

M.R. Cimberle,

A.S. Siri, F.C. Matacotta 2

C. Ferdeghini,

C. Rizzuto,

M. Ferretti,

and E. Olzi - Supercon. Sci. Technof. 1,

J.O. Willis, T. Ishida

M. Putti, C.L. Olcese, 30-(1988).

M.E. McHenry, M.P. Maley and H. Sheinberg

Z'rans.on Magnetics 25, 3

C.A. Costa,

G.L. Nicchiotti,

2502 (1989)

and H. Mazaki - J, Appi.

Phys. !Z?,6798 (1981)

-

IEEE