The Cryotron Superconductive Computer Component

8/20/2019 The Cryotron Superconductive Computer Component

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Memorandum 6M-38U3

Page 1 of 16

Division 6 - Lincoln Laboratory

Massachusetts Institute of Technology

Lexington 73, Massachusetts

SUBJECT: THE CRYOTRON — A SUPERCONDUCTIVE COMPUTER COMPONENT

To:

David R. Brown

From:

Date:

Approval:

Abstract:

Dudley A. Buck

August 22,

Torben H.

Meisling

Tne study of nonlinearities in nature suitable for computer

use has led to the cryotron, a device based on the destruction

of superconductivity by a magnetic field. The cryotron, in

its simplest form, consists of a straight piece of wire about

one inch long with a single-layer control winding wound over

it.

Current in the control winding creates a magnetic field

which causes the central wire to change from its superconduct

ing state to its normal state. The device has current gain,

that is, a small current can control a larger current and it

has power gain so that cryotrons can be interconnected in

logical networks as active elements. The device is also small,

light, easily fabricated, and dissipates very little power.

1. The Cryotron Principle

APPROVED FOR PUBLIC RELEASE. CASE 06-1104.


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I

Memorandum 6M-38U3 Page 2

The resistivity of many superconductive materials is relatively

high at room temperature, especially those which nave high transition

temperatures such as niobium, lead, tantalum, etc. It is interesting that

relatively poor conductors become superconductors at low temperatures whereas

good conductors such as gold, silver, and copper do not. The resistivity

of superconductive materials drops as they are cooled. Just above their

superconductive transition, the resistivity is between 10-1 and io-3 of

their room temperature resistivity, depending on the purity and mechanical

strain in a particular sample.

Below the superconductive transition the resistivity is exactly

zero.

That it is truly zero is vividly demonstrated by an experiment now

in progress by Professor S. C. Collins at M. I.T. wherein a lead ring has

been carrying an induced current of several hundred amperes since March

16, 1

0

5U>

without any observable change in the magnitude of the current.

1.2 Destruction of Superconduct vity by a Magnetic Field

The foregoing discussion of the superconductive transition is

valid only in zero magnetic field. With a magnetic field applied, the onset

of superconductivity occurs at a lower temperature. If the intensity of

the magnetic field is increased, the transition temperature is still lower.

A plot of the transition temperature as a function of the applied magnetic

field is more or less parabolic in shape, levelling out as absolute zero

is approached. Such a plot for several common elements is given in Figure

1.

If the temperature is held below the transition temperature for

one of these materials, the resistance of that material is zero. Its

resistance will remain zero as a magnetic field is applied until that



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I n a t y p i c a l c r y o t r o n , t h e r e s i s t a n c e b e in g c o n t r o l l e d i s i n t h e

fo rm o f a s t r a i g h t p i e c e o f w i r e a b o u t 1 i n c h i n l e n g t h . Th e magne t i c

c o n t r o l f i e l d i s g e n e r a t e d b y c u r r e n t i n a s i n g l e - l a y e r w i n d i n g w h ic h i s

w ou nd o v e r t h e c e n t r a l w i r e ( F i g u r e 3 , t o p ) . The c e n t r a l w i r e i s a n a l o g o u s

t o t h e p l a t e c i r c u i t o f a v ac uu m t u b e a nd t h e c o n t r o l w i n d i n g i s a n a l o g o u s

t o t h e c o n t r o l g r i d . I n t h i s c a s e , t h e p l a t e r e s i s t a n c e i s z e r o i n t h e

c u t o ff r e g i o n an d r i s e s r a p i d l y a s g r i d - c u r r e n t c u to f f i s r e a c h e d .

1 . 3 S u p e r c o n d u c t i n g C o n t r o l W i n d in g

T h e c o n t r o l w i n d i n g i s m ade o f a s u p e r c o n d u c t i n g w i r e w h ic h h a s a

r e l a t i v e l y h i g h t r a n s i t i o n t e m p e r a t u r e . N io biu m ( f o r m e r l y c a l l e d c olu m biu m )

i s u se d b e c a u s e i t h a s a v e r y h i g h t r a n s i t i o n t e m p e r a t u r e a n d c an b e d ra w n

i n t o f i n e w i r e w h ic h i s s t r o n g . L ea d o r l e a d - p l a t e d w i r e i s a se c o n d

p o s s i b l e c o n t r o l - w i n d i n g m a t e r i a l .

A t th e t e m p e r a t u r e u s e d , t h e c o n t r o l w i n d in g r e m a i n s a s u p e r c o n

d u c t o r a t a l l t i m e s , a n d w o u l d r e m a i n so e v e n i n m a g n e t i c f i e l d s m uch

h i g h e r t h a n t h o s e b e i n g u s e d t o c o n t r o l th e c e n t r a l w i r e . T h e r e f o r e , t h e r e

i s no r e s i s t a n c e i n t h e c o n t r o l w i n d i n g . A m a g n e ti c f i e l d , o nc e e s t a b l i s h e d ,

n e e d s no f u r t h e r e n e r g y f o r i t s s u p p o r t ^ t h e c o n t r o l c u r r e n t i s m a i n t a i n e d

a g a i n s t z e r o b a c k v o l t a g e . S i m i l a r l y , a l l i n t e r c o n n e c t i n g w i r e i s a l s o

s u p e r c o n d u c t i n g .

2 . The C r yo t ro n a s a Dev i ce

2 . 1 S t a t i c C h a r a c t e r i s t i c s

T he r e s i s t a n c e o f t h e c e n t r a l w i r e o f a t y p i c a l c r y o t r o n i s

p l o t t e d a s a f u n c t i o n o f c u r r e n t i n t h e c o n t r o l w i n d in g i n F i g u r e U . T he



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Memorandum 6M-38Ii3 Page h

current.

The magnetic field, H, at the surface is given by:

where H is in ampere-turns per meter

I is in amperes

d is in meters.

If H is given in oersteds, I in amperes, and d in mils (thousandths

of an inch) this becomes

H

= 157.5 j

oersteds d mils

It will be noted that the transition characteristics are very

sharp for high gate currents. The additional sharpness is a peculiarity

of the measuring technique wherein a current is passed through the gate

circuit and the voltage across the gate circuit is measured. When resis

tance suddenly appears, I^R loss in the gate circuit causes heating which

lowers the critical field and speeds switching.

The magnetic field due to the control winding is along the axis

of the central wire while the self-field of the wire due to its own current

is tangential to the wire. Tne two fields thus add in quadrature and the

resulting net field is the vector sum of two fields. Results indicate

that the superconducting central wire reaches its critical field when the

net field reaches a certain value, regardless of which way the net field

points in relation to the center line of the wire. In one experiment,

the curves of Figure

k

were reproduced exactly for all four combinations

rrd



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Memorandum 6M-38U3

Page 5

c u r r e n t th r e s h o ld th an th e f i r s t c r y o t r o n c o u ld h a n dle th ro u g h i t s

s u p e r c o n d u c t in g g a te c i r c u i t .

The c o n t r o l f i e ld i s r e l a te d to th e c o n t r o l c u r r e n t b y th e

number of tu rn s per inch in the co ntr o l winding , and the se l f f i e l d i s

re la ted to the ga te cur ren t by the d iamete r o f wire used in the ga te

c i r cu i t . Cur ren t ga in , K, i s simp ly g iven by :

I

=

Kd

I

For a given pi tc h c on tro l wind ing and a given gat e wire diam ete r , the

c u r r e n t g a in i s s p e c i f i e d . F ig u r e 5 i s a p l o t o f l in e s of c o n s ta n t K a s

a func t io n of winding p i tch and ga te wire d iam ete r . For th e c ryo tron

who se c h a r a c t e r i s t i c s a r e p l o t t e d i n F ig u r e U# K • 7 . The c u r r e n t

ga in ac tu a l ly observed for a g iven c ryo tron is o f ten le ss than ca lcu la t ed ,

presumably due to the co ns tr i c t io n of sup ercu r ren ts by smal l normal reg ion s

which nu c le a te about f laws in the wire sur f ace . Co ntro l-cu r ren t th re sho ld

p o in t s th u s fo rm a lo c u s in th e g a t e c u r r e n t - c o n t r o l c u r r e n t p la n e wh ic h

l i e s on an e l l i p s e of s ma l le r ma jo r -to - min o r a x i s r a t i o .

2 .3 Power Gain and i/R Time Constant

The input power to a cryotron, exclusive of eddy current and

r e l a x a t i o n lo s s e s , i s the p r o d u c t o f th e e n e r g y s to r e d in th e ma g n e ti c

f ie ld of the control winding and the f requency at which the control wind

ing i s en erg ized :

2

f L I

c c



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Memorandum 6K-38U3

Page 6

Power gain, G, can be approximated by:

X

V J 2

R

power out

m

g ii „ 1 / g \ g

power i n ,

T T

2 f l l / L

f I * *0 c

c c

In the pulse circuits of section 3* the gate current of one

cryotron becomes the control current of another^ I • I • For this condi

tion, the frequency at which the power gain becomes unity is:

R

f = _£

max L

c

which is the reciprocal of the L/R time constant of the circuit. The L

and R are on different cryotrons, but since large numbers of identical

cryotrons are involved, one can speak of the L/R time constant of a given

cryotron as being the fundamental time constant of the circuitry.

If a given cryotron is made longer while holding the pitch of

the control winding constant, the resistance and inductance increase

together such that the l/R time constant is not affected. The L/R time

constant is thus independent of cryotron length.

If the diameter of a given cryotron is made smaller while

holding the pitch of the control winding constant, the resistance increases

inversely as the diameter squared, while the inductance decreases directly

as the diameter squared. The i/R time constant thus decreases as the

fourth power of the diameter.



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C ir cu i t speed can a ls o be inc rea sed by us i ng a ho l low ce n t ra l

w i r e . Su p e r c o n d u c t iv i ty i s a s k in e f f e c t , p e n e t r a t in g b u t a few h u nd re d

atom la y er s , and th ere for e the core of a w ire can be removed and the wir e

w i l l s t i l l h av e z e ro r e s i s t a n c e i n i t s su p e rc o n d u ct i ng s t a t e . The r e s i s

tance in the normal s t a te , however , w i l l be h igh er by the ra t io of the

o r ig in a l c r o s s - s e c t io n a l a r e a to th e new c r o s s - s e c t io n a l a r e a . The c o r e

need no t ac tu a l ly be removed, p rov ided i t i s made to have a r e l a t iv e ly

h i g h r e s i s t i v i t y . W ire w i t h a h i g h - r e s i s t i v i t y c o re a nd a s up e rc o n d uc t in g

s h e l l c an b e f a b r ic a te d b y v a p or p l a t in g .

2.U Eddy C urr en ts

I t has been shown in Faber t h a t th e dela y, c , due to eddy

c u r r e n t s in th e d e s t r u c t io n o f s u p e r c o n d u c t iv i ty o f a w i r e b y a lo n g i tu d in a l

m a g n et ic f i e l d i s :

2

T - con st. K

d

. A

e

/>

U - H

c

)

wher e H is the external magnetic field, H is the threshold magnetic field

an d

/°

is the resistivity. The switching time varies directly as the square

of the diameter and inversely as the resistivity, and is a function of the

amount by which the threshold magnetic field is exceeded.

As the circuits of section 3 are speeded up by making cryotron

diameters smaller, there will be a speed range where eddy currents become

important. Lowering the diameter still further and increasing the pitch

proportionally should then increase the speed as the inverse square of the

diameter, since both circuit L/R time constants and eddy current time



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Memorandum 6M-38U3

Page 8

with a current gain of two. As soon as a superconducting path is estab

lished over the surface of the wire, the cryotron is in its superconducting

stat e—even if the center of the wire requires additional time to become

superconducting. While it is not anticipated that this transition will

be a major source of delay, it is interesting to note that this delay is

one which depends on the length of the cryotron.

As circuit speeds are increased by increasing the resistance of

the central wi re , thereby shortening l/R circuit time constants and

minimizing eddy current effects, a fundamental limit to the ultimate speed

exists in the form of relaxation losses. The exact frequency repion in

which these losses will become predominant is not known , but from experi

ments with superconducting coaxial cable and wave guide resonators, an

estimate is available which places the limit between 100 megacycles and

1P00 megacycles.

3. Cryotron Computer Circuitry

The low impedance level of cryotron circuitry dictates a high-

impedance power supply (current source) with circuit elements connected

in series. Each element allows the current a choice among two or more

paths only one of which is superconducting; all of the current flows

through the superconducting path. The current encounters zero back voltage

except when the paths are changing. The standby pcwer is therefore zero.

Several circuits, representative of those found in digital computers, are

described below.

3.1 Flip-Flop

A b is ta b le elem ent , one of the most common in a di g i ta l computer,



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Memorandum 6M-38U3

Page 9

c r y o t r o n s i s r e s i s t i v e a n d t h e o t h e r i r s u p e r c o n d u c ti v e o The g a t e c i r c u i t s

a r e j o i n e d a n d a r e a d - o u t c u r r e n t p u l s e i s a p p l i e d a t t h e j u n c t i o n . The

r e a d - o u t p u l s e w i l l ch o o se o n e p a t h o r th e t h e r , d e p e n d i n g o n t h e s t a t e

o f t h e f l i p - f l o p . The f l i p - f l o p w i t h r e a d - i n a nd r e a d - o u t c r y o t r o n s i s

shown i n F i gure 6 .

A ny n um b er o f i n p u t c r y o t r o n s c a n b e a d d e d i n s e r i e s w i t h t h o s e

a l r e a d y d e s c r i b e d ( F i g u r e 7 ) t o s e t th e f l i p - f l o p t o o ne s t a t e o r t h e

o t h e r . C o n n e c t e d a s s u c h , t h e y a r e OR g a t e s ; a n y o n e o f th em a c t i n g a l o n e

c a n s e t t h e f l i p - f l o p . S i m i l a r l y , a d d i t i o n a l c r y o t r o n ; c a n b e a dd ed w i t h

t h e i r g a t e c i r c u i t s i n p a r a l l e l w i t h t h e c o n t r o l w i n d i n g o f th e i n p u t

c r y o t r o n a l r e a d y d e s c r i b e d , b e h a v i n g a s AND g a t e s ( F i g u r e 9 ) . The f l i p -

f l o p s e t c u r r e n t i s b y p a s s e d t h r o u g h on e o r m o re o f t h e s e p a r a l l e l g a t e s

u n l e s s a l l of th em a r e r e s i s t i v e . T h is l a t t e r c o n n e ct io n i n v o l v e s s u p e r

c o n d u c t o r s i n p a r a l l e l , i n w h ic h c a se t h e c u r r e n t d i v i d e s i n v e r s e l y a s t h e

i n d u c t a n c e o f t h e p a r a l l e l p a t h s .

A d d i t i o n a l r e a d - o u t c r y o t r o n s ca n b e a d d e d i n s e r i e s w i t h t h o s e

a l r e a d y d e s c r i b e d . S i n c e t h e i r c o n t r o l w i n d i n g s a r e s u p e r c o n d u c t i n g , t h e

a d d i t i o n a l c r y o t r o n s do n o t a d d a n y r e s i s t a n c e t o t h e f l i p - f l o p . The

a d d i t i o n a l i n d u c t a n c e i n c r e a s e s t h e i / R t im e c o n s t a n t o f t h e c i r c u i t , h o w

e v e r , l e n g t h e n i n g t h e t r a n s i t i o n t im e b e tw e e n s t a t e s .

3 . 2 M u l t i v i b r a t o r

T h r ee f l i p - f l o p s m a de o f o n e - i n c h p i e c e s o f t h e c r y o t r o n s t o c k

w h os e c h a r a c t e r i s t i c s a r e g i v en by F i g u r e

h

h a v e b e en s t u d i e d i n a m u l t i -

v i b r a t i n g c i r c u i t ( F i g u r e 9 ) . The r e a d - o u t c r y o t r o n s o f f l i p - f l o p A a r e

c o n n e c t e d i n s u ch a w ay a s t o s e t f l i p - f l o p B t o t h e s t a t e o p p o s i t e t h a t o f

A . A s i m i l a r c o n n e c t i o n b e t w e e n B a n d C c a u s e s C t o a ss u m e t h e s t a t e



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Memorandum 6K-3QU3 Page 10

The t i m e t a k e n f o r t r a n s i t i o n f ro m o n e t i m e p e r i o d t o t h e n e x t

i s a f u n c t i o n o f t h e t r a n s f e r c u r r e n t . I f t r a n s i t i o n o c c u r s a t a f i x e d

t h r e s h o l d c u r r e n t v a l u e , t h e f i n a l v a l u e o f th e r i s i n g c u r r e n t i n a g i v en

c o n t r o l w i n d i n g d e t e r m i n e s t h e f r a c t i o n o f t h e i / R t i m e c o n s t a n t r e q u i r e d

t o r e a c h t h a t t h r e s h o l d v a l u e . I f t h e f i n a l v a l u e i s ( a ) t i m e s t h e

t h r e s h o l d v a l u e , t h e t im e r e q u i r e d t o r e a c h t h e t h r e s h o l d i s g i v e n b y :

t • i / R l n ( a / a - l ) . T he p a r t i c u l a r m u l t i v i b r a t o r c i r c u i t d e s c r i b e d c o m p le te s

t h e r o u n d - t r i p t h r o u g h i t s s i x t im e p e r i o d s a t t h e r a t e o f 1 0 0 t o 1 ,0 0 0

t i m e s p e r s ec o nd d e p e n d i n g o n t r a n s f e r c u r r e n t . H ie h i g h e r f r e q u e n c y

g i v e s i n d i v i d u a l t i m e p e r i o d s of 16 7 m i c r o s e c o n d s d u r a t i o n .

To m o n i t o r t h e t r a n s i t i o n s o f o ne o f t h e f l i p - f l o p s , a n a d d i t i o n a l

c r y o t r o n g a t e i s a d d e d w i t h i t s c o n t r o l w i n d i ng i n s e r i e s w i t h o n e s i d e

o f t h e f l i p - f l o p . A c u r r e n t s o u r c e i s c o n n e c te d t o i t s g a t e c i r c u i t . W hen

t h e c o n t r o l c u r r e n t i s z e r o , t h e g a t e c i r c u i t i s a s u p e r c o n d u c t o r a nd t h e

v o l t a g e i s z e r o . W hen t h e c o n t r o l c u r r e n t r e a c h e s t h e t h r e s h o l d v a l u e ,

t h e e ja te c i r c u i t b e co m es r e s i s t i v e a n d d e v e l o p s a v o l t a g e w h i c h i s a m p l i

f i e d a n d d i s p l a y e d . T y p i c a l v a l u e s a r e : R

c

0.01 ohm, I • 100 ma;

V * 1 m i l l i v o l t . T he ta m e c u r r e n t w a ve fo rm i s n o t p r e s e r v e d b y t h e

m o n i t o r i n g g a t e d u e t o i t s i n h e r e n t n o n l i n e a r i t y p l u s t h e s h a r p e n i n g o f

i t s t r a n s i t i o n du e t o l 2 R h e a t i n g a s i t be co m es r e s i s t i v e .

3 . 3 M u l t i t e r m i n a l S w i tc h

D i s t r i b u t i n g a p u l s e am ong s e v e r a l w i r e s c a n b e a c c o m p l i s h e d b y

a c r y o t r o n sw i t c h ( F i g u r e 1 0 ) . I n f o r m a t i o n i s f e d i n t o t h e s w i t c h f ro m

c r y o t r o n f l i p - f l o p s , h e r e r e p r e s e n t e d b y t o g g l e s w i t c h e s . O ne f l i p - f l o p

c a u s e s t h e od d o r e v en ro w s o f t h e s w i t c h t o b e r e s i s t i v e , a s e co n d f l i p -

f l o p c a u s e s o dd o r e v en p a i r s t o b e r e s i s t i v e , a t h i r d f l i p - f l o p c a u s es

o dd o r e ve n f o u r s t o b e r e s i s t i v e , a n d s o o n . A s i n g l e p a t h s u r v i v e s



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Memorandum 6M-38U3 Pag e 1 1

INPUT

A

1

0

1

0

1

0

1

0

INPUT

B

1

1

0

0

1

1

0

0

CARRY

IN

1

1

1

1

0

0

0

0

SUM

1

0

0

1

0

1

1

0

CARRY

OUT

1

1

0

1

0

0

0

Table n . Binary Add ition Table

the sum f l ip - f lo p to i t s proper s t a te . A s im i lar group of ga tes develops

the carry for the fo l low ing stage . Note that a l l c ir cu i ts are in se r ie s

from a current source power supply.

The foregoing binary adder des ign i s described to i l lu st r a te

the way in which switch es and gate s can be interco nn ected . A design having

fewer cryotron s per stage is av ail ab le wherein the carry is handled by a

la tt ic e network shown in Figure 12. The la be l beside each of the s ix

con trol windings ind ica te s when i t i s to be ener gized . The A • B • 0 and

A • B • 1 windings can each be made of two cryotr ons in a p a r a ll e l AND



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- J*

Memorandum 6M-38U3 Pa ge 12

3.fp S t e p p i n g R e g i s t e r

S t e p p in g r e g i s t e r s a r e com monly u s e d f o r r e c e i v i n g d i g i t a l

i n f o r m a t i o n i n s e r i a l f or m a t o ne p u l s e r e p e t i t i o n f r e q u e n c y an d a f t e r a

p r e d e t e r m i n e d n um b er o f b i n a r y b i t s ha v e b e en s t o r e d , s h i f t i n g t h e i n f o r m a

t i o n o u t a t a d i f f e r e n t f r e q u e n c y . A s e c o n d common u s e f o r s h i f t i n g

r e g i s t e r s i s t o a c c o m p l i s h th e c o n v e r s i o n b e tw e e n d i g i t a l i n f o r m a t i o n i n

s e r i a l a n d p a r a l l e l f o r m . T he s t e p p i n g r e g i s t e r s i n common u s e a r e m ade

o f v ac uu m t u b e s , t r a n s i s t o r s , o r m a g n e t i c c o r e s . C r y o t r o n s ca n a l s o be

u s e d i n t h e sam e s e r v i c e . E a ch s t a g e o f t h e s h i f t r e g i s t e r c o n s i s t s o f

tw o c r y o t r o n f l i p - f l o p s w i t h r e a d - i n an d r e a d - o u t c r y o t r o n s . O ne t r a n s f e r

c i r c u i t s e t s t h e s e c o n d o f t h e tw o f l i p - f l o p s o f e ac h s t a g e t o c o r r e s p o n d

t o t h e s t a t e o p p o s i t e t h a t o f t h e f i r s t . The c o u p l i n g l i n k t o a c c o m p l i s h

t h i s i s s i m i l a r t o t h e o n e d e s c r i b e d i n s e c t i o n 3» 2 w h i ch i n t e r c o n n e c t s

s t a g e s o f t h e m u l t i v i b r a t o r . A s ec on d t r a n s f e r c i r c u i t s e t s t h e f i r s t

f l i p - f l o p o f e a ch s t a g e t o c o r r e s p o n d t o t h e s t a t e o p p o s i t e t h a t o f t h e

s e co n d f l i p - f l o p o f t h e s t a g e to i t s l e f t . A l i n e o f s u ch s t a g e s s e r v e s a s

a s h i f t i n g r e g i s t e r , c a p a b le o f s h i f t i n g d i g i t a l i n f o r m a t i o n to t h e r i g h t .

I n f o r m a t i o n ( ON E'S o r ZE RO 's) f e d i n t o t h e f i r s t f l i p - f l o p i n s y n c h r o n i s m

w i t h t h e s e c o n d o f t h e t wo t r a n s f e r p u l s e s ( c a l l e d ADVANCE B p u l s e ) , w i l l

a d v an c e t h r o u g h t h e s t e p p i n g r e g i s t e r o n e s t a g e f o r e a c h p a i r o f t r a n s f e r

p u l s e s , ADVANCE A an d ADVANCE B, which ar e d is p la c e d in t im e. F ig u re lU

s ho ws tw o s t a g e s o f a c r y o t r o n s t e p p i n g r e g i s t e r . P a r a l l e l o u t p u t g a t e s

are not shown.

3 . 6 C o i n c i d e n t - C u r r e n t C i r c u i t s

M any i n t e r e s t i n g c i r c u i t s c a n b e m ade o f c r y o t r o n s w i t h tw o o r

m o re c o n t r o l w i n d i n g s w ou nd o v e r e ac h o t h e r i n s u c h a w ay t h a t t h e n e t

m a g n e t i c f i e l d a f f e c t i n g t h e c e n t r a l w i r e i s du e t o t h e sum o f t h e m a g n e t i c

f i e l d s o f t h e i n d i v i d u a l w i n d i n g s . The d - c c r y o t r o n c h a r a c t e r i s t i c s of



13/32

Memorandum 6M-38U3

Page 13

U . E n g i n e e r i n g a C r y o t r o n S y st em

U«l Low-Tempera tu re Env i ronm ent

T he m o s t u n u s u a l r e q u i r e m e n t of a c r y o t r o n s y s t em i s t h a t i t

o p e r a t e a t a t e m p e r a t u r e n e a r t h e a b s o l u t e z e r o . T en y e a r s a g o t h i s

r e q u i r e m e n t w o u l d h a v e p r e c l u d e d s e r i o u s t h o u g h t of s uc h a s y s t e m .

T o d ay , h o w e v e r, s u ch a n o p e r a t i n g t e m p e r a t u r e i s r e l a t i v e l y e a s y t o

ac h i e v e . ^ Th i s change i s ma i n l y due t o t he work of Samuel C . C o l l i ns

w ho se h e li u m l i q u i f i e r s r e v o l u t i o n i z e d t h e f i e l d o f l o w - t e m p e r a t u r e

p h y s i c s . A r t h u r D. L i t t l e , I n c . o f C a m br id g e, M a s s a c h u s e t t s , h a s b u i l t

s e v e n t y C o l l i n s h e li um l i q u i f i e r s o f a b - l i t r e - p e r - h o u r c a p a c i t y . The

l i q u i f i e r a t M . I . T . l i q u i f i e s 27 l i t r e s p e r h o u r . S t o ra g e o f l i q u i d h e l iu m

h a s a l s o i m p r o v e d . C o m m e r c ia l ly a v a i l a b l e d o u b l e D e w ar s w h i c h u s e l i q u i d

n i t r o g e n i n t h e o u t e r D ew ar l o s e l e s s t h a n o ne p e r c e n t of t h e i r l i q u i d

h e l i u m p e r d a y .

T he h e a t d i s s i p a t e d b y a c r y o t r o n s y s t e m c a u s e s e v a p o r a t i o n o f

t h e h e l i u m . I f t h e a v e r a g e p o w er d i s s i p a t e d p e r c r y o t r o n i s 1 0~ k w a t t ,

a n e s t i m a t e b a s e d o n p r e s e n t e x p e r i m e n t a l u n i t s , a 5 , 0 0 0 - c r y o t r o n c o m p ut er

w o uld d i s s i p a t e o n e - h a l f w a t t . T he l a t e n t h e a t o f v a p o r i z a t i o n o f l i q u i d

h e l iu m a t U .2 K i s 5> c a l o r i e s p e r g r a m , i t s d e n s i t y i s 0 » 1 2 5 7 , an d t h e r e

f o r e o n e - h a l f w a t t c o r r e s p o n d s t o a n e v a p o r a t i o n r a t e of 0 . 9 3 l i t r e p e r

h o u r . A c o n t i n u o u s s y s t e m w h i ch r e c y c l e s h e l i u m w o u l d b e m o s t e c o n o m i c a l

f o r a s t a t i o n a r y i n s t a l l a t i o n ^ a t e n - o r t w e n t y - l i t r e c h a rg e a t t h e ti m e

o f l a u n c h i n g w o uld s u f f i c e f o r p o r t a b l e s y s t e m s .

The t e m p e r a t u r e o f a l i q u i d h e l i u m b a t h c an b e c o n t r o l l e d b y

c o n t r o l l i n g t h e p r e s s u r e o f t h e b a t h . T a b le I I I g i v e s t h e b o i l i n g p o i n t

o f h e l iu m a t v a r i o u s p r e s s u r e s . B elo w 2 . 1 9 K , t h e s o - c a l l e d l a m b d a - p o i n t ,

l i q u i d h e l iu m e x h i b i t s u n u s u a l p r o p e r t i e s w hi ch m ay p r o v e u s e f u l i n a



14/32

Memorandum 6M-38U3 Pa ge Hi

Pr e s s u r e

mom. Hg.

0.001

0 .0 1

0 .1

1 .

10.

100.

200.

300.

Uoo.

5oo.

600.

700.

710.

Temperature

degrees K

0.657

0.791

0.982

1.269

1.71.3

2.638

3.067

3.368

3.605

3.803

3.975

U.127

u.ua

Pr e s s u r e

num. Hg„

72 0

o

730.

7U0.

750.

760.

770.

780.

790.

800.

900.

1000.

1500.

1720.

Temperature

degrees K

U.156

li .170

U.18U

U.198

l i .211

U.225

U.239

U.252

U.266

h.UO

li.52

5.03

5 .20

Table i n . Bo i l ing Poin t o f He lium

U«2 P hys ical Co nstru ction



15/32


extreme lew temperatures. Some are relatively good thermal insulators

(stainless steel and cupro-nickel) and may be used for mechanical support.

There is no basis for the common impression that everything falls apart

just below JAN specifications (-85 C) .

U.3 Input, Output, and Power Supply

Input pulses to cryotron circuits involve current amplitudes

which are easily achieved in the terminal equipments commonly associated

with digital computers. Since the voltage level is low, input of informa

tion to a cryotron system involves no unusual problems.

Connecting the output pulses of a cryotron system to terminal

equipment, on the other hand, is difficult due to the low power level of

the cryotron circuitry. Power cryotrons can be designed to increase the

power level, but it appears that vacuum-tube or transistor amplifiers

are necessary to bring the level up to that of most output equipments.

Magnetic amplifiers with superconductive control windings are an interest

ing possibility for power amplification.

Power supplies for cryotron systems are easy to achieve. The

low impedance of the circuitry dictates a current-source power supply.

A battery with a series resistance is adequate.

>. Conclusion

The cryotron in its present state of development is a new circuit

component having power gain and current gain so that it can be used as an

active element in logical circuits. It is easily and inexpensively

fabricated from commercially available materials and its size is small.



16/32

Memorandum 6M-38I;3 Pa ge

16

D r a w i n g s A t t a c h e d :

F i g u r e

1

C-6333k

F i g u r e

2

A-63O87

F i g u r e 3 A-63088

F i g u r e

B-63091

F i g u r e 5 B-63U9I

F i g u r e

6

A-63090

F i g u r e

7

C-6329U

F i g u r e

8

C-63291

F i g u r e

9

C-63293

F i g u r e 10 C-63292

F i g u r e

11

C-63338

F i g u r e 12 B-63335

F i g u r e

13

C-63336

F i g u r e

lit

C-63337

F i g u r e

15

A-63679

F i g u r e

16

A-63678

D i s t r i b u t i o n L i s t :

Group

63

S t a f f

Group

35

S t a f f

Group 65 S t a f f

M.

A.

H e r l i n

D 321

B .

G.

F a r l e y

R.

P.

Mayer

» L. L. S u t r o

R.

F.

J e n n e y



17/32

C 63334

F 2969

SN - 1220

H

c

GA U S S

FIG . I

1000

900

800

700

600

500

400

THRESHOLD

MAGNETIC FIELD

3 0

°

vs TEMPERATURE

2 0

°

FOR SE VE RA L ,oo

COMMON

SUPERCONDUCTORS

2 3 4 5 6

T E M P E R A T U R E °K



18/32

A - 6 3 0 8 7

F 2862

SN-1169

H

N O R M A L

R E G I O N

SUPERCONDUCTING

REG

I

ON

4.2° K

FIG. 2

T H R E S H O L D M A G N E T I C F I E L D

A S A F U N C T I O N O F T E M P E R A T U R E

F O R A S U P E R C O N D U C T O R



19/32

•

I

r\

£\

n n n

n

)

S I N G L E C R Y O T R O N

F I G . 3

C R YO T RO N B I S T A B L E E L E M E N T

( F L I P - FL O P )



20/32

B 63091

F 2865

SN 1172

*

r €

n

rj

S I N G L E L A Y E R . 0 0 3 N I O B I U M

0 0 9 T A N T A L U M

.01

n

u

n

.0075

h

9 .005

OHMS

.0025

CRYOTRON GATE

vs.

CONTROL

100

2 0 0 3 0 0

I M I L L I A M P E R E S

c

RES

I

S T A N C E

CURRENT

400



21/32

B 63491

F 2974

SN - 1225

5 0 0

4 0 0 -

C O N T R O L

3 0 0 -

W I N D I N G

PITCH ru

T U R N S

2 0 0

PER INCH

100 -

0

1 2 3 4 5 6 7 8

C E N T R A L W IR E D I A M E T E R ~ M I L S

CURRENT GAIN vs CONTROL WINDING

PITCH AND CENTRAL WIRE DIAMETER



22/32

A - 6 3 0 9 0

F-2864

SN-1171

ZE RO INPUT I ONE INPUT

9 9 SUPPLY 9 o

€

a

a

€

a

a

n

{I

r

D

a

D

a

D

H-a

a

o

a

a

D

a

D

>

O

Q-Q

a

D

a

TJ TJ

SUPPLY

a

u

n

u

JH

n

£

1

D

H - Q

1

n

CJ

n

D

n

u

a

u

}

u

ONE

O U T P U T

C R Y O T R O N

C R Y O T R O N S

READ

F I G .

G

F L I P - F L O P

t

ZERO

OUTPUT

WITH READ - IN

AND RE A - OU T C RY OT RO NS



23/32

C-63294

F 2968

SN 1219

A

C

c

)

I)

• )

Z E R O

I N P U T S

o -

B

o -

X

c

c

c

)

)

• )

S U P P L Y

S U P P L Y

O N E

N P U T S

W I T H

C R Y O T R O N FL I

P-FLOP

O R G A T E S

IN

B O T H

SI

D E S



24/32

C 63291

F 2965

SN 1216

I

S U P P L Y

Z E R O

C

I N P U T C

D

ONE

P I N P U T

d

(CD,

D

D

B

C

C

d

Y

D

D

I N PU T

P U L S E

S U P P L Y

F l C i . U

C R Y O T R O N F L I P - F L O P

W I T H

AND

G A T E S

IN ONE

S

I DE



25/32

o

Q .

o

CD

a

o

_i

u.

i

0 .

tr

h-

<

cr

DQ

>

o

or

h-

o

> -



26/32

C-63292

F-2966

S N - 1 2 1 7

r-C

•S

€

€

€

•a

€

R E A D

n n

TD O

o n

era

O-

Q .

LTD

n n

era

_Q

o n

U U

_Q

o

L T U

CL

n.

era

1

cnx

O

4

a

O-

n n

t r o

n n

t3TD

n

a

wo

L

T)

p_

TJ

n n

era

^ C ON T R O L J ^

O Q

U~U

_Q

n

enr

o o

~0~T7

Q Q

Cr t7

I

C O N T R O L

Q- Q

cr

p_

v~o

_Q JQ

Crcr

Q Q

o~o

v

8 POSITION

C R Y O T R O N S W I T C H

-°

o

I

-o

2

-°

3

-o

4

-o

6

•o 7



27/32

C - 6 3 3 3 8 * *

F 2973

SN - 1224

CARRY

OUT

SUM

FLIP-FLOP

00 00 Oo 00

0 1 0 I

A INPUT B INPUT

CARRY

IN

ONE STAGE OF A BINARY ADDER


APPROVED FOR PUBLIC RELEASE CASE 06 1104


28/32

B 63335

F 2970

SN-1221

W

A = B = 0

? Q n

a

FIG.

12

CARRY NETWORK

o o




29/32

C-63336

F 2971

SN 1222

*

I CARRY

OUT

J21

A=l

r€

— •

u

D-

U~

CT

^ X B=0

m̂

- « - •

0 CARRY

OUT

iK

n

L

Q

i

r

u

B

n

b

n

n

y l

0

0 0

B

0

B

l

A=l

T 7

^ S ^

/

0 \ i

T 7

- Q

SUM

F L I P -

FLOP

€

O O

A= B

A * B

BINARY ACCUMULATOR STAGE



30/32

in

H i

T 7

cr

^b^££

a o

• c r

i O .

<

u_

o

CO

j LU

] o

8

<

h-

(X)

cr

LU

K

CO

CD

LU

cr

o

z

CL

Q_

LU

co




31/32

A - 6 3 6 7 9

F I G .

15

EXPERIMENTAL CRYOTRON CIRCUITS




32/32

A - 6 3 6 7 8

*

FIG. 16

3 - CRYOT RON- F L I P- F LOP M ULT I V I BRAT OR


The Cryotron Superconductive Computer Component

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