NBS TECHNICAL NOTE 635

Some Applications of

Cryogenics to High Speed

Ground Transportation
NATIONAL BUREAU OF STANDARDS

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$

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Some Applications of Cryogenics

to High Speed Ground Transportation

VD. Arp

AJ. Clark T.M. Flynn

Cryogenics Division

Institute for Basic Standards

National Bureau of Standards

Boulder, Colorado 80302

NBS Technical notes are designed to supplement the

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-*• " ^

*"»*»„ ot *

U.S. DEPARTMENT OF COMMERCE, Frederick B. Dent, Secretary

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts, Director

Issued February 1973
National Bureau of Standards Technical Note 635

Nal. Bur. Stand. (U.S.) Tech. INole 635, 29 pages (February 1973) CODEIN: 1NBTNAE

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D. C. 20402

(Order by SD T-atalog No. CI 3.46:635)
CONTENTS

Page

1. INTRODUCTION 1

2. WAYS OF LEVITATION 5

2. 1 Air Cushion 5

2. 2 Magnetic Levitation/Suspension 5

2. 2. 1 Attraction Between Electromagnets

and Steel Rails 6

2. 2. 2 Repulsion Between Permanent Magnets . 8

2. 2. 3 Repulsion Between a Superconducting

Train Magnet and Conductors in the

Guide way 10

3. STATE-OF-THE-ART IN THE U. S. OF MAGNETIC

SUSPENSION 14

4. FOREIGN PROGRAM PLANS 15

5. PROPULSION 17

6. SOME CRYOGENIC TECHNICAL PROBLEMS 17

6. 1 Helium Refrigeration 19

6. 2 Materials 19

7. FUTURE DEVELOPMENT 20

8. REFERENCES 23

SOME APPLICATIONS OF CRYOGENICS TO

HIGH SPEED GROUND TRANSPORTATION

Vincent D. Arp, Alan F. Clark and Thomas M. Flynn

The current status (December 1972) of -worldwide

research on high speed ground transportation techniques

is reviewed. Particular attention is given to studies of

magnetic levitation using superconducting magnets, including comparison with alternative magnetic techniques

and with air suspension systems. Superconducting levitation appears to be a strong contender in the U.S. Department of Transportation hopes to select in the late 1970'

s

the best of the possible levitation techniques for subsequent

advanced development. Cryogenic engineering research

needed in support of major development of a superconducting levitated system is identified.

Key words: Levitation; magnetic suspension; materials

fatigue data; refrigeration; superconducting magnets;

transportation.

1. INTRODUCTION

The status of transportation in this country was summarized

by Senator Vance Hartke (1972), Chairman of the Senate Surface Transportation Subcommittee: "We have regretably allowed our transportation network to grow in an unplanned, uncoordinated, fashion. We have

expended too little effort in integrating - fusing - the development of our various modes of transportation. We have given too little thought

and attention to how transportation might be planned to structure re- gional or national development in a practical manner. We have, in

short, created a crisis."

The changing balance of transportation use in this country is seen directly in table 1 .
Table 1. Intercity Passenger Traffic

Year

I960

Li ft to Dra

Ratio*

g Perc ent of int ercity p assenger--miles

Private auto 20 86 89 90 89 87

Airway 20 2.0 3.2 4.3 6.3 9.8

Bus (excludes 20 5.2 3.6 2.5 2.6 2.2

schoolbu 3) Railroad 150 6.4 4.0 2.8 1.9 1. 1

Canal Barge 1000 0.23 0.24 0.34 0.34 0.34

An index of merit, the ratio of the weight of the vehicle to the force

required to keep it moving at a given speed.

Mass ground transport, and railroads in particular, have

suffered dramatic decreases in passenger miles of travel, while air

travel has risen correspondingly.* At the same time, auto transport

has only just about held constant on a percentage basis, probably due in

part to the 60 billion dollar Federal Highway Assistance Program,

which is now 77% complete. Airlines have been assisted by local, state,

and federal support. Rail travel, on the other hand, has fallen in the

quantity of passenger train-miles available. In principle, however, rail

service should be about the most efficient way of moving people and

goods, as judged by the lift-to-drag ratios for various types of transport

shown in figure 1 (Gudenjahn and Wipf, 1971).

It is important to note that successful operation of the high speed

Tokaido Line in Japan has resulted in measurable decrease in the
OOOf

hp per ton

(74WkgH

)

Magnetic suspension

experiment

20 40 6O8OIOO 200 400 600

Miles per hour [1 mph = 1-6 km h"1

] Figure 1 Lift to drag ratios as a function of speed for various types

of transportation (Guderjahn and Wipf, 1971).
localized air traffic. In recognition of these and related facts, the

Office of Research, Development and Demonstration (ORDD)* in the

Federal Railway Administration (FRA) is investigating new methods

of ground transportation, with speeds of up to 500 mph (800 km/hr)

under consideration for intercity travel. However, even at speeds

above about 125 to 150 mph (200 to 250 km/hr) wheels become impractical. This is the case because the suspension system, upon which the

vehicle weight is concentrated, becomes incapable of absorbing or accommodating to the high frequency shocks from residual irregularities in the wheels, roadbed, or track. Accordingly, there is no question that contact between the train and the track must be eliminated

by either air cushion or magnetic suspension for speeds in the range

of 250 to 500 mph (400 to 800 km/hr) which are becoming a national

goal for intercity ground transportation. Air cushion technology

currently has a development lead, but magnetic suspension potentially

has a much higher efficiency and lower adverse environmental impact.

Magnetic levitation, floating one magnet above another on the

simple principle that like poles repel one another, has become really

practical and dependable for very large magnets only in the last few

years with the advent of workable superconductors. Superconductivity

is found only at very low temperatures, and this forges an indispensable

link between cryogenics and transportation. The remainder of this

paper focuses primarily on the essential role of cryogenics in magnetic

levitation. However, if a cryogenic system -were an integral part of

a train for levitation purposes, it might be expedient to exploit the

benefits of cryogenics for superconducting generators and propulsion

motors as well. This latter topic is touched upon but briefly.

* formerly known as the Office of High Speed Ground Transportation

(OHSGT)
2. WAYS OF LEVITATION

2. 1 Air Cushion

The ORDD of the Federal Railway Administration of DoT has

sponsored the development of Tracked Air Cushion Vehicles (TACVs)

since 1967, with maximum speeds targeted at 300 mph (500 km/hr),

limited by vehicle wind resistance. The TACV is both supported and

guided in a concrete guideway by air cushions provided by on-board

compressors .

Outside of the USA, England and France have major demonstration programs underway on TACV, with tentative plans for usage in

airport shuttle service. The top speed reached by the French propellerdriven Aerotrain was 265 mph (430 km/hr) on January 22, 1969, but

its noisy propeller creates a severe environmental impact problem.

At present, TACV research enjoys a comfortable lead on magnetic

vehicle levitation research. Its potential disadvantage as compared

to superconducting magnetic levitation includes: (1) high track cost

because of the small vehicle to roadway clearance (1 to 2 cm), and

(2) the necessity for a heavy and somewhat noisy on-board mechanical

power source to provide the air flow.

2.2 Magnetic Levitation/Suspension

Magnetic fields can be employed for magnetic "cushions"

analogous to the way that air is used to support and guide an air

cushion vehicle.

Proposals embodying this general concept date back to the early

1900's, but have been given serious attention only in the past few years

as high field superconductivity has come of age. The required magnetic

fields can be generated by permanent magnets, electromagnets (generally
superconducting), or eddy currents in a conducting sheet or loop due

to relative motion with an opposing magnet. Often, some sort of

magnetic propulsion by linear electric motors is considered in addition

to the magnetic levitation, and it is possible in principle to use the

same magnets for both operations (Richards and Tinkham, 1972). The

various possible levitation systems are outlined in table 2, with one

exception: Clark (1971) has suggested that to conserve rights -of-way,

the track might be built in conjunction with a superconducting power

line to provide a track-based magnetic field which could levitate either

a passive eddy current shield on the bottom of the vehicle or a superconducting magnet on board the vehicle. It is not certain that the

possibly disparate requirements of power transmission and vehicle

levitation could simultaneously be satisfied, and it appears that tests

of this suggestion will have to wait for further superconducting power

line development.

2.2.1 Attraction Between Electromagnets and Steel Rails

In the attraction system, a servo- controlled electromagnet is carried on the vehicle. The attraction between the electromagnet and

steel guide rails provides lift and guidance. A gap of about . 5 in

(12 mm) can be maintained between magnet and rail at a power expenditure of about 1 kW per metric ton of suspended weight. This small gap

has to be monitored and controlled by a very fast acting and reliable servo- system, since this suspension technique is inherently unstable.

Two attractive- rail test vehicle programs are being explored

by the German Ministry of Transport. In the system developed by

Krauss-Maffei (KM), the gap is held nearly constant and the unavoidable irregularities of the guide rails must be cushioned by a secondary suspension system. In the Messerschmitt-Bolkow-Blohm
Table 2. Features of Various Suspension Systems

Roadbed Magnetic Vehicle Magnetic Field

Field

Permanent Electromagnets

Magnets (generally superconducting)

Pe rmanent Small lifting force. Would provide greater lift Magnets Small vehicle clearance. and clearance than the all (very expensive; Stability problems re- permanent magnet system.

difficult to keep quire additional track clean). control. Very low magnetic drag

(Pohlgreon, 1966).

Induced Eddy (Same as above). Can support high loads with Currents in Con- (Has never been high clearances at speeds

ducting Sheets or seriously proposed). above about 40 to 80 km/hr

Loops. using superconducting

magnets.

Being studied in USA, Japan,

Germany, Canada.

High Permeability Impossible: inherently Fail-safe operation is Magnetic Rail. unstable and uncon- difficult to achieve.

trollable attraction Two test trains are running

between the magnet in Germany, using conven- and the rail. tional electromagnets.

Small vehicle clearance. Very low magnetic drag.

Inherently unstable but can

be controlled.
(MBB) system, the gap is allowed to vary, and no secondary suspension

is used. An additional difference between the two schemes is that

Krauss-Maffei has dispensed with the vertical steel rail and derives

both lift and guidance from each electromagnet. Schematic drawings

are given in figure 2. Both of the German vehicles achieved successful

demonstration in barely one year's time, and are impressive evidence

that the technique is within the state-of-the-art. Because of relatively

short lengths of test tracks, top speeds to date have been about 60 mph

(100 km/hr). The track must be constructed and maintained to very

tight tolerance in order to obtain good ride quality at 300 mph (500.

km/hr). Because of the inherent instability in this type of suspension,

however, the feedback-controlled levitation system must have a high

degree of redundancy and protective circuitry built into it to assure

safe operation in the event of every conceivable possible component

failure or failures. The tests in Germany are being watched very carefully, since the system has had no major development problems to date.

Whether appropriate redundancies can be built into the control system

to guarantee safe daily operation is not known at this time.

2. 2. 2 Repulsion Between Permanent Magnets

The recent development of rare-earth cobalt permanent magnets

possessing high intrinsic coercivity gives new impetus to the old idea of

using the repulsion between like poles to support and guide a vehicle.

This technique is by now quite well known, having been demonstrated

years ago by Westinghouse in a single-passenger vehicle (Kerr and

Lynn, 1961) and lately by Hitachi in the small-scale magnetically sus- pended train displayed at EXPO 70. Pre-rare-earth cobalt materials

provided gaps of less than a centimeter and were subject to selfdemagnetization. The advantages of permanent magnets for suspension
MAGNETIC SUSPENSION - Attractive

THE ELECTROMAGNETS ON THE TRAIN ARE ATTRACTED TO AN IRON PLATE IN THE GUIDEWAY

OVERHEAD GUIDEWAY STRUCTURE

BOGIES WITH SUPPORT, GUIDANCE, AND PROPULSION SYSTEMS

21

en r~rn r~i—1

1—

m

SCHEME "A " : Train suspended beneath track.

mmii i hi mil ii i f i i • 11 mil in i in i it llm i ii i till —

d

FERROMAGNETIC PLATE IN GUIDEWAY S^S EFT7

] tt

GAP SENSING

ELECTROMAGNETS AND CI

BOGIE

23 i—i

i r~r-1 m—i H

BOGIES WITH SUPPORT, GUIDANCE, AND PROPULSION SYSTEMS

GUIDEWAY STRUCTURE

SCHEME "B" - Train levitated above track.

Figure 2. Schematic diagram of two possible attractive-suspension

systems.
are that there is no induced drag and no power is required for levitation.

The cost of the guideway is probably the most overwhelming drawback.

Estimates range from $4. 5 to $9 million per kilometer, and this is based on a very optimistic projection of ultimate RCo magnet costs of

$33/kgm, or little more than the cost of the raw materials. Finally,

the problem of maintaining a clean track, smooth and free of magnetic

litter, would be significant.

2. 2. 3 Repulsion Between a Superconducting Train Magnet and

Conductors in the Guideway

The first suggestion for vehicle levitation with superconducting

magnets came from Powell in 1963, subsequently improved and made

more detailed by he and Danby in 1966. Later they developed the

"null flux" suspension idea. The history of this development, along

with a concise technical summary, is presented in their 1971 paper.

As superconducting magnets began to prove themselves in high

energy physics applications, more attention was given to this magnetic

levitation. Consideration was given to magnetic suspension for a high

speed rocket test sled and other studies appeared by Guderjahn and

Wipf (1969) at atomics International, and Coffey, Barbee, and Chilton

(1969) at the Stanford Research Institute (SRI). Guderjahn and Wipf

(1971) and Powell and Danby (1971) have since published excellent

reviews. Richards and Tinkham (1972) have summarized technical

features of magnetic lift, drag, and propulsion systems.

The essence of the superconductive repulsion system is the use

of superconducting magnets in the vehicle which induce eddy currents

in the aluminum guide-way when the vehicle is moving. These guideway currents react with the moving magnetic field in the vehicle to

10
produce a repulsive supporting force. Guidance is obtained by the

same techniques and by designing the aluminum guideways to produce

lateral forces on the vehicle. It may prove possible to shape the

guideway in such a way that the same superconducting magnet in the

vehicle can be used for both suspension and guidance. Two schemes are shown in figure 3.

An important feature of the eddy- current- track levitation systems

is that the magnetic drag rises to a peak in the low speed region, nominally

-1/2

at about 50 km/hr and then decreases, being proportional to (velocity)

in the high velocity limit. Magnetic lift, on the other hand, rises to

a maximum somewhere in this same speed range and then remains

constant as the speed increases. Since operating costs for a given cargo

weight will tend to scale inversely with lift to drag ratio, there is con- siderable interest in providing very high speed magnetic levitation sys2 terns. Aerodynamic drag is proportional to (velocity) and becomes

comparable with magnetic drag somewhere in the neighborhood of

200 km/hr. This leads to the suggestion that perhaps the train should run in an evacuated or partially evacuated tunnel to reduce aerodynamic

drag and take advantage of the high lift-to-drag ratios obtainable at high speeds .

The optimum configuration of the eddy- cur rent track structure

remains to be determined. Powell and Danby (1966) have suggested a "null flux" scheme giving lift to drag ratios in the range 100 to 500

and allowing reasonable clearance (^20 cm) between the vehicle and

track structure, but requiring a fairly complex track structure and

giving a rather stiff suspension. Kolm (1972) favors a much simpler,

trough- like continuous- sheet track giving a suspension much less

sensitive to minor track irregularities, but lift-to-drag ratios not

11
MAGNETIC SUSPENSION - Repulsive

THE SUPERCONDUCTING MAGNETS ABOARD THE MOVING TRAIN ARE REPELLED BY EDDY-CURRENTS IN THE TRACK CIRCUITS.

SUPERCONDUCTING MAGNET ON TRAIN

STATIONARY TRACK CIRCUIT LOOPS - HORIZONTAL LOOP PROVIDES LIFTING FORCE

VERTICAL LOOP PROVIDES DIRECTIONAL GUIDANCE

IN ONE CONCEPT. THE TRACK CIRCUITS ARE CLOSED LOOPS OF COPPER OR ALUMINUM WIRE.

OPPOSITE MAGNETIC FORCE CAUSED

BY EDDY CURRENTS DUE TO MOTION

OF TRAIN MAGNET

IN ANOTHER CONCEPT. A CONTINUOUS CURVED SHEET OF ALUMINUM

IS USED INSTEAD OF THE TRACK CIRCUIT LOOPS

Figure 3. Schematic diagram of two possible repulsive-suspension

systems employing superconducting magnets.

12
much more than 10 or 20. The Japanese are experimenting with a "ladder-track" which gives lift-to-drag ratios comparable with the

sheet track. Guderjahn and Wipf (1971) suggest that a hybrid system

employing some iron in the eddy current track may be advantageous.

The lift- to- drag ratios obtainable with the null- flux system at high

speed in an evacuated tunnel would be truly remarkable: Powell and

Danby estimate that such a vehicle with a lift-to-drag ratio of 500

would coast (without propulsive power) 640 kilometers while its speed

dropped from 960 to 800 km/hr. This is equal to the distance from

Washington, D.C. to Boston, and more than the length of the Tokaido

high speed rail line. One can conceive of using this fact to minimize

the propulsive requirements of an active-track system. A further

advantage of high lift-to-drag ratios comes from the reduced total

energy requirement for transportation on a national scale--an

important factor. Selection of an optimum track configuration depends

on a wide number of system and operational parameters.

Of all the proposals and work on superconducting levitation

systems, the superconducting coils themselves receive relatively

little attention since their use seems straightforward. The ambient

magnetic fields experienced by the magnet windings will be in the

neighborhood of 3 T (30 kilogauss), somewhat lower than those generally

met in other superconducting magnet applications. Current densities

in the coils are in the range 2 x 10

4

to 5 x 10 4,2, A/cm , higher than

standard practice for high field magnets, but consistent with the smaller

ambient fields expected for this application. The magnets would be

operated in the persistent current mode, so that the levitation would

not fail if an external power supply were to fail; such persistent mode

operation is also within the state of the art. In order to hold the weight

of the magnet to a reasonably low value, the modern dynamically- stabilized, twisted multifilament NbTi conductors without too much copper

13
would probably be used. If track irregularities should cause too high

an a.c. ripple at the magnet, these could be shielded out by an eddy

current shield so that operational losses would be low.

A concise summary of the present situation comes from Dr.

John Harding (1971) of the ORDD: "All aspects of the repulsive superconducting suspension have by now been evaluated in sufficient depth

that it can be stated that the system is technically feasible. It cannot

be faulted on any single factor, such as cryogenics, superconductivity,

or magnetic shielding. If the superconducting magnetic suspension

is abandoned, it will have to be because of a combination of factors

and not any particular shortcoming."

3. STATE-OF-THE-ART IN THE U.S. OF MAGNETIC SUSPENSION

The U.S. Department of Transportation has a strong, long

range interest in magnetic levitation through its Office of Research,

Development and Demonstration (ORDD). In early 1971, Ford and SRI

were the successful bidders for an ORDD contract oriented to determine

whether magnetic levitation is a practical alternative to wheels or air

cushions for suspending and guiding high speed ground vehicles. These

companies are contributing funds approximately matching those of

ORDD to their projects for a total effort of about one-half million

dollars. Ten different bids for these contracts were received by ORDD.

These contracts at Ford and SRI were renewed in March 1972 at

about the same funding rate. In 1972, also, Kolm and Thornton of MIT

recieved funding from NSF for studies of what they call the Magnaplane.

This is a rather specific system intending to utilize superconducting

magnets moving above a sheet aluminum track and linear synchronous

propulsion.

14
A small private company -was formed about a year ago

to try to build a small full-scale system, but it has given up this

approach at this time.

4. FOREIGN PROGRAM PLANS

The ORDD maintains close contacts with these various national

high speed ground transportation programs, and there is every reason

to believe that technical information exchange is unimpeded.

Work is going on in Japan, Germany, and Canada. The

Japanese effort is the largest, amounting to $10 million per year,

most of which -will be for construction and operation of a 400 meter

superconducting magnetic levitation test track. They had a small

(four passenger size) vehicle in operation on the track in October of

this year (1972), levitated by superconducting magnets running above

discreet coils in the track. They are considering primarily active

track propulsion, which avoids the problem of pickup of electrical

power by the fast moving vehicle. Future tests of linear synchronous

propulsion are anticipated as an alternative to the linear induction

motor.

In Japan, the decision is of some urgency inasmuch as capacity on the New Tokaido Line (NTL) between Tokyo and Osaka is expected to reach saturation by 1980. In 1970, 85 million intercity passengers were

carried on the NTL express trains at a profit of over $300 million.

During the busiest hour, nine NTL expresses with a combined capacity

of 10,460 passengers leave Tokyo for Osaka. Rather than expand the

present system for additional capacity, the Japanese National Railways

(JNR) is directing its research toward magnetically levitated trains

which can convey passengers from Tokyo to Osaka in just over one hour.

15
The German Ministry of Transport is funding both attractive

and repulsive magnetic suspension vehicle programs. The attractive

rail program, utilizing conventional electromagnets and a very small

magnet-to- rail clearance, has produced two test vehicles, one at Messerschmitt-Bolkow Blohm (MBB) and the other at Krauss-Maffei

(KM) . Similar conceptually, these vehicles differ in the techniques

chosen to provide guidance, stability, and vibration isolation of the

passenger compartment.' The repulsive suspension program, utilizing

superconducting magnets, has been funded more recently at Seimans,

and has not yet produced any models comparable with the MBB and

KM vehicles

.

The Canadian Department of Transport has just initiated a study of superconductive systems for high speed ground transportation.

The activity will be conducted at the Institute for Guided Ground Transport at Queens University in Kingston, Ontario. The Canadian program

will concentrate on superconducting magnet design, the cryogenics

problems, and the development of a linear synchronous motor concept

deriving thrust from switched powered coils in the guideway.

Tests and decisions made outside of the USA will undoubtedly

have an influence over our own decisions scheduled in the late 1970's.

The Japanese test track studies will undoubtedly be an important input

to the U.S. decision-making process. The Japanese are currently about

two years ahead of the U.S. towards the goal of a working system,

though the U.S. appears to have a broader base of studies of system

alternatives. The Japanese are putting larger sums of money into

their studies than the U.S., and they hope to have a superconducting

levitated train running bet-ween Tokyo and Osaka by 1980.

16
5. PROPULSION

Possible propulsion systems to be used -with magnetic levitation are summarized in table 3. Only the linear electric motors are being

seriously considered by any of major world-wide studies at this time,

though the aerodynamic propulsion systems have been mentioned as

possibilities. The linear electric motors have the great advantage of

being quiet and pollution- free, and capable of operation in an evacuated

tunnel. Vehicle-mounted superconducting coils for a linear induction

motor could conceivable provide both propulsion and lift, even at zero

speed. This can be done through the use of a.c. powered superconducting coils (Richards and Tinkham, 1970), or rotating d.c. coils providing a magnetic paddle wheel or propeller effect (Borcherts, 1972).

Alternating current losses in superconducting coils would have to be

decreased by a dramatic factor before the a.c. system becomes feasible,

Linear synchronous propulsion requires only that power be fed into

stationary coils in track in the immediate vicinity of the vehicle, such

that the field of these stationary coils pushes on the superconducting

magnets in the vehicle. Power must be supplied to each succeeding

track coil in synchronism with the vehicle movement, and variable

frequency power supplies will have to be developed to make this scheme

practicable

.

6. SOME CRYOGENIC TECHNICAL PROBLEMS

Cryogenic technology will be essential to the superconducting

levitation system. This technology is well in hand for the purposes of

laboratory and test model development. However, a full-scale working

transportation system will demand a degree of reliability and serviceability of the cryogenic components which is beyond present standards,

17
Table 3. Propulsion System

Method Advantage Disadvantage

Aerodynamic:

propellors or

jet engines.

Requires no development;

works independently of vehicle clearance.

Noise and fumes: very high

vehicle weight since fuel must be carried. Could not be used in evacuated tunnel.

Linear induction

motor in the vehicle .

Does not require variable

frequency input power;

allows easy control of starting and stopping (not true, however, if used also

for levitation: Richards

and Tinkham, 1970) compact

propulsion unit. Works in vacuum if necessary; no

noise.

Requires small vehicle to track clearance (1-2 cm);

transmission of power

from a line to the high

speed vehicle is very

difficult.

Linear synchronous

motor in the track .

Allows high vehicle clearance

(20 cm), and lower vehicle

weight; appears to permit

safe operation of closely

spaced vehicles; no power

transmission to the vehicle

is required. Works in vacuum if necessary; no

noise.

Requires variable frequency

power services and complicated controls to activate

that section of track which

the vehicle occupies, and

make a smooth transition

to the next section.

Aerodynamic:

partially evacuated tunnel ahead

of the vehicle

Power source can be conveniently separated from the vehicle or track; may be

required in any case for speeds above 500 km/hr.

Low efficiency: difficult to control precisely or with

multiple units; requires

low vehicle to tunnel clearance. Requires

alternate technique for

starting from an unevacuated station.

Impulse-jet:

track-based

air jets are

activated as the

train passes.

( Mouritzen, 1972)

Convenient location of conventional power sources (turbo-compressors) at intervals along the track. Can utilize schemes of energy storage in compressed air. High vehicleto-track clearance.

Could not be used in an evacuated tunnel. Noisy, though

not as much so as propellers

or jet engines. Low effi- ciency, 20-25%.

18
and must be considered carefully. There is no reason to believe that

the scale-up in technology cannot be done successfully, but there are areas -where additional knowledge must be developed in order to do the

job with assurance. These are discussed here briefly.

6.1 Helium Refrigeration

Maintenance of the superconducting magnet at 4 K for weeks or months on end -will be a necessity for superconducting levitation. Some

suggest that a liquid helium supply be simply replenished from a central

storage reservior at convenient intervals, much as one now puts ice on

a train. However, the drain on the earth's helium resource would be

very large if the boil- off helium were not collected, assuming a large

national train and track system. It is likely that on-board refrigeration

will be superior from an operational standpoint. However, refrigerator

reliability would have to be extended over that available at this time.

This would call for a substantial effort, especially to increase the

mean time between failure of room-temperature refrigeration compressors

The Refrigerator Sub- Task of the DoC-NBS Presidential Initiative in

Cryogenics for the Electrical Industry has as its goals increasing

refrigerator reliability and optimizing refrigerator efficiency. Thus,

this technology is directly transferable from the DoC program.

6 . 2 Materials

The availability of reliable superconducting coils, which was

initially thought to be the major drawback of the induced levitation

schemes, is now considered to be well within the present state-of-the-art.

Nonetheless, there are unknown problems of building, supporting, and

maintaining the superconducting coils in daily operation. For instance,

the forces on the superconducting magnet at 4 K must be transmitted

to the vehicle by some sort of solid connection which must not increase

19
the helium heat load to unworkably high values. Composite materials,

such as the fiber reinforced plastics, seem to excel for this application,

and in fact have been suggested in one form or another by all the superconducting levitation papers which have touched this topic.

A major problem which this brings up is the almost total lack of

fatigue studies on materials of all kinds at low temperatures, as well as more general lack of properties data: expansion coefficients (generally

anisotropic with oriented fibers), complete stress-strain data as a function of temperature, sensitivity to notches or cracks, aging effects

for extended service, thermal conductivity, etc. Completely unknown

at this time is the effect of fatigue upon the electromagnetic properties

of the system. These material problems are congruent with those of

the DoC-NBS program on superconducting generators.

7. FUTURE DEVELOPMENT

The late 1970's appear to be the U.S. target date for selection

of the optimum levitated- vehicle system for major development in

this country. Tests and evaluations of all potential systems - TACV,

attractive rail, repulsive superconducting, and possibly even advanced

wheel concepts - should be complete by then. No one system has a clear

advantage at this time, in that all except the wheel appear to be able to provide vehicle transportation at speeds up to 300 mph (500 km/hr)

without relying on yet-to-come technological breakthroughs. It appears

most probable that selection will be based upon combinations of system

parameters, using criteria which are not clearly defined and ranked at present. Examples of such criteria include cost, safety, ease of

switching, control of close- spaced vehicles, the need for speed as compared to the need for convenient stop and start service operation,

20
possible extension to speeds higher than 300 mph (500 km/hr),

on-board vehicle power requirements, liquid helium service requirements, freedom from noise adjacent to the track, freedom from fuel

combustion products along the track, allowable development time

scale, availability of large blocks of electric power, etc.

In these days of concern over environmental problems, it appears that the magnetic levitation systems may be favored for being

more pollution-free than the TACVs. Some DoT engineers believe

that the superconducting system could prove superior to the attractive

rail system even if low-cost reliable control systems are developed

for the servo- controlled electromagnet system. The major cost in a total system will be in the production, installation and maintenance

of the guideway, they believe. Because the superconducting system

works with a larger gap between vehicle and guideway, it would allow

for lower costs in manufacture, installation and maintenance.

The need for advanced forms of ground transportation seems

compelling as evidenced by government- sponsored research programs

in four major countries including ours. The U.S., which may make

the largest use of such a system in the long run, may be contributing

a disproportionately small share of the research and development cost

for magnetic levitation, about $0. 5 million out of a world wide spending

of over $10 million per year.

A high speed ground transportation system represents a gigantic

capital investment. The 515 km New Tokaido Line, a high speed conventional rail link between Tokyo and Osaka, had cost about $1 . 1 billion

when service was initiated in October 1964. The estimated cost of a proposed Tracked Air Cushion Vehicle system offering 2.3 hour travel

time for the 650 miles (400 km) between Washington and Boston is

$2.7 billion.

21
The degree of interest, as measured by the international scale

of the research on the problem to date, suggests strongly that a positive

decision to proceed with a full scale program will be made in the U. S.

in the late 1970' s, when comparative merits of the alternative systems

will have been evaluated. Superconducting levitated vehicles are in

contention, but lagging over other levitation systems in the degree of

development -work to date. The chances that a superconducting levitation

system will be selected and developed in the U. S. are impossible to assess, being dependent on complex technical, economic, and social

forces, but it is not unreasonable to believe that they are in the 10% to 50% range.

A decision to proceed with a full-scale superconducting levitation

system would have major impact in the cryogenics industry. At the

present time, annual sales in this diverse industry are about $1 . 5 billion, of which only a very small fraction is derived from superconducting

and liquid helium temperature components. In order to service a large

transportation system with many superconducting levitated vehicles

running continuously over a wide geographical area, it is not unreasonable

to believe that annual sales of superconducting components and support

equipment could reach the neighborhood of several hundred million

dollars. It would be appropriate to tackle the major developmental

research in the cryogenics program at an early stage.

22
8. REFERENCES

Borcherts, R. H. , "Mathematical Analysis of 'Permanent' Magnet

Suspension Systems, " J. Appl. Phys. 42, 1528 (1971).

Borcherts, R. H. , to be published (1972).

Clark, A. F. , "Combination of power transmission line and an active

track for a magnetically suspended high speed train, " to appear in

J. Appl. Phys. (Aug 1972).

Coffey, H. T. , Barbee, T. W. , and Chilton, F. , "Magnetic suspension

and guidance of high speed vehicles, " Conf. on Low Temperatures and

Electric Power, IIR Annexe, p. 311 (1969).

The Economist, p. 55 (May 8, 1971).

Guderjahn, C. A. , and Wipf, S. L. , "Magnetic Suspension and guidance

for high speed trains by means of superconducting magnets and eddy

currents, " Adv. in Cryogenic Eng. 15 (1969).

Guderjahn, C. A. , and Wipf, S. L. , "Magnetically levitated transportation, " Cryogenics 11, 171 (1971).

Harding, J. T. , "Progress in magnetic suspension applied to high

speed ground transportation, " presented at the 17th Annual Conf. on Magnetism and Magnetic Materials, Chicago, Illinois (Nov 1971).

Hartke, Senator Vance, "Replacing our hodge-podge transportation, " reported in Astronautics & Aeronautics, 10, 52 (Feb 1972).

Kerr, C. , and Lynn, C. "Roller road", Westinghouse Engineer (Mar

1961).

Mouritzen, G. , "Impulse-jet transportation system, " Mech. Eng. , p. 12 (Feb 1972).

Pohlgreen, G. R. , "Guided land transport, " Proc. Inst. Mech. Engrs.

181 , 145 (1966).

Powell, J. R. , "The magnetic road: a new form of transport, " paper

63-RR4, ASME Railroad Conference (Apr 1963).

23
Powell, J. R. , and Danby, G. T. , "High speed transportation by

magnetically suspended trains, " ASME paper 66-WA/RR-5, Winter

Annual Meeting of ASME, New York (1966), also published in Mech.

Eng. 89, 30 (1967).

Powell, J. R., and Danby, G. T. , "Magnetic suspension for levitated

track vehicles, " Cryogenics 11, 192 (1971).

Richards, P. L. , and Tinkham, M. , "Magnetic suspension and

propulsion systems for high speed transportation, " J. Appl. Phys.

43, 2680 (1972).

Strobridge, T. R. , "Refrigeration for superconducting and cryogenic

systems," IEEE Trans. Nucl. Sci. NS - 1 6. (Proc. 1969 Particle

Accelerator Conf. , Washington D. C. (Mar 1969).

24
form NBS-114A (1-71) U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBS TN-6352. Gov t Accession No.

3. Recipient's Accession No.

4. TITLE AND SUBTITLE Some Applications of Cryogenics to High Speed

Ground Transportation

5. Publication Date February 1973

6. Performing Organization Code

7. AUTHOR(S)

V. D. Arp, A. F. Clark and T. M. Flynn

8. Performing Organization

10. Project/Task/ Work Unit No. 2750101

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS, Boulder Labs

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

11. Contract/Grant No.

12. Sponsoring Organization Name and Address

Same as Item 9

13. Type of Report & Period Covered

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant bibliography or literature survey, mention it here.)

The current status (December 1972) of worldwide research on

high speed ground transportation techniques is reviewed. Particular

attention is given to studies of magnetic levitation using superconducting

magnets, including comparison with alternative magnetic techniques and

with air suspension systems. Superconducting levitation appears to be

a strong contender in the U.S. Department of Transportation hopes to select in the late 1970's the best of the possible levitation techniques

for subsequent advanced development. Cryogenic engineering research

needed in support of major development of a superconducting levitated

system is identified.

17. KEY WORDS (Alphabetical order, separated by semicolons) Levitation; magnetic suspension; materials fatigue data; refrigeration;

superconducting magnets; transportation.

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29

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