CM) HEAVY ION BEAMS FOR INERTIAL FUSION* TF Godlove ... - SLAC

SLAC-PUB-2524 May 1980

CM) HEAVY ION BEAMS FOR INERTIAL

FUSION*

T. F. Godlove Office U.S,

of

Inertial

Department

Fusion of Energy

Washington,

DC

20545

and William Stanford

B. Herrmannsfeldt

Linear

Accelerator

Stanford,

CA

Center

94305

ABSTRACT The United (ICF) of the

is

States'

described

Preliminary

with

high

energy

beams of heavy

recent

nkeded

calculations

In a companion

of

quadrupole paper

developments

confinement

paper,

and energy

in an electrostatic

in inertial

in this

the use of intense power

program

in this

to initiate the

on the ions

thermonuclear

transport focussing

proceedings,

in low velocity

emphasis

fusion

of intense structure

studies to provide burn.

ion

beams

are discussed.

R. A. Jameson describes

accelerators

for

heavy

ion

fusion.

Submitted to Low Energy Ion Beams-2 Conference, April 14-17, 1980 Bath, England,

*Work supported by the Departnient of Energy, Contract DE-AC03-76SF00515.

I, 1

INTRODUCTION Intense .

needed

beams of heavy

to compress

tritium

fuel.

If

sufficiently pellet in

high it

itself,

the range

ratio

which

gains

relatively

centrally

and heat the

ignited

require

the

initiation

cold,

high

densities

without

is

excessive

and the

to the pellet

is

generically

of drivers

.former

category at

power

are solid

to achieve

pellet

fuel

'as the

incident

fuel

(ICF)

delivers

lasers

gas lasers

such as CO2 (10 micrometers)

several

short

ion

defined

on the pellet.) burn

in

surrounding

the

released

by the

must be compressed ._

and focussed

lasers

is

gains

of a propagating

Fusion

which

state

1 micrometer;

Among the

of the

to

heating.

lengths

micrometer.

inertia

energy

seem to have the

wavelength

by the

known as the

lasers

deuteriumenough.at

by the energy

Confinement device

energy

long

fusion

ignited

the

confined

gain

density

main body of

Inertial

above process

operating

(Pellet to the

fuel

containing

is

possible

yield

high

high

fuel

energy

This

pellets:

pellets

and temperature

is believed

ignition.

two classes

compressed

density

first

The term

can be ,used to convey

small

of 100 or more.

of'fusion

Such high

ions

given

the pulse driver.

potential

to the

of energy

At present, of igniting In the

beams of ions. such as neodymium

operating

glass

a longer

wave-

and HF (3 micrometers)

operating

methods

is

at fractions

two candidates

stand

of

and a

out:

2

multiple diodes

.beams of protons of high

of heavy

ions

voltage

required

from

100 range of the

(Nuckolls

uncertainty

hold

pellet

for

scaling

Laboratory, PBFA II,

ANTARES, at the

at the

The above years

on laser

and the channelling

is

reasonably

net

energy

realized.

facilities

coupling,

stability plasma

Sandia

1983-1985

(Yonas

National

the

ignition

(pellet (1979))

then

large

the

NOVA glass

laser

Laboratory,

100-300

National

In the

the major

Accelerator, 3 megajoules.

operation

more definitive

of multiple

kilojoules;

Albuquerque,

ablative

during information

compression,

case of PBFA II, ion

goal stored

U.S.

Scientific

Beam Fusion

to begin

provide

output/capacitor

suitable

major

scaling,

and overlap

of a few

nonlinear

of the

Particle

of

a peak power

Thus,

highly

Laboratory,

process.

gain

a radius with

are

three

are expected

wavelength

with

drivers.

Los Alamos

and the

and should

successful, gain

and ion

National

and beams

a pellet

having

The energies

40 kilojoules;

for

together

are as follows:

Livermore

the

and power density

These estimates

laser

in

systems;

estimates

to demonstrate

ICF facilities

CO2 laser,

energy

on a pellet

performance.

at the Lawrence

the

both

generated

accelerators.

energy

(1979)).

are required

planned

the

Recent

100 terawatts

millimeters

facilities

of pulse

driver.

ions

switching

energy

2 to 4 megajoules

of

light

power

by high

amounts

the

from

order

pulsed

produced

Unprecedented

or other

beams on the of breakeven energy)

pellet if pellet or even

may be

'.

HEAVY ION FUSION Thcheavy scene.

ion

method

Following

an exploratory Funding

University

of Maryland.

year

1976,

detailed

currents

Los Alamos the

lead

and light 0

programs

Laboratories.

in pellet

Laboratory,

the

Research

(1979)

Los Alamos

Laboratory

workshop

and Smith

design, at the National

and the

has been held

(1978))

each

the most recent

et al --

(1980)).

Scientific

Laboratory

ion

is

for

The range-energy

a combination

are well

technical

an important

relations

for

knownand

even in the hot

Recently

the

has been designated

Heavy Ion program

option

classical,

National

at

(Herrmannsfeldt

for

ions

established

.such as b-earn stability

drivers

heavy

(1976))

issues

laboratory

ion

Berkeley

al

accelerator

National

The heavy

programs

A two-week

(Arnold

(Judd -et

and Arnold,

in vacuum and gases

the Naval

Laboratory,

ICF driver.

and by Martin

1976.

to smaller

National

Scientific

at high

in

and beam transport

Livermore

emphasizing

was held

were coupled

design,

since

by Maschke

1977 with accelerator . Brookhaven and Lawrence

These programs

Lawrence

newcomer on the

in

the Argonne,

reactor

a relative

suggestions workshop

began

is

as

direction.

alternative

to laser

of reasons,

as follows:

the

stopping

of energetic

are believed

plasma

of the

to be completely imploding

target

wall. @D

Building the

on decades

studies

of heavy

to date ions

of high

energy

accelerator

indicate

that

the required

can be generated

and focussed

development, intensities onto

a pellet

'

4

from

a range

sufficient

and -ci the walls Particle

0

pellet improves

and the

required

energy

High

energy

rate

Both methods

linear

ability

accelerators

to focus is

(multifor

the beams

reduced

as the

have good inherent

and already

developed

were narrowed a conventional

for

rf

current

multiplication;

propelling

one bunch

the bunch require

and increase some induction

repetition

in 1978 to two quite

linac

with

a system

of

and a single-passof ions

the

using

current

cavities

waveform

during for

shaping

acceleration.

final

stages-.of

compression. Beam requirements

design set

to be required

per megajoule

designs

linac

to compress

to the high

capability.

rings

induction

elements

increases.

approaches:

'storage

cost

efficiency

Accelerator different

the

is,

focussing

favorably

now believed

That

gain.

the

chamber.

scale

energies

electrical

bunch

of a reactor

accelerators

megajoule)

0

to,protect

and accelerator

of parameters

studies a high

and for gain

representing

have evolved

design

has been adopted system

a. compromise

comparisons.

for

to the point

purposes

Total

energy pulse

energy

3.0 GeV 3 MJ

pellet where

of additional

These parameters

pellet: Kinetic

between

are,

for

a

5

Peak power -

Pulse

length

(at

Pulse

length

(total)

Radius Ions final previous

in

length

final

atomic

and radius

the kinetic

energy

charge

that

be required

with

has decreased by a factor

forces,

and

of

particularly

a low ion for

The number of Comparison

have each increased

indicate will

one or two,

by design.

of space

beam transport,

probably

2.5 mm

mass 200 are assumed.

shows that

Considerations

two.

16 ns 40 ns

to be determined

workshops

the pulse about

left

peak)

on pellet

at or above

beams is

150 TW

charge

state,

a reasonable

number

of

beams.

RF LINAC Accepted and Alvarez iated

rf

designs

linacs

employ

extrapolated

beam current

the

required

increases

space

with

kinetic

rapidly

has been proposed downstream linacs Jameson

of

linac

to build operating

frequency (1980)

allowed

phase

conventional

to their The basic

limits.

the maximum beam current for

relatively

empirical

design

energy,

up the

Since

f in binary

show an example

of

calcu-

is

to achieve

the

allowed

a system

of

Nf is

sequence.

"funneling"

of a funneled

filled

Fig. rf

acceleration

current

In this

current.

at frequency

and'/or

problem

at each stage

volume.

Wideroe

‘system from

a N upstream

3 and Table linac

system.

I of

6

Since

at each transition

are mergea

by filling

can in principle is expected

linac

and remains the

(1980)

impressive

800 mu.

are important the

blowup

should

the

of heavy

at high

ions

room for

features

low-beta

is

creativity

system

of

storage

ions.

The rings

extracted

w .-.,_..

“_

,.._,

-c

___,._

.r_

..__^_

._-

--

growth

advances

linac

rf

for

The conclusion

is

linac

system

unlikely

producing

in

beam

a

energetic

beams

efficiency.

Consid-

the engineering

to reduce

the

.

but

represents

electrical exists

an

of beam stability

blowup the

chosen

is

at 'L 300 mA, transverse

clearly

design

complexity

of

components.

FOR RF LINACS -

less

rings

Typically,

than

that that

can be accelerated needed

is used to accumulate

filled

and transported

simultaneously.

Alverez

questions

and high

funneling

far

are

major

a limitation.

the maximum current still

volume

In the example

final

method

power

multibeam

Because

space

some emittance

described

and longitudinal

understood

such as the

linac

the

was that,

CURRENT MULTIPLICATION ----

rf

in

In any event,

well

the

current

expected

conservative,

two beams

the phase

be attainable.

At such currents

must be calculated.

erable

just

and may represent

not

cycles,

In practice

techniques

1979 workshop

is

rf

linac

to be measured.

beam current

by Jameson

from

alternate

be conserved.

By employing in

to a doubled-frequency

sequentially to the five

for

the 'pellet, the high

and then

pellet

from

to ten

rings

in an

all

the

a

energy ions

are

the rings

are required

with

7

radii

of'50-100

meters.

the

product of h from the linac

prior

the into

here

and an Argonne

each ring C.

the most recent

studies

"test

b:d"

system

Coherent

in the

rings.

on experience

with

protons

a structure

than

that

coupling the

the millisecond

impedance

growth

In one workshop i.1: the

ring

two to four of ring

is

MV per

growth

Atomic residual

in

sections,

connection

l

C.

described

the

just

Again

we

designs

in

the work-

may limit

1979 workshop effect

of

25 ohms.

the

instability

a bunch

This

losses,

is

It

is

the

based

tolerable also

quite

may be longer

However,

compression

sixty

turns

both

the

process

necessarily

estimates effort

are potentially cross

by a factor using

is

the ongoing

atomic

fields

of crossing

tolerable

called

for.

charge-changing troublesome

sections.

information

seven

entails

Using

of 2% has been calculated

more detailed

rf

indicate

whether'internal

some relevant

Again,

that

more detailed

a beam loss

injected

need more study.

in about

gas interactions,

beam case. In this

but

Nt

instability

time.

Preliminary

collision

uncertainties cross

rate

turn.

resonances.

emittance

for

from

turns

conceptual

at the

indicate

time

l

since

Estimates

design

achieved

N,

l

longitudinal

accumulation

and the

the number of

are well

impedance

growth

is obtained

and the bunch compression

I = I,

beam current

possible

Nt,

N,,

Thus,

shop proceedings.

for

multiplication

number of rings

to extraction,

summarize

Current

would

measurements

or

due to estimated for

the

3 MJ

be desirable. effort

at the

8

University

of Belfast

signif,ica-rttly, workshop

should

This

workshop

(Jorna

(1980)).

small

deflect

an incoming

emitted

from

subsequent

beam into

a septum

could

at the be held

available

on the

result

the

in

septum

1979 workshop

to 5 10'4/cm2

in a recent

1979 accelerator

septum

normally

losses

Very

region. that

used to

of gas and debris

significant

indicate

base

at the

A cloud

a ring.

data

described

highlighted

beam loss

beam entering

estimates should

and others.are

problem

concerns

the

effort

proceedings

A new potential

increase

the

for

the

preliminary septum

loss

of septum.

INDUCTION LINAC In this

method

a single

and low-beta

sections

final

in a long

best

energy overall

to the

(Hoffman,

Laslett

The Berkeley

(Q 6km) linear

space

charge

and Smith group

to no less

that

cell

pulse the

accomplished rear

of

a gradual

to For

accelerator. is maintained

throughout

has chosen shift

requires

accelerated

induction

limit

injector

the

close

accelerator

(1980)).

to 60" phase 24" per

beam from the

the peak beam current

equivalent

method

current

% 1OA at % 5MeV) is

(e.g.,

efficiency

transverse

high

the

of oscillation by space

by ramping

the

front.

The large

single

"sausage"

"beads"

of charge

in the

rf

linac.

higher

of charge

cell.,

of

strength

depressed

The induction

charge.

accelerating

has slightly

focussing

per

(shortening)

compression

the beam pulse

transverse

linac

the beam

waveform

so that

velocity

than

contrasts

with

the s lo5

9

rf

The-cIinduction method because

storage

rings.

demonstrated of

light,

of

this

tions

method

there

is

However, for

is

method.

because

an prgent

density,

i structure

effects.

a test

bed accelerator these

a linnc

questions

of errors,

(1980)

by the

the

system

and been

at the velocity demonstration

issue

is

the

the beam against bunch

gives

than

have only

experimental

stability

proposed

linacs

technical

waveform

funnel

essentially

need for

Jameson

conceptually

induction

The most serious

in charge

simpler

traveling

and transverse

to address

is

no need for

electrons

there

longitudinal

linac

fluctua-

end effects,

a'brief

and

description

Lawrence

Berkeley

of Laboratory

experimentally.

INJECTORS FOR XNDUCTION LINACS Jameson

(1980)

describes

the

developed

at LBL as an injector

To extend

this

concept of periodic

is

by Jameson.

described

strong

focussing

for

to longer

add a system

system

drift

tube

the

pulse

using

linear

system

induction

length,

electrostatic However,

linac

it

is

focussing. recent

accelerator.

proposed

to

One such system

studies

electrostatic

being

indicate

quadrupoles

that

a

may be more

effective. For the purpose ion

beams,

the

for

which

range are

of the generation

definition

electrostatic

"low

the G x 5 forces,

too weak to overcome

range,

of

the

forces

space

and transport

energy" for

might

practical

charge

well

Within for

intense

be the

magnetic

forces.

are more effective

of

energy

fields, this

focussing.

I .

: 10

For heavy

at

low charge

states,

energy

to several

MeV.

ions,

range

of-low

range

of experience

using

magnetic

these

techniques

There

are,

with

extends

gradient naturally

the

and broad

focussing

systems

to interest

in applying

to transport with electrostatic quadrupoles. . some notable differences between electric however, focussing

differences,

in general,

particles

by the

Stability

systems

electric

(1979)

there

is

a range

phase

advance

per

without

space

Laslett

.charge,

to a lower

current

which

extensively current)

stability

is

leading

the

limiti'ng

the

edge of

is

the

(1980)) current the beam.

for

This

only

shift

without

inducing limit, advance

quadrupole

a given

ion

on the

dependence

found

that

by the

advance due to space

to the,maximum instabilitkcs. that

has been

o. = 60",

(at

down to 0 = 24" at the

electrostatic

depends

phase

corresponds

shift

is

can be..defined

which

case of phase

for

and numerically it

a.given

stability

to a phase

that,

(1980)

a maximum phase

advance,

For the

limit.. (Laslett

there

of a transport

studied,

that

period;

has been examined

techniques,

transport

focussing

phase

and Smith

can be transported

One example

done on the charged

systems

By both

stable

charge,

These

examination.

the work

transport

and others. for

require

fields.

by Hoffman,

by Haber

that

stem from

in magnetic

analytically

found

leads

definition

The versatility

alternating

quadrupoles

and magnetic

zero

the

is

system,

and kinetic

focussing plotted

voltage in Fig.

it

is

energy, at 1.

11

There

are relationships

and apertzre transport

which

length)

A series

studies able

limits

using

potential

lines

presence

of the

is

outlined

a system

in

the

space

to the

to examine Numerical

parameters.

(Herrmannsfeldt transport

(1979)) problem

in Fig.

to be distorted

charge.

The elliptical

beam cross

of

the

which

fringe

were started

fields

by a step

by the section

on the beam

at the-ends

function

a

The equi-

2.

are observed

orbits

are

within

figure

approximated

are

length

(quadrupole

underwalr

these

two dimens.ional

The effects

quadrupole

fraction

using

program

by the particle

. envelope.

packing

as shown by the example

lens,

period

the beam to be matched

are presently

tracing

the

emittance,

must be specified.

of

a ray

to calculate

quadrupole

the

of calculations

stability

transverse

must be met for In addition

line.

length/available

the

between

in the

of each particle's

momentum. Although calculations, are

it

is

it

appears

early

the other

tested

Since

longitudinal in the tube

in

these effects

being

the

necessary

are rf play

numerical

quadrupole

calcul

developed

ations

they

are not

described

as an injector

the

systems

in which

for

by Jameson

bunched fully

situation

are being

described

beams and simulated

above. the

tools

by analogy

Experimentally,

systems, a part,

of these

calculations

made earlier. electric

results

the MEgALAC and RFQ systems

two dimensional

linac

all

the

electrostatic

way around;

already

(1980).

studies

to report

that

in hand to make these

to the magnetic is

too

linear

The drift induction

I 12

accelerator added.

at LBL will

.iG order

necessary

to get

magnetic

transport

electrostatic

FINAL

to extend

it

through

the it

is

sy‘stems

'Since

pulses.

low energy not

range

it

before

surprising

are the

focussing

one can test

that

subject

is

the

of so much interest.

BEAM TRANSPORT

it

target, rings

to achieve

is

or the

this

line

space

induction

charge

force

previous

work

directly

with

uniform

charge

is

this

large-scale

momentum spread

without at the of

3% onto

the effect

be costly.

codes

has proved

The design

particle

space

a 4 mm target charge

by using

to be valuable

is

is

designs

and by starting

channels.

codes that

is

capable

for

At the

approached

including

non-

designs

by Brown and of

focussing

a

85% of- the beam.

expected

study

being

adequate

to 'be substantial. beam lines

and others

the

Little

1979 workshop.

more final

(1979) for

Considerable

One system

charge.

an increasing

problem

clear

1979 workshop

Work by Haber

quadrupole-focussing

is

storage

Thus,

and with

simulation It

the

line.

current.-.

at the

at the

compressing

transport

in momentum,

question

of space

may be avoided

would

the

increasing.

distributions.

either

ballistically

way through a spread

beam intensity

(from

of non-space-charge

discussed

The problem

tostillbe

applicable.

can be formulated

However,

linac)

due to the

by modification

Peterson

the bunches

with

was given'to

final

for

on their must deal

attention

the necessary

necessary

longitudinally,

long

.

quadrupole

to longer

systems,

focussing

In order

both

have electrostatic

using

but simulation

of beam transport 1979 workshop

Haber

in

.

.

13

reported

that

code for'final

Experimentally

initiated‘: focus

use of the

conditions Studies

by the

of

large

low energy

final

of gas,

transport

reactor

radius

particle

ICF reactor

I has been to adopt

while

plasma

to explore

the boundaries

final

Among these

are pressure

and current,

the vacuum case

of choice,

the

are complicated

the

method

to model

the reactor

and pellet

studies,

had been

beams. in

energy

and geometry,

studies

may be possible

number of-variables.

species

definitive

using

it

focus

momentum distribution, Pending

requirements.

approach

in

(p < 10'3

continuing

and

the HIF program

to 10'4

studies

Torr)

of transport

of operating

more

as the in gas and (Jorna

parameters.

(1980)). One of the is

the

thick

favored

conceptual

Livermore-developed

lithium

jets

the past

of year

consistent of the

liquid it

with lithium

lithium

fall

the is

use of heavy

adjusted

that

ion

reactor

method,

are used as the

has been recognized

Studies

pressure.

laser-driven

In this

scheme

wall.

During

first

this

concept

beams provided

to provide

the the

concept

in gas/plasma

transport

may be

the

appropriate

aimed at adapting

designs

temperature

lower

to heavy

vapor ions

are continuing. Recent summarized e

progress by Jorna

More detailed instability

et al --

(1980).

calculations

studies

Briefly: of

have been performed.

the

filamentation

has been

I14

The effect

of.a

e^lectrons

can cause

cases

is

filamentation parameters

the method

studies

velocity

these

electrons

beam. where

if

to rely

longer

focal

to strengthen

the

the

two-stream of

the pellet

on lower distance belief

onset

kinetic (lo-15

that

energy m).

the vacuum case

of choice.

in

conceptual

accelerator

to the

ion

to disappear

.-CONCLUSION AND ACKNOWLEDGEMENTS Considerable overall progress driver

of knock-on

damped and before

are changed

tend

of

at Q 1 Torr

collision

(< 5 GeV) and/or

field

of the

tends

stream

in some calculations.

self

"window"

instability

remains

the

defocussing

The pressure

These results

moving

has been included

For extreme

0

forward

designs

and recently

Special

systems.

use of electrostatic

has been made in heavy

quadrupole

in

ion

the

attention

is being

focussing

in

low given

this

connection.

No insurmountable difficulties have been found in the designs . but much work needs to be done to determine more accurately the effects

of high

storage

rings

tive

features

continue fusion.

beam intensities and in of

the

final

the heavy

to make it

in

the

focus.

ion method,

a sound investment

accelerators

proper,

The combination first for

of

enunciated inertial

in

in attrac1976,

confinement

15

The authors ion

comgunity

for

are

indebted

much of

.

the

to,numerous

colleagues

information

in

this

in review.

the

heavy

16

REFERENCES --1.

Arnold

R C 1979 Editor

Workshop 2.

Haber

I

September (1979)

September 3.

et -Study

Herrmannsfeldt

Hoffman

al

1980 Editors

Session

Laslett

I,

Workshop

Heavy Ion

1979 LBL (to be published). Program

(to

SLAC-226

Paper

S, Kim Y K, Magellsen Report

of the for

to be published Judd -et al

Systems,

in Low-Velocity

this

Proceedings

Particle

Workshop

on Atomic

Linacs

(1980).

G, Rudd E, Tidman

Heavy Ion Fusion

for .

D and Yu S

and Plasma Physics

December

1979 ANL 80-17

(1980).

1976 Editors

Fusion

Transport

of the

be published).

in

Requirements

L 1980 Stability._

in Long Periodic

Heavy Ion Fusion,

Inertial

of the

Trajectory

L J and Smith

Advances

Jorna

Report

November

Jameson R A 1980 Recent

Editors

8.

the Heavy Ion Fusion

1979.

Accelerators

7.

of

W B 1979 Electron

K-V Distribution

6.

Heavy Ion Fusion

1978 ANL-79-41.

Prpceedings

Herrmannsfeldt

November 5.

of the

1978 ANL-79-41

Accelerator 4.

Proceedings

July

ERDA Summer Study 1976 LBL-5543.

of Heavy Ions

for

.

17

9.

Laslett

L J 1980 private

electrostatic magnetic field

the

Nuckolls

Smith

relation

the magnetic

Vol.

the work

for

electric

field)

to transform

October

Program

Annual

Report

1978

1. Proceedings

of

the Heavy Ion Fusion

1977 BNL-50769

Yonas G 1979 IEEE Transactions 4160.

the

for

two methods. .

L W 1978 Editor

Workshop 12.

B is

using

J H 1979 pg 3-1 Laser

UCRL-50021-78 11.

are made by adapting

systems

E = BcB (where

between 10.

quadrupoles transport

Calculations

cominunication:

on Nuclear

Science

NS-26

I_ 18

FIGURE CAPTIONS 1.

Calculated

quadrupole

electrode

edge of the beam, per

A longitudinal

assumed.

If

the 'electrodes

beam.then

the

2.

square

potential

of the

packing

are moved radially

(end view)

electrostatic

quadrupole Distortion

of

evident.

Transverse

motion

the

are shown by the for

Cs+l, of

co = 60" 2/3 is

away from

in proportion

3 MeV Cssl

of one quadrant

due to an elliptical

section.

is

fraction

at the

the to

aperture.

lines

tion

for

must be increased

Equipotential

envelope

required

ampere of current,

and u = 24'.

the

voltage

field

lines

of particles short

line

at 1 ampere.

of an beam cross

by space near

segments.

charge

is

the beam The calcula-

140

I

I

I

I

I

I

I

Quadrupole Focusing Voltage at Beam Edge per Ampere of Cl’

120 100 80 60 40

Phase Advance:

20 0 3 - 80

L

I

0

I

I

I

~=24O, q=60°, I

I

2 3 4 5 KINETIC ENERGY Fig. 1

I=IA I=0 I

I

6 (MeV)

7

8 3799A6

Fig. 2