! ELECTRON-BEAM WELDING OF 500~MHz ... - SLAC

!

ELECTRON-BEAM WELDINGOF 500~MHzACCELERATION RESOiATORS

ELEKTR~NENSTRAHLSCHWEI~SEN

voN

500-MHZ-BESCHLEUNIGUNGSRESONATOREN

i ____-_.._._^. -____-I____

__--___-----.-.---._-.--

H,

::

‘.(E)‘* If Ti

---. ----..----_

HARTWIG,

KOUPTSIDIS,

K,

REINECKEN

UNKNOWN

STANFORD LINEAR ACCELERATORCENTER Stanford,

J,

-.----_ - -___~---_--.~_-.-- .._. - _._______._- .^_....

California

ADDIS TRANSLATlONS IiVTERNATIONAL 3220 alpine road pork-h valley, cdifornia 94025 (415) 854-6732

1. Introduction The discovery

of new elementary

storage

(1) at the German Electron

rings

burg

and at the Stanford

U.S.

demonstrates

the

elementary-particle Besides

the

two linear

into

Accelerator

Center

importance

of these

instruments

accelerators

tubes

at an energy

are recorded these

the

in modern

R.F.

storage

1973.

can be stored

circumference.

machines

diagrammatically

R.F.

SLAC in

ring

In this and brought

up to 2 x 5 GeV in two separate

collision All

the double

the end of

and positrons

300 m in

detectors. trated

since

approximately

of this

DESY in Ham-

(40 and 300 MeV) and the

at DESY in Hamburg,

electrons

collision

Synchrotron

Linear

DORIS has been in operation ring,

by the use of electron

research.

7 GeV synchrotron

storage

particles

The reaction

and investigated

by sensitive

on the

tract

in Figure

DESY land

vacuum products

are illus-

1.

structure

structure

Figure 1. Diagrammatic illustration of all accelerator installations on the DESY land tract.

PE.TRA

1

Experimental

results

shown that tially

it

is

higher

necessary

expansion

stage

into

collision

long

for

lifetime

of 100 MV is resonators

stored

electrons

and positrons

in two straight

To keep the

total

costs

grammatically

with

coupled

the

will

drift

preferred

2.

The structure sections (3). 2

energy

of and

by radia-

arc of

the

of

this

320 R.F.

of the

storage

system

losses

raising

of

is

the ring.

the

expansion the

a voltage

DORIS storage

first

ring.

ensure

voltage,

stored

stage.

coupling

resonators

be required.

resonators

first

accelerating

energy

acceleration

5 coupled

in Figure

therefore

the

pieces

low and without

64 such resonators

a structure

the

4 MW for

5-cell

substantially, of

into

and in the

to cover is

In the

was

2 x 19 GeV.

accelerating

The 500 MHz frequency

1).

Facility]

and simultaneously

For this

are provided

power required

and is

the

a circumference

the beam, a radio-frequency

The R.F.

inductively

substan-

can be stored

up to

pass

losses

same as in the DESY synchrotron

for

have

reason,

in PETRA lose

as they

energy

necessary.

(Figure

having

at an energy

light

these

ring

and positrons

and positrons

synchrotron

A total

with

For that

to DORIS (2).

storage

electrons

To compensate

losses

rings

rings

Tandem Ring Accelerator

of this l),

The electrons

ring

storage

energies.

1974 as a supplement

2304 m (Figure

of

storage

of PETRA (Positron-Elektron-Tandem-Eingbeschleuniger-

in

brought

electron

to build

[Positron-Electron

proposed

tion

existing

stored-particle

construction Anlage)

from

are proposed.

Two alternatives

are illustrated in Figure

is more economical

dia-

2a with in operation

Acceleration section: Driftsection structure with inductive

WI

I w I

i Acceleration with coupling

section:

via

Iris structure electric field

the

Figure a) Diagrammatic illustration section structure b) Diagrammatic illustration structure 2. Engineering The diameter structure's

requirements: of

the

resonance

A cell

length

is

in the middle

fed

detuning

accelerator

is

range and for

over is

drift-

of

iris

a five-cell

the primary

factor

It

is

ca.

selected.

with ca.

of a five-cell

techniques

frequency.

cell

2

fabrication

X/2 = 300 mm is

and can be detuned This

cells

i

400 mm for

The five-cell

a maximum R.F.

1 MHz by means of

provided

mainly

compensation

of 3

determining

for

frequency

the

power of two tuning operation variations

the

500 MHz. structure 125 kW elements. of the due to

radiation is

exposure

required

during

in measuring

fabrication.

diameters During

operation

outside of the

can rise

tuning

structure

The ultrahigh storage

likewise of

Ncm3/s.cm2

order that

range

water

might

occur.

tight

jumps from

The surface

conductivity

greatly

affects

structure. of

condition in regions

the

With

13 MR/m of

structure

the

combined of high

structure cells'

loading

of the

frequency

drifts

rises,

the drift

good cooling

disks of the

without

is

necessary.

resonator

and

cooling.

For

exhaust gas rate (2, 4 *. QD \< 10 -9 Ncm3/s Welds

and vacuum must be avoided localization

and repair

must be heatable

to ultrahigh

of

to

in leaks

at least

vacuum in the

event

of

15OOC to 3OOC. and roughness

impedance

a smooth structure with

the

we have:

The structure

temperature

To avoid

be realized

a fast

15OOC and must remain

thermal

conditions

channels

to make possible

on the

the

of

and leaktightness

cooling

tolerances

due to temperature

cannot

the

of

accuracy

mm.

25 kW.

vacuum operating

ring

between

to

high

dimensions the

20.15

and especially

components

lo-lo

range

Accordingly,

critical

at maximum power,

cells the

the

effects.

For example,

are in the

individual

all

and thermal

and thus

copper

of the

surface,

the R.F.

field-strengths

cooling in order

duction

surface

losses

in the

a maximum impedance

can be achieved

intensive

inner

(3). is

A good surface

required to prevent

especially the pro-

of a multipactor plasma there due to field emission and 1 cm3 under * Tr. note: Ncm3 is that amount of gas which occupies "standard conditions" of O°C and 760 Torr. 4

secondary

emission

Heretofore, by the

(4).

acceleration

electroforming

method

can be fabricated highest-grade realized mally

with

easily

for

ration

the

methods times

seams with

with

minimal

the material.

it

thermal

This

relatively

facilities

weldment

out

of the

OFHC * copper

a relatively * Tr.

note:

high

the

This

conductivity

OFHC = oxygen-free

to achieve

costs

for

very

that good weld

distortion

so that

structure

of

developed

and

the welding

in existing

preliminary welding

unit

tests and a

was proposed. was selected

to OFHC copper, alloy

which

is

as

the use of

can be welded

high-conductivity 5

would

of PETRA accele-

was chosen

conductivity

Parallel

it

fabrication

series

10 years,

electrical

opti-

the PETPA accelera-

has been further

structure

is

be

work was to investigate

Accordingly,

was examined.

good thermal

of

and minimal

an electron-beam

material.

alloy

possible

acceleration

acceleration

with

fabricating

AlMgSi0.5

with

series,

welding

in the past

large

of a small

large

method

can also method

to reduce

loading

can be performed.

were carried

the

is

welding

has become widespread of the

it

structures from

this

the present

relatively

the

electrolytically

costs

Electron-beam

because

method,

Although

in order

preferably

water-cooling

fabrication

of the

structures.

purpose

method.

The aim of

new fabrication and delivery

accuracy

the production

raise

structures.

By this

An intensive

by this

applicable

were fabricated

(5).

higher

copper.

substantially tion

resonators

required

well,

has

to cool

the

and can be readily

structure,

weight

thereby

drawback, could

i.e.

could

also

lower

electrical

be obviated

lytically

The proposed ported

a great

conductivity the

The single

deal.

compared

inner

surface

to copper, electro-

sputtering.

weldment

in the

be reduced

by copper-plating

or by d.c.

The structure's

machined.

and the welding

results

achieved

are re-

following.

3. Weldment Figure for

3 shows the weldment The disks

PETRA.

welded

together

The disks

of

machined disk

must

undesired would

weld

This

for

greater

and weld

These weld problems,

sections

of

the

resonator

cavity.

are made from

operation

of

5-10 W/cm2.

as close

as possible

requirement

would

great

rounds

effort

and

of the

and for

the

Therefore, to the

lead

vacuum and water

with

forged

temperatures

1OOOC during load

structure

are electron-beam

The surface

seams between only

acceleration

a good

inner

sur-

unavoidably channels,

by taking

to

which apart

the

structure.

Therefore, of bores

than

the disk

be repairable

acceleration

rings

thermal

necessary.

drift

shape.

lower

of

a 5-cell

sections

final

remain

water-cooling is

the

the drift

maximum occurring

face

of the

with

to the

of

seams on the

seams are readily since

water

safety,

they

outside

repairable

need only

cooling (Figure

the

disk

by means

4) was proposed.

and present

be water-tight 6

of

(test

no special pressure

=

9 bar)

after

proposed fully

several

cooling

adequate

thermal

suffices for

a copper

shocks

for

from

a disk disk

15OOC to

30°C.

made of AlMgSi0.5

due to the better

The and is

thermal

con-

ductivity.

b%Nhdb*X

Detail

sdur’n

scfdf*-B bVLI1,

c-o

Section

C-D

EzizalhdbwI

‘Detail.

Neldment structure.

7

X

-

Section A&B (onZy .?,!

Figure 3 of a five-cell

at

PETFW acceleration

at Y --i

s&at

CD

Sbction L CD '.

CAVITY-DISK Figure 4 W a ter cooling of the drift-section The rings

of the

resonator

forged

part

rolled

to a circle.

beam weld

with

the neck for

required

for

would make the alteration square the

water

final

chosen, tially

of

the

here

thermal

by using

since

(especially

loading

eutectic

and phosphorus-containing

of

welding copper

8

welded

surface. the

ring

ring

material filler

inert

amounts of

a copper

weldment)

difficult

For cooling

are electron-beam inner

by two electron-

large

for

of the

properties.

the

the

the

due to ring,

or TIG welded When a TIG weld

can be reduced (AlSill metal

for

a

and a sheet

A TIG [tungsten

machining

the metal's

of

flange

are connected

also,

method

subsequent

machining

the lateral

longitudinally.

with that

pipes

are made from two parts:

The two parts

seams executed

weld was dispensed heat

cavity

disk.

for

before is

substanAlMgSi0.5

copper).

Only

gas]

a good thermal

contact

required

for

The most

difficult

disks

these

since

the entire

that

all

addition,

for

residues

that

formation can

of

4. Preliminary Preliminary welding parts

two welded

the

disk

welding unit

with

operating

pumps.

beam gun with maximum current rotationally equipped

the

tests

static

root

is

filled

up in

can be removed. must

In

be as smooth

Therefore,

as

it

was

as in Figure

separating

line

3:

prevents

due to a 30'

the

inclination,

pockets.

of

range

with

an electron-beam

company in Hamburg on lo-mm-thick and AlMgSiO.5

The unit's

alloy.

2.6 x 2.6 x 2.6 m could reach -4 mbar within 10 minutes of 10

The built-in

60 mA.

(but

and dynamic

relocatable)

voltage

The welded

and longitudinally with

root

were performed

a maximum operating of

between

For vacuum-related

which,

gas

weld

and results

dimensions

of diffusion

is

of the weld

be prepared

root

at an aircraft

pressure

final

or holes.

parts

beneath

made of OFHC copper

tainer

the

forming

tests

the

agents

no drops

the

without

3).

cleaning

an uncontrolled

now appear

by

machining

(Figure

frequencies

proposed

of

presented

gap must be completely

of

and must exhibit

The offset

is

there

possible

or tightness

welds.

welding

radio

strength

a post-weld

impossible

reasons, order

braze problem

and rings,

practically

and no high

parts

by jigs. deflection

of

conthe by means

electron-

150 kV supplied could

The unit of

the

be moved was also beam.

a

Macrosections

of weld

are illustrated unit

seams obtained

in Figure

are compiled

in Table

5.

on copper

The associated

and AlMgSiO.5 data

for

the welding

1.

b)

4

Figure 5 Macrosections of electron-beam weld on copper (a) and AlMgSi0.5 (b). Parameter Sheet thickness Beam voltage Beam current Focal point Welding speed Wagging form Wagging frequency Wagging direction Wagging amplitude

seams

OFHC copper 10 mm 150 kV 52 mA -100 mm 9.7 mm/s i-u 400 Hz Parallel to the seam 2mm

Table 1 Choice of parameters for electron-beam welding of lo-mm-thick OFHC copper and AlMgSi0.5 alloy.

10

AlMgSi0.5 10 mm 120 kV 34 mA 0 31 mm/s AM 2 kHz Parallel to the seam 2mm

The copper bath

parts

before

were pickled

welding

and rinsed

AlMgSiO.5

parts,

machining

and subsequent

For the

the best

copper

beam would In both along All

of

the

rather weld

than

welds

best

By the middle acceleration

of

structures

with

R.F.

a dry

only

of the

with

electron

surface. by wagging

the beam

seam.

and withstood

several

heatings

treatments.

two aluminum

1976,

point

the weld

(6) the weld

shock

For the

weld was possible

were achieved

seams were vacuum-tight

after

pickling

(6).

The focal

results

acid

water.

were obtained

degreasing

across

nitric

deionized

100 mm below

to 15OOC and subsequent

tested

with

the beam.

have to lie

cases,

the usual

a lo-mm-deep

parts,

an underfocussing

with

prototypes

are to be fabricated

of

the

by this

PETRA method

and

power.

Acknowledgements The authors

are indebted

discussions

and suggestions

Boernsen

and W. Mcller

H. Gerke for

to Mister

for

and to Messrs. performing

the

clarifying

G. Benedetti, trial

P.

welds.

References (1) Science: Charm.

The New Particle Science,

(2) PETRA Proposal,

Mystery:

189 (19751, German Electron

(1974). 11

pp.

Solid

Clues

Now Lead to

443-445. Synchrotron

DESY, Hamburg

(3) Gerke,

H.,

(4) Priest,

communication.

Multipactor

D.H.:

high-power cf.

private

microwave

effects

and their

Microwave

tubes.

prevention

Jour.,

in

10 (1963)

55.

(5) Gerke,

H. and W. Quarz:

double-ring

storage

Cavity

resonators Kerntechnik

system.

for

a 3 GeV

5 (1974)

pp.

246-

251. (6) Sanderson, weldability 4 (1972)

A., of 7, pp.

A.N. three

Taylor

and R.J.

aluminum

250-255.

12

alloys.

Stearn: Metal

Electron-beam Construction