916 Dynamitron

Radiat.

Phys. Chem. Vol. 42, Nos l-3,

Printed

in Great

Britain.

pp. 555-557, reserved

All rights

0146-5124/93

1993 Copyright

TWOPROBLEMSON THE 3,000/40/916

0

$6.00

+ 0.00

Pergrmon Press Ltd

1993

DYNAMITRON

ZHAO FENC and CHENCYAN-WU Chemistry

RadiaticJn

Jilin

City,

Jilin

Research

Institute

Province

132011

P.R.China

THE VACUUMSYSTEMUNDERTHE INFLUENCEOF THE ENVIRONMENT As we all rings

know, a vacuum system

used

system

almost

system

gets

system

perfect

which,

Dynamics,

Inc.

system,

its

for

Dynamitron America

is mostly

scan

bellows

lo-’

a leak

operation

while

occurred

in the

0

the

vacuum

to keep the

of

vaouum

of an accelerator.

institute

0 rings.

was imported in July

For

had a leak

Aluminium

make the vaouum

work

is essential

well-

joint the

same joint

vacuum was also

the

vaauum vaouum

Torr.

In

flanges

the vacuum came into while

high

1X10-*

of two

range

Radiation

conditioned

reaches

in the

from

of 1987.Its

the

of the accelerator

vacuum system

but also

the maintenance It

at our

operation

of an accelerator.

of 10-c

of

Torr.

the

In July

in the range of

Torr.

After

locating

clear

corrosion

spread

the

leak

through

mixture

the

has

on the been

outside there

leaked

two flanges

known

everywhere

two flanges. And dense is a kind

aluminium

0 ring surfaces

pipes the It

ozone

vapor in

because

scan

was difficult

,?f the

was observed

of the

Besides.

there

that

aluminium

to inside.

than ring

the

there 0

That was was a lot

was

ring

the

of

glycerine

into

and

reason

water

and

the drift the water

in the

vault

oxidation. cause

pipe

a

it why

oil

a

555

leak.

system

came from the condensed in summer.

inside three

the

space off

was

substances

acted

would go through electrolysis

water between

the

accelerator

Moreover *

water

The condensed

to volatilize the

The corrosion

equipments

by the exhaust

and came into

while

These

heating

the vault

The water

vault.

two years. to

other

was drawn

of the wet weather for

was produced less

the

horn along

of gas of strong for

from outside

the oi I came from

that

it

surfaces

and the 0 ring.

and condensed down onto

the belowsr

sealing

two times.

The glycerine

the

sealing

the

the vault.

gap. which

on both

whole surfaces

on the water-cooled flowed

and removing

vestige

the vacuum system

It

the normal

with aluminium

the

of 1990,

and then is delicate.

operating

vacuum without and the

part

make vacuum better

in 1985 and came to operate

sealed

November of 1988, horn

unit

of courser

and clean

important

not only

become a perpetual less,

The 3,000/40/918 system

is one

in the vacuum system

narrow workiagr on

the

the whole

perhaps

ZHAOFENG and CHENGYAN-WU

556

aocompanied

the corrosion

In the

of 199%

fall

the condensed place

water

action.

the glycerine

heating

was prevented.

by now. The vacuum is still

On the other

hands

by the blower electron

for

the electron

This

beam was stopped

The carbon

from the hall carbon

only

but also

layer

helped

weakened

with

the perfect

It

that

time

hall

and

has been

the

scan

was carbonized

on the window for

the window

generate

the air-cooling in about

a new one had to be replaced

interfered

at

was blown onto on it.

would grow to 1 mm in thickness

layer

window from overheating, undoubtedly

not

with

in

Torr.

to form a hard up.

to be cleared

vapor

were moved from the

replaced

the window and condensed

beam bombardment

difficult

l?*:lO-*

the glycerine cooling

epuipments

The 0 ring

vacuum system

effect

every

and the

which heat

the

it

was

beoause

to the window.

8 months.

with

windo!u under

To prevent

the

5 or 6 months.

This

normal

operation

of

the accelerator. After

moving

greatly

the glycerine

and it was easy

assembled

at it

reastinr

that

up with

had been used until

from the accelarattir’s

accelerator

in a fine

because

cleaning,

are

hard

working

the deposit soft

rtn

cloth

the

using

the beginning

installations

to keep

window

alcohol.

of

will

say that a lot

leak hunting

reduced

The

For

1992.

will

do

more to

perfect.

I

can’t

of a lot

operation

best

window

the

to

vacuum

other

it

say

that

the

is

system more

and

problems

won’t but

done,

vacuum

the

That

vacuum

is easier

of work we have on

keep

system.

of the

speaking,

make a bad influence

to the daily

our

the

and conditioning

Comparatively

any more because

the environment

of trouble

and should even

the vacuum system

on the vaouum system

give

operation condition,

work and ti~ie-consuming.

time-saving occur

equipments+ it

was replaced.

%%.benifit

all

time

heating to clear

system

I and

of the accelerator.

THE RESISTANCE iIF HVDBTD AFFECTED BY RADIATION The High Voltage series-connected,

Divider

and the Beam Tube Divider

multisection

of the carbon

resistors

of radiations

the operation

The HVD consists is attached its

resistance

high

valtagr

is subject

high

In November value

metering,

with It

resistor

to increase

of the accelerator

+f’ series-connected

to the negative

::jeter ing circuit.

carbon

the

strings voltage

of 1988.

it

“‘its ras!.

to solve

the

as a result

of aging

carbon

and the

resistors

and ground

was ftxnrd that this

consist

resistance

t:jf value

effects

be influenced.

+f six

This

Dynami tran Because

will

terminal

same extent.

of

assemblies.

would only problem

as

every affect via

of 22 Mohm and the

string

high

voltage

had increased

the accuracy calibration

of the of

the

indicated high votagz reading in the analog control of the metering circuit. For BTD. the series-connected strings of twelve carbon resistors of 10 Mohm are terminated separately to their corresponding dynodes of the beam tube in a serial

8th International

Meeting on Radiation Processing

arrangement to form a linearly gradient It was notioed in 1988 that every string

field had

along the axial length a different resistance

minimum 150 Ohm and the maximum 220 Mohm. Therefore, destroyed.

This

to occur

frequently

divided opened

high at

Because

that

of each

treated

it

are

the vessel value

be seen

and stopped

This

the problem strings

also

of the

rated

accelerator

That

linearly

gradient

but also

because

was one of reasons

resistors on the

was adjusted the

in our oountry,

strings

to about

sparks

better

still

field

caused

of

why

the

the

an emergency

were jumped so 140 Mohm. The

disappear

during

and the accelerator

was

sparks unevenly

vessel

was

measure

had

that

later

the

resistanoe

operation

operation,

of

the

the convergence

has been working

very

of

well.

The

in use now.

was opened of each

that

about

of aging treatment

the

beam to diverge

the

for

string

resistance

maintenance for

in lQ90 and 1991,

it

BTD was 150 Mohm and for

of all

the

strings

was known

HVD 150 Mohm.

had approached

the

that Thus

constant

increasing.

The mechanism result

the

some resistors

beam turns

resistance could

get

string

strings

Two times the

operation

on the beam tube.

has shown that

the electron

the electron

of the beam tube. value, the

time.

we couldn’t

accelerator

caused

only

during

voltage

that

to be taken valuce

not

557

the

resistance

and radiation of BTD strings

on resistance give

a

value

effects

and tending

is available

increment

good result

for

increment

long-term

the

carbon

to a constant

as a kind

of the carbon the

of

as

is out of this

of emergency resistors.

resistors

The

measure treated

use on the accelerator.

to

a

paper. solve

resistor