Indian Spallation Neutron Source

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Nov 16, 2013 (3 years and 8 months ago)

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100 MeV
-

1 GeV Proton Synchrotron


for

Indian Spallation Neutron Source


Gurnam Singh

Beam Dynamics Section

CAT, Indore

CAT
-
KEK
-
Sokendai School on Spallation Neutron Sources, 2004

BASIC LAYOUT OF INDIAN
SPALLATION NEUTRON SOURCE

100
MeV
Linac

Linac to PS

Transfer Line

PS to Target

Transfer Line

100 MeV


1 GeV

PROTON

SYNCHROTRON (PS)

T
a
r
g
e
t

H
-

Source

RFQ

4.5
MeV

Outline:


1.
Preliminary

design

aspects

of

Rapid

Cycling

Proton

Synchrotron

2.
Linac

to

Synchrotron

Transfer

Line

Preliminary

design aspects

Of

Rapid Cycling

Proton Synchrotron

Key parameter in a spallation source

Beam Power

P
beam

= q.N
p
.E .R



=

I.E



P
beam
:Beam power (W) at target



q

:Charge on proton (C)



N
p

:No. of protons in ring



E

:Final proton energy (eV)



R

:Repetition rate (Hz)



I

:Average current at target (A)

To increase the beam power


Two Ways

Increase beam energy


Large machine, big cost

Increase beam Current


Severe space charge


Collective beam instabilities

Choose optimum energy & current

Accelerator choice

Full Energy Linac

&

Accumulator Ring

Linac

&

RCS


High

power

achievable

but

high

cost


High

injection

energy

means

very

tight

beam

loss

control

at

injection


High

injection

energy,

so

more

heating

of

injection

foil


Low

injection

energy,

thus

more

space

charge

problem


Rapid

acceleration,

means

powerful

RF

systems


Ceramic

chamber

Indian Spallation Neutron Source


100 MeV Linac & RCS based


Beam power




:100 kW


Final energy of the beam

: 1 GeV


Average current



: 100



[@ 25 Hz Repetition Rate]



2.4


13

protons in synchrotron

Design Considerations

1
.

Injection

energy

100

MeV



The

first

estimation

of

current

in

the


synchrotron

is

made

by

space

charge


tune



shift
.



x
y
y
f
y
p
y
a
a
a
B
R
Nr








3
2
=>

For

the

required

N,

the

tune

should

not

cross

any

dangerous

resonances
.

Thus

tune

should

have

sufficient

room

for

movement
.

In

our

design,

allowable

tune

shift

taken

as

0
.
2
.

For

decreasing

the

tune

shift

(for

enhancing

the

average

current

handling

capability

of

the

synchrotron)


*

Increase

the

injection

energy

=>

Increase

the

cost

of

Linac
.

*

Decrease

the

N

and

increase

the

repetition

rate,

so

that

average

current

remains

same

=>

Constraints

from

technology

and

frame

overlap

in

time

of

flight

type

experiments
.

*Increase

the

bunching

factor

at

injection

=>

Deciding

factor

of

RF

programme

of

the

machine
.

2
.

Beam

loss

control


Beam

loss

control

is

of

major

concern

in

the

high

intensity

machines
.

1
W/m

is

the

allowable

limit

of

uncontrolled

loss

for

hands

on

maintenance
.

=>

@

injection,

average

beam

power

10

kW

Uniform

loss

on

whole

length

of

ring

gives

the

upper

most

limit
:

2
%

allowed

uncontrolled

loss
.


=>

Thus

for

controlled

loss,

betatron

and

momentum

collimators

needed
.

3. Sufficient space


Large

dispersion

free

straight

sections

are

needed

for


1
)

RF

systems
.


2
)

Betatron

collimators

3
)

Injection

systems


4
)

Extraction

system

Apart

from

these,

other

systems

which

should

be

accommodated

in

the

ring

are

diagnostic

devices,

vacuum

pumps,

correctors

etc
.

4.
High tune for working well below the


瑲t湳楴楯n

Options for the lattices

Many

lattice

configurations

can

fulfill

these

requirements
:




For

making

an

arc

with

achromatic

conditions


1
.

FODO

with

Missing

dipole

scheme

(IPNS,



KEK
-
JAERI

etc
.
)


2
.

Achromat

design

(eg
.

SNS)




Obtaining

the

long

straight

dispersion

free

sections


1
.

FODO


2
.

Doublet/

Triplet

structures


Lattice for the ISNS



FODO

structure
:


Simple,

smooth

variation

of

beta

function

means

less

prone

to

errors
.




Missing

dipole

for

the

dispersion

matching




Four

superperiods


The

four

long

straight

sections

will

be

used

for

the

injection

system,

collimators

(beam

collimatoss),

RF
-

system

and

extraction

system

respectively
.


Four

superperiods

have

better

stability

for

structure

resonance

than

the

three

period

structure
.

M
HALF UNIT CELL


One period


0
5
10
15
20
25
30
35
40
45
50
-2
0
2
4
6
8
10
12
14
16
18

Qf2

Qd2

Qf1

Qd1

Qf1

Qd1

Qf3

ARC SECTION


Half
-
cell length of FODO:

4.425 m


Total cells in arc:



4 (one period)


Total straight section cells:

2 (one period)


Quadrupole families:


5 (3f & 2d)


Length of the period:


53.1 m


Length of long straight:


4

3.875=15.5 m



Choice of tune

90


phase

advance

per

cell

requires

a

tune

of

6
.
0
,

so

the

tune

of

the

machine

is

kept

near

6
.
0
.

In

horizontal

plane,

it

is

higher

than

the

6
.
0

and

in

vertical

plane

it

is

on

the

lower

side
.

But

it

has

wide

tunability

range

and

it

can

be

operated

at

split

and

un
-
split

working

points
.






Structure & half integer resonance diagram

( upto 4
th

order)

Shaded region is the space for different tune options


y



x











































5

6

7

8

4

5

6

7

3

X
=20


X
+2

y
=20


X
+2

y
=16

2

X
+2

y
=24

2

X
-


y
=8

3

X
-


y
=12

3

X
+

y
=28


X
+3

y
=24

5.5

6.5

(6.88, 5.88)


X
-


y
=1


X
-


y
=0







(7.3, 6.3)

(6.3, 6.3)

* Further selection depends on imperfection
resonance

The

lattice

can

have

various

tune

points

in

these

regions
.

Primarily

selected

tune

is

6
.
88

and

5
.
88

[other

options

are

6
.
3
,

6
.
3

and

7
.
3
,

6
.
3

(higher

tunes)]
.

Tune

is

far

away

from

resonance

up

to

3
rd

order
.

Tune

drift

of


0
.
2

(due

to

space

charge)

does

not

hit

any

resonance

up

to

3
rd

order
.



Lattice parameters

0
5
10
15
20
25
30
35
40
45
50
-2
0
2
4
6
8
10
12
14
16
18
Bx
Bz
Eta
Fx
Fz
Preliminary tracking results with sextupoles

(without error)

Horizontal phase space, 5000 turns

Vertical phase space, 5000 turns

Initial co
-
ordinates are chosen corresponding to maximum
displaced particle in both the planes with 1%

p/p.



Further optimization needed in sextupoles for vertical plane.

H
-

Injection






500


s

(

300

turns

)

pulse

length

of

H
-

ions

from

100

MeV

linac

to

be

injected

through

a

stripping

foil
.





Constraints

imposed

by

Liouville’s

theorem

on

conventional

multi
-
turn

injection





湯n

慰灬y



瑨楳

捡獥
.










possible

to

inject

a

large

number

of

turns
.

Goals Of Injection






To fill transverse acceptances (

x

=

y
= 300


mm
mrad) in K
-
V distribution



uniform filling


avoid excessive space charge forces




牥晥牲敤e慳⁩湪散瑩潮灡楮瑩t


Injection Paintings

Horizontal Phase Space : Variable Bump by four
bump

magnets located in a long straight section





Angle of Injection





Peak of the bump at the stripping foil





Minimum number of traversal of beam




through the foil






Partially

stripped

particles

H
0

do

not

pass

through

high

magnetic

field

(

centre

of

QD

)










Sripped

H
-

(Magnetic

field)



畮睡湴敤

桡汯

景牭慴楯i

慲潵湤

捩牣畬慴楮

灡牴p捬敳

Layout of the injection system of ISNS

Time Dependence of Four Kick Bump Angles

Orbit

Bump

and

its

Slope

at

the

Location

of

Stripping

Foil

(Injection

Point)

vs

Injection

Turn

Number

Bending Angle with Injection Turn Number

0
50
100
150
200
250
300
350
0
10
20
30
40
50
60
70
Y - Amplitude
X - Amplitude
Amplitude of Betatron Oscillations (mm)
Injected Turn Number (N)
Amplitude of Betatron Oscillations of Injected Particles
with Turn Number During Injection

Painting in vertical normalized phase space

Spatial distribution of nearly 350 injected turns

Striping Foil





Thickness of the foil:

(High stripping efficiency )


At 100MeV 60

朠捭
-
2


is adequate


• Foil materials:





Polyparaxylene,carbon


or


Aluminium oxide



Beam loss and Collimators



The

lattice

should

accommodate

the

collimators

(betatron

and

momentum)

for

controlled

loss
.

At

injection

only

2
%

particle

loss

is

allowed

(if

distributed

uniformly

all

over

the

length)

in

the

ring
.



Key parameter in collimator design:

Phase advance between primary and secondary
collimators and their apertures



Collimators

remove

the

Halo

from

the

beam

at

the

predefined

locations
.





The

first

collimator

scatters

the

halo

particles,

with

low

impact

parameter
.

Due

to

scattering,

the

amplitude

increases

and

these

are

collected

at

secondary

collimator,

which

is

placed

at

a

proper

phase

advance
.

Proper phase and critical kick is given by

2
1
cos
n
n
opt


n
1

and

n
2

are

the

apertures

of

primary

and

secondary

in

terms

of

beam

size
.

The

critical

kick

is

2
1
2
2
n
n
K
c


Phase difference between primary and secondary collimator

X


Plane: 158


and n
2
/n
1
=1.08

Y


Plane: 144


and n
2
/n
1
=1.20



Material choice in collimators



Two Effects:



When a proton traverse through a primary collimator, it
loses energy. If this loss is high, particle may be out of
bucket or longitudinal acceptance. (Acceptance of ring
1%)




The primary collimator has to give a large kick, so
protons hit the secondary collimator with large impact
parameter. This kick is largely imparted through the
multiple Coulomb scattering.


The

first

effect

demands

a

very

thin

collimator,

which

does

not

cause

the

much

energy

loss
.



The

second

effect

demands

a

high

Z

material
.

Thus

choices

are

among

Pt,

W

etc
.



Other

requirements

are

good

thermal

conductivity,

high

melting

point,

good

polishing

capability,

radiation

damage
.


As

high

Z

has

the

shower

effects,

which

is

drawback
.

Therefore,

for

proper

choice

of

material

and

optimization

of

its

thickness,

simulation

studies

are

essential
.




Tentative

locations

of

betatron

collimators

In

next

period

to

injection
.

44
46
48
50
52
54
56
58
60
62
-2
0
2
4
6
8
10
12
14
16
18
Bx
Bz
Eta
Fx
Fz
y
-
plane

x
-
plane

Phase difference between primary and secondary collimator

X


Plane: 158


and n
2
/n
1
=1.08, beam sizes at the collimators: 4.2cm, 3.8 cm, 3.2 cm

Y


Plane: 144


and n
2
/n
1
=1.20, beam sizes at the collimators: 3.8cm, 5.6 cm, 3.6 cm

10
12
14
16
18
20
22
24
26
28
30
32
34
36
38
40
42
44
-2
0
2
4
6
8
10
12
14
16
18


x


y
D
x


x


y
Lattice parameters (m)
Path length (m)


Tentative locations of momentum collimators

Phase difference between primary and secondary collimator

X


Plane: 150


and n
2
/n
1
=1.15

In arc next to injection system.

Preliminary beam diagnostic
requirements



48 Beam position monitors ( one @ each quadrupole).


Beam loss monitors distributed all over the ring.



Beam profile monitors.



Current monitors (Average and Pulse).

Parameter

Value

Beam power

100 kW

Energy

0.1


1.0 GeV

Repetition Rate

25 Hz

Circumference (m)

212.4

Periodicity

4

No. of bending magnets

24

Bending angle

15


per magnet

Bending Magnet Field

0.207
-

0.789 T

Bending radius (m)

7.1626

No. of quadrupoles

48

Maximum gradient (T/m)

4.5

Nominal tune point

6.88, 5.88


x,max
,

y,max
(m)

16.4, 16.4

No. of sextupoles

16 (two families 8F and 8D)



Parameters of Synchrotron

Parameter

Value

D
max

(m)

2.4896

Chromaticity

-
8.954,
-
7.640

Momentum compaction

0.031989



-
transition

5.591

Dispersion free straights

4

3.874=15.5 m / period

Straight with dispersion

2

3.875=7.75 m / period


RF

(MHz)

1.21


2.47 for h = 2

Revolution Time

1.65


0.81
µs

Peak energy gain per turn

60 keV

Beam size (max)

9.6 cm @ 1%

p/p @ Qf1

Emittance after painting

300


mm.mrad after injection
in both planes

Peak RF voltage

120 kV



Parameters of Linac (injector)

Parameter

Value

Energy

100 MeV

Pulse length

500

s

Pulse current

25 mA

Energy spread

0.3 %

Emittance (normalized)

0.23


mm mrad

Magnet apertures

Magnet

Max


(m)

Max D

(m)

Strength

(m
-
2
)

Good
field
radius

(mm)

Qf1

16.4

2.6

-
0.67

120

Qd1

16.1

2.5

0.56

100

Qf2

16.1

0.0

-
0.64

100

Qd2

16.4

0.0

0.61

100

Qf3

13.2

2.5

-
0.67

120

BM

~8

~2

0.8 T

100, 100



Linac to Synchrotron

Transfer Line



Design Philosophy


To match the beam parameters from the linac output
to synchrotron injection point.


To provide the adequate space for installation of
various components, as


1.RF cavity for energy jitter correction.


2.Diagnostic elements
(Profile monitors,

Current monitors, Beam position monitors

and Beam loss monitors).


3.Dump line.


4.Bumpers for injection painting.


To install collimators for control of beam loss.

-10
0
10
20
30
40
50
60
70
-15
-10
-5
0
5
10
15
20
25
30


x


y


x
Optics parameters (m)
Path length (m)


Optics parameters of Transfer Line

Matching section


4 Quads

2 FODO

Achromat

1 FODO

Matching section


4 Quads

-10
0
10
20
30
40
50
60
70
-15
-10
-5
0
5
10
15
20
25
30


x


y


x
Optics parameters (m)
Path length (m)
Primary collimator

Secondary collimator X

Secondary collimator Y

RF Cavity

Parameter

Value

Length

62.95 m

No. of quadrupoles

21 (11 F & 10 D)

Maximum strength (m
-
2
)

6.1

No. of dipoles

2

Bending field (T)

0.65


x,max
,

y,max

(m)

27.6, 15.8


x,inj
,

y,inj
, D
inj
(m)

0.99, 1.95, 0.00


x,ext
,

y,ext
, D
ext

(m)

13.0, 2.5, 0.0

Conclusions

Only

preliminary

linear

studies

have

been

carried

out
.




Studies

to

be

carried

out


1
.

Non
-
linear

behavior

and

sextupole

scheme

2
.

Detailed

studies

of

Longitudinal

dynamics

with

space

charge

and

deciding

the

RF

program

3
.

Space

charge

issues

and

beam

loss

control

4
.

Detailed

studies

of

injection

and

extraction

5
.

Design

of

transfer

lines

5
.

Transverse

and

Longitudinal

instabilities




























2
2
2
2
1
2
2
2
2
g
b
B
a
a
a
B
Nr
y
y
f
x
y
y
f
y
p
y










Exact formulation of Tune Shift

(including the image terms)


y



x











































5

6

7

8

4

5

6

7

3

X
=20


X
+2

y
=20


X
+2

y
=16

2

X
+2

y
=24

2

X
-


y
=8

3

X
-


y
=12

3

X
+

y
=28


X
+3

y
=24

5.5

6.5

(6.88, 5.88)


X
-


y
=1


X
-


y
=0







(7.3, 6.3)

(6.3, 6.3)