1- Short pulse neutron sourcePulse length: ~ 1s

Repetition rate: 50 – 60 Hz

Average beam power: ~ 1.5 MW

Beam energy: 1 – 8 GeV

Particle type: protons or H-

Spallation Neutron Source (ORNL)

Overview

Wf = 1 GeV, If = 1.5 mA (average), then P = 1.5 MW.

Average ion source current estimated to be Is = 2-2.5 mA (in order to account for transverse and longitudinal losses along the LINAC, as well as chopped portions of the beam).

Repetition rate = 50 Hz, Duty Factor = 6%, then Is = 33-42 mA (peak).

H- source LEBT RFQ CCL SCL HEBTMEBT DTL

StorageRing

Target

90 MeV 200 MeV 1 GeV

352.2 MHz 704.4 MHz

15 m 400 m

3 MeV

WARM PART OF THE LINAC

Ion source LEBT RFQ MEBT

(H-) (3 solenoids) (4-vane, 352 MHz) (Quads, rebuncher, chopper)

5 m 3 m 4 m 4 m

DTL CCL

(Álvarez, 6 tanks, 352 MHz) (4 modules, 704 MHz)

40 m 60 m

SCL

50 keV 50 keV 3 MeV

3 MeV 90 MeV 200 MeV

Normalized transverse emittances estimated to grow from 0.2 pi mm mrad (ion source) to less than 0.5 pi mm mrad (end of warm linac).

RFQ OUTPUT ENERGY

The power loss at energies above the neutron production threshold in Cu (~2.6 MeV) is very low (ESS Bilbao RFQ design).

The superconducting Linac

Saclay design of a 5-cells high beta 704 MHz cavity

Medium beta Saclay cavity withits helium tank and tuning system

• Two kinds of cavities depending on the beam energy• = 0.6 cavities up to 400 MeV• = 0.9 cavities for energy up to 1 GeV

• Construction of about 10 medium beta cryomodules and 15 high beta cryomodules • Use of 15 bars He system for the 70K thermal shield -> no need of LN2 = only one coolant (helium)

e

pB

Beam rigidity:

657.5B 651.29B 1 GeV 8 GeV

B = 0.617 T → = 9.168 m → Circ. = 57.6 mMagnetic field Radius Circumference

Only dipoles! We need more space for other elements.

Arc section: 90 m, Straight section: 90 m, Total circumference: 180 m

Storage ring

Cells: 12 → Cell length: 7.5 m, Dipoles/cell: 2 → Total dipoles: 24

angle = 360/24 = 15°r

→ dipole length = 2.4 m sector dipole

Arc section - 3 FODO cells

Arc section

B

gk

k

1f

f4

L

2sin

FODO FODO/Doublet

x (max) = 12 my (max) = 11 m

D (max) = 3.6 mD (rms) = 1.4 m

Qx = 5.29Qy = 5.21

tr = 3.21GeV = 2.1

-10

0

10

20

30

40

50

0 20 40 60 80 100 120 140 160 180s [m]

x,

y,D

[m]

D

x

y

-10

0

10

20

30

40

50

0 20 40 60 80 100 120 140 160 180s [m]

x,

y,D

[m]

D

x

y

x (max) = 45 my (max) = 25 m

D (max) = 3.4 mD (rms) = 2.7 m

Qx = 3.29Qy = 3.17

tr = 3.31GeV = 2.1

kD = -0.589 m-2

kF = 0.573 m-2

kD = -0.498 m-2

kF = 0.501 m-2

FODO

FODO/Doublet

x (max) = 24 my (max) = 17 m

D (max) = 3.8 mD (rms) = 1.4 m

Qx = 6.29Qy = 5.22

tr = 5.11GeV = 2.1

-10

0

10

20

30

40

50

0 20 40 60 80 100 120 140 160 180s [m]

x,

y,D

[m]

D

x

y

x (max) = 16 my (max) = 28 m

D (max) = 4 m

Qx = 6.23Qy = 6.20

tr = 5.23

Parameters of the storage ring at SNS:

kD = -0.637 m-2

kF = 0.778 m-2FODO/Doublet

1 GeV: 35 Neutrons/Proton

8 GeV: 207 Neutrons/Proton

10-9 10-8 10-7 10-6 10-5 10-4 10-3 10-2 10-1 100 10110-7

10-6

10-5

10-4

10-3

10-2

10-1

100

101

Ne

utr

on

s/P

roto

n

Neutron energy [GeV]

1 GeV 8 GeV

Proton beam

Many materials can be used: lead, tantalum, tungsten

But mercury was chosen:• not damaged by radiation• high atomic number, making a source of numerous neutrons• liquid at room temperature -> dissipate the temperature rise better than a solid