ADSRs and FFAGs

Roger Barlow

7 Jan 2008 Workshop on ADSRs and FFAGs Slide 2

The ADSR

Accelerator Driven Subcritical Reactor

Accelerator

Protons ~1 GeV

Spallation Target

Neutrons

Reactor Core

Neutron multiplication factor typically k=0.98

7 Jan 2008 Workshop on ADSRs and FFAGs Slide 3

ADSR properties

• Manifestly inherently safe: switch off the accelerator and the reactor stops

• Uses unenriched 238U or 232Th as fuel

• Large flux of neutrons can transmute waste from conventional reactors (especially Pu)

7 Jan 2008 Workshop on ADSRs and FFAGs Slide 4

Accelerator requirements

Proton Energy ~ 1 GeV For 1GW thermal power:• Need 3 1019 fissions/sec (200 MeV/fission)• 6 1017 spallation neutrons/sec (k=0.98 gives 50

fissions/neutron)• 3 1016 protons/sec (20 spallation neutrons each)Current 5 mA. Power = 5 MWHigh current rules out synchrotron Compare: PSI proton cyclotron: 590 MeV, 72 MeV injection2mA, 1MW

7 Jan 2008 Workshop on ADSRs and FFAGs Slide 5

Rubbia’s Energy Amplifier

• 1 GeV,10 mA, 42 MHz, 3 cyclotron stages– 10 MeV (dual)– 10-120 MeV– 120-990 MeV

• Very challenging

(order of magnitude

harder than PSI)

7 Jan 2008 Workshop on ADSRs and FFAGs Slide 6

Myrrha

• 350 MeV, 5 mA

• Linear Accelerator for reliability

• Dual RFQ to 5 MeV

• SC Linac 111 m long

(various alternatives)

Proposed demonstrator for ADS incineration

Stress need for reliability

LINACs can be made with redundancy

7 Jan 2008 Workshop on ADSRs and FFAGs Slide 7

KURRI

3 stage FFAGs at 120Hz0.1 – 2.5 MeV

2.5 – 20 MeV ( ½)

20 – 150 MeV (?)

Current ~1 nA

‘ADS demonstrator’

Aim: study neutron production

7 Jan 2008 Workshop on ADSRs and FFAGs Slide 8

FFAGCyclotron:

B constant, R varies

Nonrelativistic:

Low energies

FFAG:

R varies slightly

B varies with R but not t

High currents

High energies

Rapid acceleration

Synchrotron:

R constant, B varies

Magnets cycle

Low currents

7 Jan 2008 Workshop on ADSRs and FFAGs Slide 9

FFAG energies

Increase in p= increase in B x increase in R

How big an increase in B can we manage?

• Magnet design

• Lattice

Realistic – factor 2: Optimistic – factor 4

How big an increase in R can we manage?

Realistic – factor 1: Optimistic – factor 2

7 Jan 2008 Workshop on ADSRs and FFAGs Slide 10

Problems

• Injection and extraction are difficult

• Successive orbits are close together

• Gaps are small

• If we can break symmetry – racetrack instead of circle – life gets a lot easier

• Even so, the fewer rings the better

7 Jan 2008 Workshop on ADSRs and FFAGs Slide 11

Scenarios

Realistic 1 ring72 MeV injector (Phillips

Cyclotron)1 ring to 262 MeV

Optimistic 1 ring6 MeV RFQ injector

1 ring to 1.004 GeV

Ruggiero 2 ring50 MeV injector 2 rings to 1GeV

Realistic multiring5 MeV RFQ injectorRing 1 to 20 MeVRing 2 to 77 MeVRing 3 to 281 MeV

Ring 4 to 880 MeV

7 Jan 2008 Workshop on ADSRs and FFAGs Slide 12

FFAG frequencies

As particle energy increases: v increases T falls f increases L increases T increases f fallsFor cyclotrons these cancel exactlyFor FFAGs these may cancel

approximately. May get away with constant RF frequency

Or can scan using low Q Finemet cavities. Go from CW to pulsed operation – high frequency and high duty cycle

~MHz

~kHz

~50%

7 Jan 2008 Workshop on ADSRs and FFAGs Slide 13

nsFFAGs

Conventional (scaling) FFAGs:

B( R)Rk

No Chromaticity:

Focussing scales with momentum

Constant tune

resonances avoidable

Nonscaling FFAGs: B( x)x

Focussing changes with momentum

resonances unavoidable but harmless(?)

More compact aperture

More compact ring (all magnets bending)

EMMA is prototype

7 Jan 2008 Workshop on ADSRs and FFAGs Slide 14

Way forward

Conventional wisdom says:

ADSRs use cyclotrons (low energy) or Linacs (expensive)

FFAGs could provide a better alternative and make the whole show viable