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Design Studies for RIA Fragment Separators

A.M. Amthor

National Superconducting Cyclotron Laboratory, Michigan State UniversityDepartment of Physics and Astronomy, Michigan State University

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RIA Concept

High-Resolution Separator

Large-Acceptance Separator

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Motivation: ISOL and Gas Stopping

Optimum productionmethod for low-energy beams

Standard ISOL technique

Two-step fission

In-flight fission + gas cell

Fragmentation + gas cell

ISOL Committee Task Force Report (1999)

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Motivation: Beam Energy and Momentum Acceptance

Above: Fragment beam of 78Ni produced from 86Kr. At the RIA energy of 400MeV/u the acceptance should be greater than 10%.

Left: Production of various fragments for fixed current and acceptance. Acceptance determines energy of turnover point (here 10% dp/p)

J. Nolen ANL

0 100 200 300 400 500 600 700 800 900 100011001200

E/A ( MeV/u )

1

10

100

FragmentationISOLIn-flight fission

211Fr

132Sn,96Kr

110Zr

80Zr

11Li

138Sn

78Ni

114Zr

159Nd

Δp/p = 10%

Re

lativ

e M

ass

Se

pa

rate

d Y

ield

s

0

1

2

3

4

5

6

7

8

9

0 5 10 15 20

600 MeV/u

400 MeV/u

200 MeV/u

100 MeV/uYiel

d (p

ps/p

μA)

Momentum Acceptance (%)

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Fragment Separators

N

Z

N

Z

N

Z

Fragments after target

Fragments at wedge

Fragments after FP

SpecificationsBρmax = 6Tm

Δp/p = 5%Δθ = ±40mrΔφ = ±50mrCompensated to 3rd orderLargest acceptance of current facilities

Note: Isotope yield diagrams are from 86Kr78Ni simulation with primary beam of 140MeV/u

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Thick Wedges andTwo-stage Fragment Separation

CAARI 2004 talk by A. Stolz

Al 450 mg/cm2

Al 300 mg/cm2

Al 190 mg/cm2

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RIA Separators

Preseparator

• Maximized production rate

• 100 mr in horizontal and vertical

• 12% momentum acceptance

• low optical aberrations (< 2 mm)

High-Resolution Separator

• Maximized quality and purity

• Two-stage fragment separation

• 80 mr in horizontal and vertical angular acceptance

• 6% momentum acceptance

• d/M = 2.5m

The RIA concept makes use of two fragment separators.

PreseparatorMomentum Compensator

Gas-Stopping Cell

Beam

PreseparatorHigh-Resolution Separator

High-Energy Area

Beam(up to 400 kW)

Target

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PreseparatorThe compensated third order system passes approximately 73% of fragments uniformly distributed in a 6-D phase space ellipse with a and b from ±50mr and with δ distributed over a full width of 12%.

Target

NSCL

Beam

WedgeIsotope

Slits

Beam

Dump

Additional wedge at beam Additional wedge at beam dump?dump?

Additional stage of separation Additional stage of separation for gas cell separator?for gas cell separator?

• Significant higher order aberrations (>3rd order)

• Up to 200kW power on beam dump

• Primary beam often within momentum acceptance and sometimes with |δBρ|< 1%

• Higher energy and greater neutron excess of fragment beams increases magnetic rigidity (10Tm)

• Range compressed fragments to be stopped in 0.5 atm-m gas cell, requires aberrations < 2mm

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Momentum Compensator

Specifications:

• Full angular and momentum acceptance from preseparator

• Momentum resolving power R>1000

• d/M = 2.5m

Diagram: H. Weick et al., NIM B 164-165 (2000) 168

FWHM = 32 atm-m 4He

FWHM = 0.93 atm-m 4He

Ion

Gui

de,

Coo

ler a

ndB

unch

er

Above: Range compression of 350 Mev/u 130Cd produced from 500 MeV/u 136Xe(MOCADI simulation)

130Cd

0

0.5

1

1.5

2

0 500 1000 1500 2000 2500

Rang

e FW

HM (a

tm-m

)

Resolving Power

350 MeV/u 130Cd range width

Gas

Cel

l &

Noz

zle

Mon

oene

rget

ic

Deg

rade

r

Dis

pers

ive

Ele

men

ts

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Simulation Methods& Needed Improvements

(x|θδ) aberration – angled wedges

Dispersive focal plane

A. Stolz, CAARI 2004

Fragment production in thick wedges

Profile wedge degrader

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Acknowledgements

Additional thanks to:

RIA R&D is funded in part by the U.S. Department of Energy (Grant No. DE-FG03-03ER41265) and Michigan State University.

The NSCL is funded in part by the National Science Foundation (Grant No. PHY-01-10253) and Michigan State University.

Collaborators:

B.M. Sherrill 1,2

D.J. Morrissey 1,3

A. Nettleton 1,2

A. Stolz 1

O. Tarasov 1

1National Superconducting Cyclotron Laboratory, Michigan State University2Department of Physics and Astronomy, Michigan State University 3Department of Chemistry, Michigan State University

Ion Optical Program GICOa combination of GIOS and COSY 5.0 written at University of Giessen, 1986 -  1998 by Martin Berz, Bernd Hartmann, Klaus Lindemann,  Achim Magel, Helmut Weick

The MOCADI program was developed in PL/I by T. Schwab, H. Geissel, and A. Magel at Giessen University in Germany.

N. Iwasa translated MOCADI 1.34 into C on a DEC VMS operating system and developed it further.