tri p in-flight separator, ion catcher and rfq cooler/buncher e. traykov tri p project and...

TRIP in-flight separator, ion catcher and RFQ cooler/buncherE. Traykov

• TRIP project and facility• In-flight magnetic separator• Ion catcher• RFQ test and design• Simulations• Conclusion

TRIP Group:G.P. Berg, U. Dammalapati, S. De, P.G. Dendooven, O. Dermois, G.Ebberink, M.N. Harakeh, R. Hoekstra, L. Huisman, K. Jungmann, H. Kiewiet, R. Morgenstern, J. Mulder, G. Onderwater, A. Rogachevskiy, M. Sohani, M. Stokroos, R. Timmermans, E. Traykov, L. Willmann and H.W. Wilschut

TARGISOL Winter School, 17-23 February 2005

Trapped Radioactive Isotopes: icro-laboratories for Fundamental Physics

ISOL vs. In-flight separation


• Thick target• Diffusion• Secondary ion source • Electro-magnetic separator• Post accelerator needed for secondary reactions

• Thin target • Primary beam and products not stopped in the target• Product velocities close to that of primary beam • Electro-magnetic separator directly following target • Post accelerator not needed for secondary reactions

* Drawing taken from Thomas Baumann’s course - Fragment separators

TRIP project and facility

IonCatcher

RFQCooler

MOT

Beyond the Standard Model

TeV Physics

Nu

clea

r P

hys

ics

Ato

mic

Ph

ysic

sP

arti

cle

Ph

ysic

s

ProductionTarget

MagneticSeparator

MeV

meV

keV

eV

neV

AGORcyclotron

AGOR cyclotronIon catcher (thermal ioniser or gas-cell)

Low energy beam line

RFQ cooler/buncher MOT

MOT

D

D

DD

Q

QQ

Q Q

QQ

Q

Magnetic separator

Production target

Wedge


QDQD

QD QD

AGOR HI beam

Target chamber 1

Target chamber 2

Low energy beam

Traps

Ion catcher+

RFQ

Fragmentation separatorBeam rigidity B 3.6 TmProduct rigidity B 3.0 TmAngle, vert., horiz. 30 mradMomentum Acceptance 2.5%Resolving Power 1000Dispersion 2.0 cm/%

Fragmentation modeGas-filled

recoil mode

Gas-filled recoil separator Beam rigidity B 3.6 Tm Product rigidity B 3.0 Tm Angle, vert., horiz. 30 mrad Momentum Acceptance 2.5% Resolving Power 2000 (no gas filling)* Dispersion 3.8 cm/%

* In the gas-filled mode the resolving power is limited by multiple scattering in the gas

DD DD


TRIP separator – a double mode magnetic separator

Carbon target

21Na

TRIP separator – isotope selection in fragmentation mode


B = P/q selectionB = P/q selection +Focusing

B2

B3

B1

B3>B2>B1

Focal plane dE detector: dE-TOF

Beam:21Ne (43 MeV/u)

Wanted:21Na

CH2 target

21Na

TRIP separator – isotope selection in fragmentation mode


B = P/q selectionEnergy loss +

B = P/q selection +Focusing

Degrader selection

Focal plane dE detector: dE-TOF

Beam:21Ne (43 MeV/u)

Wanted:21Na

21Na


TRIP ion catcher – a thermal ioniserDiffusion * Effusion ** Ionisation

Material Min. thickness log(D0) EA D Ha

a Work function Max. temp. Melt. temp.

[m] [cm2/s] [kcal/mol] [cm2/s] [eV] [ms] [s] [eV] [K] [K]

(p=10-4 mbar)

Niobium 0.2 3.5 4.3 2300 2741Molybdenum 0.1 4.5 2400 2883

Tantalum 0.1 -0.9 88 8.0E-10 6.3 0.5 0.35 4.2 2800 3269Tungsten 0.6 -1.4 93 5.0E-11 6.4 50 36 4.5 3000 3683Rhenium 10 -2.5 80 8.0E-11 7.4 100 70 5.1 2800 3453Graphite 0.01 -6.5 20.3 3.0E-09 2.6 4.5 - 5.0 2600 3773

Diffusion: Delay parameter 0=2.D/d2D=D0.exp(-EA/kT)

D: Diffusion coefficient D0, EA: Arrhenius coefficientsEffusion: Mean delay time=1/=(a+f)a=C1.exp(C2.Ha/T)a, f: sticking and flight times

Ha: Enthalpy of adsorptionIonization: Ionization efficiency i=N/(1+N) =ni/n0=exp((-Wi*)/kT)

N: Amplification factor : Degree of surface ionizationni,n0: ion and neutral densities

Amplification factor < number of collisions ()

Thermal calculations using Femlab

R. Kirchner, NIM B70 (1992) 186-199 (* for 208Pb ions, 2300 K, ** a and for 238U ions, 2800 K)

Beam from the separator (i.e. 21Na)

Our RFQ cooler/buncher concept

Buffer gas pressure (He): ~10-1 mbar

RFQ ion cooler RFQ ion buncher10eV thermal

Trap position

U+Vcost

-(U+Vcost)

2 x 330 mm

Switching on end electrodes

• RF capacitive coupling• DC drag resistor chain

• Electronics designed for large range of isotopes• UHV compatible design and materials

• Standard vacuum parts (NW160)

~10-3 mbar


RFQ cooler prototype tests

• RFQ in vacuum• Transverse cooling• Velocity damping• With and without a drag voltage on the segments

133Cs+ beam, initial energy: 10eV

0

50

100

150

200

250

1.0E-03 1.0E-02 1.0E-01

Pressure [mbar]

Cu

rren

t [p

A]

.

Current through aperture Current on electrode Total current

Tests:


RFQ cooler/buncher design

Pressure

cooler

: ~10-

1 mbar

~10-3 m

bar He b

uffer g

asSeparate connections

for trap segments

Changeable separation electrodeswith different aperture diameters

Buffer gas: Helium for light ions (i.e. Na-21)(Heavier gas may be considered for Ra ions)

Kapton foil12.5m 120 pF

Stainless steel rods

OFHC copper

Preset frequencies:0.5MHz, 1 MHz, 1.5 MHz

RF amplitude:150 V (peak-to-peak)

UHV compatible resistors for drag voltage:Uncoated, 2.2 k


Simulations and calculation of E field

• Simulations• Real 3D geometry• Material properties • Geometry separated to smaller parts• Fine mesh and grid size• 3D electric field map (RF and DC)

RF electric potential DC drag potential

FEMLAB calculation examples:

F(x,y,z,t) = m*(dV(x,y,z,t)/dt) F(x,y,z,t) = E(x,y,z,t)*q

dV(x,y,z,t) =(E(x,y,z,t)*q/m)*dtdr(x,y,z,t) =dV(x,y,z,t)*dt


Program input:• Ion charge • Ion mass • KE • Phase space distribution• Electric field map (RF and DC)• fRF

• RF amplitude• Drag voltage step• Gas pressure• Standard ion mobility• Number of ions• Time step

Program output:• Single ion tracing• Phase space distribution• Confinement• Transmission through exit aperture

Ion tracing and distributions

0)2cos(22

2

uqad

uduu

2

t

Mathieu equation:

08

220

mr

zUau

220

4

mr

zVqu

aU

qV

qmax = 0.908

RF only (U=0)

• Ion tracing in RFQ guide• Buffer gas cooling + DC drag• Phase space distributions • Ion trapping and extraction• Confinement and transmission

Ion trajectories in vacuum

-3

-2

-1

0

1

2

3

0 25 50 75 100 125 150 175 200 225 250 275 300 325

z [mm]

x, y

[m

m]

Buffer gas cooling

-3

-2

-1

0

1

2

3

0 25 50 75 100 125 150 175 200 225 250 275 300 325

z [mm]

x, y

[m

m]

Transverse distribution after RFQ guide

-1000

-800

-600

-400

-200

0

200

400

600

800

1000

-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1

x, y [mm]V

x, V

y [m

/s]


Optimization using the simulations • Main goal: collect all ions• Confinement and transmission• Optimize parameters (regions of stable operation):

• pressure and type of gas• aperture diameters• beam settings at entrance• drag voltage step• potentials on separation electrodes • accumulation time (buncher)• trap potential depth and shape

• Questions:• phase dependence (cooler-buncher)• phase dependence (switching)• where do we loose ions (why?)

Exit RFQ guide

-2000

-1500

-1000

-500

0

500

1000

1500

2000

-0.002 -0.001 0 0.001 0.002

x, y [m]

Vx,

Vy

[m/s

] .

Velocity distribution at exit of RFQ1

0

50

100

150

200

225 1125 2025 2925 3825 4725 5625 6750

longitudinal velocities [m/s]

nu

mb

er o

f io

ns

. ~ 2 eVq=0.5p=0.025 mbardrag voltage=0.5V

Buffer gas pressureRF: 1500 kHz, 21Na+, 10 eV 950 m/s maximum transverse velocity0.5 V drag voltage step

0

10

20

30

40

50

60

70

80

90

100

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

q parameter

%

0.1 mbar 0.1 mbar 0.15 mbar 0.15 mbar 0.075 mbar

0.075 mbar 0.05 mbar 0.05 mbar 0.025 mbar 0.025 mbar

Gas pressure drag voltage


Drag voltage and pressure dependence

Drag voltage step21Na+, 10 eVPressure: 0.01 mbarRF: 1500 kHz 950 m/s maximum transverse velocity2 mm aperture

0

10

20

30

40

50

60

70

80

90

100

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

q parameter

%

0.5 V 0.5 V 0.1 V 0.1 V 0.2 V 0.2 V

0.01 mbar – too low, exit energy high

Drag voltage step21Na+, 10 eV

Pressure: 0.025 mbarRF: 1500 kHz

950 m/s maximum transverse velocity2 mm aperture

0

10

20

30

40

50

60

70

80

90

100

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

q parameter

%

0.5 V 0.5 V 0.1 V 0.1 V

0.025 mbar low pressure limit


Frequency and focus dependence

0

10

20

30

40

50

60

70

80

90

100

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

q parameter

%

1.5 MHz 1.5 MHz 1 MHz 1 MHz 0.5 MHz 0.5 MHz

Frequency21Na+, 10 eV0.1 mbar buffer gas pressure950 m/s maximum transverse velocity0.5 V drag voltage step2 mm aperture

Higher frequency is preferred

0

10

20

30

40

50

60

70

80

90

100

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

q parameter

%

950 m/s 950 m/s 1450 m/s 1450 m/s 450 m/s 450 m/s

Maximum transverse velocity21Na+, 10 eV

1500 kHz radio frequency950 m/s maximum transverse velocity

0.5 V drag voltage step2 mm aperture

Beam properties at entrance: just focus


Cool and select

Mass selectivity for 23Na+ / 21Na+

Scan line:U/V = const=0.17

220

8

mr

zUau

220

4

mr

zVqu

m>M

Mm<M

mass resolution frequency

q

a

RF and DC operation: Mass filter

0.706

0)2cos(22

2

uqad

uduu

2

t


LEBL and optimization of parameters (work in progress)

• LEBL parts:• Extraction tube • Einzel lenses• Electrostatic steerers • Quadrupole deflectors

Low energy beam line

RF

Q c

oole

r/bu

nche

rMOT

MOT

EL

EL

EL EL EL

EL

EL

EL EL

QD QD

ET

Ion catcher


Magneto-Optical Traps for 21Na decay studies (work in progress)


Collector MOT- Designed for optimal collection- Large laser beam diameter

Decay MOT- 4 recoil collection

- Multi-detector setup for -detection

Detector ports

Equipotential rings

MCP for recoils

Conclusion

• TRImP project well on track• Magnetic separator working, short-lived isotopes separated

• Work on design and building of a thermal ioniser• RFQ cooler and buncher system ready

• All parts to be tested together soon


tri p in-flight separator, ion catcher and rfq cooler/buncher e. traykov tri p project and...

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