A new RFQ cooler: concept, simulations and status

Trapped Radioactive Isotopes: icro-laboratories for Fundamental Physics

E. Traykov

• TRIP project and facility• Our concept• Prototype tests• Our design• Simulations• Conclusion

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

Krakow, 3-6 June 2004

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 (gas-cell or thermal ioniser)

Low energy beam line

RFQ cooler/buncher MOT

MOT

D

D

DD

Q

QQ

Q Q

QQ

Q

Magnetic separator

Production target

Trapped Radioactive Isotopes: icro-laboratories for Fundamental Physics

Wedge

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

Trapped Radioactive Isotopes: icro-laboratories for Fundamental Physics

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:

Trapped Radioactive Isotopes: icro-laboratories for Fundamental Physics

Our 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

Trapped Radioactive Isotopes: icro-laboratories for Fundamental Physics

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:

Trapped Radioactive Isotopes: icro-laboratories for Fundamental Physics

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

Trapped Radioactive Isotopes: icro-laboratories for Fundamental Physics

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

Trapped Radioactive Isotopes: icro-laboratories for Fundamental Physics

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

Trapped Radioactive Isotopes: icro-laboratories for Fundamental Physics

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

Trapped Radioactive Isotopes: icro-laboratories for Fundamental Physics

Cool and select (work in progress)

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

Trapped Radioactive Isotopes: icro-laboratories for Fundamental Physics

LEBL and optimization of parameters (work in progress)

Trapped Radioactive Isotopes: icro-laboratories for Fundamental Physics

• LEBL simulations:• 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

Conclusion

• Novel RF coupling and DC resistor chain tested on prototype RFQ• Results from simulations in good agreement with experiment

• Mechanical, electrical and vacuum design completed• RFQ cooler and buncher system ready soon

• Continue with simulations (LEBL)

Trapped Radioactive Isotopes: icro-laboratories for Fundamental Physics