Simulations and tests for PIPERADESimulations and tests for PIPERADE

P. Ascher, K. Blaum, M. Heck, S. Naimi

Piperade Meeting, 27th-28th May 2013, Bordeaux

SImultaneous Magnetron and resonant COnversion

- Dipolar excitation at the magnetron frequency -

- Quadrupolar excitation at (+ +- ) for the conversion of the radial modes

M. Rosenbusch et al, Int. J. M. Spec., 325-327, 51-57 (2012)

M. Kretzchmar, Int. J. M. Spec., 325-327, 30-44 (2012)

One SIMCO conversion

Allows to center the ions selectively without buffer gas -> prevents charge-exchange reactions and damping of the motion that decreases

mass resolving power

R+

R-

SIMCO excitation: Introduction

SIMCO excitation

Advantages of SIMCO

No Buffer gas

Mass independent (like BG)

Same selectivity as a quadrupole excitation (same resolution for a given time)

BUT for BG cooling a magnetron exc and a cooling time afterwards are needed!

→ SIMCO is faster (for a given time, SIMCO has a higher resolving power)

Contaminants are brought further compared to the ions of interest, the contaminants can even leave the trap (depends on the magnetron exc parameters…)

SIMCO excitation vs BG Cooling

SIMCO Exc during 60ms

Mag Exc during 4 ms + Quad Exc during 60ms + Cooling time of 100 msP=1e-4 mbar

Time (ms) Time (ms)

R+, R

- (m

m)

R (m

m)

R+, R

- (m

m)

R (m

m)

Time (ms) Time (ms)

2 ions species: 136Te, 136Sb

SIMCO excitation vs BG Cooling

SIMCO Exc during 60ms

Mag Exc during 4 ms + Quad Exc during 60ms + Cooling time of 100 msP=1e-4 mbar

Time (ms) Time (ms)

Time (ms) Time (ms)

R+, R

- (m

m)

R+, R

- (m

m)

R (m

m)

R (m

m)

SIMCO excitation

What is tricky with SIMCO…

One conversion is needed (exactly), time excitation is crucial!

Ions probe radial anharmonicities of the E/B fields during the exc (like BG)

No Buffer gas

Initial conditions crucial! (in particular radial dispersion)

this is not a cooling method, the conditions at the end will not be better than before

During the excitation, the ions probe radial anharmonicities of the trap (B field inhomogeneities)

B2=5.6 (corresponding to an homogeneity of 10 ppm over 5 mm)

B2=0.3 (corresponding to an homogeneity of 5ppm over 5 mm) -> WITCH Magnet (Oxford)

Time (ms) Time (ms)

Time (ms) Time (ms)

R (m

m)

R (m

m)

R (m

m)

R (m

m)

B2=5.6 (corresponding to an homogeneity of 10 ppm over 5 mm)

R (m

m)

R (m

m)

Time (ms) Time (ms)

SIMCO excitation

What is tricky with SIMCO…

One conversion is needed (exactly), time excitation is crucial!

Ions probe radial anharmonicities of the E/B fields during the exc (like BG)

No Buffer gas

Initial conditions crucial! (in particular radial dispersion)

this is not a cooling method, the conditions at the end will not be better than before

Inittial conditions are crucial!

Radial dispersion

But if they are all off-centered this is ok because we can change the phase…

R (m

m)

R (m

m)

R (m

m)

R0 = 1 mm R0 = 2 mm

R0 = 3 mm

Time (ms)

Time (ms) Time (ms)

SIMCO excitation: Simulations

Initial magnetron motion?

R+(t), R-(t)

mag.motion - mag.exc

= -/2 = 0

SIMCO excitation during 15 ms

R+(t), R-(t)

R+(t), R-(t)

Initial conditions Z direction

B2=0.3 (corresponding to 10 ppm over 3 cm) B2=3 (correspondingto 100 ppm over 3 cm)

z= 30 mm

R (m

m)

R (m

m)

Time (ms) Time (ms)

Increasing the number of ions… the main problem is the shielding effect

Initial conditions (x, y, z) = (0.5 mm, 0.5 mm, 15 mm)

512 ions Scaling factor of 2: ~ 1000 contaminants

2 ions of interest

Initial conditions (x, y, z) = (0.5 mm, 0.5 mm, 2 mm)

R (m

m)

R (m

m)

Time (ms) Time (ms)

Time (ms) Time (ms)

R+, R

- (m

m)

R+, R

- (m

m)

Tests at MPIK

Quadrupolar excitation

SIMCO excitation

0 100000 200000 300000 400000 500000 600000

0

100

200

300

400

500

600

700

800

Dip

ola

r si

gn

al

Nb cycles

0 100000 200000 300000 400000 500000 6000000

50

100

150

200

250

DIp

o;ar

sig

na;

NB cycles

Time (ms)

R+, R

- (m

m)

R+, R

- (m

m)

Time (ms)

Tests with MCP detection

An aperture was installed after the trap in order to see a count-rate resonance, but it was not possible to shoot through the aperture

-> Initial magnetron motion too high….

A phosphore screen detector was installed

-> Beam not aligned

What is crucial to improve: the tilted magnetic field and the injection in the trap:

Magnetic field:

An engineer from BRUKER will come in the next weeks to shim again the magnet

Injection: the RFQ is designed and built, still electronics has to be developed…

SIMION simulations of the RFQ in progress

Tests @ MPIK

SIMCO tests in the preparation trap:

- We need to use the RFQ to have good conditions

- No vacuum possible if we use the RFQ

FIrst tests of SIMCO will be done in the measurement trap:

No aperture after the second trap but position-sensitive detector (even better!)

First of all is to look at the beam spot position depending on the excitation time

and at the same time the TOF as a function of the exc time

The method will be investigated up to 100 ions (very high number of ions for SHIPTRAP)

Tests @ SHIPTRAP/GSI