Study of Associative Detachment Using RF Ion

Trap with Electron Spectrometer

�. Rou£ka1, P. Jusko1, A. Podolník1, T. Kotrík1, R. Pla²il1,J. Glosík1, D. Gerlich1,2

1Mathematics and Physics Faculty, Charles University in Prague - Czech Republic2Faculty of Natural Sciences, Chemnitz University of Technology - Germany

3rd ITS LEIF Winter School, Pralognan, France,10th March 2010

Outline

I The associative detachment of H−

I Research plans 22PT vs ES-MPT

I MAC-E �lter

I Detection, balance of particles

I Planned tests

The Associative Detachment of H−

H− + H→ H2(v , j) + e−(E ) + 3.5 eV

I Energy of detached electron is related to quantum state of H2

I Di�erent theories give di�erent rate constants

I Measurement of electron energy distribution can giveinformation on reaction dynamics and verify theory

Electron energy distribution and rotational state

of a H2 produced in AD [�íºek et al, J Phys B, 1998]

Cosmological importance of AD

I Mechanisms of H2

production:1 H + e− → H− + γ

H− + H→ H2 + e−

2 H + H+ → H+2

+ γH + H+

2→ H2 + H+

[Glover et al, Ap J, 2006]

I The �rst one is dominant except for high red shifts

I H2 - important coolant during protogalaxy formation

I Rate constant uncertainity ⇒ model parameters ofprotogalaxies di�er by orders of magnitude

Research plans

Investigations is split in two parts

I Temperature

dependence of rate

constant

I H− ions captured in22-pole trap

I Interaction with H beam

I T > 10 K

I Energy distribution of

produced electrons

I ES-MPT apparatus

I Information on quantum state ofH2 and reaction dynamics

I 8-pole trap, electronspectrometer

ES-MPT apparatus

Electron Spectrometer - Multipole Trap

RF storage ion source

Quadrupole - guidingand mass selection

Octopole ionguide

Magnetic collimator

Electrostatic filter

MCP detector

Atomic hydrogen source

Compact8-pole trap

Artist's impression of ES-MPT

Magnetic adiabatic collimation, MAC-E �lter

I Adiabatic invariant in mag.�eld µ = E⊥/B = const.

I E⊥ transforms to E‖ indecreasing B

I Resolution

∆E

E=

B2

B1

0

0.2

0.4

0.6

0.8

1

0 0.5 1 1.5 2 2.5 3 3.5 4

sign

ál[a.u.]

brzdné nap¥tí [V]

B1/B2 = 10B1/B2 = 1

I Requested resolution∆E : E ≈ 1 : 30

I Integral spectrum - up to 100 %e�ciency

Design of electron spectrometer - MAC-E �lterMain coils Focusing coil

MCP detectorFerromagnetic shielding

I Magnetic �eld in trap

generated by "Helmholtz" coils

I Field in collimator is weakened

by ferromagnetic shielding

I Ferromagnetic material

enhances the �eld homogenity

in the trap

velocity vector transformation

0

10

20

30

B [m

T]

axial field

Bmin

Bmax

0.0 0.1 0.2 0.3 0.4z [m]

0.00.20.40.60.81.0

U [V

]

potential barrier

Interaction of RF trap with magnetic �eld

10-6 10-5 10-4 10-3

pressure [torr]

10-3

10-2

10-1

100

101

conf

inem

ent t

ime

[s]

B=30mTB=0mT

I F × B drifting in magnetic�eld

I Lifetimes una�ected bymagnetic �eld

I ∼ 40 collisions beforeleaving trap

Construction of electron spectrometer

I Con�guration of coils,electrodes, and vacuumchambers of MAC-E �lterhas been designed

I Spectrometer is compatiblewith available parts

I Parts are being produced inVakuum Praha

Most of the parts arrived from workshop last friday

Thanks for your attention