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FT-ICR Detection System for KATRIN

Motivation and Experimental Set-up

The FT-ICR Penning Trap Detection System (a prototype of a cylindrical three-electrode Penning Trap) in Heidelberg is being developed for KATRIN external Link [1-3]. The KATRIN experiment has been designed to measure the mass of the electron antineutrino directly with a sensitivity of 0.2 eV, one order of magnitude better than the present upper limit. The intended sensitivity will be obtained by analyzing the end-point of the β spectrum from the decay of tritium gas molecules T2 → (3HeT)+ + e- + νe  .

The KATRIN set up [1-4] comprises a gaseous tritium source, a transport section external Link pre-spectrometer, the main spectrometer and the detector. In the main spectrometer the electrons from the decay are guided by a strong magnetic field and analyzed using electrostatic fields. The tritium gas is removed from the system by differential pumping and cryogenic trapping. The formation of ion clusters (T2n+1)+ which decay with different end-points than T2, will prevent unambiguous analysis of the end-point of the tritium decay. Therefore, the knowledge of the concentrations of these ions is essential to evaluate the β spectrum.

FT-ICR detection system at the MPIK in Heidelberg
Figure 1: FT-ICR detection system at the MPIK in Heidelberg - click for bigger version

The best way for a precise determination of these concentrations is the use of Penning traps with FT-ICR detection systems. Actual photos of the set up in MPIK-Heidelberg and the FT-ICR Penning Trap are shown in Figure 1 and 2, respectively. More details can be found in Ref. [4]. These Penning Trap systems will be located in the transport section (see also Fig. 1 of Ref. [4]).

FT-ICR Penning trap
Figure 2: FT-ICR Penning trap - click for bigger version

 

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Recent Results

There are three main results so far [4]. One of them is that the amplitude of the FT-ICR signal was recorded for corresponding νexc frequency for different species. The amplitude of the FT-ICR signal versus excitation frequencies are shown for the He+, H2O+ ions in Fig. 3. The other result is that the FT-ICR signal at νrf = ν+ was recorded for different potentials applied to the end-cap electrodes. Applying a linear fit to the data (see Fig. 5 of Ref.[4] and using the mass value of the interested ion, the magnetic field was obtained. This measurement was done for the He+ and H2O+ ions. The last recent result is that the Penning Trap was dedicated to determine the minimum number of the ions needed to observe an FT-ICR signal at room temperature. For further details, see Ref. [4]. All the measurements were performed at room temperature and all the species (He+, N2+, and H2O+) were identified by exciting the ion motion at their modified cyclotron frequency.

Amplitude of the FT-ICR signal versus excitation frequency
Figure 3: ν+ is the modified cyclotron frequency. Amplitude of the FT-ICR signal versus excitation frequency (νexc) for He+ ions (Top), and for H2O+ ions (Bottom) (Based on Ref.[4])

 

References

4.   A broad-band FT-ICR Penning trap system for KATRIN
M.Ubieto-Díaz, D. Rodríguez, S. Lukic, Sz. Nagy, S. Stahl, K. Blaum
Int. J. Mass Spectrom. 288, 1-5 (2009) external Link
3.   Neutrino mass limit from tritium β decay
E.W. Otten and C. Weinheimer
Rep. Prog. Phys. 71, 086201 (2008) external Link
2.   The Q-value of tritium β-decay and the neutrino mass
E.W. Otten, J. Bonn and Ch. Weinheimer
Int. J. Mass Spectrom. 251, 173-178 (2006) external Link
1.   KATRIN Design Report 2004
Report by the KATRIN Collaboration (pdf, 8.97 MB) external Link
FZKA7090 (pdf, 9.33 MB) external Link
NPI ASCR Rez EXP-01/2005
MS-KP-0501