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Variable Energy Cyclotron Centre, Kolkata

Penning Trap Developement

Penning trap is a device to store charged ions and sub-atomic particles. In a homogeneous magnetic field, a charged particle would undergo circular motion and be radially confined, but it would not be axially confined. It can be shown that a charged particle can be trapped both radially and axially by putting it in a strong homogeneous magnetic field and weak inhomogeneous (electrostatic potential being quadratic with the axial and radial distances from the center) electrostatic field. Under the action of such magnetic and electric fields, a charged particle undergoes a complicated motion comprising axial oscillation, cyclotron motion and magnetron motion. The frequencies of the axial and cyclotron motions depend on the mass of the charged particle. Since it is possible to measure frequencies very accurately, one can measure the mass of the trapped charged particle very accurately by undertaking precision measurements of its axial and cyclotron frequencies. Usually Penning traps are used for high precision mass measurements of the charged particles. However Penning traps are also used for many other purposes such as quantum computation, neutrino-electron angular correlation studies in beta decay etc.

 

 At VECC, we are building a cryogenic Penning trap facility where the trap would be at liquid helium (4 K) temperature and plan to put in radioactive ions in it. In addition to mass measurements, our emphasis would be to measure the kinetic energies of the recoiled nuclei from the beta decay and electron capture processes. In this way, we plan to measure Q-values of the beta decay processes with high precision using our Penning trap system. Such high precision Q-value measurements of beta decay processes are required for various tests of Standard model (such as the unitarity of CKM matrix elements). Very high precision measurements of the end-point of the recoil nuclei from the beta decay processes might also provide us a new method to directly measure the mass of an electron neutrino.

 

 

 

 

Photograph of the proto-type cryogenic Penning ion trap developed at VECC.