Cyclotron:The cyclotron is a cyclic charged particle accelerator. The concept of cyclotron was originated by E.O. Lawrence in 1929. In a cyclotron, alternating electric field (voltage) is applied between two "Dee" shaped hollow electrode (that is when one electrode is positive then the other one is negative) which provides acceleration to the positively charged particles. Dee shaped hollow electrodes are placed between north and south poles of an electro-magnet. The magnetic field helps to bend the charged particles path in circular orbit. The charged particles are produced in an ion source located in the centre of the cyclotron. During acceleration, the pressure in the accelerating chamber is maintained around 2 x 10-6 torr (1 torr = 1mm of Hg)..

The time taken by the particles or particle revolution frequency, inside the hollow electrode to complete one semicircular path (which is governed by the magnetic field) is made equal to the reversal of the alternating voltage applied in the hollow electrodes. So every time particles reaching the Dee edge will find favorable electrode polarity for acceleration. .

Cyclotrons at VECC: At present, there are two cyclotrons in VECC for accelerating light and light heavy ions. One of them is called as room temperature cyclotron and the other one is superconducting cyclotron. Typical energy of the accelerated particles from room temperature cyclotron is 80 MeV alpha and 20 MeV proton. The design energy of charged particles from superconducting cyclotron is much higher compared to room temperature cyclotron.

K130 Room Temperature Cyclotron:

The variable energy cyclotron (also known as K-130 cyclotron), first of its kind in India, became operational in June 16, 1977. The cyclotron can deliver high energy light ion beams (alpha, proton, and deuteron) and high charge state light heavy ion beams (Nitrogen, Oxygen, Neon and Argon) for performing experiments to various institutions from all over the country. The machine is designed to accelerate protons from 6 to 60 MeV, deuterons from 12 to 65 MeV and alpha from 25 to 130 MeV.

The K-130 cyclotron has been operating round-the-clock and delivering light ion beams (proton, alpha etc.) for experimental use in four beam lines. Low energy alpha beams (1.0 MeV to 7.2 MeV) which are likely to address the requirements of nuclear physicists have been developed.

Ions Energy
Extracted beam
current (µA)
Beam current (µA) delivered
on target as per demand
Alpha 30 - 65 10.0 µA 3.0 µA
Proton 7.5 - 18 25.0 µA 25.0 µA

Beam Quality:
Energy Resolution: The beam has energy spread (∆E/E) 0.5% (FWHM). The energy spread after the analyzing magnet is 0.025% (FWHM).

Time structure: The beam from the cyclotron consists of short pulses of small duration (1 to 10 ns) at the interval of (50 to 200 ns).

Emittance: The radial and axial emittance of the external beam is of the order of 50 and 70 mm-mrad respectively.

K500 Superconducting Cyclotron:

The superconducting cyclotron at Variable Energy Cyclotron Centre, Kolkata, is the first compact superconducting cyclotron in Asia. A large superconducting solenoid is used to energize the poles of the cyclotron magnet and it is self shielded by an annular yoke. The magnet can produce maximum magnetic field of 5 Tesla. The technical challenges of using superconducting coil in cyclotron have been aggravated by the characteristic compactness the cyclotron. This 100 Ton machine, a cylindrical structure of 3 meter diameter and 2.2 meter height, can produce a maximum energy of 80 MeV/A for lighter ions and 5-10 MeV/A for heavier ions covering the whole range of the periodic table.

The extraction system consists of two active electrostatic deflectors and eight passive magnetic channels installed around the periphery of the cyclotron poles covering a full turn. At the extraction radius the high energy beam is pulled out of its circulating trajectory by the electrostatic deflectors and then it is guided by the magnetic channels almost 330 degrees till it comes out of the machine. Then the extracted beam is transported to the experimental hall by a 13 m long beam line. Threading of the high energy beam through the deflectors and magnetic channels imposed a long list of technical challenges.

Two ECR ion sources of frequency 14.4 GHz will provide low energy beam for the cyclotron. Horizontal beam transport lines from each of the sources merge to a common horizontal beam line. Then a 90° bending magnet bends the beam in the vertical beam transport line for axial injection in to the cyclotron. An electrostatic spiral inflector is used to feed the beam in to the acceleration plane at the cyclotron central region.