S. Dechoudhury

Observation of room temperature ferromagnetism in Mn–Fe doped ZnO

A room temperature ferromagnetic Fe doped ZnO bulk sample has been synthesized by co-doping 2 at% Mn with 2 at% Fe in ZnO. The final firing temperature for the preparation of the Zn0.96Mn0.02Fe0.02O sample is the same as the final firing temperature for the preparation of the Zn0.98Mn0.02O sample and in this case it is found to be 490 °C. It has been found that room temperature ferromagnetism in Zn0.96Mn0.02Fe0.02O is a factor of 1.6 times more than that observed in Zn0.98Mn0.02O samples. The size of the saturation magnetic field for the Zn0.96Mn0.02Fe0.02O sample is, however, only a factor of 7 times more than that observed for nanocrystalline undoped ZnO.

33.7 MHz heavy-ion radio frequency quadrupole linac at VECC Kolkata

A 33.7 MHz heavy-ion radio frequency quadrupole (RFQ) linear accelerator has been designed, built, and tested. It is a four-rod-type RFQ designed for acceleration of 1.38 keVu, qA> or =116 ions to about 29 keVu. Transmission efficiencies of about 85% and 80% have been measured for the unanalyzed and analyzed beams, respectively, of oxygen ((16)O(2+), (16)O(3+), (16)O(4+)), nitrogen ((14)N(3+), (14)N(4+)), and argon ((40)Ar(4+)). The system design and measurements along with results of beam acceleration test will be presented.

Design and development of a radio frequency quadrupole linac postaccelerator for the Variable Energy Cyclotron Center rare ion beam project

A four-rod type heavy-ion radio frequency quadrupole (RFQ) linac has been designed, constructed, and tested for the rare ion beam (RIB) facility project at VECC. Designed for cw operation, this RFQ is the first postaccelerator in the RIB beam line. It will accelerate A/q < or = 14 heavy ions coming from the ion source to the energy of around 100 keV/u for subsequent acceleration in a number of Interdigital H-Linac. Operating at a resonance frequency of 37.83 MHz, maximum intervane voltage of around 54 kV will be needed to achieve the final energy over a vane length of 3.12 m for a power loss of 35 kW. In the first beam tests, transmission efficiency of about 90% was measured at the QQ focus after the RFQ for O(5+) beam. In this article the design of the RFQ including the effect of vane modulation on the rf characteristics and results of beam tests will be presented.

A gas-jet transport and catcher technique for on-line production of radioactive ion beams using an electron cyclotron resonance ion-source

Radioactive ion beams (RIB) have been produced on-line, using a gas-jet recoil transport coupled Electron Cyclotron Resonance (ECR) ion-source at the VECC-RIB facility. Radioactive atoms∕molecules carried through the gas-jet were stopped in a catcher placed inside the ECR plasma chamber. A skimmer has been used to remove bulk of the carrier gas at the ECR entrance. The diffusion of atoms∕molecules through the catcher has been verified off-line using stable isotopes and on-line through transmission of radioactive reaction products. Beams of (14)O (71 s), (42)K (12.4 h), (43)K (22.2 h), and (41)Ar (1.8 h) have been produced by bombarding nitrogen and argon gas targets with proton and alpha particle beams from the K130 cyclotron at VECC. Typical measured intensity of RIB at the separator focal plane is found to be a few times 10(3) particles per second (pps). About 3.2 × 10(3) pps of 1.4 MeV (14)O RIB has been measured after acceleration through a radiofrequency quadrupole linac. The details of the gas-jet coupled ECR ion-source and RIB production experiments are presented along with the plans for the future.

Design and development of deflector cavity for the non- interceptive bunch length measurement system

A non-interceptive bunch length detector system for the measurement of bunch width of accelerated beam has been designed and developed. This detector system is based on emitted secondary electrons produced by a primary ion beam hitting a thin tungsten wire placed in the beam path.The measurement of the longitudinal beam shape for wide range of beam energy, intensity as well as ion species is possible with this detector. One of the main components of the detector system is a RF deflector cavity used to deflect electrons in correlation with rf phase of the accelerator. The detailed design, development with measurement results of the deflector cavity resonator have been reported in this paper.

Physics design of rod type proton Radio Frequency Quadrupole linac

A Radio Frequency Quadrupole (RFQ) linac delivering 800 keV, 5 mA protons has been designed. It is envisaged as first injector of the proton driver that will be used for production of proton-rich radioactive beams in the proposed ANURIB facility. The option of rod-type structure at frequency of 80 MHz has been chosen owing to ease of mechanical fabrications and to avoid detrimental nearby dipole modes present in vane type structure. Optimization of parameters has been carried out for a viable length and power of RFQ in order to avoid any infrastructural complexity. Conventional method of keeping focusing factor and vane voltage constant along the length of RFQ has been adopted. Results of detailed beam dynamics and RF structure design, space charge induced effects and corroborative particle tracking with realistic 3D fields of modulated vane has been presented.

Longitudinal bunch length measurement of RFQ beam using in-house developed detector system

We report here the bunch width measurement of 98keV/u ion beam accelerated through a 3.4 m long 37.8 MHz Radio Frequency Quadruple (RFQ) linac using a minimally interceptive approach. The detector system for this measurement has been indigenously developed and is based on secondary electron emission from tungsten filament on being hit by ion beam, followed by a capacitive loaded helical resonator cavity. A Channeltron Electron Multiplier (CEM) detector is used for detection of electrons. The design, development and optimization of various parameters of bunch width detector system along with its deflector cavity applicable in the low frequency regime (few tens of MHz) have been discussed. The measured bunch profile of accelerated Nitrogen beam from RFQ is in close agreement with the estimated profile obtained via simulation.

Coupler induced transverse kick and emittance growth in single cell elliptical cavities of 10 MeV superconducting electron linac injector

A Capture Cryo Module (CCM) consisting of two single cell 1.3 GHz, β = 1, niobium cavities is being developed for the superconducting electron linac injector at VECC. Electron beam of 100 keV and 2 mA from a thermionic gun will be accelerated in the CCM and thereafter in an Injector Cryo Module (ICM) to 10 MeV. Single cell cavities in the CCM are independently phased and a coaxial TTF-III coupler is chosen for rf power coupling into each cavity. The presence of the coupler perturbs the field symmetry of the cavity introducing local transverse kicks to the incoming electron beam in the coupler region. Numerical analysis taking into account the changing velocity profile as well as the off-axis field seen by the electron as it moves through the cavities has been carried out for estimating the kick. The variation of the kick with longitudinal position of electrons in the beam bunch introduces transverse emittance growth. This has been calculated using the field seen by the electron. The analytical calculations are compared with results from particle tracking with simulated 3D fields. It is found that coupler induced kick does not appreciably change the emittance values at 10 MeV.

Multiple charge beam dynamics in alternate phase focusing structure

Asymmetrical Alternate Phase (A-APF) focusing realized in a sequence of 36 Superconducting Quarter Wave Resonators has been shown to accelerate almost 81 % of input Uranium beam before foil stripper to an energy of 6.2 MeV/u from 1.3 MeV/u. Ten charge states from 34+ to 43+ could be simultaneously accelerated with the phase of resonators tuned for 34+. A-APF structure showed unique nature of large potential bucket for charge states higher than that of tuned one. Steering inherent to QWRs can be mitigated by selecting appropriate phase variation of the APF periods and optimization of solenoid field strengths placed in each of the periods. This mitigation facilitates multiple charge state acceleration scheme