H. K. Pandey

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.

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.

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.

Analysis and measurement of high power vacuum-tube RF transmitters: Matrix method

High power radio frequency transmitters have been developed for the heavy ion linear accelerator of RIB project at VECC Kolkata. It works at 40 kW CW power in the frequency range of 32–39 MHz. The new approach of analysis and design of this transmitter has been carried out using ABCD matrix. It uses a linear small-signal AC model with input, output and inter stage matching circuits for Tetrode tube amplifier cascaded with Triode tube based diver amplifier. The analytical as well as measured S-parameter results are presented in this paper.

Analysis of a high power grounded grid triode amplifier

A high power amplifier has been developed for the RIB program, where in a typical 1 kW triode based amplifier drives a high power 40 kW (CW) radio frequency amplifier for the frequency range of 32 MHz to 39 MHz. This driver amplifier has been realized in grounded grid configuration. The analysis of this amplifier has been carried out using ABCD parameters method. It uses a linear small-signal AC model of the triode with its matching circuits. The analytical as well as measured result is presented for this vacuum tube triode amplifier.

RF coupler and frequency tuning system design for RFQ cavity of VEC-RIB

Variable energy cyclotron centre (VECC) is presently developing an isotope separator on-line (ISOL) postaccelerator type of radioactive ion beam (RIB) facility. A 33.7 MHz, 1.7 meter long heavy-ion radio frequency quadrupole (RFQ) linear accelerator has recently been commissioned. The design of loop coupler for RF power feeding and also of a tuner for fine frequency tuning of this RFQ cavity are presented.

Design and Implementation of Multi-Hormonics RF Wave Generator using Lumped-Element Components

Triangular and Sawtooth wave generation at RF frequency is one of the important tasks for the design of buncher circuit in particle accelerators to increase the bunching efficiency. On the basis of Fourier series method different non-sinusoidal signals like triangular, sawtooth etc. are generated with combination of harmonics of sinusoidal signal with different amplitude and phase. These multi harmonic non-sinusoidal waves can be generated using passive RF components like phase-shifter, hybrid-coupler, power combiner/divider etc. This paper deals with lumped element approach for design and implementation of line phase shifters, 3-dB hybrid coupler and power divider/combiner, which have been used for the generation of triangular and saw tooth wave forms at 25 MHz. The ABCD (transfer) matrix formulation is used for the analytical prediction of the performance of these components. Experiments have been carried out to validate the analytical results.