Radio Frequency Electronics Group

About Radio Frequency Electronics Group

The Radio Frequency Electronics (RF) Group of IUAC is an Accelerator Support Group, which is responsible for the development, operation, and maintenance of various RF systems that are essential for the particle accelerators. The group plays a vital role in operating the Beam Pulsing System of the Pelletron accelerator during the pulsed beam runs. In addition, the RF Group is actively engaged in the design and development of new RF instrumentation and system upgrades to meet evolving research requirements and enhancing the manpower capbilities. These contributions are critical for sustaining reliable accelerator operations and enabling advanced experiments for the user community. The RF Group also manages a wide range of high-power RF amplifiers, microwave sources, and RF control electronics used across IUAC’s major accelerator facilities, including the Pelletron, High Current Injector (HCI), Superconducting Linac (SC-LINAC), Free Electron Laser (Delhi Light Source), and the Low Energy Ion Beam accelerator. The group is involved in the design, development, operation, repair, and periodic preventive maintenance of these systems to maximize uptime, improve performance, and enhance in-house technological development at IUAC. The RF power sources under its care cover a broad frequency range (4 MHz to 17.9 GHz) and power levels ranging from a few hundred watts to several tens of megawatts, incorporating both air-cooled and water-cooled amplifier types. In addition to technical responsibilities, the group also contributes to human resource development by training newly joined scientist trainees, apprentice trainees, and other technical staff, thereby strengthening the skilled manpower base at IUAC.Read more

The primary activities include-

• Maintenance and Operation of Pelletron Beam Pulsing System
• Maintenance of RF Amplifiers installed at various facilities at IUAC
• Maintenance of LLRF electronics installed at various facilities at IUAC
• Development of high-power RF amplifiers and low-power control electronics
• Development of Nuclear Instrumentation modules

RF Amplifiers

At the Inter-University Accelerator Centre (IUAC), RF amplifiers play a crucial role in driving the accelerating structures (RF cavities) by providing the required radio-frequency power for generation of RF fields to effect the beam acceleration. These amplifiers are especially designed to deliver high power at precise frequencies, ensuring efficient acceleration of charged particle beams in both linear accelerators and superconducting LINAC modules. The amplifiers are integrated with control and monitoring systems that maintain amplitude and phase stability, which are essential for minimizing beam energy spread and losses. Over the years, IUAC has developed expertise in designing, testing, and operating RF amplifiers ranging from low-power solid-state units used for diagnostics to high-power vacuum tube–based amplifiers required for the main accelerating cavities. Continuous upgradation and rigorous testing of these amplifiers help in improving reliability, efficiency, and compatibility with evolving accelerator technologies, thereby supporting a wide range of nuclear physics experiments and user programs. The installed capacity of RF amplifiers and RF sources at IUAC range from 4 MHz to 17.9 GHz with RF power ranging from tens of hundreds of Watts in Pelletron to hundreds of Watts in SC-LINAC to tens of hundreds of kilowatts in HCI to megawatts in FEL. Below is a combined picture of installed amplifiers in various beamlines. Details of each facility is given in the following sections.Read more

120 W, broadband Solid State RF Power Amplifier

A broadband solid state RF power amplifier is capable of delivering 120 Watts of power (CW) in frequency range of 10MHz – 50MHz (+/-1.5 dB) has been successfully developed with state of the art RF components for general purpose application. It is being used with Multi Harmonic Buncher (MHB) of Pelletron Accelerator at IUAC. The amplifier gain is built across three stage cascaded pre-amplifier, driver and power amplifier sections. Its subsystems are RF switch, a compact SMPS unit, control board and a directional coupler. The CATV block QBH-2832 is used as a pre-amplifier, RF MOSFETs MRF151 and MRF151G are used as driver and power amplifier respectively. The RF MOSFETs are operated at 36V dc with gate biasing of 5V regulated by LM723, a versatile regulator chip. Amplifier control circuit is operated at +24Vdc. The power devices are mounted on copper heat spreader and in turn mounted on water cooled aluminium heat sink for high thermal stability and reliability. The power monitoring is possible with directional coupler and front panel power meter. The amplifier is enclosed in a 3U - 19” rack mountable standard aluminium cabinet.Read more

Specifications

RF Amplifiers of Superconducting Linac (SC-LINAC)

The superconducting Linear Accelerator (SC-LINAC) acts as the energy booster for the tandem Pelletron accelerator and in future for HCI as well. The LINAC beam line consists of a total of 27 quarter-wave resonators (QWR) which are Niobium based superconducting RF cavities. These QWRs are house in 5 different cryostats. Each cavity requires a 400 W RF high power RF amplifier operating at 97 MHz. Initially, some of these VHF amplifiers were made in collaboration with Bharat Electronics Limited while rest of the amplifiers were indigenously developed at IUAC. Below is the field deployment of various RF amplifiers in the LINAC beamline.Read more

400W, 97MHz Solid State VHF RF Power Amplifier

A 400W, 97MHz (CW) solid-state RF power amplifier has been developed to power the Superconducting LINAC cavities. The amplifier gain is built across three stage cascaded pre-amplifier, driver and power amplifier sections. Its subsystems are RF switch, a compact SMPS unit, control board and a directional coupler. The BGA6589 MMIC is used as a pre-amplifier, LDMOS BLF571 and MRE6VP61K25H are used as driver and power amplifier respectively. The amplifier includes various crucial protections against high VSWR, over temperature and input over drive. The amplifier is also provided with digital control and display for various parameters and RS232 interface for remote control and monitoring. All power modules are thermally managed using a water-cooled aluminium heat sink. The amplifier is housed in a 2U, 19-inch rack-mountable aluminium enclosure.Read more

Specifications

RF Amplifiers for High Current Injector (HCI)

The high power RF infrastructure installed at the High Current Injector of IUAC consists of various RF cavities used for ion beam bunching and acceleration. Starting from the HTS-ECR based ion source which is excited by a klystron based microwave generator (1.7kW, 18GHz) which is operating in Ku-band of microwave regime or alternatively through a TWT amplifier operating in the same frequency regime, the ion beam can be bunched using a Multi-Harmonic Buncher(MHB) structure similar to IUAC Pelletron accelerator. A 100 W (10MHz -50MHz) broadband solid state-RF power amplifier is developed indigenously and deployed to enable the bunching mechanism. It is followed by a Radio Frequency Quadrupole cavity which fed by a tetrode based (Y567B) 120 kW, high power RF amplifier operating at 48.5 MHz. This amplifier is a commercial one of the M/s QEI-RF Inc., USA make. The RFQ is followed by a Spiral Buncher(SB) cavity which is fed with an indigenously developed 3kW, 48.5 MHz RF power amplifier. Ion beam from the spiral buncher enters a series of Drift Tube LINACs marked as DTL #1 to DTL #6 which are all 97 MHz RF cavities responsible for increasing the beam energy. All the DTL cavities are powered by commercial high power RF amplifiers which are either M/s DB Science, Italy make or M/s QEI-RF Inc., USA make. DTL #1 amplifier is rated for 6kW RF power, DTL #2 and 3 amplifiers are rated for 20 kW RF power each, DTL #4 and 5 amplifiers are rated for 28 kW amplifier RF power each and DTL #6 amplifier is rated for 30 kW RF power. All the amplifiers from DTL #1 to DTL #5, are solid-state amplifiers whereas the DTL #6 is a triode based amplifier. After DTLs, two more sets of spiral bunchers are available marked as SB #2 and 3 which are provide by a similar indigenously developed 3kW, 48.5 MHz solid- state RF power amplifiers. Below is the picture of installed high-power RF infrastructure in the main HCI beamline. In addition to the RF amplifiers, the group also work in close collaboration with the water systems group to ensure the correct flow rate of Low Conductivity Water which is of utmost importance for the smooth operation of various tube based amplifiers.Read more

High Power RF System for Free Electron Laser (FEL-DLS)

The high-power RF system of FEL facility is entirely different from all the existing facilities at IUAC. It mainly consists of a Toshiba make S-band (2860 MHz), 25 MW Klystron as an RF power amplifier. The mode of operation is pulsed with a very low duty cycle of ~0.004% (maximum 4 microsecond pulse ON time at a maximum 50 Hz repetition rate). So, the pulsed low power RF signal generated by the LLRF is first amplified upto 230 W using a solid-state, pulsed 700 W RF driver power amplifier of make M/s Microwave Amps. Ltd. The high RF power is fed to the klystron input cavity whose cathode is operated at 251 kW, 255 A pulsed DC generated by a state-of-the-art solid-state high-power klystron modulator of make M/s Scandinova Systems A.B. Output of the klystron is fed to a 2.6 cell, normal conducting RF photocathode gun cavity fabricated in collaboration with KEK Japan through an in-vacuum, WR284 based rectangular waveguide RF delivery system. Various waveguide components like E-bend, H-bend, Directional Couplers, RF windows etc. have been installed. Ion pumps of make M/s Gamma Vacuum provide a very high vacuum of the range 1x10-9 mbar. To protect the klystron with huge reflections coming from the load (cavity), an SF6 based 4-port circulator based RF Isolator has also been installed. Entire RF system is protected by a rugged Beckhoff PLC based fast interlock mechanism. The RF group is responsible and trained to maintain, and resolve all the problems that occur with RF Driver Amplifier, High Voltage Charging Capacitor Power Supplies, High Voltage IGBT Switches and other interlock units. Apart from the preventive maintenances (twice per year), RF group also undertakes monthly periodic maintenance of the RF high-power system and the chiller units installed at the facility. Below is the figure of high-power RF system of FEL.Read more

Low-Level Radio Frequency (LLRF) Controls

Low-Level RF (LLRF) control systems at IUAC are essential for the stable and precise operation of its accelerator facilities. These systems regulate the amplitude and phase of RF fields in the resonating structures of the Pelletron beam pulsing system,Superconducting Linear Accelerators (SC-LINAC), High Current Injector (HCI), and the Free Electron Laser (FEL-DLS).

LLRF Controls of High Current Injector (HCI)

The HCI employs fully in-house developed LLRF controls, demonstrating IUAC’s indigenous expertise. These LLRF systems operate on the Generator Driven principle wherein the cavity is made to follow the frequency of the external master oscillator signal. All the deployed systems in HCI are built using analog RF electronics that offer fast response times and operational flexibility. Various interlocks and protection mechanisms are integrated to safeguard the RF amplifiers and cavities from arcing, quenching, or excessive reflected power. With these controls, the HCI can deliver long-duration stable beams for user experiments, significantly enhancing accelerator performance and reliability with minimum downtime. In the initial phase, prototypes of the basic modules—namely amplitude and phase control systems and frequency tuner controls—were developed jointly by the BTS and LLRF groups. Subsequently, the RF group developed the remaining control modules required for the entire HCI facility, adding several features to enable complete remote operation. LLRF controls for the Multi-Harmonic Buncher (MHB), Radio Frequency Quadrupole (RFQ), three Spiral Bunchers, and six Drift Tube Linac (DTL) cavities have been installed and are operational. The frequency of operation is 12.125 MHz along with its two higher harmonics for the MHB, 48.5 MHz for the RFQ and Spiral Bunchers, and 97 MHz for the DTL cavities.Read more

The HCI LLRF Controls include-

• Amplitude and Phase Controllers
• Frequency Tuner Controllers
• MHB Controller
• Master Clock Distribution Module
• LLRF-VME Interface modules
• RF Multiplexer based Parameters Monitor modules