Jignesh Soni

Two RF Driver-Based Negative Ion Source Experiment

Multidriver-based radio-frequency (RF) ion sources have emerged as the most promising option for producing the plasma in large ion sources required for fusion applications. In India, under domestic long-term fusion program, a negative ion source development program has been initiated. A 100-kW inductively coupled single RF driver-based negative ion source (ROBIN) has been installed and it is operational at the Institute for Plasma Research. The next step is to move to a multidriver source and address to several issues related to configuration and operation. A two-driver-based twin source has been configured for this purpose. The experimental plan is divided into two phases: 1) plasma operation phase and beam extraction and 2) acceleration phase. A vacuum chamber has been specially designed to accommodate these phases of operations. The data acquisition and control system (DACS) of the experimental system is designed based on International Thermonuclear Experimental Reactor-COntrol Data Access and Communication (ITER-CODAC) guidelines. Probe and spectroscopy diagnostics constitute the principal diagnostics. This paper presents the experimental system with emphasis on the aspects of mechanical, electrical, and DACS integration.

Power supply system for negative ion source at IPR

The first step in the Indian program on negative ion beams is the setting up of Negative ion Experimental Assembly – RF based, where 100 kW of RF power shall be coupled to a plasma source producing plasma of density ~5 × 1012 cm-3, from which ~ 10 A of negative ion beam shall be produced and accelerated to 35 kV, through an electrostatic ion accelerator. The experimental system is modelled similar to the RF based negative ion source, BATMAN presently operating at IPP, Garching, Germany. The mechanical system for Negative Ion Source Assembly is close to the IPP source, remaining systems are designed and procured principally from indigenous sources, keeping the IPP configuration as a base line. High voltage (HV) and low voltage (LV) power supplies are two key constituents of the experimental setup. The HV power supplies for extraction and acceleration are rated for high voltage (~15 to 35kV), and high current (~ 15 to 35A). Other attributes are, fast rate of voltage rise (< 5ms), good regulation (< ±1%), low ripple (< ±2%), isolation (~50kV), low energy content (< 10J) and fast cut-off (< 100μs). The low voltage (LV) supplies required for biasing and providing heating power to the Cesium oven and the plasma grids; have attributes of low ripple, high stability, fast and precise regulation, programmability and remote operation. These power supplies are also equipped with over-voltage, over-current and current limit (CC Mode) protections. Fault diagnostics, to distinguish abnormal rise in currents (breakdown faults) with over-currents is enabled using fast response breakdown and over-current protection scheme. To restrict the fault energy deposited on the ion source, specially designed snubbers are implemented in each (extraction and acceleration) high voltage path to swap the surge energy. Moreover, the monitoring status and control signals from these power supplies are required to be electrically (~ 50kV) isolated from the system. The paper shall present the design basis, topology selection, manufacturing, testing, commissioning, integration and control strategy of these HVPS. A complete power interconnection scheme, which includes all protective devices and measuring devices, low & high voltage power supplies, monitoring and control signals etc. shall also be discussed. The paper also discusses the protocols involved in grounding and shielding, particularly in operating the system in RF environment.

Overview of ion source characterization diagnostics in INTF.

INdian Test Facility (INTF) is envisaged to characterize ITER diagnostic neutral beam system and to establish the functionality of its eight inductively coupled RF plasma driver based negative hydrogen ion source and its beamline components. The beam quality mainly depends on the ion source performance and therefore, its diagnostics plays an important role for its safe and optimized operation. A number of diagnostics are planned in INTF to characterize the ion source performance. Negative ions and its cesium contents in the source will be monitored by optical emission spectroscopy (OES) and cavity ring down spectroscopy. Plasma near the extraction region will be studied using standard electrostatic probes. The beam divergence and negative ion stripping losses are planned to be measured using Doppler shift spectroscopy. During initial phase of ion beam characterization, carbon fiber composite based infrared imaging diagnostics will be used. Safe operation of the beam will be ensured by using standard thermocouples and electrical voltage-current measurement sensors. A novel concept, based on plasma density dependent plasma impedance measurement using RF electrical impedance matching parameters to characterize the RF driver plasma, will be tested in INTF and will be validated with OES data. The paper will discuss about the overview of the complete INTF diagnostics including its present status of procurement, experimentation, interface with mechanical systems in INTF, and integration with INTF data acquisition and control systems.

Indian Test Facility (INTF) - a status update

The Indian Test Facility (INTF) for Neutral Beams is designed with the objective to not only test the performance of an ion source but also to characterize the transmission of the Neutral Beam to a length of 20.66 m and thereby generate adequate database on the quality of the beam that is required for the CXRS diagnostics for measurement of Helium ash content in the fusion plasma.

Conceptual Design, Implementation and Commissioning of Data Acquisition and Control System for Negative Ion Source at IPR

Negative ion Experimental facility has been setup at IPR. The facility consists of a RF based negative ion source (ROBIN)—procured under a license agreement with IPP Garching, as a replica of BATMAN, presently operating in IPP, 100 kW 1 MHz RF generators and a set of low and high voltage power supplies, vacuum system and diagnostics. 35 keV 10A H‐ beam is expected from this setup. Automated successful operation of the system requires an advanced, rugged, time proven and flexible control system. Further the data generated in the experimental phase needs to be acquired, monitored and analyzed to verify and judge the system performance. In the present test bed, this is done using a combination of PLC based control system and a PXI based data acquisition system. The control system consists of three different Siemens PLC systems viz. (1) S‐7 400 PLC as a Master Control, (2) S‐7 300 PLC for Vacuum system control and (3) C‐7 PLC for RF generator control. Master control PLC directly controls all the subsystems ex...

Indian Test Facility (INTF) and its updates

To characterize ITER Diagnostic Neutral Beam (DNB) system with full specification and to support IPRs negative ion beam based neutral beam injector (NBI) system development program, a R&D facility, named INTF is under commissioning phase. Implementation of a successful DNB at ITER requires several challenges need to be overcome. These issues are related to the negative ion production, its neutralization and corresponding neutral beam transport over the path lengths of ~ 20.67 m to reach ITER plasma. DNB is a procurement package for INDIA, as an in-kind contribution to ITER. Since ITER is considered as a nuclear facility, minimum diagnostic systems, linked with safe operation of the machine are planned to be incorporated in it and so there is difficulty to characterize DNB after onsite commissioning. Therefore, the delivery of DNB to ITER will be benefited if DNB is operated and characterized prior to onsite commissioning. INTF has been envisaged to be operational with the large size ion source activities in the similar timeline, as with the SPIDER (RFX, Padova) facility. This paper describes some of the development updates of the facility.

Indigenous Manufacturing Realization of TWIN Source and Its Auxiliary

Indian negative-ion source development program has gained momentum with planned integration of Indian Test Facility (INTF) for International Thermonuclear Experimental Reactor (ITER)—Diagnostic Neutral Beam (DNB) characterization at the Institute for Plasma Research (IPR). Eight RF driver-based negative-ion source, being developed for DNB will be tested and operated in INTF. The Two driver-based Indigenously built Negative ion source (TWIN) source provides a bridge between the operational single driver-based negative-ion source test facility, ROBIN in IPR, and an ITER-type multidriver-based ion source. The source is designed to be operated in continuous mode with 180 kW, 1 MHz, 5-s on/600-s off duty cycle and also in 5-Hz modulation mode with 3-s on/20-s off duty cycle for three such cycles. The complete design of TWIN source and its test facility, from conceptual to detailed engineering, has been carried out in IPR. The manufacturing design has been optimized to match the capability of Indian manufacturers, without compromising on the specifications. Some examples of optimization are: 1) an improvised design of the Faraday shields where electrodeposition has been replaced by vacuum brazing; 2) a simplified design of the side walls of the plasma source, where jointing process is simplified, without the application of Electron Beam Welding; and 3) introduction of a fiber reinforced polymer-based integrated electrical and vacuum isolation scheme that replaces the application of a large ceramic. Finite-element analysis (FEA) based on heat load and structural load calculation ensure the functionality and structural integrity of each component of the source. Due to nonnuclear environment in TWIN source experimental area, vacuum brazing is an acceptable manufacturing process. The contract for manufacturing of the ion source has been awarded to an Indian manufacturing company for the first indigenous production of a large-size fusion grade ion source. TWIN source is designed in such a way that it can be operated both in air mode (RF driver coil antennas are exposed to air) as well as vacuum mode. (Whole source is immersed inside vacuum.) The TWIN source shall be manufactured as per ASME guidelines for pressure vessel. Experiments on the TWIN source are foreseen in the last quarter of 2015, as all the auxiliary systems such as 180-kW, RF generator system, vacuum vessel with pumping station, cooling water system, data acquisition and control system, and other power supply systems are already installed in the lab premises. This paper discusses the FEA-based engineering design, simplified manufacturing design, manufacturing experience with highlighting quality control, and the system integration activities undertaken for the TWIN source test facility.

Design & development of electrical system for TWIN source

TWIN Source (TS) experimental setup is a stepping stone towards INTF, a test-bed to characterize ITER Diagnostic Neutral Beam (DNB) and its ion source. in IPR, India. The electrical system for TS experiments involves design of the scheme, layout, procurement activities, testing, installation & commissioning of power supplies, LT Panels, cables, High Voltage (HV) transmission line, HV deck, RF shielding, grounding and bonding for its safe, reliable and successful operation. The operation of TWIN source will try to mimic some operational features of INTF / DNB source like, 5Hz modulation with 3s ON 20s OFF duty cycle, Few kA current through Plasma Grid (PG) ,based transverse magnetic field electrical feedthroughs through high voltage bushing (HVB) and source operation in vacuum immersed condition. The control of those power supplies will be carried out through CODAC type data acquisition and control platform. The TS electrical system comprises of 180kW 1MHz RF Generator (RFG) system, Filament Heating power supply (16VDC, 10A), Filament Bias power supply (128VDC, 1A), Grid Bias power supply (60VDC, 333A), Filter field power supply (3VDC, 6kA), 150kVA 50Hz 100kVDC isolation transformer, HV transmission line, Air Circuit Breaker (ACB) based LT Panel of 1600A and 800A with 50kA breaking current capacity. This paper discusses the schematic layout of the electrical system, operational modes of 180kW 1MHz RFG including the interfaces with cooling water system and electrical interface with CODAC type Data Acquisition & Control System (DACS). It also discusses the design of HV transmission line & its prototype, shielding, grounding & bonding and highlights the design considerations to mitigate challenges of HV isolation during beam extraction & acceleration mode.

Characterization of cesium vapor delivery system for negative ion sources

Establishing control parameters for the delivery of cesium is paramount for the successful operation of the high current multi megawatt negative ion beam sources, required for fusion. The merit parameter of cesium lies in its attribute of reducing the work function of the surface of the plasma grid of the ion sources and facilitate the production of negative ions (of H/D) by the surface production process.