Upendra Prasad

Evaluation of Ferrocene Derivatives as Burn Rate Modifiers in AP/HTPB-Based Composite Propellants

Some ferrocene derivatives like 2,4-dinitrophenylhydrazine derivative of acetyl ferrocene, 1-pyrrolidinylmethyl ferrocene, di-ter-butyl ferrocene and 1,3-diferrocenyl-l-butene (DFB) have been synthesised and characterised by infrared, nuclear magnetic resonance, ultraviolet, iron content, etc. To study the effect of their incorporation on performance, ammonium perchlorate/hydroxyl-terminated polybutadiene-based composite propellants containing these derivatives have been prepared and studied for burn rates, tensile strength and percentage elongation followed by their static test evaluation. A comparison of the properties of propellant containing solid and liquid ferrocene derivatives has been made with those containing Fe/sub 2/O/sub 3/ and n-butyl ferrocene, respectively. The data clearly indicates that these ferrocene derivatives are better than Fe/sub 2/O/sub 3/ and n-butyl errocene. Also, DFB is the best among these derivatives. Like composite propellants, DFB increases burn rate in fuel-rich propellants also.

SST-1 Status and Plans

The Steady State Superconducting Tokamak (SST-1) is currently being refurbished in a mission mode at the Institute for Plasma Research with an ultimate objective of producing the first plasma in early 2012. Since January 2009, under the SST-1 Mission mandate, a broad spectrum of refurbishment activities have been initiated and pursued on several subsystems of SST-1. Developing sub-nano-ohm leak-tight joints in the magnet winding packs, developing single-phased LN2-cooled thermal shields, developing supercritical-helium-cooled 5-K thermal shields for magnet cases, ensuring thermal and electrical isolations between various subsystems of SST-1, testing of each of the SST-1 toroidal field (TF) magnets at 4.5 K with nominal currents, testing each of the modules and octants of the SST-1 machine shell in representative experimentally simulated scenarios, augmentation and reliability establishment of the SST-1 vacuum vessel baking system, time synchronizations among various heterogeneous subsystems of SST-1, large data-storage scenarios, and integrated engineering testing of the first phase of the plasma diagnostics are some of the major refurbishment activities. Presently, the SST-1 device integration is in full swing. The cold test of the assembled SST-1 TF and poloidal field magnets began in December 2011. Following the successful testing of the SST-1 superconducting magnet system and engineering validations of the machine shell, the first plasmas will be attempted in SST-1. The first plasma will be ~ 100-kA limiter assisted with the available volt-seconds and could possibly be assisted by ECCD/LHCD.

Quench Detection System for TF Coil-Test Campaigns of SST-1

Testing of all superconducting toroidal field (TF) coils of a steady-state superconducting tokamak (SST-1) in nominal currents of 10 000 A under supercritical helium-cooled conditions was an essential prerequisite of SST-1 machine reassembly and subsequent refurbishment. Testing of individual TF coils at its full operational load of >;1 MA in its winding pack necessarily demands to test these coils with all the interlocks coupled with precise protection elements. A quench detection (QD) system is an essential and integral part of this testing since any irreversible off-normal scenario leading to the magnet quench must be promptly detected, and the energy from the magnet must be extracted with equal promptness to protect the magnet within the defined dump time, avoiding thermal stresses in the winding pack. An active fail-proof electronics QD system has been developed for the detection of resistive transitions in any part of the SST-1 TF coil. The difference configuration method has been adopted and exploited in the QD system for comparing the voltage drop measured in each of the double pancakes and interpancake joints of the TF coil. This paper describes the scheme of the QD system and precautions taken ensuring enhanced reliability and redundancy, as well as the results obtained in the due course of all the 16 SST-1 TF magnet tests.

Precision Signal Conditioning Electronics for Cryogenic Temperature and Magnetic Field Measurements in SST-1

As a part of refurbishment of Steady-state Superconducting Tokamak-1 (SST-1) at the Institute for Plasma Research, India, all 16 toroidal field (TF) magnets of SST-1 have been individually tested in cold with nominal current in a dedicated experimental cryostat. The magnets were cooled down to 4.5 K using either supercritical or two-phase helium, after which they were charged up to 10 kA of transport current. Precise cryogenic temperature and magnetic field measurements in the experimental configuration were mandatory. Temperatures were required to be accurately measured at several locations in the magnet and hydraulic circuits, whereas the field measurements were carried out at few predefined locations on the magnet case. Highly accurate in-house modular signal conditioning electronics had been developed for low temperature and high magnetic field measurements for such large magnets. This paper describes the scheme of the measurement, precautions taken for enhanced reliability, precautions taken for long-term offset stability in cryogenic environment, and the results of SST-1 TF magnet tests.

Measurement of Electromagnetic and Thermal Stresses on Conduction-Cooled Joints of the SST-1 Spare TF Coil

Low-dc-resistance superconducting joints in toroidal- and poloidal-field (TF and PF, respectively) coils of the steady-state superconducting tokamak-1 (SST-1) at the Institute for Plasma Research (IPR) is under testing. The feasibility of conduction-cooled leak-tight joints made between two double pancakes in the winding pack of the TF coil is validated through experiments. The configuration of these conduction-cooled joints is comprised of a prefabricated SS304L oxygen-free high-conductivity copper leak-tight termination, into which the unconduited and soldered portion of the cable-in-conduit-conductor (CICC) is inserted. Once the cable space is inserted inside the prefabricated piece, solder filling is carried out, and the joints are realized by overlapping the mating ends and soldering them together. The supercritical helium flowing through the CICC exits prior to the termination length, and the joints are cooled by conduction. The joints are subjected to I × B-induced and bending-induced stresses during SST-1 operational scenarios. These stresses can lead to leaks in the joint region if they exceed the material strength or the brazing/welding strength. Both the thermal and electromagnetic stresses that developed at the copper-stainless steel prefabricated brazed region are measured on the SST-1 spare TF coil. These stresses are measured using the strain gauges during the cooldown and the charging of the spare TF coil up to its operational current of 10 kA at a conventional 4.5 K and 4 bar of supercritical helium forced flow. The electromagnetic-stress behavior at the time of quench that occurred accidently during the spare TF coil test at an 8 kA transport current was also studied. The signal-conditioning electronics required for this measurement are engineered and tested at the IPR before its implementation to the spare-TF-coil test campaign. The measured thermal and electromagnetic stresses are found to be in good agreement with the simulated finite-element Ansys results.

Performance of Joints in SST-1 Magnets

Novel sub-nano ohm leak tight joints were one of the primary objectives of the refurbishment of Steady State Superconducting Tokamak (SST-1). In total, there are 130 such shake-hand type of joints which have been fabricated on the winding packs of SST-1 Toroidal Field (TF) and Poloidal Field (PF) superconducting magnets. These joints have been validated to be performing per their design specifications in the assembled SST-1 TF and PF magnets during the first cool-down and charging of the assembled and integrated SST-1 superconducting magnet systems. This paper describes the novel aspects of design, process establishments, technology development, testing and qualifications of such joints on the single magnets in both two phase and supercritical flow conditions as well as the joints performances in the assembled SST-1 TF and PF magnets.

First Engineering Validation Results of SST-1 TF Magnets System

All SST-1 superconducting Toroidal Field (TF) and Poloidal Field (PF) magnets have been refurbished, integrated, and assembled onto the SST-1 machine shell in mid of 2012. Fabrication of sub nano-ohm, leak tight DC joints in superconducting magnets winding packs, enhancing the insulation strength in operating conditions, and test qualifying all the magnets prior to their integration in SST-1 machine shell were the primary refurbishment aspects. All assembled SST-1 TF magnets in SST-1 machine shell have since been successfully cooled down employing 1.3 kW SST-1 Helium Refrigerator/Liquefier system maintaining helium leak tightness under all temperature conditions. The TF magnets have experimentally demonstrated thermo-mechanical behavior as per the design as well as excellent flow uniformity amongst various parallel paths. Subsequently, these TF magnets have been increasingly charged so as to create a magnetic field of 1.5 T at the SST-1 major radius of 1.1 m. This is the first occasion, when cable-in-conduit wound toroidal field magnets have been successfully operating with two phase flow in a Tokamak application. The first plasma in SST-1 has been successfully obtained in June 2013 where the SST-1 TF magnets have demonstrated excellent functional characteristics. The confidence boosting engineering and functional validation test results of SST-1 TF magnets as well as its performance during the recent SST-1 plasma campaign have been elaborated in this paper.

Preliminary Design of Central Solenoid of SST-2 and Demo

Preliminary design of the central solenoid (CS) for SST-2 and Indian DEMO reactor has been initiated. The expected maximum magnetic field calculated by magnet design code MAC at the conductor location is ~13 T. The key role of the CS magnet is for initiating efficient plasma current and maintaining it for longer duration. In order to maximize the CS capability, the higher magnetic field with a greater magnetic flux linkage is required, and this could be possible with a large area of the solenoid. CS consists of a number of modules acting independently, each following an individual current profile leads to a better initial null formation, plasma current build up, longer pulse duration, and good shaping. Hence, the function of CS is to provide the required volt-sec for plasma initiations, sustaining plasma current, and to provide good equilibrium for few hundreds of seconds. For this purpose, it is advantageous to split CS into many modules. The dimensional parameters of various modules, tentative model, volt-sec capability, and allowable ramp rates are the prime requisites for CS design. The total volt-sec requirements for long pulsed plasma, which include plasma initiation, ramp up, flat top, and ramp down, are estimated using plasma properties. In this estimation, inductive flux and resistive flux requirements are estimated using appropriate analytical or empirical formula. In the flat top, only resistive flux is considered. The duration of the flat top is about few hundreds of seconds, and for steady-state operation of the reactor, during the flat top, the noninductive current drive mechanism will fully sustain the plasma current. This methodology is applied to typical ITER-like discharges and compared with ITER CS available volt-sec. The same methodology is used to estimate for SST-2 and Indian DEMO reactor. The radial buildup of inboard side of Tokomaks is obtained through a system code which uses physics and engineering constraints. This provides the available space for the CS coil. It is observed that the negative convertor operation is needed to enhance the available volt-sec. In order to fulfill the plasma physics requirements with the available inner bore area and height, a multimodule CS coil is proposed with Nb3Sn conductor. This work has been carried out for ITER CS to validate the procedure and applied to SST2 and DEMO. The tentative model of CS coil, calculation methodology of magnetic field, expected electromagnetic forces, stored volt-sec, and current ramp-up and ramp-down requirements will be presented in this paper.

Cryogenic Acceptance Tests of SST-1 Superconducting Coils

Toroidal field (TF) and poloidal field (PF) coils of steady-state superconducting tokamak (SST-1) have been fully refurbished to ensure cryostable and low-dc-resistance interpancake and intercoil joints, helium leak tightness of the winding pack, and ) 10 MΩ winding pack to ground insulation resistance under cold conditions. As per SST-1 mission mandate, all TF coils and PF3 Top had been cold tested at full operational parameters. A dedicated large coil test facility was integrated for these tests. Specially adapted solutions such as magnet preparation cum transport stand, demountable busbar supports, demountable sensor mountings, reusable joints for busbar connections inside cryostat, etc., were developed. These measures led to timely and successful completion of cold tests and integration of the magnet system on to the SST-1 machine shell. The functionality of various diagnostics of the magnet system was also established during these tests. Details of coil refurbishment, test facility, test campaigns, and some important test results are reported in this paper.

Precision signal conditioning and front-end electronics for temperature and field measurements in SST-1 TF magnets

As a part of refurbishment of Steady-state Super-conducting Tokamak-1 (SST-1) at Institute for Plasma Research, India, all sixteen Toroidal Field (TF) magnets of SST-1 have been individually tested in cold with nominal current in a dedicated experimental cryostat. The magnets were cooled down to 4.5 K using either super critical or two phase helium, after which they were charged upto 10 kA of transport current. Precise temperature and field measurements in the experimental configuration were mandatory. Temperatures were required to be measured accurately at several locations in the magnet and hydraulic circuits, where as the field measurements were carried out at few predefined locations on the magnet case. Highly accurate in-house modular signal conditioning electronics had been developed for accurate temperature and field measurements. This paper describes the scheme of the measurement diagnostics, precautions taken for enhanced reliability and long term offset stability in cryogenic environment, and the results of TF magnet tests.