INDIA | FUSION IPR’s larger tokamak, SST-1, was equipped with a divertor


configuration right from its inception – designed, as it was, to explore the interaction between the plasma and the first wall of the tokamak in steady-state discharges. SST-1 has a major radius of 1.1m and a minor radius of 0.2m, elongation of 1.7 and triangularity of 0.4–0.7, toroidal field of 3T and a plasma current of 220kA. Auxiliary heating and current drive is carried out using a LHCD mechanism while primary heating is done by ICRH and neutral beam injection (NBI). SST-1 of course has superconducting magnetic coils instead of the copper ones seen on Aditya-U, a steady-state current drive and heat and particle exhaust, all of which facilitate a long pulse operation. SST-1 was given a short-term upgrade, beginning in


October 2019, which included installation of a pair of PF-3 current leads — required for moderately-shaped plasmas — a radio frequency (RF) spiral antenna assembly for alternate preionization and startup experiments and various diagnostics. Whether lower hybrid absorption can be realized by modifying loop voltage, as has reportedly been observed in other tokamaks such as Japan’s TRIAM is currently being explored on the SST-1. As such, long- duration plasma discharges of around 650ms have been obtained in SST-1 using both single long-pulse LHCD and multiple short-pulse LHCD. Though SST-1 was set up with a mix of indigenous and


imported systems, IPR has worked intensively since then to ensure that future systems and upgrade packages for its existing assets are executed using domestically sourced components. For instance, while the original conductor for SST-1 had been imported from Japan during the late 1990s, it is now available from domestic sources. As such, IPR’s sub-system development effort in partnership with Indian industry has yielded domestically sourced large-volume ultra- high vacuum (UHV) systems, copper and superconducting magnets, cryogenic systems (both liquid helium and liquid nitrogen based), large cryostats for testing at low temperatures, plasma surface-cleaning methods, high current pulsed, shaped, regulated power supplies, control, monitoring and data acquisition systems, plasma diagnostics, very high power RF heating & current drive systems and neutral beam systems for heating and current drive.


A lot of this has also been catalysed through India’s


participation in ITER, which saw New Delhi emphasising domestic developmental work in the areas of magnet, divertor and cryopumping systems.


ITER-India India’s contribution to ITER, dubbed ‘ITER-India’ is being run as a special project under IPR. It was in December 2005 that India became the full seventh member of ITER with a 10 per cent ‘in- kind’ contribution share out of a total of 150 distinct procurements. India’s Larsen & Toubro supplied the ITER’s cryostat, which is the world’s largest vacuum application stainless steel vessel. It weighs 3850 tonnes, with a height of 30m and a diameter of 30m. The cryostat was installed in 2020. ITER-India is also responsible for supplying a number of other critical components and sub-systems, such as cryolines and a cryodistribution system for ITER’s cryoplants; in-wall shielding, which requires around 9000


blocks from 70,000 precision cut plates; a cooling water and heat rejection system; ICRF source system; diagnostic neutral beam system to detect He ash during the D-T phase of the ITER plasma; plasma diagnostics; power supplies for DNB, ICRF and ECRF systems; two gyrotron sources of 1MW power output at 170GHz for 3600s pulse length; X-ray crystal spectroscopy; electron cyclotron emission as well as various optical fibers, detectors, visible spectrometers and opto- mechanical components. Participation in ITER has led to significant blanket and


divertor technology development initiatives in India. In particular, identification of special materials that provide long life and low induced radioactivity in the extreme environments associated with tokamak operations has been emphasised. In fact, a Cu-Cr-Zr alloy with total impurity levels not


exceeding 0.1 per cent has been developed as a back plate material for mounting PFCs used in ITER. Alongside research into blanket materials there is also a thrust toward towards developing fusion fuel cycle and tritium systems. With India now confident of being able to scale up


tokamak size, field strength, heating power and pulse length, the focus is inevitably shifting towards fusion reactor design, materials and remote handling. After all, the ultimate aim is to be able to build an optimised power generating reactor that is affordable, reliable and maintainable in a cost-effective manner.


SST-2 and then DEMO In a bid to consolidate all that has been achieved via homegrown tokamaks and participation in ITER, India’s fusion community is now looking forward to construction of a large tokamak based fusion reactor called SST-2, due by around 2027. SST-2 is likely to be a low fusion gain reactor that will


have a fusion power output of 100-300MW and may use Indian lead lithium ceramic breeder and helium-cooled ceramic breeder (HCCB) blankets for tritium breeding, besides a He-cooled divertor. The fusion-fission hybrid approach may also be explored


via SST-2, especially given India’s three-stage nuclear programme, which aims ultimately to breed a large fissile inventory of U-233 from the country’s Th-232 deposits. The transmutation of long-lived nuclear waste from fission reactors and the possibility of using fusion neutrons as a driver in thorium-based sub-critical fission reactors will also be investigated. Ultimately, SST-2 alongside what is gained from ITER


operations will pave the way for realising and qualifying technologies related to a D-T fusion cycle for India’s own DEMO programme. For instance, IPR is planning to perform an integral test


by ‘covering the out-board side of SST-2 with a breeding blanket while the in-board side is covered with a shielding blanket’ in a manner similar to what will take place in a DEMO reactor. India intends to attract foreign partners for setting up a DEMO reactor beginning sometime in 2037. Seen as a power source leveraging virtually inexhaustible fuel supply (due to the ready availability of deuterium in seawater and the prospect of breeding tritium), attractive safety characteristics and muted environmental impact, fusion may yet emerge as an element of India’s move towards a net-zero carbon economy by 2070. ■


www.neimagazine.com | February 2022 | 55


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