The High-Luminosity LHC (HL-LHC), due to start operations in 2029, will deliver about 10 times more data than has been accumulated during the previous LHC runs. The CMS collaboration is getting ready to profit from sub-percent precision on many Standard Model (SM) processes and to probe physics beyond the SM, both directly and through studies of higher-order effective operators. Studying rare processes, such as double-Higgs production, rare tau-lepton decays and Higgs couplings to second-generation fermions, will also be a central part of the programme. New ideas will certainly lead to improvements beyond the statistical scaling of uncertainties, bringing us closer to observing these rare processes. While high-precision tests of the SM will surely be the ultimate legacy of the LHC experiments, CMS will also keep searching for clear signs of new physics by investigating the many signatures accessible at the HL-LHC.

To exploit the HL-LHC physics potential, the CMS collaboration is building an optimised detector that pushes technologies to new heights. This major “Phase II” upgrade will enable the subdetectors to sustain the increased luminosity, which results in greater radiation damage and higher particle rates – the innermost pixel layer, for example, will see three billion hits per second per square centimetre. The CMS tracker and the calorimeter endcap will be replaced, a new minimum-ionising-particle precision timing detector (MTD) and a new luminosity detector will be installed, almost all of the existing electronics will be replaced, and additional muon forward stations will be mounted. 

High granularity 

The key to achieving the necessary HL-LHC performance is to enhance the granularity of the detector significantly. This reduces the maximum occupancy per readout cell while considerably increasing the readout bandwidth and processing power of the trigger system, thereby fully exploiting the higher collision rates. As a novelty, all CMS detector designs are tuned to allow full particle-flow reconstruction at the hardware-based level-1 trigger (operating at 40 MHz), while precision timing information, which contributes to the high-level-trigger decision, is exploited by highly optimised software mostly running on graphics processing units.

CMS is currently transitioning from the prototyping to the production phase on several major items. The novel gas electron multiplier (GEM) detector concept, used to detect muons produced in the very forward region, was deployed for the first time on a large scale during long shutdown 2 (LS2): 144 chambers in the first station are fully integrated into the ongoing data taking and the second station will be fully installed in a year-end technical stop before LS3 (see “GEM of a detector” image). Finishing endcap-muon upgrades in advance of LS3 allows the collaboration to minimise the repositioning of the CMS disks during LS3 and to reduce its overall duration. In this spirit, CMS has already finished the replacement of all front-end electronics of the cathode strip chambers. The replacement of the drift-tube electronics in the barrel muon detectors will take place in LS3, and an installed small-scale drift-tube demonstrator is already proving its performance.

The exceptional performance of the current all-silicon tracker provides a solid platform for even further improvements. A main novelty for Phase II is the level-1 track trigger, which reconstructs tracks with transverse momentum above 2 GeV, made available at a rate of 40 MHz. Profiting from the experience with pixels from Phase I, the whole Phase II tracker will use dual-phase CO₂ cooling, ultra-lightweight mechanics, DCDC converters for the powering of the outer tracker, and serial powering for the pixel system, thereby reducing the amount of material by a factor of two compared to today. To reduce the occupancies expected at the highest foreseeable number of collisions per bunch crossing (pile-up), the outer-tracker channel count will increase from 9 million strips to 42 million strips plus 170 million macro-pixels, providing unambiguous z-position measurements. With six barrel layers and five double-disks per endcap, the outer tracker is optimised not only for standalone tracking but also for vertexing, a prerequisite for the track trigger (see “Outer tracker” image). 

The outer tracker is already in production, having overcome most engineering and prototyping challenges. ASICs (application-specific integrated circuits) and sensors are being delivered and the order for the hybrids (which host integrated circuits and connections in the front-end modules) has been submitted. The inner tracker (pixel system) will feature two billion micro-pixels, compared to the 125 million at present. Four barrel layers plus 12 disks per endcap enable excellent track seeding and b-quark jet identification over the pseudorapidity range |η| < 4 (much broader than today’s |η| < 2.5). The inner tracker system aspects are understood, sensors will be ordered soon, and teams are waiting for the final readout ASIC to begin module production.

A new era of calorimetry 

The high-granularity calorimeter (HGCAL) in the forward region starts a new era of calorimetry. It is a radiation-tolerant 5D imaging calorimeter with spatial, energy and precision-timing information (see “HGCAL on display” and “High-granularity calorimetry” images). The deployment of machine-learning algorithms will further enhance its potential to establish the HGCAL as a blueprint for future calorimeters. The HGCAL has 6.4 million channels, two orders of magnitude more than the current endcap calorimeters, including both silicon cells (with an area of 0.5 or 1 cm²) and scintillator tiles (4 to 32 cm²) read out by silicon photomultipliers (SiPMs). The electromagnetic section consists of 26 active layers of silicon sensors interleaved with copper, copper-tungsten and lead absorbers. It is followed by the hadronic section, which is made of 21 active layers of silicon and scintillator tiles, separated by steel absorbers. All in all, 600 m² are equipped with silicon sensors (three times the area of the tracker) and 400 m² with SiPMs-on-tiles. 

The hexagonal-shaped sensors and the modules mimicking bee-hive structures are a design feature of the HGCAL. The hexagonal structure makes optimal use of the circular silicon wafer, therefore being cost-effective. With the sensor design and evaluation completed, mass production has started. The development of silicon sensors that are sufficiently radiation-tolerant for HL-LHC conditions, for both the HGCAL and the tracker, has taken considerable effort. It is also worth noting the use, for the first time in particle physics, of passive sensors processed on 8-inch wafers – another essential feature for covering larger areas at an affordable cost.

The electromagnetic calorimeter (ECAL) barrel and its 61,200 lead-tungstate crystals, which were instrumental in the discovery of the Higgs boson via its decay to two photons, will be retained and equipped with new front-end electronics capable of sustaining the higher rates and trigger latency (see “ECAL upgrades” image). Faster signal processing will result in a much-improved time resolution of 30 ps for high-energy photons (and electrons), enabling precise primary-vertex determination. 

The novel track trigger and the much-improved cell granularity allow the full implementation of the particle-flow reconstruction (based on field-programmable gate arrays, FPGAs) already in the level-1 trigger. The single-crystal granularity that will be provided by the ECAL barrel, even at the trigger level, together with the 3D imaging features of the HGCAL, provide crucial information to precisely follow the path of all particles through the entire detector. This opens the possibility of establishing a full menu of cross-particle triggers and of using FGPA-based machine learning at the level-1 trigger. Trigger algorithms have been prototyped in FPGAs and demonstrated in a multi-board “slice test”. In order to efficiently process the 63 Tb/s input bandwidth, the system is equipped with 250 FPGAs, with an output rate of 750 kHz and a latency of 12.5 μs.

Bright times ahead

For the luminosity measurement, CMS is following a strategy analogous to the one for the trigger, exploiting data from various subdetectors with the ambitious goal of 1% offline (2% online) uncertainty. Achieving this precision requires an understanding of the detector systematic effects, such as linearity and stability, at the per-mille level. A dedicated silicon-pad-based luminometer with an asynchronous readout will help in quantifying systematic uncertainties and beam-related backgrounds, and will play an essential role in the CMS (and LHC accelerator) commissioning.

CMS will enter further uncharted territory in the precision-timing domain with the MTD. For the barrel system, the challenge is to adapt the cost-effective LYSO crystal + SiPM technology, similar to that used in PET scanners, to sustain the HL-LHC rates and radiation. An interesting detail is the use of micro-Peltier elements (thermo-electric coolers) to further decrease the local temperature on the SiPMs, thus counteracting the effects of radiation damage. The endcaps use a new twist on well-established silicon tracking technology: low-gain avalanche detectors, with an additional thin implant within the sensor to generate internal gain. The MTD covers the full solid angle up to |η| = 3 to mitigate pile-up, boost the sensitivity to searches for long-lived particles, and enhance the physics capabilities during heavy-ion runs by providing particle identification capability via time-of-flight measurements.

The high-granularity calorimeter in the forward region starts a new era of calorimetry

All these individual systems are combined into the CMS Phase II detector. Technical coordination is choreographing the integration and has established a detailed schedule for LS3, taking all the detector and external requirements and constraints into account. To maximise the time for detector installation and commissioning during LS3, a huge effort is ongoing in preparing the site in advance. New buildings are already under construction to house the new service infrastructure, such as chillers for the detector CO₂ cooling, uninterrupted power systems and detector- and dry-gas systems. During LS3, the biggest challenge will be to decommission all the legacy systems, including services, that will be replaced by new detectors, and then fit all the new pieces together.

The CMS Phase-II upgrade is a multi-faceted project involving more than 2000 scientists, students and engineers from institutes and industrial companies in more than 50 countries. Initially discussed prior to the first LHC operation and defined by the CMS technical proposal in 2015, the CMS Phase II upgrade together with upgrades to the other LHC detectors will ensure that maximal physics is extracted under the challenging conditions of the HL-LHC. 

Sometimes, it seems, mere proximity is the engine-room of opportunity. That’s certainly the case for two of Japan’s flagship large-scale research centres – the SPring-8 (Super Photon Ring 8 GeV) synchrotron facility and SACLA (the SPring-8 Angstrom Compact free-electron LAser) – which are co-located adjacent to each other on the main campus of Harima Science Park City in Hyogo Prefecture. 

It’s now two years since a joint research group from SPring-8 Center, which is managed by Japan’s premier research agency RIKEN, and the Japan Synchrotron Radiation Research Institute (JASRI), responsible for promoting the use of SPring-8, succeeded in utilising the linear accelerator of the SACLA X-ray free-electron laser (XFEL) facility as an injector for the SPring-8 storage ring. 

The upsides were immediate, impressive and – crucially – sustained. For starters, the 25-year-old injector of SPring-8, which hitherto was used exclusively for beam injection, has been superseded by the SACLA linear accelerator – reducing the electricity consumption needed to support SPring-8 operation by roughly 20%. Equally significant, the quality of the electron beam injected into the storage ring has been enhanced markedly – a breakthrough that will underpin the upgrade plan of SPring-8 to a fourth-generation light source (SPring-8-II) capable of generating X-ray beams hundreds of times brighter than the current facility. 

Legacy problems, creative solutions

By way of context, the previous, dedicated injector for the SPring-8 storage ring consisted of a 1 GeV linear accelerator and an 8 GeV synchrotron booster. The emittance of the resulting injection beam was about 200 nm-rad, which is far larger than the specification of the future SPring-8-II (at 10 nm-rad). There were legacy technology issues as well: both injector accelerators were more than 25 years old, while the associated (and somewhat decrepit) high-voltage power substation was itself in need of a root-and-branch overhaul. 

Cue some creative thinking and the game-changing idea of deploying SACLA’s low-emittance electron beam for SPring-8 beam injection (and in parallel to its core function as a source of XFEL photon beams for front-line research). Herein an engineering win-win began to take shape: on the one hand, the opportunity to decommission (rather than renovate) the high-voltage substation; on the other, to simultaneously reduce SPring-8’s electricity consumption significantly by shutting down the old injector accelerators (which were always maintained in operational mode despite the only intermittent requirement for beam injection). Underpinning it all is the fact that the SACLA linear accelerator is always online for the XFEL research users, so no additional cost or energy consumption accrues when sending a small number of electron-beam pulses from SACLA to the SPring-8 storage ring.

In the early design phase of SACLA (around 2008), and with engineers anticipating the future possibility of beam injection to SPring-8, the nominal beam energy of SACLA was set at 8 GeV to match the SPring-8 storage ring. The direction of the SACLA electron beam was also fixed towards SPring-8 to facilitate the envisaged beam-injection
scenario. To join things up, the two accelerators are linked by a beam transport line – the XFEL to Storage ring Beam Transport (XSBT) – which was constructed at the same time as the SACLA facility (see images “Better together” and “Joined up”). 

When it comes to the technical specifics, the SACLA beam repetition rate is set at 60 Hz, with the electron-beam pulses distributed on a pulse-by-pulse basis in three directions with the help of a “kicker” magnet: along two XFEL beamlines (BL2 and BL3) and down the XSBT beamline. What’s more, the electron-beam energies for XFEL user experiments are often adjusted in a range between 5 and 8 GeV depending on laser wavelengths, while the energy needs to be fixed at 8 GeV for the beam injection. It is therefore essential to control the electron-beam parameters pulse-by-pulse to allow XFEL user experiments and the SPring-8 beam injection to proceed in parallel. 

Synchronisation is nothing without control

Operationally, the preparation of the SACLA beam-injection scheme took about two years in design, planning and commissioning. The first task for the project team was to synchronise the two accelerators, given that they run on different reference clock frequencies (238 MHz for SACLA; 508 MHz for SPring-8). Since the two frequencies do not have a harmonic relation, the injection timing naturally goes off with respect to the target RF bucket of SPring-8 by a maximum ±2.1 ns. A novel timing system was subsequently developed to provide the necessary synchronisation. 

In top-up injection mode, which keeps a constant stored current within the storage ring, SPring-8 sends a beam request to SACLA when the stored current decreases under a certain threshold. Once SACLA receives the request, the timing system first searches out a point where the timing difference is at a minimum. By delaying the beam injection up to 197 µs, there should be a point where the timing difference becomes smaller than 105 ps. In a second step, a slight frequency modulation is applied to the SACLA 238 MHz reference clock, such that SACLA and SPring-8 are finally synchronised to within 3.8 ps (RMS).

Another significant piece of work involved retrofitting the accelerator control system. To change the accelerator parameters pulse-by-pulse, it is necessary for accelerator components to “know” the destination of the next beam pulse. That granular data (at the level of an individual pulse) is therefore sent through a “reflective memory network” to key components and subsystems – for example, RF sources and magnet power supplies – such that these devices can then operate with prestored parameters corresponding to the relevant beam destination. 

Meanwhile, all diagnostic data are saved in a database with a pulse tag number so that the measured data, such as beam trajectories and charges, can be distinguished among the three beam destinations (BL2, BL3 and XSBT). It is like there are three accelerators independently running with different beam energies and parameters. In day-to-day operation, three operators adjust and tune the accelerators by looking at the monitor and control panels for the three beams versus the respective destinations. Using the pulse tag number, XFEL users are also able to see which pulses were used for the beam injection, so that these pulses can be eliminated from their experimental data. 

A final core deliverable for the project team was to ensure the bulletproof reliability of SACLA – since the storage ring cannot operate without beam injection. In short, if the linear accelerator of SACLA fails to provide electron beams, close to 60 experiments on the SPring-8 beamlines are at risk of grinding to a halt. Redundancy is the key here: to promptly recover from unexpected troubles, the team installed back-up components for crucial accelerator devices, such as the electron gun, kicker magnet and RF sources.  

Going live

During the early-stage evaluation of the new beam-injection scheme, two other issues came into play: electron bunch purity and magnetic hysteresis of the kicker magnet. The electron bunch purity is a ratio of electron charges contained in an electron-injected RF bucket and an empty bucket on the storage ring. 

It is an important figure of merit – not least for ensuring low background noise in time-resolved experiments. A bunch purity of between 10^–8 and 10^–10 is typically required at SPring-8, while the electron bunch charge of SACLA is around 200 pC – i.e. even a single electron outside the beam pulse could degrade the bunch purity. 

It turned out, however, that a small number of electrons were detected 18 ns after the main beam pulse during the initial experimental runs. After detailed investigation, the project team found that these electrons were slipping out from the main pulse and making a round trip between two RF cavities at the injector section of SACLA. Consequently, they were delayed by 18 ns and being injected into unexpected RF buckets on the storage ring. The solution: remove the delayed electrons using an electric sweeper and an RF knockout system – a breakthrough that, in turn, yielded the required bunch purity of 10^–10. 

At the far-end of SACLA’s linear accelerator, electron-beam pulses are deflected horizontally in three directions by a kicker magnet. The polarity of the kicker current is negative for BL2, zero for BL3 and positive for XSBT. As a consequence, the beam orbits of the pulses just after the beam injection (i.e. two to three times a minute) deviate from the optimum trajectory inside the XFEL undulators – seriously degrading pointing stability and laser power within the SACLA beamlines. To overcome this issue, the excitation pattern of the kicker magnet is modified slightly after the beam injection, such that the hysteresis effect is now suppressed within an angular deviation of 1 µrad (i.e. less than 10 % of the laser spot size). 

With those “issues arising” addressed successfully by the project team, it’s instructive to look at the high-level operational performance of the new beam-injection arrangement. To fill up the storage ring with a nominal stored current of 100 mA, the electron beam is injected at 10 Hz from SACLA. The process takes about 10 minutes – roughly twice as fast as the old injector. Once the storage ring is filled, top-up injection gets underway to keep the stored current at a constant level. In top-up mode, the electron beam is injected typically 2–3 times every minute. Measuring the transverse beam sizes at the injection point of SPring-8 shows that the size of the electron beam from SACLA is significantly narrower versus that from the old injector, with the beam quality represented by emittance improving from 200 nm-rad to 1 nm-rad – more than satisfying the criteria for the future SPring-8-II.

Green machines

Alongside those sustained performance improvements, there are other notable wins to report for the SACLA beam-injection arrangement. After a probation period of six months, the old SPring-8 injector and its power station were shut down in April 2021, yielding a 5 MW saving in electricity consumption and an impressive 20% reduction in the SPring-8 power bill (i.e. versus current SPring-8 plus the old injector).

Further operational efficiencies are in the works for SPring-8-II given the global surge in energy prices and the shared commitment (with SACLA) towards carbon neutrality by 2050. By using cutting-edge, short-period, in-vacuum undulator technologies in SPring-8-II, for example, the electron-beam energy will be reduced from 8 GeV to 6 GeV without changing the X-ray radiation energy range. Replacing accelerator electromagnets with permanent magnets will enable additional reductions in power consumption. The ultimate goal of SPring-8-II, and with user operation pencilled in to begin no later than 2030, is a 50% reduction in power consumption versus the current SPring-8.

The ultimate goal is a 50% reduction in power consumption for SPring-8-II versus the current SPring-8

Similarly ambitious plans are taking shape for the SACLA-II upgrade, which will take place after the completion of SPring-8-II. The end-game: a 1 kHz repetition rate using conventional (rather than superconducting RF) accelerator technologies. With traditional RF acceleration, of course, more than 99.99 % of the input power is dissipated as heat – rather than accelerating the electron beam – so the challenge for SACLA-II is to boost this extremely low conversion efficiency, thereby increasing the repetition rate without increasing the power consumption. 

While none of this will be straightforward, it’s evident that the path to a “greener” and more sustainable accelerator complex is rapidly coming into view.

The estimated annual global incidence of new cancer cases was upwards of 19 million in 2020, with more than 70% of people suffering from the disease resident in low- and middle-income countries (JCO Global Oncology 2022 8 e2100358). What’s more, according to forecasts from the International Atomic Energy Agency published on World Cancer Day in February 2022, the total number of cancer deaths worldwide is forecast to rise by 60% over the next two decades – to 16 million people a year – with those same low- and middle-income countries suffering the brunt of the escalation. India finds itself in the eye of this healthcare storm, with the domestic burden of cancer cases projected at between 1.9 and 2 million in 2022 – a burden, moreover, that’s also projected to increase over time.

Fundamentally, this is a question of supply (high-quality cancer treatment) versus demand (rising cancer incidence) for India – not least when it comes to the challenges associated with rolling out accessible and affordable radiation therapy facilities at the national level. Right now, there are around 545 clinical radiotherapy units across India (180 ⁶⁰Co-based teletherapy systems and 365 electron linacs). Most of the e-linacs are supplied by commercial manufacturers, with 50% of these systems located in private hospitals – and therefore beyond the reach of the majority of Indian citizens. 

To drive down the cost of radiotherapy treatment, while simultaneously opening up access to more cancer patients, the Society for Applied Microwave Electronics Engineering and Research (SAMEER) in Mumbai has been prioritising technology innovation in e-linacs for several decades (with financial support from the central government’s Ministry of Electronics and Information Technology, also known as MeitY). 

Accessibility, affordability, availability 

A case study in this regard is the medical electronics division of SAMEER, which initiated an R&D programme for a 4 MeV e-linac for cancer therapy in the late 1980s. The initial outcome: an S-band, side-coupled linac (operating at π/2 mode at 2.998 GHz) developed for electron acceleration. The SAMEER development team later integrated the linac with other core subsystems in collaboration with the Central Scientific Instruments Organisation, Chandigarh, and the Post Graduate Institute of Medical Education and Research (PGIMER), Chandigarh, with the completed linac commissioned at PGIMER in 1991. 

This original machine was called Jeevan Jyoti-I. SAMEER engineers went on to build three more e-linac variations on the Jeevan Jyoti-I theme, with all units duly commissioned and operating in hospitals. Subsequently, under the Indian government’s Jai Vigyan initiative, SAMEER built six more radiotherapy units (with an increased energy of 6 MV) and installed these systems in hospitals. One more machine is being commissioned in 2022 – initially using commercial microwave sources from SAMEER (though these will eventually be replaced with a domestically developed 2.6 MW magnetron).

Multipurpose proton accelerators

India’s Department of Atomic Energy (DAE) plans to exploit the country’s rich natural sources of thorium to bolster the domestic nuclear energy programme, simultaneously exploring new methods for dealing with high-level nuclear waste as well as the at-scale production of medical radioisotopes for the diagnosis and treatment of cancer.

Consider the so-called accelerator-driven subcritical reactor (ADSR), a next-generation nuclear reactor design formed by coupling a substantially subcritical nuclear reactor core (using thorium as fuel) with a high-intensity, high-energy proton accelerator. The latter generates a copious beam of spallation neutrons to sustain the fission process – activating the thorium without needing to make the reactor critical (i.e. turning off the proton beam results in immediate and safe shut-down of the reactor). Another benefit of the ADSR scheme is the relatively short half-lives of the waste products.

Within this context, DAE’s R&D laboratories have started work on a high-current 1 GeV proton accelerator (see “Collective endeavour” figure). In the first phase of construction of a 20 MeV normal-conducting linac at Bhabha Atomic Research Centre (BARC), scientists accelerated a 2 mA proton beam from an ion source using a four-vane RF quadrupole (generating a 3 MeV proton beam with 65% transmission). Earlier this year, the BARC team boosted the proton energy to 6.8 MeV through the first drift-tube linac (with a peak beam current of 2.5 mA and an average beam current of 1 μA with 93% transmission). At Raja Ramanna Centre for Advanced Technology (RRCAT), meanwhile, several warm-front-end ion sources and associated subsystems are under construction (including low-energy beam transport, RF quadrupoles, medium-energy beam transport and a drift-tube linac). 

Operationally, collaboration is a defining theme of India’s R&D effort on proton accelerators – not least through its scientists’ direct participation in the Proton Improvement Plan II (PIP-II), an essential upgrade and ambitious reimagining of the Fermilab accelerator complex in the US. Several Indian institutions are front-and-centre in the PIP-II initiative, designing and developing room-temperature and superconducting magnets, superconducting RF cavities, cryomodules and RF amplifiers for the PIP-II project team. 

BARC and the Inter-University Accelerator Centre (IUAC) in New Delhi, for example, initially supplied two single-spoke-resonator cavities for testing at Fermilab, while end-to-end infrastructure for niobium-cavity fabrication and testing has been established at RRCAT. Several niobium superconducting cavities – required in both the PIP-II project and the Indian proton accelerator programme – have since been fabricatedand tested successfully.

Innovation pathways

One thing is clear: India’s e-linac R&D effort continues to gather momentum. The next step is to enhance the technology for dual photon energies (6 and 15 MeV) from the same linac, along with multiple electron energies (from 6 to 18 MeV) for treatment. A prototype of a novel dual-energy linac has already been put through its paces, delivering beam-on-target at SAMEER. The energy is varied by introducing a plunger in the coupling cavity in the acceleration section. Industry partners are being sought as the system undergoes final quality assurance and control checks.  

Parallel technology programmes – covering both e-linacs and proton cyclotrons – are also underway to support domestic production of medical radioisotopes used in the diagnosis and treatment of cancer. For example, a 30 MeV, 5–10 kW linac project (incorporating two 15 MeV sections) is being lined up for the production of ^99mTc from ⁹⁹Mo (the former being required in a nuclear imaging procedure called single-photon-emission computerised tomography, commonly known as SPECT). The ⁹⁹Mo will be produced from ¹⁰⁰Mo using Bremsstrahlung photons, with the latter emitted after accelerated electrons are incident on a target. Tests of the first accelerating structure (15 MeV) are in progress and the full energy of 30 MeV is expected to come online next year. 

India and CERN: a win–win partnership

Following India’s associate membership at CERN from 2017, the country’s scientists and engineers continue to build on a rich and diverse legacy of contributions spanning core accelerator technologies and participation in front-line high-energy physics experiments. This is a legacy that extends across more than 50 years of collaboration. In the 1990s, for example, the RRCAT contributed to LEP, while the Indian High-Energy Heavy Ion Physics Team contributed to the WA93 experiment at the CERN-SPS. An international cooperation agreement between India’s Department of Atomic Energy (DAE) and CERN was signed in 1992 to deepen ties and extend the scientific and technical cooperation between India and CERN. Those developments, in turn, paved the way for the decision (in 1996) of India’s Atomic Energy Commission to take part in the construction of the LHC – specifically, to contribute to the development of the CMS and ALICE detectors. India became a CERN Observer State in 2002, and the success of the DAE–CERN partnership on the LHC led to a new cooperation on novel accelerator technologies, shaping DAE’s participation in CERN’s Linac4, SPL and CTF3 projects. 

Elsewhere, the Variable Energy Cyclotron Centre (VECC) in Kolkata is leading a project to build an 18 MeV medical cyclotron – a machine that will reduce the cost of production for positron-emitting radioisotopes. In terms of operational specifics: the system will accelerate negative hydrogen ions (H^–) from an external, multicusp volume ion source, while a carbon stripper foil will alter the charge state of the ions from negative to positive ahead of extraction. Progress to date is encouraging: engineering design of the main magnet is complete and a 1 mA current has been extracted from the H^– ion source. 

Further technology innovation is evident in the field of hadron therapy, which uses proton or ion beams to deliver precision tumour targeting with zero exit dose – a capability that clinicians estimate could improve therapeutic outcomes in 15–20% of cancer patients who receive radiotherapy. Recognising the potential here, Indian clinics have recently purchased and installed two 230 MeV proton cyclotrons, supplied by Belgian equipment maker IBA, in a pivot towards next-generation cancer treatments. 

Further progress has been reported by a collaboration between SAMEER and KEK, Japan’s High-Energy Accelerator Research Organisation. Jointly, the two partners have completed conceptual design studies for a multi-ion therapy machine based on a novel digital accelerator concept. The system is basically a fast-cycling induction synchrotron with a specialised beam-handling capability. (For context, the accelerating devices of a conventional synchrotron, such as RF cavities, are replaced with induction devices in an induction synchrotron.) It is possible, for example, to inject particles at nearly 200 kV DC directly into the main ring and, as such, the induction synchrotron does not need a separate injector. 

In a related initiative, the Tata Memorial Centre Mumbai, and Raja Ramanna Centre for Advanced Technology (RRCAT), Indore, have come up with a preliminary design for a 2 MeV injector and a 70–250 MeV proton synchrotron that may also be suitable for variable-energy beam delivery and other ion-beam therapies.