India at CERN

Published : Jul 27, 2012 00:00 IST

At the Raja Ramanna Centre for Advanced Technology in Indore, scientists with the superconducting magnets supplied to CERN. A file picture.-M. LAKSHMAN

At the Raja Ramanna Centre for Advanced Technology in Indore, scientists with the superconducting magnets supplied to CERN. A file picture.-M. LAKSHMAN

The Raja Ramanna Centre for Advanced Technology was the lead DAE laboratory for the accelerator part of the Indian collaboration in the LHC.

We have reached a milestone in our understanding of nature. That is how Rolf D. Heuer, the soft-spoken Director General of CERN (European Organisation for Nuclear Research) described their prized catch announced to the world on July 4, which scientists have been looking for and working hard to create in the laboratory for three decades. But Heuer also emphasised that further work was needed. As a layman I would say we have it, but as a scientist I have to say, what do we have? We have discovered a boson. Now we have to determine what kind of boson it is. The quest to establish the attributes of the newly found boson will be pursued relentlessly as the story is not yet over.

However, what is remarkable is that two independent detectors set up at the Large Hadron Collider (LHC) the Compact Muon Solenoid (CMS) and the A Toroidal LHC Apparatus (ATLAS) as well as earlier inferences from the detectors at Tevatron (near Chicago) have all led to the same conclusion, that a new boson of about 125 GeV (giga electron Volt) has been discovered.

While this discovery is certainly a great triumph for the scientists, we must mention that the design and construction of the LHC is itself a stirring saga that involved perhaps a million or more persons across the globe. Set up in a 27-kilometre-circumference tunnel, which straddles the Swiss-French border, the LHC took over a decade to construct with unparalleled international participation, in which India contributed both to the accelerator and to the detectors, which are meant to unravel the mysteries of nature. It will be appropriate to recall these aspects.

The LHC has two interleaved synchrotron rings. Proton beams travel in these in opposite directions (clockwise and counterclockwise) and are made to cross at specified collision points in the LHC tunnel. The design of the machine was started about two decades back and went through numerous iterations. The main magnetic elements of the LHC are its two-in-one superconducting dipoles and quadrupoles built out of niobium-titanium-copper (Nb-Ti/Cu) superconductors which operate at 1.9 K (using super-fluid helium). In all, the LHC has 1,232 main dipoles (each about 15 m in length) and 392 arc quadrupoles. These are integrated with corrector magnets to ensure that the proton beams remain on course. Proton beams are injected at 450 GeV and then ramped up in energy before collisions occur. Currently each beam is raised to 4 TeV (tera electron Volt) energy, although it is designed to go up to 7 TeV. The oppositely travelling proton beams can cross at six places where collisions occur, and the collision products are studied using different detectors. India joined the LHC enterprise in 1996.

While CERN and some laboratories of the Department of Atomic Energy (DAE) have worked jointly for decades, a formal cooperation agreement was signed only in 1991 by the then Director General of CERN, Carlo Rubbia, and Chairman of Indias Atomic Energy Commission (AEC), P.K. Iyengar. In 1996, using that agreement, the DAE accepted CERNs invitation to participate in the construction and utilisation of the LHC. For this a protocol was signed by C.H. Llewellyn Smith, the then Director General of CERN, and R. Chidambaram, the then Chairman of the AEC. It envisaged an in kind Indian contribution towards the accelerator construction, valued at 34 million Swiss francs. Later, in 2002, the Director General of CERN, Luciano Maiani, and the Chairman of the AEC, Anil Kakodkar, enhanced this limit.

The lead DAE laboratory for this (accelerator part of the LHC collaboration) was the Raja Ramanna Centre for Advanced Technology (RRCAT) the new name of the DAE centre in Indore and the task to identify specific items for Indian contribution was left to a joint committee co-chaired by the Director of the RRCAT and the in-charge of the LHC. After identifying the delivery items, the two sides signed nearly 30 addenda, spelling out the technical details of the items, the time schedule, the payment terms, and so on.

The arrangement worked well and the cumulative Indian contribution came to about 44 million CHF (Swiss francs). A variety of subsystems were identified for delivery, and the prototypes that were built qualified through a series of tests conducted at CERN. During the prototype development, it became necessary to make design changes, not only to conform to the final requirements but also to reengineer them to bring down production cost. After all the qualifications were met, bulk quantities of subsystems were manufactured by Indian industry and delivered to CERN under the overall supervision of the RRCAT.

The items that were mass-produced and delivered included precision motion positioning system (PMPS) jacks, superconducting corrector magnets, heater discharge power supplies, local protection units, and so on. The production of PMPS jacks was done in two industries, in Indore and Bangalore. In all, 7,080 units were supplied to CERN and 280 out of these had to meet even tighter tolerances and allow for remote operation. The development of corrector magnets was completed at the RRCAT, and they were mass-produced in two industries, in Bhopal and Bangalore. Each corrector totalling about 2,000 in all was taken through warm and cold tests before dispatch to CERN. The LHC superconducting magnets are powered with a current up to 13 kA and require protection in case of a quench (resistive transition) or other failures. If a quench is detected, the protection system is activated. Electronics Corporation of India Limited (ECIL) manufactured the system under a team led by engineers of the Bhabha Atomic Research Centre (BARC).

In addition to hardware, India provided expert manpower for several tasks. Teams of Indian specialists worked at the Superconducting Magnet Test Hall SM18 (at CERN) for around five years and performed complete tests and measurements on a full series of magnets that in all amounted to almost 100 man-years. The positive experience with regard to magnet evaluation work prompted CERN to seek and receive Indian help for commissioning some LHC subsystems. These included cryogenic systems as well as a variety of electronic hardware. Indian scientists and engineers provided almost 25 man-years of help for the LHC subsystem commissioning work.

Apart from contributing to the LHC accelerator, India has also contributed to the two detector facilities, namely, CMS and ALICE. While CMS is a general purpose detector, ALICE is particularly meant to study collisions of heavy ions (like lead nuclei) to study the conditions that existed on a nanosecond time scale after the Big Bang and producing matter in its quark gluon plasma state. The Tata Institute of Fundamental Research (TIFR) has handled the Indian part of the CMS detector, coordinating, building and erecting the detector system, while the Variable Energy Cyclotron Centre (VECC) and the Saha Institute of Nuclear Physics (SINP) in Kolkata handled these tasks for ALICE.

The job involved the development, fabrication and installation of detector components that included the Outer Hadron Calorimeter (HO) and the Electromagnetic Calorimeter (ECAL) for CMS and the Photon Multiplicity Detector (PMD) and the Muon Chamber arm for ALICE. In addition, these institutions built regional tier 2 centres (part of the worldwide LHC grid) in Mumbai and Kolkata so that Indian scientists can take part in the analysis of the LHC data.

In the course of building the detectors, a number of spin-offs have resulted, including radiation detectors for the DAEs programmes and the MANAS chip built by Semiconductor Complex Limited (SCL), Chandigarh. India also contributed about 50 man-years of software work to develop problem-tracking software, middleware for the grid operation, and so on.

Why the excitement?

To answer this question let us go back to the beginning. In class IX in school one is taught about the mass of a body as the quantity of matter in it. But this statement hardly tells us much. For physicists, the puzzle remains as to what bestows mass on particles. Indeed, this question has interested particle physicists for about half a century, and one of the puzzles that the LHC can help us understand is the origin of the mass of particles; more importantly, experimentally check out the ideas first proposed in 1964 by Peter Higgs and others. In such a description of nature, what bestows different masses to different particles is the variation in the strength of their coupling to the omnipresent Higgs field and the Higgs boson, which is itself a quantum of excitation of the Higgs field. How do we verify if this idea is right or wrong? Physicists know only one way: check out the predictions experimentally.

The problem, however, is twofold: to create the Higgs boson in the laboratory and to establish that it has the attributes it is supposed to have. Remarkably, the opportunity created by the LHC offering proton-proton collisions at a higher energy as compared to proton-antiproton collisions that the Tevatron offered has made the task of creating a Higgs boson less arduous.

As for detecting whether a Higgs boson has been produced or not, one relies on looking at the decay products (of Higgs) that unambiguously confirm that indeed a new entity was formed. Happily for us, both the experiments, that is, using the CMS and the ATLAS detector system at CERN, have managed to sift out enough evidence (from a total of 800 trillion p-p collisions) to attest to the discovery of a new boson of about 125 GeV energy.

While we can expect the intensive effort to build up statistics to continue in the coming future, it would certainly be fair to say that it is time for champagne for all those who have worked hard over the past two decades. Some of us involved in this journey do have a sense of satisfaction that the efforts we had put in have at last started to bear fruit.

V.C. Sahni is the former Director of RRCAT (November 2003-July 2009) and currently the Homi Bhabha Chair Professor at BARC. He was also the Indian Co-Chair of the Joint Coordination Committee for DAE-CERN Collaboration.

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