In response to the 2013 Update of the European Strategy for Particle Physics, the Future Circular Collider (FCC) study was launched, as an international collaboration hosted by CERN. This study covers a highest-luminosity high-energy lepton collider (FCC-ee) and an energy-frontier hadron collider (FCC-hh), which could, successively, be installed in the same 100 km tunnel. The scientific capabilities of the integrated FCC programme would serve the worldwide community throughout the 21st century. The FCC study also investigates an LHC energy upgrade, using FCC-hh technology. This document constitutes the second volume of the FCC Conceptual Design Report, devoted to the electron-positron collider FCC-ee. After summarizing the physics discovery opportunities, it presents the accelerator design, performance reach, a staged operation scenario, the underlying technologies, civil engineering, technical infrastructure, and an implementation plan. FCC-ee can be built with today’s technology. Most of the FCC-ee infrastructure could be reused for FCC-hh. Combining concepts from past and present lepton colliders and adding a few novel elements, the FCC-ee design promises outstandingly high luminosity. This will make the FCC-ee a unique precision instrument to study the heaviest known particles (Z, W and H bosons and the top quark), offering great direct and indirect sensitivity to new physics.

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FCC-ee: The Lepton Collider: Future Circular Collider Conceptual Design Report Volume 2

Particle physics has arrived at an important moment of its history. The discovery of the Higgs boson, with a mass of 125 GeV, completes the matrix of particles and interactions that has constituted the “Standard Model” for several decades. This model is a consistent and predictive theory, which has so far proven successful at describing all phenomena accessible to collider experiments. However, several experimental facts do require the extension of the Standard Model and explanations are needed for observations such as the abundance of matter over antimatter, the striking evidence for dark matter and the non-zero neutrino masses. Theoretical issues such as the hierarchy problem, and, more in general, the dynamical origin of the Higgs mechanism, do likewise point to the existence of physics beyond the Standard Model. This report contains the description of a novel research infrastructure based on a highest-energy hadron collider with a centre-of-mass collision energy of 100 TeV and an integrated luminosity of at least a factor of 5 larger than the HL-LHC. It will extend the current energy frontier by almost an order of magnitude. The mass reach for direct discovery will reach several tens of TeV, and allow, for example, to produce new particles whose existence could be indirectly exposed by precision measurements during the earlier preceding e+e– collider phase. This collider will also precisely measure the Higgs self-coupling and thoroughly explore the dynamics of electroweak symmetry breaking at the TeV scale, to elucidate the nature of the electroweak phase transition. WIMPs as thermal dark matter candidates will be discovered, or ruled out. As a single project, this particle collider infrastructure will serve the world-wide physics community for about 25 years and, in combination with a lepton collider (see FCC conceptual design report volume 2), will provide a research tool until the end of the 21st century. Collision energies beyond 100 TeV can be considered when using high-temperature superconductors. The European Strategy for Particle Physics (ESPP) update 2013 stated “To stay at the forefront of particle physics, Europe needs to be in a position to propose an ambitious post-LHC accelerator project at CERN by the time of the next Strategy update”. The FCC study has implemented the ESPP recommendation by developing a long-term vision for an “accelerator project in a global context”. This document describes the detailed design and preparation of a construction project for a post-LHC circular energy frontier collider “in collaboration with national institutes, laboratories and universities worldwide”, and enhanced by a strong participation of industrial partners. Now, a coordinated preparation effort can be based on a core of an ever-growing consortium of already more than 135 institutes worldwide. The technology for constructing a high-energy circular hadron collider can be brought to the technology readiness level required for constructing within the coming ten years through a focused R&D programme. The FCC-hh concept comprises in the baseline scenario a power-saving, low-temperature superconducting magnet system based on an evolution of the Nb3Sn technology pioneered at the HL-LHC, an energy-efficient cryogenic refrigeration infrastructure based on a neon-helium (Nelium) light gas mixture, a high-reliability and low loss cryogen distribution infrastructure based on Invar, high-power distributed beam transfer using superconducting elements and local magnet energy recovery and re-use technologies that are already gradually introduced at other CERN accelerators. On a longer timescale, high-temperature superconductors can be developed together with industrial partners to achieve an even more energy efficient particle collider or to reach even higher collision energies.The re-use of the LHC and its injector chain, which also serve for a concurrently running physics programme, is an essential lever to come to an overall sustainable research infrastructure at the energy frontier. Strategic R&D for FCC-hh aims at minimising construction cost and energy consumption, while maximising the socio-economic impact. It will mitigate technology-related risks and ensure that industry can benefit from an acceptable utility. Concerning the implementation, a preparatory phase of about eight years is both necessary and adequate to establish the project governance and organisation structures, to build the international machine and experiment consortia, to develop a territorial implantation plan in agreement with the host-states’ requirements, to optimise the disposal of land and underground volumes, and to prepare the civil engineering project. Such a large-scale, international fundamental research infrastructure, tightly involving industrial partners and providing training at all education levels, will be a strong motor of economic and societal development in all participating nations. The FCC study has implemented a set of actions towards a coherent vision for the world-wide high-energy and particle physics community, providing a collaborative framework for topically complementary and geographically well-balanced contributions. This conceptual design report lays the foundation for a subsequent infrastructure preparatory and technical design phase.

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FCC-hh: The Hadron Collider

The Compact Linear Collider (CLIC) is a TeV-scale high-luminosity linear $e^+e^-$ collider under development by international collaborations hosted by CERN. This document provides an overview of the design, technology, and implementation aspects of the CLIC accelerator. For an optimal exploitation of its physics potential, CLIC is foreseen to be built and operated in stages, at centre-of-mass energies of 380 GeV, 1.5 TeV and 3 TeV, for a site length ranging between 11 km and 50 km. CLIC uses a Two-Beam acceleration scheme, in which normal-conducting high-gradient 12 GHz accelerating structures are powered via a high-current Drive Beam. For the first stage, an alternative with X-band klystron powering is also considered. CLIC accelerator optimisation, technical developments, and system tests have resulted insignificant progress in recent years. Moreover, this has led to an increased energy efficiency and reduced power consumption of around 170 MW for the 380 GeV stage, together with a reduced cost estimate of approximately 6 billion CHF. The construction of the first CLIC energy stage could start as early as 2026 and first beams would be available by 2035, marking the beginning of a physics programme spanning 25-30 years and providing excellent sensitivity to Beyond Standard Model physics, through direct searches and via a broad set of precision measurements of Standard Model processes, particularly in the Higgs and top-quark sectors.

The Compact Linear Collider (CLIC) – Project Implementation Plan

The compact linear collider (CLIC) study is exploring the scheme for an electron–positron collider with high luminosity and a nominal center-of-mass energy of 3 TeV. The CLIC predamping rings (DRs) and DRs will produce, through synchrotron radiation, ultralow emittance beam with high bunch charge, necessary for the luminosity performance of the collider. To limit the beam emittance blow-up due to oscillations, the pulse generators for the DR kickers must provide extremely flat, high voltage, pulses. The specifications for the DR extraction kickers call for a 160- or 900-ns duration flat-top pulse of ±12.5 kV, with a combined ripple and droop of not more than ±0.02% (±2.5 V) for each pulse: an inductive adder is a very promising approach to meet the specifications. Recently, the first 20 layer, 12.5 kV, full-scale prototype inductive adder has been assembled at CERN and testing has commenced. This paper presents flat-top stability and repeatability measurements of the output waveforms of this full-scale prototype inductive adder for CLIC DR kicker systems. The pulse waveforms have been recorded with an oscilloscope which has nominally 16-bit resolution and allows measurements of minimum and maximum envelope curves for a large number of consecutive output waveforms. Both passive and active modulation methods have been applied to improve the relative flat-top stability of the prototype inductive adder to meet the specification of ±0.02%.

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Prototype Inductive Adders With Extremely Flat-Top Output Pulses for the Compact Linear Collider at CERN

A 100 TeV centre-of-mass energy frontier proton collider in a new tunnel of ~100 km circumference is a central part of CERN’s Future Circular Colliders (FCC) design study. One of the major challenges for such a machine will be the beam injection and extraction. This paper outlines the recent developments on the injection and extraction kicker system concepts. For injection the system requirements and progress on a new inductive adder design will be presented together with first considerations on the injection kicker magnets. The extraction kicker system comprises the extraction kickers itself as well as the beam dilution kickers, both of which will be part of the FCC beam dump system and will have to reliably abort proton beams with stored energies in the range of 8.5 Gigajoule. First concepts for the beam dump kicker magnet and generator as well as for the dilution kicker system are described and its feasibility for an abort gap in the 1 μs range is discussed. The potential implications on the overall machine and other key subsystems are outlined, including requirements on (and from) dilution patterns, interlocking, beam intercepting devices and insertion design. INJECTION SYSTEM The injection kicker system into the FCC is mainly dominated by the stored beam energy of the injected beam. For machine protection reasons the maximum batch length is defined to be not longer than 2.25 μs for 3.3 TeV beam. Several injection energies are being reviewed [1] whilst this paper only focuses on the 3.3 TeV beam injection. To achieve, nevertheless, a reasonable filling factor the system rise time has been defined as ≤280 ns with a repetition rate of 115 Hz. All requirements are summarized in Table 1. Magnet The required fast rise time suggests the utilisation of transmission line type kicker magnets similar to those used for injection into the LHC. Together with the system impedance, the magnet filling time will define the magnet length and number of units. Preliminary calculations show current values of up to 2.6 kA and voltages of up to 13 kV. The magnet will be an in-vacuum type design, to be equipped with a sophisticated beam screen optimized for beam impedance and fast pulsed fields. Pulse Generator The pulse generator for injection of 3.3 TeV beam has to be fast (<100 ns) to allow for a reasonable magnet filling time. For reliability reasons the design has been constrained on solid state switches. The short pulse length of 2.25 μs allows to consider an inductive adder (IA) type generator as a promising option. Table 1: Injection and Extraction Kicker Requirements. Parameter Injection Extraction Available length [m] 130 130 Kinetic Energy [TeV] 3.3 3.3-50 Angle [mrad] 0.3 0.13 Pulse length [μs] 2.25 330 Flat top tolerance [%] ±0.5 ± ~5% Field rise time [μs] 0.28 1 The IA consists of a stack of several 1:1 transformers (Fig. 1). Pulse capacitors are discharged through semiconductor (SC) switches into the primary winding. To keep the inductance of the primary circuit as small as possible the primary winding completely encloses the transformer core. The secondary winding passes through the middle of all transformer cores (Fig. 1). The cylindrical design strongly influences the main parameters such as output impedance and pulse propagation time. The number of layers defines the output voltage and the number of parallel branches, on the primary side of the transformer, defines the output current. Major components of the IA are the SC-switches, pulse capacitors, magnetic cores and high voltage freewheeling diodes [2]. Figure 1: Schematic illustration of two inductive adder layers. Advantages of the IA compared with other options such as pulse forming line (PFL) or pulse forming network (PFN) and their associated switches are [2]: Proceedings of IPAC2016, Busan, Korea THPOR049 07 Accelerator Technology T16 Pulsed Power Technology ISBN 978-3-95450-147-2 3901 C op yr ig ht © 20 16 C C -B Y3. 0 an d by th e re sp ec tiv e au th or s  Moderate requirements for switch technology hence SC-switches can be used: no thyratrons are necessary;  All primary circuits are referenced to ground: High voltage occurs only at output connectors;  Redundancy can be built in easily;  Modular design: Device is scalable, easy to adapt to certain applications. Due to saturation effects of the magnetic core the maximum pulse length is limited to approximately 3 μs, mainly depending on the voltage per layer and material properties.  Insulation material An important aspect of the IA is the insulation material between the primary and secondary transformer winding. Several materials have been analysed: air, oil, water, FC77 and epoxy. Oil turned out to be the most suitable candidate in terms of required system impedance, dimensions, rise time, costs and practicability. The minimum dimension of the stalk diameter for a 5 Ω impedance and oil as dielectric is 6.2 cm which results in an oil insulation thickness of only 1.3 mm. To ease the production of the insulation gap and to provide compatibility with the CLIC prototype a stalk diameter of 10.4 cm has been chosen resulting in an insulation gap of 2.2 mm.  Semiconductor switches Suitable SC-switches for the IA need to have fast rise and fall times, low on-state resistance as well as high voltage and current ratings to reduce the number of layers and parallel branches. Modern SiC MOSFETs are the most promising family of currently available SC-switches. Voltages of up to 1700 V and peak currents of more than 100 A with rise times below 10 ns are feasible. As this “wide band gap” technology is rather new, further development can be expected.  Pulse capacitors The pulse capacitors used in the IA must have very low inductance and suitable voltage and current ratings. To guarantee long life times the charging voltage should be derated. For the FCC IA a capacity of 52 μF and peak current values of 110 A are needed. Adding an analogue modulation (1Ω) layer in the stack reduces the capacity requirements down to a value of ~33 μF (or lower). A drawback of the analogue modulation layer is that it reduces the output voltage and hence more layers are needed to compensate this effect [3]. Custom made capacitors for this application are available and need to be tested under appropriate conditions.  Magnetic cores Probably the most critical component of the IA, not only from the technical point of view but also in terms of costs, is the magnetic core. A nanocrystalline, tape wound core will be used. For the required pulse parameters a core cross section of Ac = 25 cm2 is required. The inner diameter is defined by the system impedance, voltage and insulation material. The core height will be kept small to reduce output pulse rise time, and the outer diameter is currently dependent on production constraints. Packing factors in the range of up to 73 % can be reached for the core. Important parameters of the magnetic core are the linear flux density swing, saturation flux density, core losses and magnetizing inductance [4]. To avoid saturation the material saturation flux density needs to be as high as possible (>1 T) and biasing will be necessary to use the entire flux density span (ΔB = 2 T). The core losses should be low and the magnetizing inductance high to reduce the magnetizing current in the primary loop. Samples of cores have been ordered for tests and measurements.  High Voltage Diodes The high voltage diodes in the primary circuits of the IA carry the magnetizing current when the SC-switch is turned off. During a possible fault in which one layer is not turning on, the diodes offer a path for the load current and hence need to be fast switching to avoid over voltages. Prototype Construction and Challenges Component samples have been ordered for characterization, test and measurements to be done later in 2016 resulting in the final component selection. A prototype will be built in 2017 to prove the feasibility of pulse length, low ripple, rise time and reliability. The design of the IA prototype for the FCC study will be based on the design for the prototype IA for the CLIC DR kicker systems [3]. The components discussed can be tested with existing test equipment. The mechanical design needs to be adapted to realize oil insulation and magnetic core dimensions. Main challenges will be the realization of the small insulation gap as well as the fast rise time and long flat top. As a further option the development of a radiation hard generator is envisaged. EXTRACTION KICKER SYSTEM The extraction kicker system comprises the extraction kickers as well as the beam dilution kickers, both of which will be part of the FCC beam dump system and will have to reliably abort p+ beams with stored energies in the range of up to 8.5 GJ. Whilst different extraction insertions are still being discussed [5] all of them comprise the same basic kicker concepts further outlined in this paper. Extraction System First technical considerations on different kicker concepts have been outlined [6] and the most promising solution of a segmented kicker system has been further followed. The advantage of the segmented system is that up to 300 units per beam allow for a kick strength per unit which is not exceeding an one sigma oscillation in a prefire failure, reducing significantly the probability of an asynchronous dump event. But more importantly the short magnets also provide a low inductance and hence allow for a shorter system rise time of 1 μs, imposing significantly less beam load onto the protection devices during asynchronous dump failures [7]. In addition the lower THPOR049 Proceedings of IPAC2016, Busan, Korea ISBN 978-3-95450-147-2 3902 C op yr ig ht © 20 16 C C -B Y3. 0 an d by th e re sp ec tiv e au th or s 07 Accelerator Technology T16 Pulsed Power Technology current and voltage per unit, in comparison with the existing LHC dump system, results in reasonable generator design values, beneficially influencing the switch sele

Considerations for the Injection and Extraction Kicker Systems of a 100 TeV Centre-of-Mass FCC-hh Collider

Line-type modulators, for example pulse forming lines and pulse forming networks, which use thyratron switches, are currently used in many pulse power systems at CERN. Solid-state modulators implemented with inductive adder technology could replace thyratron based designs in many applications and potentially improve dynamic range, maintainability and reliability of the systems. This paper will discuss the application of an inductive adder for the pulse power modulator of both a future circular collider and as an upgrade to an existing, 45 year old, kicker system.

Inductive adders for replacing thyratron based modulators at CERN

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Inductive adders for replacing thyratron based modulators at CERN