David Woog

TL;DR: In this article, the physics opportunities of the Future Circular Collider (FC) were reviewed, covering its e+e-, pp, ep and heavy ion programs, and the measurement capabilities of each FCC component, addressing the study of electroweak, Higgs and strong interactions.

TL;DR: The third volume of the FCC Conceptual Design Report as discussed by the authors is devoted to the hadron collider FCC-hh, and summarizes the physics discovery opportunities, presents the FCC-HH accelerator design, performance reach, and staged operation plan, discusses the underlying technologies, the civil engineering and technical infrastructure, and also sketches a possible implementation.

Abstract: 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

Abstract: The injection system for a 100 TeV centre-of-mass collider is an important part of the Future Circular Collider (FCC) study. Due to issues with conventional kicker systems, such as self-triggering and long term availability of thyratrons and limitations of HV-cables, innovative design changes are planned for the FCC injection kicker pulse generator. An inductive adder (IA) based on semiconductor (SC) switches is a promising technology for kicker systems. Its modular design, and the possibility of an active ripple suppression are significant advantages. Since the IA is a complex device, with multiple components whose characteristics are important, a detailed design study and construction of a prototype is necessary. This paper summarizes the system requirements and constraints, and describes the main components and design challenges of the prototype IA. It outlines the results from simulations and measurements on different magnetic core materials as well as on SC switches. The paper concludes on the design choices and progress for the prototype to be built at CERN.