RF power for the Next Linear Collider

In order to maintain a reasonable over-all length at high center-of-mass energy, the main linac of an electron-positron linear collider must operate at a high accelerating gradient. For copper (non-superconducting) accelerator structures, this implies a high peak power per unit length and a high peak power per RF source, assuming a limited number of discrete sources are used. To provide this power, a number of devices are currently under active development or conceptual consideration: conventional klystrons with multi-cavity output structures, gyroklystrons, magnicons, sheet-beam klystrons, multiple-beam klystrons and amplifiers based on the FEL principle. To enhance the peak power produced by an rf source, the SLED rf pulse compression scheme is currently in use on existing linacs, and new compression methods that produce a flatter output pulse are being considered for future linear colliders. This paper covers the present status and future outlook for the more important rf power sources and pulse compression systems. It should be noted that high gradient electron linacs have applications in addition to high-energy linear colliders; they can, for example, serve as compact injectors for FEL`s and storage rings.

A bstract We study the electromagnetic form factors of electrically neutral dark-sector particles in this paper. Concretely speaking, we focus on the operators that can lead to interactions of fermionic dark states with the Standard-Model (SM) photon, including both dimension-5 (the magnetic and electric dipole moments) and dimension-6 (the anapole moment and charge radius) operators. Correspondingly, instead of the SM-photon form factors, we employ hypercharge gauge-field form factors that can induce additional couplings to the SM Z -boson. Utilizing the mono-photon production channel at future linear electron-positron colliders, the International Linear Collider (ILC) and the Compact Linear Collider (CLIC), we demonstrate that tuning beam polarization allows for simultaneous enhancement of signal-event rates and suppression of dominant SM background events, i.e. neutrino-induced processes, and hence improvement of sensitivity reach. Our analysis reveals that ILC and CLIC can probe electromagnetic form factors of dark-sector particles up to about two orders of magnitude beyond existing experimental limits. We also estimate, at the order-of-magnitude level, the validity range of the effective-field-theory (EFT) approach we adopt, finding that for the dimension-5 operators the EFT remains valid in most of the parameter regions to which the ILC and CLIC can be sensitive, while it breaks down in the entire sensitivity region for the dimension-6 operators.

We present a multimode X-band rf pulse compression system suitable for the Next Linear Collider (NLC). The NLC main linacs operate at 11.424 GHz. A single NLC rf unit is required which produce 400 ns pulses with 600 MW of peak power. Each rf unit should power approximately 5 meters of accelerator structures. These rf units consist of two 75 MW klystrons and a dual-moded resonant delay line pulse compression system [1] that produce a flat output pulse. The pulse compression system components are all over moded and most components are design to operate with two modes at the same time. This approach allows increasing the power handling capabilities of the system while maintain a compact inexpensive system. We detail the design of this system and present experimental cold test results. The high power testing of the system is verified using four 50-MW solenoid focused klystrons. These Klystrons should be able to push the system beyond NLC requirements.

The Stanford Linear Accelerator Center (SLAC) version of the 1 TeV next linear collider (NLC) requires a 4:1 increase in drive frequency, from the 2.85 GHz of the 1 TeV Stanford Linear Collider (SLC) to 11:4 GHz for the NLC. More than eight years have gone into the development of a new 75-MW klystron for powering the NLC. The increase in power density and surface RF gradient at the higher frequency have rendered previous RF window and circuit designs unusable. Following numerous catastrophic gun, cavity, and window failures, new designs have evolved that solved the problems. As history's most ambitious klystron development enters its last year, the result includes a robust 75-MW peak power solenoid-focused, 50% efficient klystron. Not far behind is a 60-75-MW periodic permanent magnet (PPM)-focused 60% efficient version that will reduce the NLC electric power bill by tens of millions of dollars per year.

The magnicon is a RF power source with circular beam deflection invented in the 1980's at Budker INP. The first magnicon with the power of 2.6 MW and efficiency of 73% at 915 MHz was built and tested in the pulse of 30 /spl mu/sec in 1985. The second magnicon was developed as a prototype RF source for a linear collider. In order to achieve power of more than 50 MW at 7 GHz, the tube was built as a frequency doubling amplifier. The following parameters finally were achieved in 1998: power of 55 MW, efficiency of 56% and the gain of 72 dB in a pulse of 1.1 /spl mu/sec. The X-band (11.424 GHz) magnicon is being developed jointly by Omega-P, Inc. and NRL as a potential high efficiency RF source for the Next Linear Collider (NLC) project. As for the 7 GHz device, this 11.424 GHz magnicon is a frequency doubling amplifier. The design has been optimized for the parameters of a 500 kV, 210 A, 1 /spl mu/sec modulator with the repetition rate of 10 Hz. This modulator was built for NRL by Titan Beta for a previous project. We present a progress report on 11.424 GHz magnicon as well as the results of the gun tests and the beam envelope measurements.

The International Linear Collider (ILC) and the Compact Linear Collider (CLIC) are the two options for a future high-energy, high-luminosity linear electron-positron collider. Both are expected to be built in stages, optimised for their physics potential. The main goals are the precision measurements of Higgs-boson and top-quark properties as well as direct and indirect searches for new physics Beyond Standard Model. In my talk I will review some of the latest results from both ILC and CLIC demonstrating their physics potential, pointing to similarities and complementarity of both projects.

We discuss the production of the doubly charged leptons in future linear electron positron colliders, such as the International Linear Collider and Compact Linear Collider. Such states are introduced in extended weak-isospin multiplets by composite models. We discuss the production cross section of and carry out analyses for hadronic, semi-leptonic and pure leptonic channels based on the full simulation performance of the silicon detector. The 3- and 5-sigma statistical significance exclusion curves are provided in the model parameter space. It is found that the hadronic channel could offer the most possible detectable signature.

A lepton collider capable of generating a luminosity of 5×1033 to 1×1034 at center-of-mass energies from 0.5 to 1.5 TeV would permit studies of fundamental interactions complementary to those planned at the Large Hadron Collider. Such energies would be more easily achieved for electrons at a linear collider than a conventional storage ring. We describe the Next Linear Collider (NLC), a proposed linear collider which utilizes room-temperature RF systems operating at 11.4 GHz to achieve the desired energies and room-temperature electromagnets and permanent magnets to achieve the extremely small beam sizes required to meet the specified luminosity goal. The NLC design has been optimized to permit electron–electron collisions as well as electron–positron collisions. We discuss a few of the detailed technical challenges which are posed by electron–electron collisions in the NLC parameter regime.

The proposed Next Linear Collider (NLC) will require over 1400 adjustable quadrupoles between the main linacs' accelerator structures. These 12.7 mm bore quadrupoles will have a range of integrated strength from 0.6 to 138 Tesla, with a maximum gradient of 141 Tesla per meter, an adjustment range of +0 to -20% and effective lengths from 324 mm to 972 mm. The magnetic center must remain stable to within 1 micron during the 20% adjustment. In an effort to reduce costs and increase reliability, several designs using hybrid permanent magnets have been developed. Four different prototypes have been built. All magnets have iron poles and use Samarium Cobalt to provide the magnetic fields. Two use rotating permanent magnetic material to vary the gradient, one uses a sliding shunt to vary the gradient and the fourth uses counter rotating magnets. Preliminary data on gradient strength, temperature stability, and magnetic center position stability are presented. These data are compared to an equivalent electromagnetic prototype.

The Next Linear Collider (NLC) will require over 5600 magnets, each of which must be highly reliable and/or quickly repairable in order that the NLC reach its 85% overall availability goal. A multidiscipline engineering team was assembled at SLAC to develop a more reliable electromagnet design than historically had been achieved at SLAC. This team carried out a Failure Mode and Effects Analysis (FMEA) on a standard SLAC quadrupole magnet system. They overcame a number of longstanding design prejudices, producing 10 major design changes. This paper describes how a prototype magnet was constructed and the extensive testing carried out on it to prove full functionality with an improvement in reliability. The magnet's fabrication cost will be compared to the cost of a magnet with the same requirements made in the historic SLAC way. The NLC will use over 1600 of these 12.7 mm bore quadrupoles with a range of integrated strengths from 0.6 to 132 Tesla, a maximum gradient of 135 Tesla per meter, an adjustment range of 0 to -20% and core lengths from 324 mm to 972 mm. The magnetic center must remain stable to within 1 micron during the 20% adjustment. A magnetic measurement set-up has been developed that can measure sub-micron shifts of a magnetic center. The prototype satisfied the center shift requirement over the full range of integrated strengths.

The Next Linear Collider (NLC) uses a damping ring for the electron beam, a pre-damping ring and a main damping ring for the positron beam to reduce the beam emittances. The requirements of the main damping ring kickers are to bend a 2 GeV beam by an angle of 2 mrad over a length of 1.2 m. This results in a required field of 139 G. The magnet aperture is 30/spl times/30 mm. The pre-damping ring kicker requirements are based on a 2 GeV beam with a bend angle of 8 mrad in 1.2 m, or a field of 308 G. The magnet aperture is 62/spl times/45 mm (H/spl times/V). A pulse width is 130 ns with rise and fall times of less than 60 ns is the same for both the pre-damping ring and main damping ring kickers. The three rings operate at a 180 Hz repetition rate. The kicker magnets being developed to meet these requirements consist of two strip line conductors in the vacuum chamber, for the pre-damping ring kickers they may be loaded with ferrite, to give a matching impedance of 25 /spl Omega/. The buses are separated from magnetic flux linkage by a grounded flux excluder, which also serves as a low impedance return for the beam current. Both busses of the magnet are driven in parallel from the same modulator and are grounded at the end opposite the feed. The modulator uses two IGBT stacks which both act as opening switches in order to meet the rise time requirements.

This report describes the physics potential and experiments at a future multi- TeV e+e collider based on the Compact Linear Collider (CLIC) technology. The physics scenarios considered include precision measurements of known quantities as well as the discovery potential of physics beyond the Standard Model. The report describes the detector performance required at CLIC, taking into account the interaction point environment and especially beaminduced backgrounds. Two detector concepts, designed around highly granular calorimeters and based on concepts studied for the International Linear Collider (ILC), are described and used to study the physics reach and potential of such a collider. Detector subsystems and the principal engineering challenges are illustrated. The overall performance of these CLIC detector concepts is demonstrated by studies of the performance of individual subdetector systems as well as complete simulation studies of six benchmark physics processes. These full detector simulation and reconstruction studies include beaminduced backgrounds and physics background processes. After optimisation of the detector concepts and adopting the reconstruction algorithms the results show very efficient background rejection and clearly demonstrate the physics potential at CLIC in terms of precision mass and cross section measurements. Finally, an overview of future plans of the CLIC detector and physics study is given and a list of key detector R&D topics needed for detectors at CLIC is presented.

In 2003, more than 2,700 scientists from around the world signed a published statement Understanding Matter, Energy, Space and Time: the Case for the Linear Collider [1-1]. The statement made clear the undisputed worldwide consensus that the next energy frontier machine after the Large Hadron Collider (LHC) should be an electron-positron linear collider with an initial centre-of-mass energy reach of 500 gigaelectronvolts (GeV), upgradable to 1 teraelectronvolt (TeV). In the same year, the International Committee for Future Accelerators (ICFA) commissioned the International Technology Review Panel (ITRP) to select from the then competing acceleration technologies a single technology that would be the basis for an international design effort towards a truly global project. The following year, 2004, the ITRP recommended to ICFA that the 1.3-gigahertz superconducting radiofrequency (SCRF) technology developed by the TESLA collaboration [1-2] should form the basis for the design of the International Linear Collider (ILC).

Polarized positrons and electrons at the linear collider

The Next Linear Collider (NLC) Injector System is designed to produce low emittance 8 GeV electron and positron beams at 120 hertz for injection into the NLC main linacs. Each beam consists of a 265 ns train of bunches (190 bunches spaced by 1.4 ns or 95 bunches spaced by 2.8 ns); each bunch has a population of up to 1.6 x 10{sup 10} particles for 2.8 ns (or 0.8 x 10{sup 10} particles for 1.4 ns). Horizontal and vertical emittances are specified to be {gamma}{var_epsilon}{sub x} = 3 x 10{sup -6} m-rad and {gamma}{var_epsilon}{sub y} = 2 x 10{sup -8} m-rad; bunch length at injection is variable from 90-140 {micro}m. Electron polarization of greater than 80% is required. Electron and positron beams are generated in separate accelerator complexes each of which contains the source, damping ring systems, linacs, bunch length compressors, and collimation regions. Investigation into the feasibility of polarized positrons for the NLC has begun; operations at 180 Hz and the centralization of the injector complex have been studied. The need for affordable, low technical risk, reliable injector subsystems is a major consideration in the design effort. This paper presents an overview of the NLC injector systems with an emphasis on changes in the design since 1999 [1] and discusses the planned R&D.