NCLinac - Technology for normal

conducting higher energy linear

accelerators (Work package 9)

Objectives:

NCLinac concentrates on the identified issues in R&D to prepare for the future HEP Particle colliders that can reach beyond the LHC; it is generally agreed that a collider of this next generation will be a linear electron-positron collider. The issues to be addressed are primarily

1. how to reach a high accelerating gradient reliably and
2. how to stabilize the beams and the machine to allow collisions of nm-sized beams without loss of luminosity. For the first, NCLinac limits its scope to normal conducting accelerator structures, complementary to work on superconducting accelerator structures foreseen in the work package SRF.

For the latter issue, synergy is actively sought and implemented between the superconducting (SC) and normal conducting (NC) linear collider approaches, where we have observed in the past that the communities of researchers had formed two separate camps. Searching their similarities rather than their differences, one goal of NCLinac is to bring these communities together again wherever possible. Issues concerning the longitudinal phase-space (phase stabilisation) are included. Other topics are the need to measure beam positions, profiles and movements to the required level of precision and to elaborate and test algorithms for their active steering. NCLinac is complementing a presently ongoing program of R&D; it uses and enforces readily established global research networks like the CLIC/CTF3 collaboration or the Global Design Effort (GDE) for the ILC. The high-gradient research will be coordinated with the existing US High-Gradient Collaboration. NCLinac will improve and make available for a wider community of researchers purpose built and recognized world-class Research Infrastructures like the CLIC Test Facility CTF3 at CERN and the DAΦNE facility at Frascati, but also the world-wide only facility to address issues for extremely small emittances, ATF2 at KEK in Japan, is included.

Task1. NCLinac Coordination and Communication

• Coordination and scheduling of the WP tasks
• monitoring the work, informing the project management and participants within the WP
• WP budget follow-up

Task2. Normal Conducting High Gradient Cavities

• Investigate fundamental high-precision, high-power and HOM damping technical and scientific issues underlying the CLIC module
• Prepare hardware to test a CLIC module in the two-beam test stand of CTF3

Task3. Linac & FF Stabilisation

• Design, build and test for stabilisation a CLIC quadrupole module in an accelerator environment
• Design, build and test for stabilisation a Final Focus test stand

Task 4. Beam Delivery System

• Develop tuning strategies at ATF2
• Optimize the Linear Collider interaction region

Task 5. Drive Beam Phase Control

• Design, build and test a low-impedance RF beam phase monitor with a resolution of 20 fs
• Design, build and test an electro-optical phase monitor with a resolution of 20 fs

Description of work:

Task 1. NCLinac Coordination and Communication

The activities of this task are to oversee and co-ordinate the work of all the other tasks of the work package concerned, to ensure the consistency of the WP work according to the project plan and to coordinate the WP technical and scientific tasks with the tasks carried out by the other work packages when it is relevant. The coordination duties also include the organization of WP internal steering meetings, the setting up of proper reviewing, the reporting to the project management and the distribution of the information within the WP as well as to the other work packages running in parallel.

The task also covers the organization of and support to the annual meetings dedicated to the WP activity review and possible activity workshops or specialized working sessions, implying the attendance of invited participants from inside and outside the consortium.

Task 2. Normal Conducting High Gradient Cavities

The energy and luminosity design parameters for CLIC are 3 TeV and 6*1034 cm-2 s-1 respectively, and CLIC stands here synonymous for any future multi-TeV linear collider. These parameters result in extremely demanding requirements for the accelerating structures in terms of the accelerating gradient (100 MV/m or higher), high-power (of the order of 100 MW), tight mechanical tolerance (microns to tens of microns) and strong higher-order mode damping (complex geometries). A further level of difficulty is encountered when the challenges must be addressed simultaneously as is the case in the CLIC module.

The CLIC Test Facility 3 (CTF3) has been constructed to address the above issues to demonstrate feasibility of a multi-TeV linear collider based on CLIC technology. This project seeks to complement ongoing efforts, which are addressing the individual requirements, by concentrating primarily on questions of the integration, i.e. to simultaneously satisfy requirements of highest possible gradient, power handling, tight mechanical tolerances and heavy HOM damping. In addition this project will enhance the expansion of the CLIC study from its origins as a CERN project to a truly international collaboration. Existing collaborations with SLAC and KEK will be built upon and included in this project.

• Sub-task 1: Design, manufacture, and validate experimentally a Power Extraction and Transfer Structure (PETS) prototype to improve CTF3.
• Sub-task 2: Explore influence of alignment errors on wake fields, elaborate and demonstrate appropriate High Order Mode (HOM) damping in the presence of alignment errors.
• Sub-task 3: Breakdown simulation: Develop and use atomistic simulations of atom migration enhanced by the electric field or by bombarding particles, understand what kind of roughening mechanisms lead to the onset of RF breakdown in high gradient accelerating structures.
• Sub-task 4: Design and build equipment to diagnose the electrons, ions and light emanating from the breakdown event both in the CTF3 Two-Beam Test-Stand at CERN and inside a scanning electron microscope in UU to analyze the surface science relevant to RF-breakdown.
• Sub-task 5: Precise assembly: Develop a strategy of assembly for the CLIC accelerating and power extraction structures satisfying the few to 10 micrometer precision requirement of positioning both radial and longitudinal taking into account dynamical effects present during accelerator operation.

Task 3. Linac & FF stabilisation

In the future linear colliders such as ILC and CLIC, beam sizes will be of the nanometre scale. In a real accelerator environment, many sources of noise such as ground motion, pumping devices, acoustic vibrations, cooling systems and others are present, sources which generate vibrations several orders of magnitude larger than the beam size. Stabilization of accelerator components such as the final focus (FF) is critical if the desired nanometre beam sizes are to be reached. It is particularly challenging for the CLIC project, where a stability of 1 nm above one Hertz is required even in the linac section, 0.1 nm above a few Hertz in the FF section. In a laboratory environment, these values could already be demonstrated. It is planned in this project to study the effectiveness of stabilisation equipment (such as seismic sensors, actuators, interferometers etc…) in a real accelerator environment. The equipment will be implemented at a CLIC quadrupole module inside the CTF3 facility, in the first stage with a quadrupole mock-up. In addition it is planned to use a CLIC standard module for comparing the vibration measurements with a laser interferometer (which can also serve as an alignment device) and the seismic sensors. The compatibility of these stabilisation devices with the alignment system that will be used in CLIC will be checked. A dedicated FF test stand will be built with a support and magnet prototype where the stabilisation will be developed. Furthermore, the stabilisation procedures will be simulated to ensure a better understanding of the beam-based feedback, stabilisation and the alignment. This will be tested on different accelerator facilities such as ATF2, CTF3 in preparation of ILC and CLIC.

• Sub-task 1: CLIC quadrupole module. CERN together with LAPP aims at demonstrating 1 nm quadrupole stability for the CLIC main linac quadrupole. Investigation of stabilisation feedback performance in different locations, e.g. an accelerator test tunnel will be performed. The aim is to demonstrate better than 1 nm stability of the main linac quadrupoles in an accelerator environment above frequencies of approximately 1 Hz. Inertial sensors will be tested and evaluated for accelerator environment (magnetic field, radiation, electrical and acoustic noise from accelerator components). The module needs a main beam linac support: study vibration isolation for the main beam quadrupole (principle, mock-up, feedback to be adapted to new boundary conditions) and build a test bench. The interferometric measurement system, developed in UOXF-DL, will be installed at the Final Focus Test stand and will be used to cross check results and extend the frequency range. CERN will also study the design and construction of main linac prototype magnet. The stabilisation of the main linac quadrupoles is one of the fundamental issues of CLIC. This activity aims to design and build a quadrupole mock-up that can serve as a model for the main linac quadrupole. New magnet manufacturing and assembly methods will be studied and implemented. The model will be used to investigate the performance of the stabilisation equipment that is also developed in this task.
  
  CERN aims at testing the compatibility (space, interferences, and complementarities) between the repositioning system (movers + associated sensors) and the stabilization system foreseen for the main beam quadrupole of CTF3/CLIC, in the real environment of the two beam test stand.

• Sub-task 2: Final Focus Test stand. LAPP together with CERN aims at exploring the potential to achieve 0.1 nm stability scale for the final doublet quadrupoles above a few Hz by working on the design, simulation, construction and installation of the support (final doublet mock-up, eigenmode analysis) and on the feedback design depending strongly on the final doublet support chosen. LAPP will adapt feedback software to new configuration and boundary conditions and continue work to reduce costs.
  
  Oxford aims at studying the design, construction and deployment of an interferometric system to measure the motion between the proposed test magnet/girder and floor. This task includes the installation of interferometric system with the goal to push for maximum resolution and the possibility to correlate results with measurements done by inertial sensors. UOXF-DL will contribute to the Development of optimized low-emittance beam transport and feedback for ILC and CLIC by completing an ILC prototype ATF2 intra-train and pulse-pulse Feedback and Final Focus system. In addition, they will study the simulation of the global luminosity performance of ILC and CLIC.

Task 4. Beam Delivery System

Key aspects and sub-systems of the ILC/CLIC beam delivery system will be developed and tested. The projects proposed here are new initiatives emerging from the results of the FP6 scheme (EUROTeV) with particular emphasis on developing and exploiting existing infrastructure at ATF2, CTF3, and PETRAIII. ATF2 will be the main international test facility for beam delivery studies over the period of FP7. Tuning procedures will be developed and tested at ATF2 and they will provide essential input into optimizing the CLIC IR region, which will also be performed in this context. Advanced BPMs will be employed and tested at the ATF2 and their integration with other systems optimized. Laser-wire measurements will also be made at PETRAIII, where a fast scanning system will be tested and the challenges of integrating a laser-wire as a reliable machine diagnostic tool will be met.

• Sub-task 1: The CI at Manchester (UNIMAN) and STFC at Daresbury will test the tuning procedures at the ATF2 and use this knowledge to optimize the designs of the interaction region of both ILC and CLIC. Different tuning procedures and tuning knobs will be tested at ATF2 to achieve the vertical beam size down to 35 nm; the proposed local chromaticity correction final focus system will be tested experimentally for the first time and various tuning procedures will also be applied to ILC and CLIC to optimize the interaction region (IR). The CLIC IR will be studied in detail, and the impact and mitigation of CLIC detector solenoid effects on the beam orbit, coupling and extraction will be considered. A further goal is to strengthen the computing infrastructure for tracking tools to be used at ATF2/ILC/CLIC and validate them experimentally.
• Sub-task 2: At RHUL, high precision BPMs will be developed and tested at the ATF2 with particular emphasis on systems integration. The implications for ILC and CLIC beam diagnostics will be determined via full simulations using these experimental results.
• Sub-task 3: At RHUL, Laser-Wire systems will be developed and tested at the ATF2 and PETRAIII with particular emphasis on high-speed operation. The implications for ILC and CLIC beam diagnostics will be determined via full simulations using these experimental results.

Task 5. Drive Beam Phase Control

Very precise synchronization between main and drive beams is required in CLIC to avoid excessive luminosity loss due to energy variations. For this reason drive beam phase errors should be reduced by a phase feedback system within about 0.1 degrees (23 fs @ 12 GHz). The front end of this feedback system will consist of a monitor able to detect the longitudinal position of the bunches with a resolution of the order of 20 fs. The coupling impedance of the monitor has to be very low due to the high beam current. RF noise and wake fields in the beam pipe must not affect the measurement and have to be rejected by proper designed filters. This device will find applications in other machines where precise high frequency beam phase detection is required. Two possible solutions will be investigated at the same time. A low impedance RF phase monitor with an integrated noise filter will be designed and built by CERN and INFN. It will be tested in CTF3 where it will also play an important diagnostic role in the optimization of the machine performances. An electro-optical monitor using periodic train of laser pulses to sample signal from wide bandwidth beam pickup will be developed and built by PSI and will be tested at the existing facilities at PSI.

• Sub-task 1: CERN will determine the specifications and will produce a conceptual design report of the RF monitor. CERN and INFN will attend together to the electromagnetic design and then they will produce a building design of the monitor. CERN will develop and realize the related electronics. INFN will build prototypes of the monitor that will be measured and tested in lab. A final version of the monitor will be built and the performances of the system will be tested in CTF3.
• Sub-task 2: The electro-optical monitor will be designed by PSI. PSI will implement prototypes of the system, which includes pick-up, laser, electro optical detector and electronics. The performances of the system will be tested in the existing facilities at PSI.

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