30. Accelerator Technology for the International Linear Collider
The DOE High Energy Physics (HEP) program supports research and development for the International Linear Collider (ILC), a 500 GeV superconducting linear electron-positron collider that will probe the energy frontier with unprecedented precision. Advanced R&D is needed in support of this project in: (a) 1.3 GHz superconducting radiofrequency (SRF) systems, (b) beam instrumentation and feedback systems, (c) magnet and fast kicker technology, (d) polarized radiofrequency (RF) photocathode sources, and (e) high reliability magnet, magnet power supply, and associated control systems. Relevance to the ILC must be explicitly described. Grant applications are sought only in the following subtopics:
a. Superconducting Radiofrequency Systems—Research is needed in a variety of superconducting RF areas to support the development of the ILC. Accordingly, grant applications are sought:
(1) to develop high gradient, 1.3 GHz superconducting RF cavities, with application to the accelerating structures needed for the ILC. Multi-cell cavities, with accelerating gradients greater than 35 MV/m and Q-factors greater than 5x109, are of particular interest. Priority areas of research focus include new cavity geometries, new materials (e.g., large grain or single crystal Nb), improved methods of cavity fabrication, advances in surface preparation and processing (particularly in electropolishing), improved control of field emission, and suppression of high-field Q-slope. Research areas which provide the promise of significant results in the next few years and techniques that are suitable for automation and industrialization are preferred.
(2) for technology to support the development of fundamental power couplers and tuners for 1.3 GHz SRF cavities. Areas of interest include improvements to current coupler design (resulting in reduced conditioning time, reduced cost, and improved reliability), new tuner designs and concepts for both fast and slow tuning, as well as inexpensive broad-band 2K microwave absorbing material with repeatable electrical properties for HOM damping and resonance suppression.
(3) to develop high efficiency 1.3 GHz modulators and klystrons, capable of operation at peak power levels on the order of 10 MW, with a pulse width of 1-3 ms, at a repetition rate of 5-10 Hz. The modulator efficiency should be greater than 75%, and the klystron efficiency should be greater than 65%. Modulator designs with a small physical footprint, a high reliability, and capable of delivering high voltage pulses suitable for direct coupling to the klystron, are of greatest interest. Grant applications also are sought to develop power distribution systems suitable for the transport of L-band microwave power at the level of 10 MW (peak).
(4) to develop digital, low-level RF systems to control the phase and amplitude of SRF cavities operating at 1.3 GHz, with loaded Q-values in the range of 106. Of particular interest are systems capable of phase control at the level 0.5o or better, and amplitude control at the level of 0.1% or better. Advanced LLRF systems capable of doing vector sum control on ILC cryomodules, thus allowing each cavity to be run at its full potential, are of interest.
(5) to develop SRF cavity processing technology (such as electropolishing) to clean and improve the smoothness of the surface of multi-cell niobium (Nb) cavities; and advanced cleaning and handling techniques to eliminate particulate contamination as a source of field emission in the cavities. The processing technology should be able to demonstrate an improvement in the accelerating gradient of the cavities.
(6) for research and development leading to the design and fabrication of ILC cryomodules for 1.3 GHz superconducting cavity strings. Each ILC cryomodule contains several 1.3 GHz cavities and couplers in their He vessels, quadrupoles, tuners, as well as a 2K helium distribution system. Improvements in cryomodule design and fabrication which will result in lower cost are of particular interest.
(7) to increase the technical refrigeration efficiency – from 20% Carnot to 30% Carnot – for large systems (e.g. 10 kW at 2K), while maintaining higher efficiency over a capacity turndown of up to 50%. This might be done, for example, by reducing the number of compression stages or by improving the efficiency of stages. Grant applications also are sought to develop improved and highly efficient liquid helium distribution systems.
(8) to develop technologies to facilitate the installation, support, and alignment of very large accelerator beam line lattice elements.
Questions – contact LK Len (lk.len@science.doe.gov)
b. Beam Instrumentation and Feedback Systems—Instrumentation and feedback systems are needed to support the development of the ILC. Accordingly, grant applications are sought to develop:
(1) fast transverse feedback systems, appropriate for controlling vertical beam jitter at the 0.1 sigma level, in linear colliders with long bunch trains (on the order of 1 ms). Areas of particular interest include systems with bandwidth sufficient to control single bunches within a train (with a bunch separation of order 100 ns), and systems that can operate on a train-by-train basis (with a train repetition period of order 5 Hz). System design should be based on the bunch parameters of the ILC.*
(2) linac beam position monitoring systems capable of single-bunch position resolution in the range of 1-10 µm (rms). High precision beam position monitors for the damping rings and beam delivery system are also of interest. The system design must be relevant for the bunch parameters of the ILC.*
(3) high resolution beam profile monitoring systems capable of measuring the emittance of a high energy electron/positron beam, with the bunch parameters of the ILC.* The emittance should be measured with an accuracy of 10% or better.
Questions – contact LK Len (lk.len@science.doe.gov)
c. Magnet and Fast Kicker Technology—Advanced magnet and fast kicker technologies are needed to support the development of the ILC. Accordingly, grant applications are sought to develop:
(1) wiggler systems suitable for use in the damping rings of the ILC. Both permanent magnet and superconducting magnet systems are of interest. Over one damping time, the uniformity of the wiggler field must be sufficient to provide a dynamic aperture of approximately 10 sigma, as determined by tracking particles characteristic of the injected positron beam. The wiggler physical aperture must provide an acceptance of approximately 5 sigma.
(2) fast kicker systems useful for single bunch injection/extraction systems in the ILC damping rings. The rise and fall time of the field seen by the beam must be close to 3-4 ns. The overall system (possibly consisting of a number of kicker modules) should be capable of delivering a 0.6 mrad kick to a 5 GeV electron beam. The kicker should be capable of burst operation at 3 MHz for a duration of up to 1 ms, at a repetition rate of 5 Hz.
(3) short-period helical undulators, suitable for use with a high-energy (>150 GeV) electron beam, to produce an intense 10 MeV photon beam. (The photons subsequently would be used to produce showers in a thin target, providing an undulator-based positron source for the ILC.) The undulator field, gap, and period must be consistent with the requirements of the ILC undulator-based source.*[reference 1]
(4) quadrupole focusing systems, capable of achieving the demagnification needed at the interaction point of the ILC, while satisfying the geometry constraints imposed by the beam crossing angle and the particle detectors. [reference 2]
Questions – contact LK Len (lk.len@science.doe.gov)
d. Polarized RF Photocathode Sources and Accelerator Magnet Technology—Grant applications are sought for the development of polarized electron sources which operate with RF guns, and consequently can provide very low emittance beams. The cathode material should have long lifetime and high quantum efficiency, and electron polarization must be greater than 85%, with an rms invariant emittance of 4πmm-mrad or less. The bunch parameters and format should be those of the ILC.*
Grant applications are also sought for the development of water cooled accelerator magnets with an extremely high reliability, characterized by a mean time to failure of greater than 10 million hours. Highly reliable power supply systems for accelerator magnets are also needed, with a mean time to failure of greater than 4 million hours. Associated high reliability electronic control systems will also be needed.
Questions – contact LK Len (lk.len@science.doe.gov)
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* The ILC linac parameters include a beam intensity of 2x1010 electrons or positrons per bunch, in trains of about 3000 bunches, separated by about 300 ns. The trains themselves occur at a repetition rate of 5 Hz. Each bunch has an rms invariant transverse emittance of about 8 μm (horizontal) by 0.02 μm (vertical), with an rms bunch length of 300 μm. Beam size at the IP is about 6 nm vertically. The energy varies from 5 GeV at the start of the linac, to 250 GeV at the end.
References:
1. Bair, G. A., et al., “TESLA: Technical Design Report: Part II—The Accelerator,” Royal Holloway Centre for Particle Physics, March 2001. (Full text available at: http://www.pp.rhul.ac.uk/hep/pubs2/2001/flc01-22.html )
2. Loew, G., et al., “International Linear Collider (ILC) Technical Review Committee: Second Report,” 2003. (Report No. SLAC-R-606) (Hard copy available from National Technology Information Service at: http://www.ntis.gov)
3. “ILC-Americas Workshop,” ILC at SLAC, Stanford, CA, October 2004, Stanford Linear Accelerator Center Website. (URL: http://www-project.slac.stanford.edu/ilc/meetings/workshops/US-ILCWorkshop/workshop.html)
4. “[First] ILC Workshop at KEK: Towards an International Design of a Linear Collider,” Tsukaba, Japan, November 13-15, 2004 Website. (URL: http://lcdev.kek.jp/ILCWS/)
5. International Linear Collider Website. (URL: http://www.linearcollider.org/cms/)
6. “2nd ILC Accelerator Workshop,” Snowmass, Colorado, USA, August 14-27, 2005 Website. (URL: http://alcpg2005.colorado.edu/)
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