Fermilab A Plan for Discovery

Chapter 6
Fermilab Accelerator Facilities
for the Intensity Frontier

Fermilab Accelerator Facilities for the Intensity Frontier

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Proton beam power

Beam power from the Main Injector (MI) for three neutrino facilities: the existing NuMI beam, the planned upgrade for NOνA and Project X.

Fermilab is transforming its accelerator facilities to meet the challenges of the Intensity Frontier era and support science at the Energy and Cosmic Frontiers. Project X is the centerpiece of the Fermilab strategy to develop a world-leading Intensity Frontier program and lay the groundwork for eventual construction of a Neutrino Factory or Muon Collider at Fermilab. The plan for the continuous evolution of the accelerator complex, as outlined below, supports discovery science at every stage. It makes the best use of assets freed up by the end of Tevatron collider operations, and provides a platform for even longer-term accelerator development. It features the following elements:

Stage One

The existing Fermilab accelerator complex, including the Main Injector synchrotron, Recycler storage ring and NuMI neutrino beamline and target, will be upgraded in 2012 to supply 700 kW beams for NOνA, Fermilab's second-generation long-baseline neutrino experiment.

The Proton Improvement Plan will upgrade the existing proton facility to deliver 33 kW of proton-beam power at 8 GeV simultaneous with NOνA operations. The PIP, which will be completed in 2016, is designed to support the operation of Fermilab's suite of neutrino and muon experiments at the Intensity Frontier and the test-beam facility for detector R&D. The complex will operate in this configuration until Project X becomes operational.

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Proton beam power

Beam power from the Main Injector (MI) for three neutrino facilities: the existing NuMI beam, the planned upgrade for NOνA and Project X.

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Stage Two

Fermilab and its national and international partners will build Project X, the world's most powerful proton facility. Project X could begin construction in 2016, and would deliver 5 MW of total beam power to the next stage of Intensity Frontier experiments with neutrinos, muons, kaons and nuclei. Based on a modern high-power H- linac, it would simultaneously deliver 2.9 MW at 3 GeV; 50200 kW at 8 GeV and 2.3 MW at any energy between 60 and 120 GeV.

Stage Three

Starting in the 2020s Fermilab, together with its national and international partners, could be preparing to build the next major accelerator. Depending on the outcome of earlier experiments and international decisions, the next accelerator could be a Neutrino Factory or Muon Collider located at Fermilab. Project X could serve as the front end for either next-generation accelerator.

Stage One: Upgrades to Existing Facilities

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Proton demand

Total proton demand from Fermilab's experiments through 2020.

Fermilab's existing proton facility consists of a 400 MeV linear accelerator, 8 GeV Booster accelerator and 120 GeV Main Injector synchrotron. The complex delivers beams to a variety of target stations including the MiniBooNE target at 8 GeV, the NuMI and antiproton targets at 120 GeV, and a test-beam facility. Two key components of the proton facility—the initial 181 MeV of the Linac and the Booster—have been operating for 40 years and rely on components that are either no longer commercially available or are at risk of being discontinued. The Linac and Booster have the potential to operate at up to 15 Hz, but limitations in the RF systems and the overall tolerance to beam loss currently limit beam cycles to 7.5 Hz. This rate will support the short- and long-baseline neutrino program through 2012.

Following the end of Tevatron operation portions of Fermilab's existing antiproton facility—the 8 GeV Recycler and Antiproton Rings—are being converted to enhance the Intensity Frontier program. Starting in 2013 the Recycler will accumulate protons in support of NOνA, and several years later the Antiproton Rings will accumulate and then resonantly extract protons for the muon complex.

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The Fermilab accelerator complex in 2020

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NOνA Upgrades

The NOνA experiment requires 700 kW of proton beam power delivered to the NuMI target, double the power produced in the Tevatron era. This power will be achieved by reducing the Main Injector cycle time and increasing the number of batches targeted, but without increasing the batch intensity. The cycle time is reduced by increasing the Main Injector acceleration rate and using the Recycler as a proton accumulation ring. Component fabrication to complete these upgrades is currently underway. Installation will start in spring 2012 and take 11 months to complete. Startup of the NOνA experimental program will begin in the spring of 2013, at which time the Booster will be able to deliver beams at 9 Hz.

Proton Improvement Plan

Further upgrades to the proton facility are required to support the balance of the near-term Intensity Frontier program—the MicroBooNE, Mu2e, and Muon g-2 experiments—in parallel with NOνA. The PIP will also provide the initial beams required by LBNE. The Proton Improvement Plan will enable the Linac and Booster to meet this program's total demands. The goals of the PIP are:

  • Increase the beam repetition rate to 15 Hz.
  • Eliminate major reliability vulnerabilities and maintain reliability at present levels (>85%) at the full repetition rate.
  • Eliminate major obsolescence issues.
  • Increase the proton throughput to more than 21017 protons per hour.
  • Ensure a useful operating life of the Linac and Booster through at least 2025.

The last goal is meant to ensure continuity of operations in the face of potential delays for Project X. The PIP is currently underway and will be completed in 2016.

Stage Two: Project X

Project X will be unique in the world in its ability to deliver high-power proton beams with flexible beam formats to multiple users. A Project X reference design has been developed based on a 3 GeV continuous-wave superconducting linac operating at an average current of 1 mA followed by a 38 GeV pulsed linac operating with a duty factor of 4%. These facilities are further augmented by upgrades to the Main Injector/Recycler complex to support higher-power operations. A total of 5 MW of beam power will be available at Project X: 2.9 MW at 3 GeV; up to 200 kW at 8 GeV; and 2.3 MW at 60120 GeV.

Project X is currently in the pre-conceptual design and development stage and a R&D program targeting the critical technical issues is underway in collaboration with 14 universities and laboratories. While no project schedule has been agreed to with DOE, Project X could be ready to begin construction as early as 2016.

Project X Reference Design

The design of Project X is driven by four main research goals:

  • Long-baseline neutrino experiments: Project X will deliver 2.3 MW of proton beam power onto a neutrino production target at any energy between 60 and 120 GeV.
  • Rare-process experiments: Project X will provide megawatt-class, multi-GeV proton beams supporting multiple precision experiments with kaons, muons and neutrinos simultaneous with the long-baseline neutrino program.
  • Muon facilities: Project X will provide a path toward a muon source for a possible future Neutrino Factory or Muon Collider.
  • Nuclei and nuclear energy: Project X will provide opportunities for implementing a program of Standard Model tests with nuclei and possible research into technologies necessary for cleaner nuclear energy.

The first three goals were defined in the U.S. Department of Energy's long-range strategic plan for high-energy physics (P5 report), which also recommended the development of a high-intensity proton facility.1 The fourth goal was developed in discussion with the broader scientific community.

The Project X Reference Design meets the high-level design criteria listed above in an innovative and flexible manner.2 The primary elements comprising the Reference Design are:

  • An H- source consisting of a CW ion source, 2.1 MeV RFQ, and Medium-Energy Beam Transport line with an integrated wideband beam chopper capable of accepting or rejecting bunches in arbitrary patterns at 162.5 MHz.
  • A 3 GeV superconducting linac operating in CW mode and capable of accelerating an average H- beam current of 1 mA, and a peak beam current of 10 mA.
  • A 3-to-8 GeV pulsed linac capable of accelerating 1 mA of peak beam current at a duty factor of up to 4%.
  • A pulsed dipole that can direct beam towards either the Main Injector/Recycler complex for neutrino experiments or the 3 GeV muon, kaon and nuclei experimental areas.
  • An RF beam splitter that can deliver the 3 GeV beam to multiple experimental areas.
  • Modifications necessary to support 2 MW operations in the Main Injector/Recycler complex.
  • All interconnecting beamlines.
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Project X linac loading pattern

Example linac loading pattern (top line) providing independent bunch patterns to three experiments (red, blue, teal lines) simultaneously. The red experiment receives bunches with a 1 MHz macrostructure and a 80 MHz microstructure; blue at 20 MHz; and teal at 10 MHz. For a peak current of 4.2 mA the average current is 1 mA, and the red, blue and teal areas receive 700, 1540, and 770 kW, respectively.

Operating Scenarios

The CW linac primarily supports a program of precision experiments with muons, kaons and nuclei at 3 GeV. Key to the success of this program is the delivery of different bunch patterns to three experiments simultaneously. This is achieved by the coordinated utilization of a wideband chopper at the linac front end and a transverse deflecting RF separator at the exit. The power available to the 3 GeV experimental program is 2.9 MW when 4% of the CW linac beam is diverted to the pulsed linac.

The pulsed 8 GeV linac operates at 10 Hz and supports the long-baseline neutrino program in concert with the Main Injector and Recycler. The pulsed linac provides 350 kW of total beam power. The power is increased to 2.3 MW by accumulating six pulses from the linac in the Recycler. The accumulated beam is then delivered in a single turn to the Main Injector for subsequent acceleration to any energy between 60 and 120 GeV. Since 60120 GeV beams do not use every available beam pulse, there is 200 kW of extra power available to support an 8 GeV experimental program when the Main Injector is operating at 120 GeV, and 50 kW available at 60 GeV.

Project X R&D Program

The Project X R&D program is well underway and consists of facility design and systems optimization studies and development of the critical underlying technologies. Foremost among the latter are the wideband chopper that provides the required bunch patterns, the system for providing multi-turn injection of H- into the Recycler, and superconducting RF development at four different frequencies. The Project X R&D program is being undertaken by a collaboration consisting of ten U.S. laboratories and universities and four laboratories in India.

Development of the wideband chopper is a key element of the R&D program. The chopper consists of a set of four kickers and a corresponding set of kicker drivers. The system is required to deliver one nanosecond rise and fall time with a one nanosecond flattop. Kicker voltages in excess of ±200 V are required and a repetition rate of 60 MHz must be supported. Helical transmission line structures have been developed that meet the kicker requirements, while MOSFET-based wideband amplifiers are being investigated for the driver.

Another key element is the system to deliver H- beam in six 4.3 msec pulses. The H- are stripped during a multi-turn injection into the Recycler, representing a 400-turn injection. Simulations indicate that 400 turns is roughly the maximum number that can be tolerated when taking into account foil heating, emittance growth, and reasonable foil survival times. However, there would be advantages to injecting the full current directly into the Main Injector in a single 26 msec-long pulse—something that is not possible with the standard foil techniques. Alternative techniques that include moving/rotating foils and laser-assisted stripping are currently under development.

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SRF development

Superconducting radiofrequency technology is being developed at Fermilab for future accelerators, in partnership with laboratories around the world.

A very significant superconducting radiofrequency development program has been underway for several years, utilizing resources at Fermilab and partner laboratories. For the CW linac, the emphasis is on developing high-Q0 cavities with gradients of approximately 15 MV/m at frequencies of 162.5, 325 and 650 MHz. Two 325-MHz cavities have been built and tested, both achieving 15 MV/m with Q0 of 1.5x1010. At 650 MHz, a number of elliptical shapes are currently being investigated in single-cell tests. For the pulsed linac, cavities with Q0 of 1x1010 and gradients of 25 MV/m are required. The development of these 1300 MHz cavities is at a more advanced stage, due to strong overlap with the International Linear Collider development program. A complete cryomodule is currently under RF testing and a second cryomodule is under construction.

Significant effort is also going into the development of RF sources. The CW linac cavities will be driven by individual sources, with up to 30 kW per source required in the 650 MHz section. Solid-state sources have been identified as the preferred technology at 325 MHz, and both solid-state and inductive output tubes are being investigated at 650 MHz.

Stage Three: Project X as a Platform for Future Facilities

The high-power linacs in Project X share many fundamental characteristics that would be required from the front end of a Neutrino Factory or Muon Collider, including approximately 4 MW of proton-beam power at an energy of 5 to 15 GeV. Unlike Project X, however, a Muon Collider requires a very low-duty-factor beam with very short, but intense, bunches. The Muon Collider under study at Fermilab requires beam to be delivered in a single bunch, with a bunch length of 23 nsec, at a 15 Hz repetition rate. A Neutrino Factory would have slightly less stringent requirements.

Meeting the Muon Collider's beam-power and bunch-structure requirements would call for a power upgrade to Project X's 8 GeV beam and additional facilities to reformat the high-duty-factor beam from Project X. A task force, jointly sponsored by Project X and the U.S. Muon Accelerator Program, has been launched to develop a feasible concept that will be fed back into Project X planning activities. This task force will report by the end of 2011; however, a number of concepts that could provide the required beam power, repetition rate and bunch formatting are already under investigation.

Notes

1 U.S. Particle Physics: Scientific Opportunities, A Strategic Plan for the Next Ten Years, May 2008, http://science.energy.gov/~/media/hep/pdf/files/pdfs/p5_report_06022008.pdf

2 Project X Reference Design Report, November 2010, http://projectx-docdb.fnal.gov/cgi-bin/ ShowDocument?docid=776