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Title: Neutrino Factory and Muon Collider Fellow

Abstract

Muons are fundamental particles like electrons but much more massive. Muon accelerators can provide physics opportunities similar to those of electron accelerators, but because of the larger mass muons lose less energy to radiation, allowing more compact facilities with lower operating costs. The way muon beams are produced makes them too large to fit into the vacuum chamber of a cost-effective accelerator, and the short muon lifetime means that the beams must be reduced in size rather quickly, without losing too many of the muons. This reduction in size is called "cooling." Ionization cooling is a new technique that can accomplish such cooling. Intense muon beams can then be accelerated and injected into a storage ring, where they can be used to produce neutrino beams through their decays or collided with muons of the opposite charge to produce a muon collider, similar to an electron-positron collider. We report on the research carried out at the University of California, Riverside, towards producing such muon accelerators, as part of the Muon Accelerator Program based at Fermilab. Since this research was carried out in a university environment, we were able to involve both undergraduate and graduate students.

Authors:
 [1];  [1];  [1]
  1. Univ. of California, Riverside, CA (United States)
Publication Date:
Research Org.:
Univ. of California, Riverside, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1176792
Report Number(s):
DOE-UCR-1487
DOE Contract Number:
FG02-07ER41487
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
43 PARTICLE ACCELERATORS; 72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; muon:cooling; ionization cooling; muon accelerator; collider physics

Citation Formats

Hanson, Gail G., Snopak, Pavel, and Bao, Yu. Neutrino Factory and Muon Collider Fellow. United States: N. p., 2015. Web. doi:10.2172/1176792.
Hanson, Gail G., Snopak, Pavel, & Bao, Yu. Neutrino Factory and Muon Collider Fellow. United States. doi:10.2172/1176792.
Hanson, Gail G., Snopak, Pavel, and Bao, Yu. Fri . "Neutrino Factory and Muon Collider Fellow". United States. doi:10.2172/1176792. https://www.osti.gov/servlets/purl/1176792.
@article{osti_1176792,
title = {Neutrino Factory and Muon Collider Fellow},
author = {Hanson, Gail G. and Snopak, Pavel and Bao, Yu},
abstractNote = {Muons are fundamental particles like electrons but much more massive. Muon accelerators can provide physics opportunities similar to those of electron accelerators, but because of the larger mass muons lose less energy to radiation, allowing more compact facilities with lower operating costs. The way muon beams are produced makes them too large to fit into the vacuum chamber of a cost-effective accelerator, and the short muon lifetime means that the beams must be reduced in size rather quickly, without losing too many of the muons. This reduction in size is called "cooling." Ionization cooling is a new technique that can accomplish such cooling. Intense muon beams can then be accelerated and injected into a storage ring, where they can be used to produce neutrino beams through their decays or collided with muons of the opposite charge to produce a muon collider, similar to an electron-positron collider. We report on the research carried out at the University of California, Riverside, towards producing such muon accelerators, as part of the Muon Accelerator Program based at Fermilab. Since this research was carried out in a university environment, we were able to involve both undergraduate and graduate students.},
doi = {10.2172/1176792},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Fri Mar 20 00:00:00 EDT 2015},
month = {Fri Mar 20 00:00:00 EDT 2015}
}

Technical Report:

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  • By providing an intense, well controlled, well characterized, narrow beam of muon neutrinos (νμ’s) and electron antineutrinos ( ν e’s) from the decay of muons (μ⁻’s) in a storage ring, a neutrino factory can advance neutrino physics beyond the current round of approved and proposed experiments using conventional neutrino beams produced from a beam of decaying pions and kaons [1, 2]. There is no other comparable single clean source of electron neutrinos (from the decay of μ +’s) or antineutrinos. A muon storage ring producing 10 19 to 10 21 muon decays per year should be feasible. These intense neutrinomore » beams can be used to study neutrino oscillations and possible CP violation. An entry-level muon storage ring that could provide 10 19 decays per year would allow a determination of the sign of Δm² 31and a first measurement of sin 213 for favorable values of this parameter. An improved muon storage ring system that could provide 10 20 muon decays per year would allow measurement of sin 213 to ~10⁻4. A high performance muon storage ring capable of providing more than 10 20 muon decays per year would allow the exciting possibility of a measurement of CP violation in the leptonic sector. An intense cold muon beam at the front end of a neutrino factory could enable a rich variety of precision muon physics, such as a more precise measurement of the muon anomalous magnetic moment (g – 2) and searches for μ -> e γ and μ⁻N -> e⁻ N conversion [3]. In addition, colliding beams of μ⁺ and μ⁻ in a muon collider can provide an effective “Higgs factory” or multi-TeV center-of-mass energy collisions [4]. A muon collider will be the best way to study the Higgs bosons associated with supersymmetric theories and may be necessary to discover them. Two neutrino factory feasibility studies have been carried out in the U.S. [5, 6]. International design efforts are now under way. The International Neutrino Factory and Superbeam Scoping Study (ISS) [7] began at the NuFact05 Workshop in June 2005 with the goals of elaborating the physics case, defining the baseline options for such a facility and its neutrino detectors, and identifying the required R&D program to lay the foundations for a complete design study proposal, and an International Design Study of the Neutrino Factory is beginning. These studies entail iterative cost and technical difficulty evaluations, thereby providing guidelines for the advancing R&D program. One of the central subsystems of a neutrino factory or muon collider is the muon cooling system. The muon beam is cooled to increase the phase space density and allow the muons to pass through smaller apertures, thus reducing the cost of the following accelerator systems. This cooling is accomplished through ionization cooling, in which the beam is passed through liquid hydrogen absorbers and then accelerated in RF cavities to restore the longitudinal momentum. Ionization cooling was proposed more than twenty years ago [8] but has not yet been demonstrated in practice. The International Muon Ionization Cooling Experiment (MICE) [9, 10] seeks to build and operate a muon-cooling device of a design proposed in Feasibility Study-II [6]. In addition to cooling the muons, MICE includes apparatus to measure the performance of the device. The experiment will be carried out by a collaboration of physicists from the U.S., Europe, and Japan at the Rutherford Appleton Laboratory in the U.K. MICE will begin operation in late 2007. Successful performance of the MICE experiment will provide the understanding needed to design a complete neutrino factory, in which the muons are cooled, accelerated, circulated in a storage ring, and decay to produce the neutrino beam. The first neutrino factory might be built in the U.S., Europe, or Japan. A Muon Collider Task Force (MCTF) has recently been organized at Fermilab.« less
  • Scenarios for capture, bunching and phase-energy rotation of {mu}'s from a proton source have been developed. The goal is capture of a maximal number of muons in a string of rf bunches with applications in neutrino factories and {mu}{sup +}-{mu}{sup -} colliders. In this note we begin with the bunching, phase rotation and cooling scenario used in neutrino factory study 2B and adapted by R. Palmer as the initial stage of a {mu}{sup +}-{mu}{sup -} collider scenario. However the scenario produces a relatively large number of bunches that must be recombined for maximal collider luminosity. In this paper we modifymore » the scenario to obtain a smaller number of bunches, and, after some optimization, obtain cases that are better for both n-factory and collider scenarios. We describe these examples and consider some variations toward an optimal {nu}-factory + collider scenario.« less
  • A passively cooled graphite target was proposed for a 1.5 MW neutrino production research facility because of its simplicity and favorable performance as a target material for neutrino production (Ref. 1). The conceptual design for the target in the Reference 1 study was a graphite rod 15 mm in diameter by 800 mm long. Figure 1 shows the graphite target rod supported by graphite spokes, which are mounted to a water-cooled stainless steel support tube. The target is radiatively cooled to the water-cooled surface of the support tube. Based on nuclear analysis results (Ref. 2), the time-averaged power deposition inmore » the target is 35 kW. If this power is deposited uniformly along the axial length of the target, the volumetric power deposition in the target is about 250 MW/m{sup 3}. The target surface temperature required to radiate the deposited power to a water-cooled tube is estimated to be about 1850 C, and the temperature at the center of the target is about 75 C hotter. The sublimation erosion rate (e), estimated assuming that the graphite is submersed in a perfect vacuum environment, can be derived from kinetic theory and is given by: e = p{sub sat} (m/2{pi} kT){sup 1/2} where p{sub sat} is the saturation pressure, m is the molecular weight, k is the Boltzmann constant, and T is the surface temperature. The saturation pressure given in Ref. 3 can be approximated by: p{sub sat} = exp(-A/T + B) where A = 9.47 x 10{sup 3}, B = 24.2, and the units of p{sub sat} and T are atmospheres and K, respectively. Using these equations, the saturation pressure and sublimation erosion rate are plotted in Fig. 2 as a function of temperature. The surface recession rate shown with units of mm/s in Fig. 2 assumes one-sided erosion. At the average power deposition value of 250 MW/m{sup 3}, the surface temperature is 1850 C resulting in a sublimation erosion rate of only 2.2 mm/day. However, if the actual power deposition were peaked by a factor of two in the axial direction, then the surface temperature would be 2260 C and the surface recession rate would be 2.8 mm/day, which is clearly unacceptable. To establish the viability of a graphite target at the reference power levels and perhaps extend the power handling performance of radiatively cooled graphite targets, a helium cover gas at nominally one atmosphere pressure was proposed as a means to greatly reduce the net erosion rate. The mean free path for a graphite atom in a helium environment at a pressure of one atmosphere is less than 0.1 mm, which means that graphite that is sublimated from the target surface will travel on average less than 0.1 mm before it interacts with the helium. Given this small mean-free-path, it can be expected that a large fraction of the graphite that is sublimated will find its way back to the graphite surface and re-condense on the target, thereby greatly reducing the net erosion rate. The primary purposes for performing the tests described in this report are to (1) verify that we can reproduce the sublimation erosion rate expected for high vacuum conditions and (2) establish the reduction in net sublimation of graphite as a function of the gas (He) pressure in a chamber that roughly simulates the stainless steel support tube discussed above. Thus far, the first objective has been accomplished, but more work is required to accomplish the second. The experimental apparatus is described in Section 2 of this report and results obtained thus far are presented in Section 3 of this report.« less
  • A passively cooled graphite target was proposed for a 1.5 MW neutrino production research facility because of its simplicity and favorable performance as a target material for neutrino production. The conceptual design for the target in the Reference 1 study was a graphite rod 15 mm in diameter by 800 mm long. Figure 1 shows the graphite target rod supported by graphite spokes, which are mounted to a water-cooled stainless steel support tube. The target is radiatively cooled to the water-cooled surface of the support tube. Based on nuclear analysis results, the time-averaged power deposition in the target is 35more » kW. If this power is deposited uniformly along the axial length of the target, the volumetric power deposition in the target is about 250 MW/m{sup 3}. The target surface temperature required to radiate the deposited power to a water-cooled tube is estimated to be about 1850 C, and the temperature at the center of the target is about 75 C hotter. The sublimation erosion rate (e), estimated assuming that the graphite is submersed in a perfect vacuum environment, can be derived from kinetic theory and is given by: e = p{sub sat}(m/2{pi} kT){sup 1/2} where p{sub sat} is the saturation pressure, m is the molecular weight, k is the Boltzmann constant, and T is the surface temperature. The saturation pressure given in Ref. 3 can be approximated by: p{sub sat} =exp(-A/T + B) where A = 9.47 x 10{sup 3}, B = 24.2, and the units of p{sub sat} and T are atmospheres and K, respectively. Using these equations, the saturation pressure and sublimation erosion rate are plotted in Fig. 2 as a function of temperature. The surface recession rate shown with units of mm/s in Fig. 2 assumes one-sided erosion. At the average power deposition value of 250 MW/m{sup 3}, the surface temperature is 1850 C resulting in a sublimation erosion rate of only 2.2 {micro}m/day. However, if the actual power deposition were peaked by a factor of two in the axial direction, then the surface temperature would be 2260 C and the surface recession rate would be 2.8 mm/day, which is clearly unacceptable.« less
  • Muon accelerators hold great promise for the future of high energy physics and their construction can be staged to support a broad physics program. Great progress was made over the past decade toward developing the technology for muon beam cooling which is one of the main challenges for building such facilities.