Engineering topics
Publications and source records attributed to Yonehara, K.
Muon collider is a considerable candidate of the next generation high-energy lepton collider machine. A novel accelerator technology must be developed to overcome several intrinsic issues of muon acceleration. Recent research and development of critical beam elements for a muon accelerator, especially muon beam phase space ionization cooling channel, are reviewed in this paper.
The Helical Cooling Channel (HCC), a novel technique for six-dimensional (6D) ionization cooling of muon beams, has shown considerable promise based on analytic and simulation studies. However, the implementation of this revolutionary method of muon cooling requires new techniques for the integration of hydrogen-pressurized, high-power RF cavities into the low-temperature superconducting magnets of the HCC. We present the progress toward a conceptual design for the integration of 805 MHz RF cavities into a 10 T Nb{sub 3}Sn based HCC test section. We include discussions on the pressure and thermal barriers needed within the cryostat to maintain operation of the magnet at 4.2 K while operating the RF and energy absorber at a higher temperature. Additionally, we include progress on the Nb{sub 3}Sn helical solenoid design.
A high pressure hydrogen gas filled RF cavity was subjected to an intense proton beam to study the evolution of the beam induced plasma inside the cavity. Varying beam intensities, gas pressures and electric fields were tested. Beam induced ionized electrons load the cavity, thereby decreasing the accelerating gradient. The extent and duration of this degradation has been measured. A model of the recombination between ionized electrons and ions is presented, with the intent of producing a baseline for the physics inside such a cavity used in a muon accelerator. Analysis of the data taken during the summer of 2011 shows that self recombination takes place in pure hydrogen gas. The decay of the number of electrons in the cavity once the beam is turned off indicates self recombination rather than attachment to electronegative dopants or impurities. The cross section of electron recombination grows for larger clusters of hydrogen and so at the equilibrium of electron production and recombination in the cavity, processes involving H{sub 5}{sup +} or larger clusters must be taking place. The measured recombination rates during this time match or exceed the analytic predicted values. The accelerating gradient in the cavity recovers fully in time for the next beam pulse of a muon collider. Exactly what the recombination rate is and how much the gradient degrades during the 60 ns muon collider beam pulse will be extrapolated from data taken during the spring of 2012.
The influence of an intense beam in a high-pressure gas filled RF cavity has been measured by using a 400 MeV proton beam in the Mucool Test Area at Fermilab. The ionization process generates dense plasma in the cavity and the resultant power loss to the plasma is determined by measuring the cavity voltage on a sampling oscilloscope. The energy loss has been observed with various peak RF field gradients (E), gas pressures (p), and beam intensities in nitrogen and hydrogen gases. Observed RF energy dissipation in single electron (dw) in N{sub 2} and H{sub 2} gases was 2 10{sup -17} and 3 10{sup -17} Joules/RF cycle at E/p = 8 V/cm/Torr, respectively. More detailed dw measurement have been done in H{sub 2} gas at three different gas pressures. There is a clear discrepancy between the observed dw and analytical one. The discrepancy may be due to the gas density effect that has already been observed in various experiments.
A high-luminosity Muon Collider requires bunch recombination for optimal luminosity. In this paper, we take advantage of the large slip factor attainable in a helical transport channel (HTC) to coalesce bunches of muons into a single one over a shorter distance than can be achieved over a straight channel.
Abstract Not Provided
The Helical Cooling Channel (HCC) was proposed for 6D cooling of muon beams required for muon collider and some other applications. HCC uses a continuous absorber inside superconducting magnets which produce solenoidal field superimposed with transverse helical dipole and helical gradient fields. HCC is usually divided into several sections each with progressively stronger fields, smaller aperture and shorter helix period to achieve the optimal muon cooling rate. This paper presents the design issues of the high field section of HCC with coil separation. The effect of coil spacing on the longitudinal and transverse field components is presented and its impact on the muon cooling discussed. The paper also describes methods for field corrections and their practical limits. The magnetic performance of the helical solenoid with coil separation was discussed in this work. The separation could be done in three different ways and the performances could be very different which is important and should be carefully described during the beam cooling simulations. The design that is currently being considered is the one that has the poorest magnetic performance because it presents ripples in all three components, in particular in the helical gradient which could be quite large. Moreover, the average gradient could be off, which could affect the cooling performance. This work summarized methods to tune the gradient regarding the average value and the ripple. The coil longitudinal thickness and the helix period can be used to tune G. Thinner coils tend to reduce the ripples and also bring G to its target value. However, this technique reduces dramatically the operational margin. Wider coils can also reduce the ripple (not as much as thinner coils) and also tune the gradient to its target value. Longer helix periods reduce ripple and correct the gradient to the target value.
Novel magnetic helical channel designs for capture and cooling of bright muon beams are being developed using numerical simulations based on new inventions such as helical solenoid (HS) magnets and hydrogen-pressurized RF (HPRF) cavities. We are close to the factor of a million six-dimensional phase space (6D) reduction needed for muon colliders. Recent experimental and simulation results are presented.
In order to demonstrate the feasibility of high pressure hydrogen gas filled RF (HPRF) cavities for muon ionization cooling, an HPRF cavity must be tested with a high intensity charged beam. When an HPRF cavity is irradiated with an intense beam each incident particle generates about 1000 electrons and ions per cubic centimeter in a high pressure cavity via ionization. These ionization electrons are influenced by the RF field and the RF quality factor goes down. This Q factor reduction will be a problem with a multi bunch beam, e.g., a muon beam for a muon collider consists of a 12 to 20 bunch train beam with 5 ns timing gap. Thus, the RF field must recover in few nano seconds. We propose to use a 400 MeV proton beam in the MTA and measure a beam loading effect in the HPRF cavity and study the recovery mechanism of the RF field.
Novel magnetic helical channel designs for capture and cooling of bright muon beams are being developed using numerical simulations based on new inventions such as helical solenoid (HS) magnets and hydrogen-pressurized RF (HPRF) cavities. We are close to the factor of a million six-dimensional phase space (6D) reduction needed for muon colliders. Recent experimental and simulation results are presented.
The LEPS/SPring-8 experiment made a comprehensive measurement of the spin-density matrix elements for gammap->phip, gammad->phipn, and gammad->phid at forward production angles. A linearly polarized photon beam at E{sub g}amma=1.6-2.4 GeV was used for the production of phi mesons. The natural-parity Pomeron exchange processes remain dominant near threshold. The unnatural-parity processes of pseudoscalar exchange is visible in the production from the nucleons but is greatly reduced in the coherent production from deuterons. There is no strong E{sub g}amma dependence, but there is some dependence on momentum transfer. A small but finite value of the spin-density matrix elements reflecting helicity-nonconserving amplitudes in the t-channel is observed.
The MuCool RF Program focuses on the study of normal conducting RF structures operating in high magnetic field for applications in muon ionization cooling for Neutrino Factories and Muon Colliders. This paper will give an overview of the program, which will include a description of the test facility and its capabilities, the current test program, and the status of a cavity that can be rotated in the magnetic field which allows for a more detailed study of the maximum stable operating gradient vs. magnetic field strength and angle.
Ionization cooling is a critical building block for the realization of a muon collider. To suppress breakdown in the presence of the external magnetic field, an idea of using an RF cavity filled with high pressure hydrogen gas is being considered for the cooling channel design. One possible problem expected in the high pressure RF cavity is, however, the dissipation of significant RF power through the beam-induced electrons accumulated inside the cavity. To characterize this detrimental loading effect, we develop a simplified model that relates the electron density evolution and the observed pickup voltage signal in the cavity, with consideration of several key molecular processes such as the formation of the polyatomic molecules, recombination and attachment. This model is expected to be compared with the actual beam test of the cavity in the MuCool Test Area (MTA) of Fermilab.
The MuCool RF Program focuses on the study of normal conducting RF structures operating in high magnetic field for applications in muon ionization cooling for Neutrino Factories and Muon Colliders. Here we give an overview of the program, which includes a description of the test facility and its capabilities, the current test program, and the status of a cavity that can be rotated in the magnetic field, which allows for a detailed study of the maximum stable operating gradient vs. magnetic field strength and angle.
To demonstrate the feasibility of a high pressure RF cavity for use in the cooling channel of a muon collider, an experimental setup that utilizes 400-MeV Fermilab linac proton beam has been developed. In this paper, we describe the beam diagnostics and the collimator system for the experiment, and report the initial results of the beam commissioning. The transient response of the cavity to the beam is measured by the electric and magnetic pickup probes, and the beam-gas interaction is monitored by the optical diagnostic system composed of a spectrometer and two PMTs.
A high pressure hydrogen gas filled RF cavity has been proposed for use in the muon collection system for a muon collider. It allows for high electric field gradients in RF cavities located in strong magnetic fields, a condition frequently encountered in a muon cooling channel. In addition, an intense muon beam will generate an electron swarm via the ionization process in the cavity. A large amount of RF power will be consumed into the swarm. We show the results from our studies of the HV RF breakdown in a cavity without a beam and present some results on the resulting electron swarm dynamics. This is preliminary to actual beam tests which will take place late in 2010.