We propose to perform a proof-of-principle demonstration of a target system based on a free mercury jet, including magnetic focusing/capture of secondary pions/muons, suitable for use in a 4-MW, 50-GeV proton beam as part of a neutrino “superbeam” and/or neutrino factory facility. Such a target system would also be provide higher intensity muon beams for the PRISM project.
The proposed studies emphasize the survival of a prototype target system against issues of single proton pulses: dispersal of the jet target by mechanical “shock” and/or vaporization due energy deposition by the proton beam, and possible damping of these effects by the strong magnetic field of the capture solenoid. A first phase of such studies has been carried out at BNL and CERN, in which the interaction of a mercury jet with a proton beam, and with a 20-T solenoid magnet, have been investigated separately, with encouraging results. Long-term issues of radiation damage and materials fatigue are to be addressed in separate studies.
Processes occurring in a radio-frequency (rf) cavity, filled with high pressure gas and interacting with proton beams, have been studied via advanced numerical simulations. Simulations support the experimental program on the hydrogen gas-filled rf cavity in the Mucool Test Area (MTA) at Fermilab, and broader research on the design of muon cooling devices. space, a 3D electromagnetic particle-in-cell (EM-PIC) code with atomic physics support, was used in simulation studies. Plasma dynamics in the rf cavity, including the process of neutral gas ionization by proton beams, plasma loading of the rf cavity, and atomic processes in plasma such as electron-ion and ion-ion recombination and electron attachment to dopant molecules, have been studied. Through comparison with experiments in the MTA, simulations quantified several uncertain values of plasma properties such as effective recombination rates and the attachment time of electrons to dopant molecules. Simulations have achieved very good agreement with experiments on plasma loading and related processes. The experimentally validated code space is capable of predictive simulations of muon cooling devices.
Plasma-jet-driven magneto-inertial fusion (PJMIF) is the only embodiment of magneto-inertial fusion that has the unique combination of stand-off implosion and high implosion velocity (50 to 150 km/s). It uses inexpensive plasma guns for all plasma formation and implosion and has potential for a relatively high repetition rate from 1 to 2 Hz. Its configuration is compatible with the use of a thick liquid wall that doubles as a tritium breeding blanket as well as a coolant for extracting the heat out of the fusion reactor. The PJMIF operational parameter-space allows for the possibility of using a sufficiently dense target plasma for the target plasma to have a high β. If such a high-β plasma could be realized, it would help to suppress micro and magnetohydrodynamic instabilities, giving its target plasma classical transport and energy confinement characteristics. Its open geometry and moderate time and spatial scales provide convenient diagnostics access. Diagnostics accessibility, high shot rate, and low cost per shot should enable quick resolution of technical issues during development, thus the potential for enabling rapid research and development of PJMIF. There are a number of challenges for PJMIF, however, including being at a very early stage of development, developing the required plasma guns, dealing with potential liner nonuniformities, clearing the chamber of residual high-Z gas between shots, and developing the repetitive pulsed-power component technologies. Over the last 3 years, the development of the Plasma Liner Formation Experiment (PLX-α) has been undertaken to explore the physics and demonstrate the formation of a spherical liner by the merging of a spherical array of plasma jets. Two- and three-jet merging experiments have been conducted to study the interactions of the jets. Six- and seven-jet experiments have been performed to form a piece of the plasma liner. A brief status report on this development is provided in this paper.
Highly resolved numerical simulations of the modulator, the first section of the proposed coherent electron cooling (CEC) device, have been performed using the code SPACE. The beam parameters for simulations are relevant to the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory (BNL). Numerical convergence has been studied using various numbers of macro-particles and mesh refinements of computational domain. A good agreement of theory and simulations has been obtained for the case of stationary and moving ions in uniform electron clouds with realistic distribution of thermal velocities. The main result of the paper is the prediction of modulation processes for ions with reference and off-reference coordinates in realistic Gaussian electron bunches with quadrupole field.
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