Highly charged dust grains immersed in a plasma can exhibit charge fluctuations in response to oscillations in the plasma currents flowing into them. This introduces a new physical efFect, namely, the electric charge on the dust particles becomes time dependent and a self-consistent dynamical variable. The consequent modifications in the collective properties of a dusty plasma are investigated.It is shown that these efFects lead to dissipative and instability mechanisms for ion waves in the plasma and can lead to interesting applications to many laboratory and astrophysical situations. PACS number(s): 52.25. Mq, 52.25.Fi, 52.35.Fp Dusty plasmas are characterized by the presence of large-sized dust grains (in the range of 10 nm to 100 pm) immersed in a partially or fully ionized plasma. These dust grains are usually highly charged (Qd 10 e -10 e) due to a variety of processes including plasma currents, photoelectric effects, secondary emission, etc. Dusty plasmas are the subject of much current interest [1 -7] due to their occurrence in various space environments (e.g. , the Earth's ionosphere, asteroid zones, planetary rings, cometary tails, interstellar clouds, etc. ) as well as laboratory devices and industrial processes (e.g. , plasmas in plasma processing, plasma etching, plasma furnace systems, edge plasmas in some magnetohydrodynamics power generators, rocket exhausts, fusion devices, etc. ). The presence of these highly charged and massive particles can significantly inBuence the collective properties of the plasma in which they are suspended, and a number of recent studies have investigated this important question [8 -10]. The primary emphasis in these studies has been on the delineation of modifications in collective properties arising from the inclusion of the dynamics of dust particles. The charge of the dust particles has been taken to be constant, and hence the analysis becomes analogous to earlier work on multispecies plasmas, particularly negative-ion plasmas, where the role of the negative-ion species is now played by the dust. In this paper we propose a different physical efFect that can arise in a dusty plasma and investigate its consequences on wave propagation and instability phenomena. We suggest that dust particles immersed in a plasma with collective perturbations can exhibit self-consistent charge Buctuations in response to oscillations in the plasma currents Bowing into them. The dust electric charge thereby becomes a time-dependent quantity and must be treated as a dynamical variable which is coupled self-consistently to other dynamical variables such as density, potential, current, etc. We show that this coupling leads to dissipative phenomena which can damp the usual ion waves and drive instabilities in certain negative-energy systems in which the ion species are streaming with respect to the dust. We also demonstrate how an anisotropic spectrum of excited ion waves can exert a mean quasilinear force on the dust particles thereby providing a mechanism for transport of dust -a proble...

A muon collider or Higgs factory requires significant reduction of the six dimensional emittance of the beam prior to acceleration. One method to accomplish this involves building a cooling channel using high pressure gas filled radio frequency cavities. The performance of such a cavity when subjected to an intense particle beam must be investigated before this technology can be validated. To this end, a high pressure gas filled radio frequency (rf) test cell was built and placed in a 400 MeV beam line from the Fermilab linac to study the plasma evolution and its effect on the cavity. Hydrogen, deuterium, helium and nitrogen gases were studied. Additionally, sulfur hexafluoride and dry air were used as dopants to aid in the removal of plasma electrons. Measurements were made using a variety of beam intensities, gas pressures, dopant concentrations, and cavity rf electric fields, both with and without a 3 T external solenoidal magnetic field. Energy dissipation per electron-ion pair, electron-ion recombination rates, ion-ion recombination rates, and electron attachment times to $SF_6$ and $O_2$ were measured.Comment: 15 p

A major technological challenge in building a muon cooling channel is operating rf cavities in multitesla external magnetic fields. We report the first proof-of-principle experiment of a high pressure gas-filled rf cavity for use with intense ionizing beams and strong external magnetic fields. rf power consumption by beam-induced plasma is investigated with hydrogen and deuterium gases with pressures between 20 and 100 atm and peak rf gradients between 5 and 50 MV=m. The low pressure case agrees well with an analytical model based on electron and ion mobilities. Varying concentrations of oxygen gas are investigated to remove free electrons from the cavity and reduce the rf power consumption. Measurements of the electron attachment time to oxygen and rate of ion-ion recombination are also made. Additionally, we demonstrate the operation of the gas-filled rf cavity in a solenoidal field of up to 3 T, finding no major magnetic field dependence. All these results indicate that a high pressure gas-filled cavity is a viable technology for muon ionization cooling.

We investigate the effect of self-consistent dust charge fluctuations on collective modes in an inhomogeneous magnetized dusty plasma. A fluid model is developed where the dust dynamics and the charge fluctuations are taken into account. It is shown that for the Rayleigh-Taylor mode both dust dynamics and charge fluctuations lead to a rapid increase of the stable regime. It is also shown that charge fluctuations can drive the drift wave unstable under certain conditions that are relevant to some astrophysical situations.

The MuCool Test Area (MTA) at Fermilab is a facility to develop the technology required for ionization cooling for a future Muon Collider and/or Neutrino Factory. As part of this research program, feasibility studies of various types of RF cavities in a high magnetic field environment are in progress. As a unique approach, we have tested a RF cavity filled with a high pressure hydrogen gas with a 400 MeV proton beam in an external magnetic field (B = 3 T). Quantitative information about the number of protons passing through this cavity is an essential requirement of the beam test. The MTA is a flammable gas (hydrogen) hazard zone. Due to safety reasons, no active (energized) beam diagnostic instrument can be used. Moreover, when the magnetic field is on, current transformers (toroids) used for beam intensity measurements do not work due to the saturation of the ferrite material of the transformer. Based on these requirements, we have developed a passive beam diagnostic instrumentation using a combination of a Chromox-6 scintillation screen and CCD camera. This paper describes details of the beam profile and position obtained from the CCD image with B = 0 T and B = 3 T, and for high and low intensity proton beams. A comparison is made with beam size obtained from multi-wires detector. Beam transmission efficiency through a collimator with a 4 mm diameter hole is measured by the toroids and CCD image of the scintillation screen. Results show that the transmission efficiency estimated from the CCD image is consistent with the toroid measurement, which enables us to monitor the beam transmission efficiency even in a high magnetic field environment.