IPAC2013 - List of Authors (Chung, M.)

Paper	Title	Page
MOPWA062	Transverse Beam Halo Measurements at High Intensity Neutrino Source (HINS) using Vibrating Wire Monitor	819
	M. Chung, B.M. Hanna, V.E. Scarpine, V.D. Shiltsev, J. Steimel Fermilab, Batavia, USA S. Artinian BERGOZ Instrumentation, Saint Genis Pouilly, France S.G. Arutunian ANSL, Yerevan, Armenia
	Funding: Research supported by the U.S. Department of Energy. Measurement and control of transverse beam halo will be critical for the applications of future high-intensity hadron linacs. In particular, beam profile monitors require a very high dynamic range when using for transverse beam halo measurements. In this study, the Vibrating Wire Monitor (VWM) with aperture 60 mm was installed at the High Intensity Neutrino Source (HINS) front-end to measure transverse beam halo. A vibrating wire is excited at its resonance frequency with the help of a magnetic feedback loop, and the vibrating and sensitive wires are connected through a balanced arm. The sensitive wire is moved into the beam halo region by a stepper motor controlled translational stage. We study the feasibility of the vibrating wire for transverse beam halo measurements in the low-energy front-end of the proton linac.

TUPFI053	Transient Beam Loading Effects in Gas-filled RF Cavities for a Muon Collider	1463
	M. Chung, A.V. Tollestrup, K. Yonehara Fermilab, Batavia, USA B.T. Freemire IIT, Chicago, Illinois, USA
	Funding: Research supported by the U.S. Department of Energy. A gas-filled RF cavity can be an effective solution for the development of a compact muon ionization cooling channel. One possible problem expected in this type of cavity is the dissipation of significant RF power through the beam-induced plasmas accumulated inside the cavity (plasma loading). In addition, for the higher muon beam intensity, the effects of the beam itself on the cavity fields in the accelerating mode are non-negligible (beam loading). These beam-cavity interactions induce a transient phase which may be very harmful to the beam quality. In this study, we estimate the transient voltage in a gas-filled RF cavity with both the plasma and conventional beam loading and discuss their compensation methods.

TUPFI058	Simulation of Beam-induced Gas Plasma in High Gradient RF Field for Muon Colliders	1478
	K. Yonehara, M. Chung, A.V. Tollestrup Fermilab, Batavia, USA B.T. Freemire IIT, Chicago, Illinois, USA R.P. Johnson, T.J. Roberts Muons. Inc., USA R.D. Ryne LBNL, Berkeley, California, USA V. Samulyak BNL, Upton, Long Island, New York, USA K. Yu SBU, Stony Brook, USA
	There is a strong limit of available RF gradient in a vacuum RF cavity under magnetic fields because the magnetic field enhances a dark current density due to electron focusing and increases probability of an electric breakdown. This limits the cooling performance. A dense hydrogen gas filled RF cavity can break this limit because the gas acts as a buffer of dark current. However, RF power loading due to a beam-induced plasma in a dense gas filled RF cavity (plasma loading effect) is crucial to design the practical cavity. Experiment shows that the plasma loading can be mitigated in denser hydrogen gas and by doping a small amount of electronegative gas in the cavity. A complicate plasma chemical reaction should be dominated in such a dense hydrogen gas condition. A beam-induced plasma is simulated by taking into account the plasma chemistry to reproduce the condition by using the supercomputer at LBNL. We will also investigate the space charge effect in a dense gas in this effort.

TUPFI059	Summary of Dense Hydrogen Gas Filled RF Cavity Tests for Muon Acceleration	1481
	K. Yonehara, M. Chung, M.R. Jana, M.A. Leonova, A. Moretti, A.V. Tollestrup Fermilab, Batavia, USA B.T. Freemire, P.M. Hanlet, Y. Torun IIT, Chicago, Illinois, USA R.P. Johnson Muons. Inc., USA
	Dense hydrogen gas filled RF cavity has a great potential to accelerate a large phase space muon beam in a strong magnetic field. The concept of novel RF cavity has been demonstrated by using an intense proton beam at Fermilab. The experimental result was agreed extremely well with the conventional dilute plasma physic. Based on the model, the beam-induced plasma in the gas filled RF cavity could be controlled by adding a small amount of electronegative gas in dense hydrogen gas. Overview of these experiments will be shown in this presentation.

TUPFI064	Beam Induced Plasma Dynamics in a High Pressure Gas-Filled RF Test Cell for use in a Muon Cooling Channel	1496
	B.T. Freemire, P.M. Hanlet, Y. Torun IIT, Chicago, Illinois, USA M. Chung, M.R. Jana, M.A. Leonova, A. Moretti, T.A. Schwarz, A.V. Tollestrup, K. Yonehara Fermilab, Batavia, USA M.G. Collura Politecnico di Torino, Torino, Italy R.P. Johnson Muons. Inc., USA
	Filling an RF cavity with a high pressure gas prevents breakdown when the cavity is place in a multi-Tesla external magnetic field. The choice of hydrogen gas provides the additional benefit of cooling a beam of muons. A beam of particles traversing the cavity, be it muons or protons, ionizes the gas, creating an electron-ion plasma which absorbs energy from the cavity. The ionization rate can be calculated from a beam intensity measurement. Energy loss measurements indicate the loading per RF cycle per electron-ion pair range from 10^-18 to 10^-16 Joules in pure hydrogen, and 10^-20 to 10^-18 Joules when hydrogen is doped with dry air. The addition of an electronegative gas (oxygen) has been observed to reduce the lifetime of ionization electrons in the cavity to below 1 nanosecond. Additionally, the recombination rate of electrons and hydrogen ions has been measured to be on the order of 10^-6 cubic centimeters per second. The recombination mechanism and hydrogen ion species, along with the three-body attachment process of electrons to oxygen, will be discussed.

Paper

Title

Page

Transverse Beam Halo Measurements at High Intensity Neutrino Source (HINS) using Vibrating Wire Monitor

819

M. Chung, B.M. Hanna, V.E. Scarpine, V.D. Shiltsev, J. Steimel
Fermilab, Batavia, USA
S. Artinian
BERGOZ Instrumentation, Saint Genis Pouilly, France
S.G. Arutunian
ANSL, Yerevan, Armenia

Funding: Research supported by the U.S. Department of Energy.
Measurement and control of transverse beam halo will be critical for the applications of future high-intensity hadron linacs. In particular, beam profile monitors require a very high dynamic range when using for transverse beam halo measurements. In this study, the Vibrating Wire Monitor (VWM) with aperture 60 mm was installed at the High Intensity Neutrino Source (HINS) front-end to measure transverse beam halo. A vibrating wire is excited at its resonance frequency with the help of a magnetic feedback loop, and the vibrating and sensitive wires are connected through a balanced arm. The sensitive wire is moved into the beam halo region by a stepper motor controlled translational stage. We study the feasibility of the vibrating wire for transverse beam halo measurements in the low-energy front-end of the proton linac.

TUPFI053

Transient Beam Loading Effects in Gas-filled RF Cavities for a Muon Collider

1463

M. Chung, A.V. Tollestrup, K. Yonehara
Fermilab, Batavia, USA
B.T. Freemire
IIT, Chicago, Illinois, USA

Funding: Research supported by the U.S. Department of Energy.
A gas-filled RF cavity can be an effective solution for the development of a compact muon ionization cooling channel. One possible problem expected in this type of cavity is the dissipation of significant RF power through the beam-induced plasmas accumulated inside the cavity (plasma loading). In addition, for the higher muon beam intensity, the effects of the beam itself on the cavity fields in the accelerating mode are non-negligible (beam loading). These beam-cavity interactions induce a transient phase which may be very harmful to the beam quality. In this study, we estimate the transient voltage in a gas-filled RF cavity with both the plasma and conventional beam loading and discuss their compensation methods.

TUPFI058

Simulation of Beam-induced Gas Plasma in High Gradient RF Field for Muon Colliders

1478

K. Yonehara, M. Chung, A.V. Tollestrup
Fermilab, Batavia, USA
B.T. Freemire
IIT, Chicago, Illinois, USA
R.P. Johnson, T.J. Roberts
Muons. Inc., USA
R.D. Ryne
LBNL, Berkeley, California, USA
V. Samulyak
BNL, Upton, Long Island, New York, USA
K. Yu
SBU, Stony Brook, USA

There is a strong limit of available RF gradient in a vacuum RF cavity under magnetic fields because the magnetic field enhances a dark current density due to electron focusing and increases probability of an electric breakdown. This limits the cooling performance. A dense hydrogen gas filled RF cavity can break this limit because the gas acts as a buffer of dark current. However, RF power loading due to a beam-induced plasma in a dense gas filled RF cavity (plasma loading effect) is crucial to design the practical cavity. Experiment shows that the plasma loading can be mitigated in denser hydrogen gas and by doping a small amount of electronegative gas in the cavity. A complicate plasma chemical reaction should be dominated in such a dense hydrogen gas condition. A beam-induced plasma is simulated by taking into account the plasma chemistry to reproduce the condition by using the supercomputer at LBNL. We will also investigate the space charge effect in a dense gas in this effort.

TUPFI059

Summary of Dense Hydrogen Gas Filled RF Cavity Tests for Muon Acceleration

1481

K. Yonehara, M. Chung, M.R. Jana, M.A. Leonova, A. Moretti, A.V. Tollestrup
Fermilab, Batavia, USA
B.T. Freemire, P.M. Hanlet, Y. Torun
IIT, Chicago, Illinois, USA
R.P. Johnson
Muons. Inc., USA

Dense hydrogen gas filled RF cavity has a great potential to accelerate a large phase space muon beam in a strong magnetic field. The concept of novel RF cavity has been demonstrated by using an intense proton beam at Fermilab. The experimental result was agreed extremely well with the conventional dilute plasma physic. Based on the model, the beam-induced plasma in the gas filled RF cavity could be controlled by adding a small amount of electronegative gas in dense hydrogen gas. Overview of these experiments will be shown in this presentation.

TUPFI064

Beam Induced Plasma Dynamics in a High Pressure Gas-Filled RF Test Cell for use in a Muon Cooling Channel

1496

B.T. Freemire, P.M. Hanlet, Y. Torun
IIT, Chicago, Illinois, USA
M. Chung, M.R. Jana, M.A. Leonova, A. Moretti, T.A. Schwarz, A.V. Tollestrup, K. Yonehara
Fermilab, Batavia, USA
M.G. Collura
Politecnico di Torino, Torino, Italy
R.P. Johnson
Muons. Inc., USA

Filling an RF cavity with a high pressure gas prevents breakdown when the cavity is place in a multi-Tesla external magnetic field. The choice of hydrogen gas provides the additional benefit of cooling a beam of muons. A beam of particles traversing the cavity, be it muons or protons, ionizes the gas, creating an electron-ion plasma which absorbs energy from the cavity. The ionization rate can be calculated from a beam intensity measurement. Energy loss measurements indicate the loading per RF cycle per electron-ion pair range from 10^-18 to 10^-16 Joules in pure hydrogen, and 10^-20 to 10^-18 Joules when hydrogen is doped with dry air. The addition of an electronegative gas (oxygen) has been observed to reduce the lifetime of ionization electrons in the cavity to below 1 nanosecond. Additionally, the recombination rate of electrons and hydrogen ions has been measured to be on the order of 10^-6 cubic centimeters per second. The recombination mechanism and hydrogen ion species, along with the three-body attachment process of electrons to oxygen, will be discussed.