IPAC2013 - List of Authors (Moretti, A.)

Paper	Title	Page
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.

TUPFI068	High Power Tests of Alumina in High Pressure RF Cavities for Muon Ionization Cooling Channel	1508
	L.M. Nash University of Chicago, Chicago, Illinois, USA G. Flanagan, R.P. Johnson, F. Marhauser, J.H. Nipper Muons. Inc., USA M.A. Leonova, A. Moretti, M. Popovic, A.V. Tollestrup, K. Yonehara Fermilab, Batavia, USA Y. Torun IIT, Chicago, Illinois, USA
	It is important to make a compact muon ionization cooling channel to increase the cooling efficiency (muon survival rate, cooling decrement, etc). A proposed scheme to reduce the radial size of RF cavities at a given resonance frequency is to insert a dielectric material into the RF cavity. In vacuum cavities, however, dielectric materials are extremely susceptible to breakdown in high power conditions. High-pressure hydrogen gas has been shown to inhibit breakdown events in RF cavities in strong magnetic fields. An experiment has been designed to test surface breakdown of alumina in RF cavities. A structure has been designed to maximize the parallel field parallel to the surface while bringing the cavity into a desired frequency range (800-810MHz). Alumina is tested in this configuration under high power conditions. The experimental result will be shown in this presentation.

WEPFI066	The RF System for the MICE Experiment	2848
	K. Ronald, A.J. Dick, C.G. Whyte USTRAT/SUPA, Glasgow, United Kingdom P.A. Corlett STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom A.J. DeMello, D. Li, S.P. Virostek LBNL, Berkeley, California, USA A.F. Grant, A.J. Moss, C.J. White STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom P.M. Hanlet IIT, Chicago, Illinois, USA C. Hunt, K.R. Long, J. Pasternak Imperial College of Science and Technology, Department of Physics, London, United Kingdom T.H. Luo, D.J. Summers UMiss, University, Mississippi, USA A. Moretti, R.J. Pasquinelli, D.W. Peterson, R.P. Schultz, J.T. Volk Fermilab, Batavia, USA P.J. Smith Sheffield University, Sheffield, United Kingdom T. Stanley STFC/RAL, Chilton, Didcot, Oxon, United Kingdom Y. Torun Illinois Institute of Technology, Chicago, IL, USA
	The International Muon Ionisation Cooling Experiment (MICE) is designed to demonstrate the effectiveness of ionisation cooling to reduce the phase space footprint of a muon beam, principally to allow the subsequent acceleration of muons for next generation colliders and/or neutrino factories. The experiment (and indeed any subsequent accelerator cooling channel based on the same principles) poses certain unusual requirements on its RF system, whilst the precision measurement of the ionisation cooling process demands special diagnostics. This paper shall outline the key features of the RF system, including the LLRF control, the power amplifier chain, distribution network, cavities, tuners and couplers, all of which must operate in a high magnetic field environment. The RF diagnostics which, in conjunction with the other MICE diagnostics, shall allow detailed knowledge of the amplitude and phase of the acceleration field during the transit of each individual Muon shall also be outlined.

WEPFI072	Analysis of Breakdown Damage in an 805 MHz Pillbox Cavity for Muon Ionization Cooling R&D	2857
	D.L. Bowring, D. Li LBNL, Berkeley, California, USA A. Moretti, Y. Torun Fermilab, Batavia, USA
	When operating in multi-Tesla solenoidal magnetic fields, normal-conducting cavities exhibit RF breakdown at anomalously low gradients. This breakdown behavior may be due to field-emitted electrons, focused by the magnetic field into "beamlets" with relatively large current densities. These beamlets may then cause pulsed heating and cyclic fatigue damage on cavity interior surfaces. If this model is correct, materials with long radiation lengths (relative to copper) may alleviate the problem of RF breakdown in strong magnetic fields. To study this phenomenon, RF breakdown was induced on pairs of "buttons" in an 805 MHz pillbox cavity. The shape of the buttons creates a local enhancement of the surface electric field, such that breakdown occurs preferentially on the button surface. Beryllium and copper buttons were tested in order to evaluate the effect of radiation length on RF breakdown performance. This poster presents an analysis of the damage to these buttons and suggests a path forward for future materials R&D related to breakdown in strong magnetic fields.

WEPFI073	A Modular Cavity for Muon Ionization Cooling R&D	2860
	D.L. Bowring, A.J. DeMello, A.R. Lambert, D. Li, S.P. Virostek, M.S. Zisman LBNL, Berkeley, California, USA C. Adolphsen, L. Ge, A.A. Haase, K.H. Lee, Z. Li, D.W. Martin SLAC, Menlo Park, California, USA D.M. Kaplan Illinois Institute of Technology, Chicago, Illinois, USA T.H. Luo, D.J. Summers UMiss, University, Mississippi, USA A. Moretti, M.A. Palmer, R.J. Pasquinelli, Y. Torun Fermilab, Batavia, USA R.B. Palmer BNL, Upton, Long Island, New York, USA
	The Muon Accelerator Program (MAP) collaboration is developing an ionization cooling channel for muon beams. Ionization cooling channel designs call for the operation of high-gradient, normal-conducting RF cavities in multi-Tesla solenoidal magnetic fields. However, strong magnetic fields have been shown to limit the maximum achievable gradient in RF cavities. This gradient limit is characterized by RF breakdown and damage to the cavity surface. To study this issue, we have developed an experimental program based on a modular pillbox cavity operating at 805 MHz. The modular cavity design allows for the evaluation of different cavity materials - such as beryllium - which may ameliorate or circumvent RF breakdown triggers. Modular cavity components may furthermore be prepared with different surface treatments, such as high-temperature baking or chemical polishing. This poster presents the design and experimental status of the modular cavity, as well as future plans for the experimental program.

Paper

Title

Page

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.

TUPFI068

High Power Tests of Alumina in High Pressure RF Cavities for Muon Ionization Cooling Channel

1508

L.M. Nash
University of Chicago, Chicago, Illinois, USA
G. Flanagan, R.P. Johnson, F. Marhauser, J.H. Nipper
Muons. Inc., USA
M.A. Leonova, A. Moretti, M. Popovic, A.V. Tollestrup, K. Yonehara
Fermilab, Batavia, USA
Y. Torun
IIT, Chicago, Illinois, USA

It is important to make a compact muon ionization cooling channel to increase the cooling efficiency (muon survival rate, cooling decrement, etc). A proposed scheme to reduce the radial size of RF cavities at a given resonance frequency is to insert a dielectric material into the RF cavity. In vacuum cavities, however, dielectric materials are extremely susceptible to breakdown in high power conditions. High-pressure hydrogen gas has been shown to inhibit breakdown events in RF cavities in strong magnetic fields. An experiment has been designed to test surface breakdown of alumina in RF cavities. A structure has been designed to maximize the parallel field parallel to the surface while bringing the cavity into a desired frequency range (800-810MHz). Alumina is tested in this configuration under high power conditions. The experimental result will be shown in this presentation.

WEPFI066

The RF System for the MICE Experiment

2848

K. Ronald, A.J. Dick, C.G. Whyte
USTRAT/SUPA, Glasgow, United Kingdom
P.A. Corlett
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
A.J. DeMello, D. Li, S.P. Virostek
LBNL, Berkeley, California, USA
A.F. Grant, A.J. Moss, C.J. White
STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom
P.M. Hanlet
IIT, Chicago, Illinois, USA
C. Hunt, K.R. Long, J. Pasternak
Imperial College of Science and Technology, Department of Physics, London, United Kingdom
T.H. Luo, D.J. Summers
UMiss, University, Mississippi, USA
A. Moretti, R.J. Pasquinelli, D.W. Peterson, R.P. Schultz, J.T. Volk
Fermilab, Batavia, USA
P.J. Smith
Sheffield University, Sheffield, United Kingdom
T. Stanley
STFC/RAL, Chilton, Didcot, Oxon, United Kingdom
Y. Torun
Illinois Institute of Technology, Chicago, IL, USA

The International Muon Ionisation Cooling Experiment (MICE) is designed to demonstrate the effectiveness of ionisation cooling to reduce the phase space footprint of a muon beam, principally to allow the subsequent acceleration of muons for next generation colliders and/or neutrino factories. The experiment (and indeed any subsequent accelerator cooling channel based on the same principles) poses certain unusual requirements on its RF system, whilst the precision measurement of the ionisation cooling process demands special diagnostics. This paper shall outline the key features of the RF system, including the LLRF control, the power amplifier chain, distribution network, cavities, tuners and couplers, all of which must operate in a high magnetic field environment. The RF diagnostics which, in conjunction with the other MICE diagnostics, shall allow detailed knowledge of the amplitude and phase of the acceleration field during the transit of each individual Muon shall also be outlined.

WEPFI072

Analysis of Breakdown Damage in an 805 MHz Pillbox Cavity for Muon Ionization Cooling R&D

2857

D.L. Bowring, D. Li
LBNL, Berkeley, California, USA
A. Moretti, Y. Torun
Fermilab, Batavia, USA

When operating in multi-Tesla solenoidal magnetic fields, normal-conducting cavities exhibit RF breakdown at anomalously low gradients. This breakdown behavior may be due to field-emitted electrons, focused by the magnetic field into "beamlets" with relatively large current densities. These beamlets may then cause pulsed heating and cyclic fatigue damage on cavity interior surfaces. If this model is correct, materials with long radiation lengths (relative to copper) may alleviate the problem of RF breakdown in strong magnetic fields. To study this phenomenon, RF breakdown was induced on pairs of "buttons" in an 805 MHz pillbox cavity. The shape of the buttons creates a local enhancement of the surface electric field, such that breakdown occurs preferentially on the button surface. Beryllium and copper buttons were tested in order to evaluate the effect of radiation length on RF breakdown performance. This poster presents an analysis of the damage to these buttons and suggests a path forward for future materials R&D related to breakdown in strong magnetic fields.

WEPFI073

A Modular Cavity for Muon Ionization Cooling R&D

2860

D.L. Bowring, A.J. DeMello, A.R. Lambert, D. Li, S.P. Virostek, M.S. Zisman
LBNL, Berkeley, California, USA
C. Adolphsen, L. Ge, A.A. Haase, K.H. Lee, Z. Li, D.W. Martin
SLAC, Menlo Park, California, USA
D.M. Kaplan
Illinois Institute of Technology, Chicago, Illinois, USA
T.H. Luo, D.J. Summers
UMiss, University, Mississippi, USA
A. Moretti, M.A. Palmer, R.J. Pasquinelli, Y. Torun
Fermilab, Batavia, USA
R.B. Palmer
BNL, Upton, Long Island, New York, USA

The Muon Accelerator Program (MAP) collaboration is developing an ionization cooling channel for muon beams. Ionization cooling channel designs call for the operation of high-gradient, normal-conducting RF cavities in multi-Tesla solenoidal magnetic fields. However, strong magnetic fields have been shown to limit the maximum achievable gradient in RF cavities. This gradient limit is characterized by RF breakdown and damage to the cavity surface. To study this issue, we have developed an experimental program based on a modular pillbox cavity operating at 805 MHz. The modular cavity design allows for the evaluation of different cavity materials - such as beryllium - which may ameliorate or circumvent RF breakdown triggers. Modular cavity components may furthermore be prepared with different surface treatments, such as high-temperature baking or chemical polishing. This poster presents the design and experimental status of the modular cavity, as well as future plans for the experimental program.