IPAC2013 - List of Authors (Bowring, D.L.)

Paper	Title	Page
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.

WEPFI092	Multipacting Simulation of the MICE 201 MHz RF Cavity	2914
	T.H. Luo, D.J. Summers UMiss, University, Mississippi, USA D.L. Bowring, A.J. DeMello, D. Li, P. Pan, S.P. Virostek LBNL, Berkeley, California, USA L. Ge SLAC, Menlo Park, California, USA
	The international Muon Ionization Cooling Experiment (MICE) aims to demonstrate transverse cooling of muon beams by ionization. The MICE ionization cooling channel requires eight 201-MHz normal conducting RF cavities to compensate for the longitudinal beam energy loss in the cooling channel. Multipacting is a resonant electron discharge produced by the synchronization of emitted electrons with the RF fields, which can cause breakdown at high power RF operation. In this paper, we present the study of the multipacting effect in the MICE 201 MHz cavities with the SLAC ACE3P code. The simulation is carried out in the cavity body, the RF coupler region, and the coaxial waveguide, with the external magnetic field from the Coupling Coil. We will identify potential RF breakdowns due to multipacting and propose a solution to suppress them.

Paper

Title

Page

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.

WEPFI092

Multipacting Simulation of the MICE 201 MHz RF Cavity

2914

T.H. Luo, D.J. Summers
UMiss, University, Mississippi, USA
D.L. Bowring, A.J. DeMello, D. Li, P. Pan, S.P. Virostek
LBNL, Berkeley, California, USA
L. Ge
SLAC, Menlo Park, California, USA

The international Muon Ionization Cooling Experiment (MICE) aims to demonstrate transverse cooling of muon beams by ionization. The MICE ionization cooling channel requires eight 201-MHz normal conducting RF cavities to compensate for the longitudinal beam energy loss in the cooling channel. Multipacting is a resonant electron discharge produced by the synchronization of emitted electrons with the RF fields, which can cause breakdown at high power RF operation. In this paper, we present the study of the multipacting effect in the MICE 201 MHz cavities with the SLAC ACE3P code. The simulation is carried out in the cavity body, the RF coupler region, and the coaxial waveguide, with the external magnetic field from the Coupling Coil. We will identify potential RF breakdowns due to multipacting and propose a solution to suppress them.