Colloquia - Fall 2014

August 26 - Chun Lin - University of Wisconsin

"Electron Impact Excitation and Optical Plasma Diagnostics: A Personal Perspective"

Abstract:

Measurements of electron impact excitation cross sections out of the metastable levels of the rare gases have enriched the basic understanding of electron excitation processes and provided new directions for optical diagnostics of plasmas. A survey of some key experiments on electron excitation is presented and is followed by discussions of new diagnostics methods including one that has connections with the Old Dominion University.

September 2 -

"Title: TBA"

Abstract:


September 16 - Gigi Ciovati - Jefferson Lab

"Non-linearities in the surface impedance of Nb for accelerator cavity applications"

Abstract:

Niobium is the most common superconductor used in radio-frequency resonators for accelerator applications. The surface impedance of a metal, whether normal conducting or superconducting, is defined as the ratio of the electric and magnetic field component of the plane wave in the metal. Expressions for the surface impedance of superconductors have been calculated since the 1950s in the limit of weak fields. The quality factor of superconducting radio-frequency cavities is inversely proportional to the average surface resistance, the real part of the surface impedance. Experiments have shown that the quality factor exhibits significant field dependencies at low, medium and high fields, revealing non-linearities in the surface resistance. Such non-linearities are related to specific surface preparation methods and typically result in an increase of the surface resistance at high fields. However, recent developments in cavity preparation methods resulted in the decrease of the surface resistance up to fields relevant for accelerator applications. In this presentation, we will review some of the experimental results on the field dependence of the quality factor of niobium and we will discuss some future challenges and opportunities.


September 23 -

"Title: TBA"

Abstract


September 30 -

"Title: TBA"

Abstract


October 7 - TBA

"Title: TBA"

Abstract:


October 14 - TBA

"Title: TBA"

Abstract:


October 21 - TBA

"Title: TBA"

Abstract:


October 28 - Frank Narducci - Naval Air Systems Command

"Extending the Coherence Time of an Atom Interferometer"

Abstract:

Atom interferometers form the basis for precision measurements. These measurements are usually done in the pristine environment of a laboratory in a magnetic shielding on the so-called "clock" transition. We have been exploring the utility of atom interferometers for magnetic field detection. As such, our experiments are performed in an unshielded apparatus on magnetically sensitive transitions. We perform standard Ramsey and spin echo measurements and find a loss of contrast after approximately 100 microseconds. Due to sensitivity to pulse errors, we have applied novel pulse sequences to correct for pulse errors in order to extend the dephasing time of the interferometer by an order of magnitude.


November 4 - TBA

"Title: TBA"

Abstract:


November 11 - Chang-Beom Eom - University of Wisconsin (CANCELLED)

"Title: TBA"

Abstract:


November 18 - Elaine Fortes - University of Maryland and NASA

"Scalar Dark Matter Candidates in Two Inert Higgs Doublet Model"

Abstract:

The IDMS3 model is an extension of Standard Model which includes two inert doublet scalars stabilized by a S3 symmetry. This model provide new candidates for dark matter. We will present an analysis for this model considering two scenarios: i) two of the scalars in each charged sector are mass degenerated due to a residual Z2 symmetry, ii) there is no mass degeneracy because of the introduction of soft terms that break the Z2 symmetry.
Both scenarios provide dark matter candidates and depending on the parameter choice pseudoscalar dark matter candidates can also be accommodated. One other interesting aspect of the IDMS3 is in the difference in the Higgs's boson's 2 photon decay ratio $R_\gamma\gamma$ compared to the one inert doublet model.


November 25 - TBA

"Title: TBA"

Abstract:


December 2 - Senior Thesis Presentations

Matthew Vogel
"Title: TBA"

Michael Kalman
"Title: TBA"

Arthur Bern
"Title: TBA"

August 26 - Chun Lin - University of Wisconsin

"Electron Impact Excitation and Optical Plasma Diagnostics: A Personal Perspective"

Abstract:

Measurements of electron impact excitation cross sections out of the metastable levels of the rare gases have enriched the basic understanding of electron excitation processes and provided new directions for optical diagnostics of plasmas. A survey of some key experiments on electron excitation is presented and is followed by discussions of new diagnostics methods including one that has connections with the Old Dominion University.

September 2 -

"Title: TBA"

Abstract:


September 16 - Gigi Ciovati - Jefferson Lab

"Non-linearities in the surface impedance of Nb for accelerator cavity applications"

Abstract:

Niobium is the most common superconductor used in radio-frequency resonators for accelerator applications. The surface impedance of a metal, whether normal conducting or superconducting, is defined as the ratio of the electric and magnetic field component of the plane wave in the metal. Expressions for the surface impedance of superconductors have been calculated since the 1950s in the limit of weak fields. The quality factor of superconducting radio-frequency cavities is inversely proportional to the average surface resistance, the real part of the surface impedance. Experiments have shown that the quality factor exhibits significant field dependencies at low, medium and high fields, revealing non-linearities in the surface resistance. Such non-linearities are related to specific surface preparation methods and typically result in an increase of the surface resistance at high fields. However, recent developments in cavity preparation methods resulted in the decrease of the surface resistance up to fields relevant for accelerator applications. In this presentation, we will review some of the experimental results on the field dependence of the quality factor of niobium and we will discuss some future challenges and opportunities.


September 23 -

"Title: TBA"

Abstract


September 30 -

"Title: TBA"

Abstract


October 7 - TBA

"Title: TBA"

Abstract:


October 14 - TBA

"Title: TBA"

Abstract:


October 21 - TBA

"Title: TBA"

Abstract:


October 28 - Frank Narducci - Naval Air Systems Command

"Extending the Coherence Time of an Atom Interferometer"

Abstract:

Atom interferometers form the basis for precision measurements. These measurements are usually done in the pristine environment of a laboratory in a magnetic shielding on the so-called "clock" transition. We have been exploring the utility of atom interferometers for magnetic field detection. As such, our experiments are performed in an unshielded apparatus on magnetically sensitive transitions. We perform standard Ramsey and spin echo measurements and find a loss of contrast after approximately 100 microseconds. Due to sensitivity to pulse errors, we have applied novel pulse sequences to correct for pulse errors in order to extend the dephasing time of the interferometer by an order of magnitude.


November 4 - TBA

"Title: TBA"

Abstract:


November 11 - Chang-Beom Eom - University of Wisconsin (CANCELLED)

"Title: TBA"

Abstract:


November 18 - Elaine Fortes - University of Maryland and NASA

"Scalar Dark Matter Candidates in Two Inert Higgs Doublet Model"

Abstract:

The IDMS3 model is an extension of Standard Model which includes two inert doublet scalars stabilized by a S3 symmetry. This model provide new candidates for dark matter. We will present an analysis for this model considering two scenarios: i) two of the scalars in each charged sector are mass degenerated due to a residual Z2 symmetry, ii) there is no mass degeneracy because of the introduction of soft terms that break the Z2 symmetry.
Both scenarios provide dark matter candidates and depending on the parameter choice pseudoscalar dark matter candidates can also be accommodated. One other interesting aspect of the IDMS3 is in the difference in the Higgs's boson's 2 photon decay ratio $R_\gamma\gamma$ compared to the one inert doublet model.


November 25 - TBA

"Title: TBA"

Abstract:


December 2 - Senior Thesis Presentations

Matthew Vogel
"Title: TBA"

Michael Kalman
"Title: TBA"

Arthur Bern
"Title: TBA"