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LNS Special Seminars- Summer 2018


 

Wednesday, June 6, 2018

    3:00 p.m.

    Kolker Room, 26-414

 

The future of High Energy Physics and China's role

Yifang Wang, Institute of High Energy Physics of Chinese Academy of Sciences

 

Abstract:

Since the discovery of Higgs, particle physics is now face a transition. What is the next step is the major questions to our field. I will discuss an initiative from China: Circular electron-positron Collider and its design and R&D progress. In addition, I will cover projects in China on cosmic-ray physics, neutrino physics, and science program in space.

 

Monday, August 6, 2018

    4:00 p.m.

    Kolker Room, 26-414

 

Scaling in Quasifree Scattering of Hadrons from Nucleons within Nuclei

R. J. (Jerry) Peterson, University of Colorado

 

Abstract:

The interior of a complex nucleus is a stew of strongly interacting nucleons and their exchanged mesons.  At suitable kinematics, electron beams have been found to scatter from individual bound nucleons in an incoherent fashion, with quasifree cross sections that add the cross sections, not the amplitudes, from individual bound nucleons.  The assumptions behind this interpretation are summarized by converting the observed data into scaling functions, which would (if all the assumptions were valid) give universal responses.  A much richer range of these responses is accessible with hadron beams, which could also suffer from the strong interaction within nuclei.   Can such hadron scattering be incoherent and quasifree, allowing access to a wide range of observables about nucleons within nuclei?  The vast range of suitable data with beams of pions, K+ mesons, and protons will be examined to see if these data ‘scale’ in three variables, indicating an understanding of the reaction mechanism, and permitting access to all six of the possible spin and isospin single-nucleon responses of nuclei.  A relativistic scaling system will be used, as for recent electron scattering quasifree data.

 

 

Thursday, August 16, 2018

    4:00 p.m.

    Kolker Room, 26-414

 

Coupling Impedance Measurement and Analysis of Critical Vacuum Chamber Components for the Advanced Photon Source Upgrade

Medani Prasad Sangroula, Illinois Institute of Technology

 

Abstract:

The Advanced Photon Source is in the design phase of a major upgrade that will increase the x-ray brightness by two to three orders of magnitude. Stably storing such an intense beam requires very strong magnets that demand a narrow gap vacuum chamber. These narrow gap chambers and the associated small aperture vacuum components must be designed with minimal coupling impedance so as to minimize potential RF-heating and to avoid deleterious collective instabilities of the electron beam. My research focuses on coupling impedance measurements, simulations, and analysis of critical vacuum chamber components for the APS Upgrade (APS-U), using both the traditional coaxial wire method and the novel Goubau line (G-line) method.

Impedance measurements of accelerator components have traditionally been done with the coaxial wire method, which is based on the fact that the TEM mode of the coaxial cable can mimic the Coulomb field of a particle beam. We describe how a similar field profile can be exploited using the fundamental TM mode to measure impedance with a G-line, which is essentially a single wire transmission line designed to propagate Sommerfeld-like surface waves. We describe in detail the measurement procedure that we have developed for the G-line, including the measurement setup and proper definition of a reference, measurement procedure and advantages, and our experience regarding how to reduce systematic experimental error that we learned over the course of the measurements. After describing the measurement techniques, we then turn to our results. Since there has been some controversy regarding the impedance cost of NEG, we first present impedance measurements of APS-U NEG-coated copper chambers based on the traditional coaxial wire method. We then discuss the impedance analysis of APS-U vacuum chamber components using the G-line, starting with our initial suite of measurements and simulations designed to benchmark and validate the novel G-line based measurement technique. We then present the measured results for the beam position monitor (BPM)-bellows assembly, gate valve liner, rf-flanges, pumping cross etc., along with some simulated results and associated analysis.

The measured results of the NEG-coated chamber show that the effect of impedance due to the 1.5-micron thick NEG coating on copper is mostly negligible up to 21 GHz, as predicted by simulations. In addition, the measured results of the APS-U BPM-bellows assembly, gate valve liner, and the pumping cross have been properly designed and manufactured to specifications, with no observable resonance peaks. On the other hand, impedance evaluations of several flange designs have displayed resonances that we subsequently attributed to improper machining and/or poor tolerance control, and we have worked to ensure future designs can be made to specifications. Finally, we show that the G-line is relatively simple and in our opinion better way to measure the impedance over a broad frequency range.

 

Monday, August 20, 2018

    4:00 p.m.

    Kolker Room, 26-414

 

Fully Staged Two Beam Acceleration at the Argonne Wakefield Accelerator Facility

Nicole Neveu, Illinois Institute of Technology

 

Abstract:

Two beam acceleration is a candidate for future high energy physics machines and FEL user facilities. This scheme consists of two independent electron accelerators operating synchronously, with bunch trains of the ‘drive’ accelerator serving as the power source for the ‘witness’ accelerator. The design, simulation, optimization, and preliminary experimental results of the drive beam line configuration will be presented. This will be the foundation for proof of principle experiments that will take place at the Argonne Wakefield Accelerator (AWA) facility.