Keyword: coupling
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MOPA64 Circular Modes for Mitigating Space-Charge Effects and Enabling Flat Beams quadrupole, space-charge, emittance, optics 189

• O. Gilanliogullari
IIT, Chicago, Illinois, USA
• B. Mustapha
ANL, Lemont, Illinois, USA
• P. Snopok
Illinois Institute of Technology, Chicago, Illlinois, USA

Funding: This work was supported by the U.S. Department of Energy, under Contract No. DE-AC02-06CH11357
Flat beams are preferred in high-intensity accelerators and high-energy colliders due to one of the transverse plane emittances being smaller, which enhances luminosity and beam brightness. However, flat beams are devastating at low energies due to space charge forces which are significantly enhanced in one plane. The same is true, although to a lesser degree, for non-symmetric elliptical beams. In order to mitigate this effect, circular mode beam optics can be used. In this paper, we show that circular mode beams dilute space charge effects at lower energies, and can be transformed to flat beams later on.

DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA64
About • Received ※ 09 August 2022 — Revised ※ 11 August 2022 — Accepted ※ 12 August 2022 — Issue date ※ 23 August 2022
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MOPA86 Conditioning of Low-Field Multipacting Barriers in Superconducting Quarter-Wave Resonators cavity, multipactoring, cryomodule, electron 249

• S.H. Kim, W. Chang, W. Hartung, J.T. Popielarski, T. Xu
FRIB, East Lansing, Michigan, USA

Funding: This is based upon work supported by the U.S. Department of Energy Office of Science under Cooperative Agreement DE-SC0000661, the State of Michigan and Michigan State University.
Multipacting (MP) barriers are typically observed at very low RF amplitude, at a field 2 to 3 orders of magnitude below the operating gradient, in low-frequency (<~100 MHz), quarter-wave resonators (QWRs). Such barriers may be troublesome, as RF conditioning with a fundamental power coupler (FPC) of typical coupling strength (external Q = 106 to 107) is generally difficult. For the FRIB \beta = 0.085 QWRs (80.5 MHz), the low barrier is observed at an accelerating gradient (Eacc) of ~10 kV/m; the operating Eacc is 5.6 MV/m. Theoretical and simulation studies suggested that the conditioning is difficult due to the relatively low RF power dissipated into multipacting rather than being a problem of the low barrier being stronger than other barriers. We developed a single-stub coaxial FPC matching element for external adjustment of the external Q by one order of magnitude. The matching element provided a significant reduction in the time to condition the low barrier. We will present theoretical and simulation studies of the low MP barrier and experimental results on MP conditioning with the single-stub FPC matching element.

DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA86
About • Received ※ 03 August 2022 — Revised ※ 09 August 2022 — Accepted ※ 11 August 2022 — Issue date ※ 21 August 2022
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TUPA44 A Personal History of the Development of the LAMPF/LANSCE Accelerator linac, operation, DTL, drift-tube-linac 449

• J.M. Potter
JP Accelerator Works, Los Alamos, New Mexico, USA

The LAMPF/LANSCE accelerator has now been operational for 50 years. I arrived as a LASL employee in Group P11 in April 1964 at the beginning stages of its development. I participated in the development of the resonant coupling principle [1] and went on to develop tuning procedures for the 805-MHz coupled cavity linac (CCL) structures and the post-stabilized drift tube linac (DTL) [2]. The resonant coupling principle is now well established as the basis for rf linear accelerators worldwide. I will discuss the development and building of the accelerator from my viewpoint as a member of a large, dedicated team of physicists, engineers, technicians, and support personnel.
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-TUPA44
About • Received ※ 02 August 2022 — Revised ※ 04 August 2022 — Accepted ※ 05 August 2022 — Issue date ※ 05 September 2022
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TUPA75 High Gradient Testing Results of the Benchmark a/λ=0.105 Cavity at CERF-NM cavity, GUI, klystron, MMI 505

• M.R.A. Zuboraj, D.V. Gorelov, T.W. Hall, M.E. Middendorf, D. Rai, E.I. Simakov, T. Tajima
LANL, Los Alamos, New Mexico, USA

Funding: This work was supported by Los Alamos National Laboratory’s Laboratory Directed Research and Development (LDRD) Program.
This presentation will report initial results of high gradient testing of two C-band accelerating cavities fabricated at Los Alamos National Laboratory (LANL). At LANL, we commissioned a C-band Engineering Research Facility of New Mexico (CERF-NM) which has unique capability of conditioning and testing accelerating cavities for operation at surface electric fields at the excess of 300 MV/m, powered by a 50 MW, 5.712 GHz Canon klystron. Recently, we fabricated and tested two benchmark copper cavities at CERF-NM. These cavities establish a benchmark for high gradient performance at C-band and the same geometry will be used to provide direct comparison between high gradient performance of cavities fabricated of different alloys and by different fabrication methods. The cavities consist of three cells with one high gradient central cell and two coupling cells on the sides. The ratio of the radius of the coupling iris to the wavelength is a/λ=0.105. This poster will report high gradient test results such as breakdown rates as function of peak surface electric and magnetic fields and pulse heating.

Poster TUPA75 [0.890 MB]
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-TUPA75
About • Received ※ 05 August 2022 — Revised ※ 11 August 2022 — Accepted ※ 12 August 2022 — Issue date ※ 01 October 2022
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WEPA53 An Open Radiofrequency Accelerating Structure gun, GUI, impedance, SRF 753

• S.V. Kuzikov
Euclid TechLabs, Solon, Ohio, USA

We report an open multi-cell accelerating structure. Being integrated with a set of open-end waveguides, this structure can suppress high-order modes (HOMs). All the accelerating cells are connected at the side to rectangular cross-section waveguides which strongly coupled with free space or absorbers. Due to the anti-phased contribution of the cell pairs, the operating mode does not leak out, and has as high-quality factor as for a closed accelerating structure. However, the compensation does not occur for spurious high-order modes. This operating principle also allows for strong coupling between the cells of the structure, which is why high homogeneity of the accelerating fields can be provided along the structure. We discuss the obtained simulation results and possible applications. Its include a normal conducting high-shunt impedance accelerator, a tunable photoinjector’s RF gun, and a high-current, high-selective SRF accelerators.
Poster WEPA53 [1.817 MB]
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA53
About • Received ※ 01 August 2022 — Revised ※ 08 August 2022 — Accepted ※ 12 August 2022 — Issue date ※ 16 August 2022
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WEPA65 On-Chip Photonics Integrated Photocathodes GUI, electron, photon, cathode 773

• A.H. Kachwala, O. Chubenko, S.S. Karkare
Arizona State University, Tempe, USA
• R. Ahsan
USC, Los Angeles, California, USA
University of Southern California, Los Angeles, California, USA

Funding: This work is supported by the NSF Center for Bright Beams under award PHY-1549132, and by the Department of Energy, Office of Science under awards DE-SC0021092, and DE-SC0021213.
Photonics integrated photocathodes can result in advanced electron sources for various accelerator applications. In such photocathodes, light can be directed using waveguides and other photonic components on the substrate underneath a photoemissive film to generate electron emission from specific locations at sub-micron scales and at specific times at 100-femtosecond scales along with triggering novel photoemission mechanisms resulting in brighter electron beams and enabling unprecedented spatio-temporal shaping of the emitted electrons. In this work we have demonstrated photoemission confined in the transverse direction using a nanofabricated Si3N4 waveguide underneath a 40-nm thick cesiated GaAs photoemissive film, thus demonstrating a proof of principle feasibility of such photonics integrated photocathodes. This work paves the way to integrate the advances in the field of photonics and nanofabrication with photocathodes to develop better electron sources.

Poster WEPA65 [0.642 MB]
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA65
About • Received ※ 26 July 2022 — Revised ※ 06 August 2022 — Accepted ※ 07 August 2022 — Issue date ※ 10 August 2022
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WEPA74 Characterization of Fully Coupled Linear Optics with Turn-by-Turn Data optics, lattice, resonance, quadrupole 805

• Y. Li, R.S. Rainer, V.V. Smaluk
BNL, Upton, New York, USA

Funding: This research used resources of the NSLS-II, a U.S. DOE Office of Science User Facility operated for the DOE Office of Science by Brookhaven National Laboratory under Contract No. DE-SC0012704.
In the future diffraction-limited light source rings, fully coupled linear optics to generate round beams is preferable. While machine tune approaching to linear difference resonances, small random errors, such as quadrupole rolls, can result in fully coupled optics. Consequently, some uncertainty exists in such optics due to random errors distributions. Given beam position monitors turn-by-turn readings, the harmonic analysis method was used to characterize the coupled Ripken Twiss parameters.

Poster WEPA74 [0.889 MB]
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA74
About • Received ※ 25 July 2022 — Revised ※ 30 July 2022 — Accepted ※ 08 August 2022 — Issue date ※ 19 August 2022
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THXD6 A Quasi-Optical Beam Position Monitor electron, site, photon, cavity 846

• S.V. Kuzikov
Euclid TechLabs, Solon, Ohio, USA

There is a strong demand for non-destructive electron Beam Position Monitors (BPMs) for non-perturbative diagnostics of the electron beam position. Challenges are related to the shortness of the electron beam and the noisy chamber environment that are typical for modern RF-driven and plasma-driven accelerators. We propose using a pair of identical high-quality quasi-optical resonators attached to opposite sides of the beam pipe. The resonators can introduce Photonic Band Gap (BPM) structures. These open resonators sustain very low numbers of high-quality modes. We intend to operate at the lowest mode among the others that are capable of being excited by the bunches. The mentioned mode has a coupling coefficient with the beam that depends on the distance between the bunch and the coupling hole. The lower this distance, the higher the coupling. Therefore, comparing the pick-up signals of both resonators with an oscilloscope, we can determine the beam position.
Slides THXD6 [3.745 MB]
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-THXD6
About • Received ※ 25 July 2022 — Accepted ※ 06 August 2022 — Issue date ※ 27 September 2022
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