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At least 937 records · Page 52
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

RF System for the MICE Demonstration of Ionisation Cooling

Muon accelerators offer an attractive option for a range of future particle physics experiments. They can enable high energy (TeV+) high energy lepton colliders whilst mitigating the difficulty of synchrotron losses, and can provide intense beams of neutrinos for fundamental physics experiments investigating the physics of flavor. The method of production of muon beams results in high beam emittance which must be reduced for efficient acceleration. Conventional emittance control schemes take too long, given the very short (2.2 microsecond) rest lifetime of the muon. Ionisation cooling offers a much faster approach to reducing particle emittance, and the international MICE collaboration aims to demonstrate this technique for the first time. This paper will present the MICE RF system and its role in the context of the overall experiment.

43 PARTICLE ACCELERATORS↗
DOE OSTI2017

ON THE COMPUTATION OF PHASE AND ENERGY GAIN FOR A THIN-LENS RF GAP USING A GENERAL FIELD PROFILE

The thin-lens representation for an RF accelerating gap has been well developed and is documented by Lapostolle [5], Weiss [6], Wangler [14], and others [9], [10]. These models assume that the axial electric field is both centered and symmetric so it has a cosine expansion. Presented here is a model that considers general axial fields. Both the cosine and sine transit time factors are required plus their Hilbert transforms. The combination yields a complex Hamiltonian rotating in the complex plane with the synchronous phase. The phase and energy gains are computed in the pre-gap and post-gap regions then aligned with asymptotic values of wave number. Derivations are outlined, examples are shown, and simulations presented.

Particle accelerators↗
DOE OSTI2017

THz and Sub-THz Capabilities of a Table-Top Radiation Source Driven by an RF Thermionic Electron Gun

Design features and experimental results are presented for a sub-mm wave source [1] based on APS RF thermionic electron gun. The setup includes compact alpha-magnet, quadrupoles, sub-mm-wave radiators, and THz optics. The sub-THz radiator is a planar, oversized structure with gratings. Source upgrade for generation frequencies above 1 THz is discussed. The THz radiator will use a short-period undulator having 1 T field amplitude, ~20 cm length, and integrated with a low-loss oversized waveguide. Both radiators are integrated with a miniature horn antenna and a small ~90°-degree in-vacuum bending magnet. The electron beamline is designed to operate different modes including conversion to a flat beam interacting efficiently with the radiator. The source can be used for cancer diagnostics, surface defectoscopy, and non-destructive testing. Sub-THz experiment demonstrated a good potential of a robust, table-top system for generation of a narrow bandwidth THz radiation. This setup can be considered as a prototype of a compact, laser-free, flexible source capable of generation of long trains of Sub-THz and THz pulses with repetition rates not available with laser-driven sources.

Smirnov, Alexei V.↗
DOE OSTI2017

Automatic Phase Calibration for RF Cavities using Beam-Loading Signals

Precise calibration of the cavity phase signals is necessary for the operation of any particle accelerator. For many systems this requires human in the loop adjustments based on measurements of the beam parameters downstream. Some recent work has developed a scheme for the calibration of the cavity phase using beam measurements and beam-loading however this scheme is still a multi-step process that requires heavy automation or human in the loop. In this paper we analyze a new scheme that uses only RF signals reacting to beam-loading to calculate the phase of the beam relative to the cavity. This technique could be used in slow control loops to provide real-time adjustment of the cavity phase calibration without human intervention thereby increasing the stability and reliability of the accelerator.

43 PARTICLE ACCELERATORS↗
DOE OSTI2018

A High Current, Short Pulse, RF Synchronized Electron Gun for the Stanford Linear Accelerator

For the generation of intense single and multiple bunches of electrons (>8 nc per bunch) for accelerator studies at SLAC, a high peak current photoemission electron gun has been developed. A gallium arsenide photocathode is illuminated by the optical beam from a frequency doubled, actively mode-locked and Q-switched Nd:YAG laser. The mode-locked optical pulses are of variable, sub-nanosecond width and occur with a spacing of 8.4 nsec, synchronized with the 2856 MHz accelerator rf. The gun is designed to be space charge limited at 15 A and 200 kV, although emission of 60 A was obtained with a 57 kV test structure, corresponding to a current density of 180 A/cm 2 . With the proper choice of laser wavelength, the electron beam may be 40% longitudinally polarized.

Sinclair, C.↗
DOE OSTI2016

Development of an Ultra Fast RF Kicker for an ERL-based Electron Cooler

The staged approach to electron cooling proposed for Jefferson Lab's Medium Energy Electron-Ion Collider (MEIC) utilizes bunched beam electron cooling with a single-pass energy recovery linac (ERL) for cooling in the ion collider ring. Possible luminosity upgrades make use of an ERL and full circulator ring and will require ultra-fast kickers that are beyond current technology. A novel approach to generating the necessary ultra fast (ns-level) RF kicking pulse involves the summation of specific subharmonics of the cooling electron bunch frequency; the resultant kicking pulse is then naturally constrained to have rise and fall times equal to the electron bunch frequency. The uniformity of such a pulse and its effects on the beam dynamics of the cooling electron bunch are discussed.

Sy, Amy V.↗
DOE OSTI2018

Helical Six-Dimensional Muon Ionization Cooling Channel with Gas-Filled RF Cavities

A six-dimensional muon ionization cooling in a helical magnet channel has been studied. The cooling performance which is analytically evaluated by solving the exact Hamiltonian is reproduced in numerical simulation. One of the key beam elements for the helical channel is a dense-hydrogen gas-filled RF cavity which realizes a compact cooling channel. Besides, a beam-induced gas plasma in the cavity can generate a plasma-focusing effect. This will generate extremely small betatron function, which realizes extremely low emittance beam.

43 PARTICLE ACCELERATORS↗
DOE OSTI2019

A Method to Reduce the Coherent Betatron Oscillations in a Muon g-2 Storage Ring Experiment using RF Fields

The muon $g-2$ storage-ring experiments store a beam of polarized muons in a weak focusing storage ring. As the ensemble of muons goes around the ring, their spin precesses, and when they decay through the weak interaction: $\mu^+ \rightarrow e^+ \nu_e \bar{\nu_\mu}$ the decay positrons are detected by electromagnetic calorimeters. In addition to the expected exponential decay in the positron time spectrum, the weak decay asymmetry causes a modulation in the number of positrons at the difference frequency between the spin and cyclotron frequencies, $\omega_a$. This frequency is directly proportional to the magnetic anomaly $a =(g-2)/2$, where $g$ is the gyromagnetic ratio of the muon, which is slightly greater than 2. The detector acceptance depends on the radial position of the muon decay, so the coherent betatron oscillations (CBO) of the muon bunch following injection into the storage ring amplitude modulates the measured muon signal with the frequency $\omega_{CBO}$. A new method using radio frequency (RF) electric fields has the potential to significantly decrease the beam CBO, and additionally to scrape the beam to reduce muon losses from the storage ring during the measurement period.

43 PARTICLE ACCELERATORS↗
DOE OSTI2019

Simulations for Field-Enhanced Conduction-Cooled Superconducting RF Electron Source

We present a novel RF design for a field enhanced electron source driven by field emission cathodes. The proposed electron source relies on the enhanced high electric field gradients at the cathode to simultaneously extract and accelerate electrons. The system will be tested in a conduction-cooled superconducting radiofrequency cavity recently demonstrated at Fermilab. In this work, we present electromagnetic and thermal simulations of the setup that support the feasibility of the design.

43 PARTICLE ACCELERATORS↗
DOE OSTI2019

Observations of Short-Range Wadefield Effects in Tesla-Type Superconducting RF Cavities

The Fermilab Accelerator Science and Technology (FAST) facility has a unique configuration of a photocathode rf gun beam injecting two TESLA-type single cavities (CC1 and CC2) in series prior to the cryomodule. To investigate short-range wakefield effects, we have steered the beam to minimize the signals in the higher-order mode (HOM) detectors of CC1 and CC2 for a baseline, and then used a vertical corrector between the two cavities to steer the beam off axis at an angle into CC2. A Hamamatsu synchroscan streak camera viewing a downstream OTR screen provided an image of y-t effects within the micropulses with ~10-micron spatial resolution and 2-ps temporal resolution. At 500 pC/b, 50 b, and 4 mrad off-axis steering into CC2, we observed an ~ 100-micron head-tail centroid shift in the streak camera image y(t)-profiles. This centroid shift value is 5 times larger than the observed HOM-driven centroid oscillation within the macropulse and is consistent with a calculat ed short-range wakefield effect. Additional results for kick-angle compensations will be presented.

43 PARTICLE ACCELERATORS↗
DOE OSTI2019

Observations of Long-Range and Short-Range Wakefield Effects on Electron-Beam Dynamics in TESLA-Type Superconducting RF

The assessments of long-range and short-range wakefield effects in TESLA-type superconducting rf cavities at the Fermilab Accelerator Science and Technology (FAST) Facility are described. A dipolar higher-order mode (HOM) of one cavity is shown to be in near resonance with the 3-MHz micropulse repetition frequency harmonic resulting in a clear sub-macropulse centroid oscillation of 100 kHz. In the short-range wakefield measurements, a head-tail transverse kick of ~100 µm is seen in the streak camera images with 500 pC/b and offsets of ~2 mm. A numerical model for the TESLA-type cavity is consistent with these latter results.

43 PARTICLE ACCELERATORS↗
DOE OSTI2015

Calculations for RF Cavities with Dissipative Material

3D simulations have been performed for a variety of SRF cavities which incorporate Higher Order Mode dampers, either in form of coaxial couplers or waveguide dampers. Instead of utilizing the rather standard approach of matching the output port of the dampers with a broadband coaxial or waveguide port, dissipative materials are modelled for RF field absorption. This for instance not only avoids the otherwise required definition of the number of modes considered for damping, which has an impact on the computational time, but also allows tailoring the load material to conform with experimental data of e.g. non-perfect absorbers. The new calculation scheme is presented. Findings are partially compared with those achieved with the standard waveguide port approach by means of external quality factors. CPU speeds are briefly discussed for both approaches.

Marhauser, Frank↗
DOE OSTI2015

RF Performance of Ingot Niobium Cavities of Medium-Low Purity

Superconducting radio-frequency cavities made of ingot niobium with residual resistivity ratio (RRR) greater than 250 have proven to have similar or better performance than fine-grain Nb cavities of the same purity, after standard processing. The high purity requirement contributes to the high cost of the material. As superconducting accelerators operating in continuous-wave typically require cavities to operate at moderate accelerating gradients, using lower purity material could be advantageous not only to reduce cost but also to achieve higher Q0-values, because of the well-known dependence of the BCS-surface resistance on mean free path. In this contribution we present the results from cryogenic RF tests of 1.3-1.5 GHz single-cell cavities made of ingot Nb of medium (RRR=100-150) and low (RRR=60) purity from different suppliers. Cavities made of medium-purity ingots routinely achieved peak surface magnetic field values greater than 70 mT with Q0-values above 1.5·1010 at 2 K. The performance of cavities made of low-purity ingots were affected by significant pitting of the surface after chemical etching.

Ciovati, Gianluigi↗
DOE OSTI2019

Nb3Sn films for SRF cavities: genesis and RF properties

Understanding of Nb3Sn nucleation and growth is essential to the progress with Nb3Sn vapor diffusion coatings of SRF cavities. Samples representing different stages of Nb3Sn formation have been produced and examined to elucidate the effects of nucleation, growth, process conditions, and impurities. Nb3Sn films from few hundreds of nm up to ~15 µm were grown and characterized using AFM, SEM/EDS, XPS, EBSD, SIMS, and SAM. Microscopic examinations of samples suggest the mechanisms behind Nb3Sn thin film nucleation and growth. RF measurements of coated cavities were combined with material characterization of witness samples to adapt the coating process in "Siemens" coating configuration. Understanding obtained from sample studies, applied to cavities, resulted in Nb3Sn cavity with quality factor 2 ×1010 at 15 MV/m accelerating gradient at 4 K, without "Wuppertal" Q-slope. We discuss the genesis of the Nb3Sn thin film in a typical tin vapor diffusion process, and its consequences to the coating of SRF cavities.

Pudasaini, U.↗
DOE OSTI2019

RF Characterization of an S-I-S’ Multilayer Sample

S-I-S’ multilayers promise to boost the performance of bulk superconductors in terms of maximum field and surface resistance. At HZB, RF-surface resistance measurements were performed with a Quadrupole Resonator (QPR) and an S-I-S’ sample (75 nm NbTiN on 15 nm AlN insulator on bulk Nb) prepared at JLab. Measurements were performed at 414, 845, and 1286 MHz at sample temperatures from 2 K up to well above the transition temperature of NbTiN of ~17.3 K. The Rs exhibits an unexpected temperature dependence: Rather than rising monotonically, as expected from BCS theory, a local maximum is observed. There is a temperature range where Rs decreases with increasing temperature. Such behavior indicates that an additional interaction between the superconducting layers may have to be included in the surface resistance model. Measurements of the baseline Nb sample prior to coating exhibited no such behavior; hence systematic measurement errors can be excluded as the explanation. The maximum field was limited by a hard magnetic quench near 20 mT, close to Hc1 of NbTiN, suggesting that the sample is limited by early flux penetration.

Keckert, S.↗
DOE OSTI2019

Study of Flux Trapping Variability between Batches of Tokyo Denkai Niobium used for the LCLS-II Project and Subsequent 9-cell RF Loss Distribution between the Batches

During the LCLS-II project a second batch of niobium was procured from Tokyo Denkai Co Ltd in order to make additional cavities. The original production material came from Two vendors Tokyo Denkai Co., Ltd. (TD) and Ningxia Orient Tantalum Industry Co., Ltd. (OTIC/NX)). It was found TD niobium required a lower annealing temperature (900°C) to obtain satisfactory flux expulsion characteristics compared to NX which required a slightly higher annealing temperature (950°-975°C). In order to ensure the new TD material performed equivalent to the niobium produced 4 year before after 900°C annealing; each heat lot of niobium had its flux expulsion characteristics parametrized and custom thermal treatments developed for each lot. Subsequent pure heat lot 9 cell cavities were made and tested. We will look at the flux expulsion characteristics of each lot, and RF loss of the 9-cell cavities produced using the individual heat lots.

Palczewski, A. D.↗
DOE OSTI2021

Multipacting Analysis of Warm Linac RF Vacuum Windows

Multipacting in accelerating structures is a complex phenomenon with which there is much to be understood. While multipacting research efforts have primarily been focused on superconducting radio frequency (SRF) systems, normal conducting accelerating structures that have a higher thermal capacity and a greater vacuum pressure tolerance could benefit from additional investigation. This research details multipacting simulation methods and the results of 3-D electromagnetic simulations of RF vacuum windows used on normal conducting linac (NCL) cavities. Possible techniques for reducing and eliminating multipacting activities in these structures are discussed.

Toby, George↗