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Commissioning, Performance, and Effect of the Quench Current-Boosting Device on a Dedicated Superconducting Magnet
Superconducting magnet training is one of the accelerator related issues attracting attention due to significant operational costs and time budget associated to it. It is especially worrisome that magnets based on the “next-generation” Nb 3 Sn technology are affected by long training. While various efforts are underway to better understand and resolve the problem a parallel path could also be investigated, a path bypassing the issue. Following the concept of fast induced over-current during magnet powering, FNAL has developed an upgradable capacitor-based device to discharge through a superconducting magnet at quench detection or operator chosen time. The 0.4 F/1 kV device has been tested on a 1-m-long dipole-coil in a “mirror” magnet configuration and conclusive results on magnet training elimination have been observed. Here in this paper we discuss the main characteristics of the device, compare simulated response and actual performance, elaborate on test drivers and outcomes. Next steps and perspectives for future use are debated.
Rapid Commissioning of Large Machine Tools Using Finite Element-Based Correction of Geometric Errors
Large computer numerical control (CNC) machine tools derive their stiffness from monolithic cast iron bases or weldments that are sometimes integral to machine motion systems like box ways or guideways. However, the sheer size of castings and even floor flatness deviations result in dimensional errors in these systems, which manifest as machine motion errors. Typical geometric alignment processes rely on an iterative approach, where measurements are taken to assess alignment (straightness, squareness, and parallelism), followed by adjustment of the machine supports (fixators or leveling pads), which can take weeks even for an experienced operator. Conversely, a novel method is proposed to shorten the correction time by eliminating the trial-and-error process in favor of a more deterministic approach guided by a finite element (FE) method. A feasibility study is conducted on a CNC polymer hybrid machine, with a steel weldment frame, supported by six leveling pads. An FE model of the frame is utilized to obtain recommended leveling pad adjustments, based on measurement of machine errors taken using a laser tracker. After a single adjustment cycle, measurements reveal that geometric errors of the machine tool are reduced from 2.22 mm of flatness deviation to 0.32 mm, achieving an 85.6% reduction. Furthermore, the entire process including measurement, adjustment, and assessment is completed in just 6 h by two operators who are not professional service engineers. In conclusion, this methodology demonstrates feasibility for scaling up, especially to large, high-precision CNC machine tools with bases mounted by fixators, offering the capability for bidirectional adjustment.
Commissioning an EUV mask microscope for lithography generations reaching 8 nm
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Laser heated pedestal growth system commissioning and fiber processing
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Fielding the LANL Gas Cherenkov Detector (GCD-3) at the National Ignition Facility: The engineering challenges of designing, analyzing, fabricating, testing, and commissioning the next-generation GCD detector and WellDIM3.9m insertion manipulator for use at NIF
We report that fielding the LANL third-generation Gas Cherenkov Detector (GCD-3) at the National Ignition Facility (NIF) revealed an array of complex engineering challenges. Fielding the GCD-3 Detector in a 3.9 meter re-entrant Well on the NIF Target Chamber required the development of a specialized detector deployment system named the WellDIM3.9m Diagnostic Manipulator (WellDIM). The most stringent design requirement entailed a no-load/no-contact condition with the Well, which dictated that all seismic loads be transferred to the Target Chamber port flange. The WellDIM transports the GCD-3 into the Well at a distance of 3.9m from Target Chamber Center. Finally, the GCD-3 Detector, outfitted with additional shielding to mitigate higher NIF backgrounds, will serve as a prototype for the future, heavily shielded “Super-GCD”.
Enhancements to commissioning techniques and quality assurance of brachytherapy treatment planning systems that use model-based dose calculation algorithms
The current standard for brachytherapy dose calculations is based on the AAPM TG-43 formalism. Simplifications used in the TG-43 formalism have been challenged by many publications over the past decade. With the continuous increase in computing power, approaches based on fundamental physics processes or physics models such as the linear-Boltzmann transport equation are now applicable in a clinical setting. Thus, model-based dose calculation algorithms (MBDCAs) have been introduced to address TG-43 limitations for brachytherapy. The MBDCA approach results in a paradigm shift, which will require a concerted effort to integrate them properly into the radiation therapy community. MBDCA will improve treatment planning relative to the implementation of the traditional TG-43 formalism by accounting for individualized, patient-specific radiation scatter conditions, and the radiological effect of material heterogeneities differing from water. A snapshot of the current status of MBDCA and AAPM Task Group reports related to the subject of QA recommendations for brachytherapy treatment planning is presented. Some simplified Monte Carlo simulation results are also presented to delineate the effects MBDCA are called to account for and facilitate the discussion on suggestions for (i) new QA standards to augment current societal recommendations, (ii) consideration of dose specification such as dose to medium in medium, collisional kerma to medium in medium, or collisional kerma to water in medium, and (iii) infrastructure needed to uniformly introduce these new algorithms. Suggestions in this Vision 20/20 article may serve as a basis for developing future standards to be recommended by professional societies such as the AAPM, ESTRO, and ABS toward providing consistent clinical implementation throughout the brachytherapy community and rigorous quality management of MBDCA-based treatment planning systems.
Commissioning a CT-compatible LDR tandem and ovoid applicator using Monte Carlo calculation and 3D dosimetry
Purpose: To determine the geometric and dose attenuation characteristics of a new commercially available CT-compatible LDR tandem and ovoid (T and O) applicator using Monte Carlo calculation and 3D dosimetry. Methods: For geometric characterization, we quantified physical dimensions and investigated a systematic difference found to exist between nominal ovoid angle and the angle at which the afterloading buckets fall within the ovoid. For dosimetric characterization, we determined source attenuation through asymmetric gold shielding in the buckets using Monte Carlo simulations and 3D dosimetry. Monte Carlo code MCNP5 was used to simulate 1.5 Multiplication-Sign 10{sup 9} photon histories from a {sup 137}Cs source placed in the bucket to achieve statistical uncertainty of 1% at a 6 cm distance. For 3D dosimetry, the distribution about an unshielded source was first measured to evaluate the system for {sup 137}Cs, after which the distribution was measured about sources placed in each bucket. Cylindrical PRESAGE{sup Registered-Sign} dosimeters (9.5 cm diameter, 9.2 cm height) with a central channel bored for source placement were supplied by Heuris Inc. The dosimeters were scanned with the Duke Large field of view Optical CT-Scanner before and after delivering a nominal dose at 1 cm of 5-8 Gy. During irradiation the dosimeter was placed in a water phantom to provide backscatter. Optical CT scan time lasted 15 min during which 720 projections were acquired at 0.5 Degree-Sign increments, and a 3D distribution was reconstructed with a (0.05 cm){sup 3} isotropic voxel size. The distributions about the buckets were used to calculate a 3D distribution of transmission rate through the bucket, which was applied to a clinical CT-based T and O implant plan. Results: The systematic difference in bucket angle relative to the nominal ovoid angle (105 Degree-Sign ) was 3.1 Degree-Sign -4.7 Degree-Sign . A systematic difference in bucket angle of 1 Degree-Sign , 5 Degree-Sign , and 10 Degree-Sign caused a 1%{+-} 0.1%, 1.7%{+-} 0.4%, and 2.6%{+-} 0.7% increase in rectal dose, respectively, with smaller effect to dose to Point A, bladder, sigmoid, and bowel. For 3D dosimetry, 90.6% of voxels had a 3D {gamma}-index (criteria = 0.1 cm, 3% local signal) below 1.0 when comparing measured and expected dose about the unshielded source. Dose transmission through the gold shielding at a radial distance of 1 cm was 85.9%{+-} 0.2%, 83.4%{+-} 0.7%, and 82.5%{+-} 2.2% for Monte Carlo, and measurement for left and right buckets, respectively. Dose transmission was lowest at oblique angles from the bucket with a minimum of 56.7%{+-} 0.8%, 65.6%{+-} 1.7%, and 57.5%{+-} 1.6%, respectively. For a clinical T and O plan, attenuation from the buckets leads to a decrease in average Point A dose of {approx}3.2% and decrease in D{sub 2cc} to bladder, rectum, bowel, and sigmoid of 5%, 18%, 6%, and 12%, respectively. Conclusions: Differences between dummy and afterloading bucket position in the ovoids is minor compared to effects from asymmetric ovoid shielding, for which rectal dose is most affected. 3D dosimetry can fulfill a novel role in verifying Monte Carlo calculations of complex dose distributions as are common about brachytherapy sources and applicators.
SU-E-T-72: Commissioning of a Standardized SRS Cone Set: Determination of the Bolus Gap Factors in a Passively Scattered Proton Beam
Purpose: To determine the proton output factors for an SRS cone set using standardized apertures and varied range compensators (bolus blanks); specifically, to determine the best method for modeling the bolus gap factor (BGF) and eliminate the need for patient specific calibrations. Methods: A Standard Imaging A-16 chamber was placed in a Plastic Water phantom to measure the change in dose/MU with different treatment combinations for a proton SRS cone, using standardized apertures and range compensators. Measurements were made with all apertures in the SRS cone set, with four different range compensator thicknesses and five different air gaps between the end of the SRS cone and the surface of the phantom. The chamber was located at iso-center and maintained at a constant depth at the center of modulation for all measurements. Each aperture was placed in the cone to measure the change in MU needed to maintain constant dose at the chamber, as the air gap was increased with different thicknesses of bolus. Results: The dose/MU varied significantly with decreasing aperture size, increasing bolus thickness, or increasing air gap. The measured data was fitted with the lowest order polynomials that accurately described the data, to create a model for determining the change in output for any potential combination of devices used to treat a patient. For a given standardized aperture, the BGF could be described by its constituent factors: the bolus thickness factor (BTF) and the nozzle extension factor (NEF). Conclusion: The methods used to model the dose at the calibration point could be used to accurately predict the change in output for SRS proton beams due to the BGF, eliminating the need for patient specific calibrations. This method for modeling SRS treatments could also be applied to model other treatments using passively scattered proton beams.
TH-C-19A-04: Commissioning and Validation of EBT3 Gafchromic Films for Measurements of Dose Profiles and Integrals of Dose in Small Fields
Purpose: The use of a primary dosimeter larger than the radiation field gives access to the integral of dose over a specified surface normal to the beam. If a relative dose profile of the beam is well known, it is then possible to calculate the distribution of the absorbed dose at any point on the considered surface. This study aims at validating the use of EBT3 gafchromic films for the measurement of 2D dose distribution and integrals of dose in small fields for such use. Methods: New EBT3 films have been fully characterized: the response versus energy, dose-rate and dose has been investigated. Profiles measured in circular field with a diameter of 20 mm have been compared to the ones measured with a diamond detector developed at CEA/LIST/LCD. The ratio of dose area products measured with EBT3 on a 6 mm and 30 mm diameter surface has been compared to the ratio measured with primary dosimeters (calorimeters) and calculated with Monte Carlo simulations. Results: There was no significant difference between the dose-calibration curves in a 6 MV and a 60Co beam. Deviation was within uncertainty bars when the dose rate inside a pulse was divided by a factor of 80 in the 6 MV photon beam. Profiles in small fields are in good agreement with the diamond profiles. Dose area product ratios obtained with EBT3, calorimeters and simulations are within 1%. Conclusion: EBT3 films are good candidates for the measurement of relative dose distribution in small fields as long as the average of several films is considered. They can be used in association with primary measurements to determinate dosimetric references in small fields and to transfer them to the end user.
SU-F-T-574: MLC Based SRS Beam Commissioning - Minimum Target Size Investigation
Purpose: To implement a MLC accelerator based SRS program using small fields down to 1 cm × 1 cm and to determine the smallest target size safe for clinical treatment. Methods: Computerized beam scanning was performed in water using a diode detector and a linac-head attached transmission ion chamber to characterize the small field dosimetric aspects of a 6 MV photon beam (Trilogy-Varian Medical Systems, Inc.). The output factors, PDD and profiles of field sizes 1, 2, 3, 4, and 10 cm{sup 2} were measured and utilized to create a new treatment planning system (TPS) model (AAA ver 11021). Static MLC SRS treatment plans were created and delivered to a homogeneous phantom (Cube 20, CIRS, Inc.) for a 1.0 cm and 1.5 cm “PTV” target. A 12 field DMLC plan was created for a 2.1 cm target. Radiochromic film (EBT3, Ashland Inc.) was used to measure the planar dose in the axial, coronal and sagittal planes. A micro ion chamber (0.007 cc) was used to measure the dose at isocenter for each treatment delivery. Results: The new TPS model was validated by using a tolerance criteria of 2% dose and 2 mm distance to agreement. For fields ≤ 3 cm{sup 2}, the max PDD, Profile and OF difference was 0.9%, 2%/2mm and 1.4% respectively. The measured radiochromic film planar dose distributions had gamma scores of 95.3% or higher using a 3%/2mm criteria. Ion chamber measurements for all 3 test plans effectively met our goal of delivering the dose accurately to within 5% when compared to the expected dose reported by the TPS (1 cm plan Δ= −5.2%, 1.5 cm plan Δ= −2.0%, 2 cm plan Δ= 1.5%). Conclusion: End to end testing confirmed that MLC defined SRS for target sizes ≥ 1.0 cm can be safely planned and delivered.
SU-G-JeP4-04: Commissioning and Acceptance Testing of Optical Surface Monitoring System On TrueBEAM STx as Per Task Group 147
Purpose: Optical Surface Monitoring system (OSMS) have been recently introduced by Varian for initial patient positioning and real-time monitoring during complex radiotherapy treatment. The purpose of this work was to implement TG 147 with OSMS. Methods: Recently we installed OSMS first of its kind in India on trueBEAM STx at our Institue. The OSMS is composed of a three cameras ceiling mounted and a Workstation. The following tests were performed to validate the system a. Calibration b. System reproducibility and drift c. Static localization displacement accuracy and d. Dynamic radiation gating delivery. The Calibration procedure consists of Daily,Monthly and MV Radiation Isocenter Calibration. The reproducibility of system was tested by monitoring the varian gating phantom test pattern for at least 120 min. Each recorded pattern was registered to the reference surface to calculate the required couch adjustment. To measure the static localization displacement accuracy of the system to detect and quantify patient shift relative to a reference image,we compared the shift detected by the surface imaging system with known couch transitions in a phantom study. The phantom was set in a motion and the radiation beam was holded by changing the threshold in the software for different clinical setups to test the dynamic radiation gating capability. Results: Daily calibration was within ±0.5 mm. The MV radiation isocentre with respect to cameras was less than 1 mm in translational axis and less than 0.5° for rotational axis. The reproducibility was found to be 0.4 mm. The maximum static displacement accuracy was 0.75 mm for the three translational axis, and less than 0.5° for rotational axis. The system was able to hold the beam with a minimum threshold of 1 mm. Conclusion: A quality assurance process has been developed as per TG 147 for the clinical implementation of an OSMS in radiation therapy.
First Beam and High-Gradient Cryomodule Commissioning Results of the Advanced Superconducting Test Accelerator at Fermilab
The advanced superconducting test accelerator at Fermilab has accelerated electrons to 20 MeV and, separately, the International Linear Collider (ILC) style 8-cavity cryomodule has achieved the ILC performance milestone of 31.5 MV/m per cavity. When fully completed, the accelerator will consist of a photoinjector, one ILC-type cryomodule, multiple accelerator R&D beamlines, and a downstream beamline to inject 300 MeV electrons into the Integrable Optics Test Accelerator (IOTA). We report on the results of first beam, the achievement of our cryomodule to ILC gradient specifications, and near-term future plans for the facility.
Final Commissioning of the MICE RF Module Prototype with Production Couplers
We report operational experience from the prototype RF module for the Muon Ionization Cooling Experiment (MICE) with final production couplers at Fermilab's MuCool Test Area. This is the last step in fully qualifying the RF modules for operation in the experiment at RAL.
Commissioning the Muon g-2 Experiment Electrostatic Quadrupole System
The Fermilab Muon g-2 experiment aims to measure the muon anomaly with a precision of 140 parts-per-billion (ppb) - a fourfold improvement over the 540 ppb precision obtained by the BNL Muon g-2 experiment. These high precision experiments both require a very uniform muon storage ring magnetic field that precludes the use of vertical-focusing magnetic quadrupoles. The Fermilab Electrostatic Quadrupole System (EQS) is the refurbished and upgraded BNL EQS, where this overview describes the Fermilab EQS and its recent operations.
Commissioning of the LCLS-II Prototype HOM Detectors with Tesla-Type Cavities at Fast
Experiments at the Fermilab Accelerator Science and Technology* (FAST) facility detected electron beam-induced high order mode (HOM) signals from Tesla superconducting cavities. This paper describes some of the signal detection hardware used in this experiment, as well as measurements of the HOM signal magnitude versus beam trajectory. These measurements were made both with a single bunch and with a train of 50 bunches at bunch charges from 400 pC/b down to 10 pC/b. The detection hardware is designed for use with the Tesla superconducting cavities of LCLS-II at SLAC** and is based on a prototype already in use at Fermilab. The HOM signal passes through a bandpass filter that is centered on several cavity dipole modes and a zero bias Schottky diode detects its magnitude. Direct comparisons were made between the FNAL chassis and the SLAC prototype for identical beam steering conditions. To support measurements with bunch charges as low as 10 pC, the SLAC detector has RF amplification between the bandpass filter and the diode detector. With this hardware, usable HOM signal measurements are obtained with a single bunch of 10 pC in cryomodule cavities as will be needed for LCLS-II.
COMMISSIONING RESULTS OF THIRD C75 CRYOMODULE FOR CEBAF
The program to upgrade CEBAF cryomodules has been implemented to enhance the energy gain of refur-bished cryomodules up to 75 MeV. This strategy in-volves reusing the waveguide end-groups from original CEBAF cavities produced in the 1990s, and existing five elliptical cell cavities are replaced with a new optimized cell shape cavity constructed from large-grain, ingot Nb material. Following fabrication, each cavity undergoes centrifugal barrel polishing and electropolishing and is tested at 2.07 K. Eight cavities are then assembled into "cavity pairs" and tested at 2.07 K before integration into the cryomodule. This paper pre-sents the outcomes of the cavity qualification for the third C75 module, providing a detailed account of the assessment in both a vertical cryostat and the acceptance test results of the cryomodule. Furthermore, efforts have been made to address performance limitations arising from field emission and multipacting
Engineering design and commissioning performance of the ESM and SIX Soft X-Ray Beamlines at NSLS-II
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