Craig E. Thorn

High Energy Gamma Ray Beams from Compton Backscattered Laser Light

Collisions of light photons with relativistic electrons have previously been used to produce polarized ¿-ray beams with modest (~10%) resolution, but relatively low intensity. In contrast, the LEGS project (Laser+Electron Gamma Source) at Brookhaven will produce a very high flux (>2×107 s-1) of background-free polarized ¿ rays whose energy will be determined to a high accuracy (¿E =2.3 MeV). Initially, 300(420) MeV ¿ rays will be produced by backscattering UV light from the new 2.5(3.0) GeV X-ray storage ring of the National Synchrotron Light Source (NSLS). The LEGS facility will operate as one of many passive users of the NSLS. In a later stage of the project, a Free Electron Laser is expected to extend the ¿-ray energy up to 700 MeV.

The legs electron spectrometer for tagging backscattered photons

Abstract A magnetic spectrometer is described for tagging a gamma-ray beam produced by Compton backscattering laser light from the electron beam circulating in a storage ring. The spectrometer, as it is now installed, has a design energy resolution of 5.5 MeV, a dispersion of 2.8 MeV/cm, and a dynamic range of 160 MeV. The energy resolution is limited by the energy spread of the stored beam. If dispersion can be introduced into the laser-electron interaction straight section of the storage ring, the resolution can be improved to be as small as 1.5 MeV, depending on the value of this dispersion. Measured properties of the spectrometer are in substantial agreement with the design values.

Cold Electronics for Giant Liquid Argon Time Projection Chambers

The choice between cold and warm electronics (inside or outside the cryostat) in very large LAr TPCs (>5-10 ktons) is not an electronics issue, but it is rather a major cryostat design issue. This is because the location of the signal processing electronics has a direct and far reaching effect on the cryostat design, an indirect effect on the TPC electrode design (sense wire spacing, wire length and drift distance), and a significant effect on the TPC performance. All these factors weigh so overwhelmingly in favor of the cold electronics that it remains an optimal solution for very large TPCs. In this paper signal and noise considerations are summarized, the concept of the readout chain is described, and the guidelines for design of CMOS circuits for operation in liquid argon (at ~89 K) are discussed.

Liquid Argon Time Projection Chamber research and development in the United States

A workshop was held at Fermilab on March 20-21, 2013 to discuss the development of liquid argon time projection chambers (LArTPCs) in the United States. The workshop was organized under the auspices of the Coordinating Panel for Advanced Detectors, a body that was initiated by the American Physical Society Division of Particles and Fields. All presentations at the workshop were made in seven topical plenary sessions: i) Argon Purity, ii) Cryogenics, iii) TPC and High Voltage, iv) Electronics, Data Acquisition and Triggering, v) Scintillation Light Detection, vi) Calibration and Test Beams, and vii) Software. This document summarizes the current efforts in each of these areas. It also highlights areas in LArTPC research and development that are common between neutrino experiments and dark matter experiments.

Summary of the second workshop on liquid argon time projection chamber research and development in the United States

The second workshop to discuss the development of liquid argon time projection chambers (LArTPCs) in the United States was held at Fermilab on July 8-9, 2014. The workshop was organized under the auspices of the Coordinating Panel for Advanced Detectors, a body that was initiated by the American Physical Society Division of Particles and Fields. All presentations at the workshop were made in six topical plenary sessions: i) Argon Purity and Cryogenics, ii) TPC and High Voltage, iii) Electronics, Data Acquisition and Triggering, iv) Scintillation Light Detection, v) Calibration and Test Beams, and vi) Software. This document summarizes the current efforts in each of these areas. It primarily focuses on the work in the US, but also highlights work done elsewhere in the world.

A GEM based TPC for the LEGS experiment

A compact time projection chamber (TPC) has been constructed for the LEGS (Laser Electron Gamma Source) experiment at BNL. The TPC uses double GEMs as the amplification stage. Position encoding is achieved through charge division using zigzag shaped anode pads. The TPC has a 35 cm diameter active area and a 50 cm long drift depth. It has more than 7000 channels of readout electronics in the form of custom designed ASICs. A novel peak sensing circuit is used to measure simultaneously the amplitude and timing of the signal peak from an anode pad. Test results from a shorter prototype version of the TPC as well as the construction of the final detector are discussed.

Computed tomography of scintillators with muons: Understanding the response to high energy gamma rays☆

Abstract A procedure is described for determining, for any point within the volume of a scintillating detector, the relative amount of light collected as the result of the deposition of a known amount of energy at that point. The response to muons traversing many well defined paths through the scintillator is combined with Fourier reconstruction techniques of computed tomography to produce three-dimensional images of the nonuniformities in light generation and collection. This information can be combined with a Monte Carlo simulation of energy deposition in electromagnetic showers to accurately predict the resolution for the detection of γ-rays of any energy. This has been applied to two large NaI(Tl) detectors and the calculated resolutions agree with measured spectra over the full range for which data are available, E γ = 6−45 MeV.

Readout electronics for the MicroBooNE LAr TPC, with CMOS front end at 89K

MicroBooNE experiment will use a ~ 100 ton Liquid Argon (LAr) Time Projection Chamber (TPC) detector, presently under construction, to observe interactions of neutrinos from the on-axis Booster Neutrino Beam and off-axis NuMI Beam at Fermi National Accelerator Laboratory. The experiment will address the low energy excess observed by the MiniBooNE experiment, measure low energy neutrino cross sections, and serve as the necessary next step in a phased program towards massive Liquid Argon TPC detectors. An overview of the front end readout architecture of the MicroBooNE experiment will be presented. The design, prototypes and the production electronics system, comprised of cold CMOS electronics, warm interface electronics and TPC digitizing electronics will be described in some detail. The results of extensive tests on the noise versus temperature and of the uniformity of response will be presented.

Front-end ASIC for a liquid argon TPC

We introduce a front-end application specific integrated circuit (ASIC) for a wire based Time-Projection-Chamber (TPC) operating in liquid Argon (LAr). The LAr TPC will be used for long baseline neutrino oscillation experiments. The ASIC must provide low-noise readout of the signals induced on the TPC wires, digitization of those signals at 2 MS/s, compression, buffering and multiplexing. A resolution better than 1000 rms electrons at 200 pF input capacitance for an input range of 300 fC is required, along with low power and operation in LAr (at 87 K). We present the characterization of a commercial technology for operation in cryogenic environment and the first experimental results on the analog front-end. The results demonstrate that CMOS transistors have lower noise and much improved dc characteristics at LAr temperature. Finally, we introduce the concept of “1/f equivalent” to model the low-frequency component of the noise spectral density, for use in the input MOSFET optimization.

R&D towards cryogenic optical links

A number of critical active and passive components of optical links have been tested at 77 K or lower temperatures, demonstrating potential development of optical links operating inside the liquid argon time projection chamber (LArTPC) detector cryostat. A ring oscillator, individual MOSFETs, and a high speed 16:1 serializer fabricated in a commercial 0.25-μm silicon-on-sapphire CMOS technology continued to function from room temperature to 4.2 K, 15 K, and 77 K respectively. Three types of laser diodes lase from room temperature to 77 K. Optical fibers and optical connectors exhibited minute attenuation changes from room temperature to 77 K.