Novel Electron-Bubble Tracking Detectors

Willis, William J.

Columbia University, New York, NY

关键词: Manufacturers;    Quantum Efficiency;    Consumer Products;    72 Physics Of Elementary Particles And Fields;    Detectors;   

DOI  :  10.2172/962396
RP-ID  :  DOE/ER41347-1
RP-ID  :  FG02-04ER41347
RP-ID  :  962396

美国|英语

来源: UNT Digital Library

【 摘 要 】

Our Columbia group, in collaboration with Brookhaven and SMU, has been carrying out R&D on tracking detectors in cryogenic liquids, including neon and helium. A cryostat purchased by this Grant capable of working temperatures down to 1 K and pressures above the critical point of neon and helium has been operated with a variety of noble fluids. Gaseous Electron Multipliers (GEM) with hydrogen additives have been operated with tracks of radioactive sources read out both by electrical charge detecting electronics, and an optical camera purchased by this Grant, measuring mobility, charge yield, transitions through phase boundaries, gain limitations, and other properties. The goal is very high resolution in large volumes. The scope of the project is the provision of a high performance camera and its installation in a cryogenic facility providing pressure up to 40 atmospheres and a temperature from ambient down to about 1 K. In this section we will address the goals and results having to do with this project and particularly the performance of the camera, and provide a summary of the status of the detector project. The technical development of digital cameras has been dominated for the last forty years by the Charge-Coupled Device technology (CCD). This allows photon recording on very small pixels on silicon planes that provide high quantum efficiency in the visible spectrum, recording the charge generated by a single photon stored on one pixel with an area of order ten microns square. The area can be up to several centimeters squared, containing a million pixels or more. The stores charge is usually read out by manipulating voltage biases to shift the charge in each pixel over to the next, and eventually out of the array and sent to an external processor and memory. Mass production has brought the cost per channel down to very small values and allowed cameras to be integrated to many consumer products. Thermal noise becomes larger than one photon on a single pixel at good temperature, and demand night vision and other demanding applications has led to intense R&D over the years, and small coolers that maintain the CCD at temperatures of more than 100K below ambient are integrated into the camera package. These systems are sold in quantity to amateur astronomers with the same silicon devices used in professional systems, provided long exposure times with less than one electron noise per pixel. In our particle readout, we are imaging a three-dimensional track drifting into the readout plane over time, and we need to read out one plane after another, and we need a high rate of pixel processing. For many years, the noise in the electronic amplifier matching the CCD to the external electronics led to noise levels of many electrons, much higher than in the CCD itself. A break-through was made by providing signal gain inside the CCD, connecting to the external line, by a Electron Multiplier CCD, using a number of electron avalanche stages, each with a small, stable gain. This device was brought out just before out application for the present Grant, provided the last link in the development chain, which allowed out optical readout concept to be implemented at reason fact. In fact, we profited from the falling cost by delaying our order for about a year, which, together with the university discount, allowed us to proceed within our budget. The camera we purchase from the firm ANDOR, which introduced the technique, comes with an extensive suite of software that allows the fast readout with different integration times, and makes a very convenient use in our application. We have been able to make images of the light signals coming from out GEM electron avalanche detectors under many conditions, with tracks of different particle types. We have reconfigured the system a number of times, using the results from the camera to learn how to change the TPC drift geometry and the GEM charge amplifier to improve performance, a process that is still going on. The camera purchase with this Grant has performed reliably and just as specified by the manufacturer and has been a trouble-free element of our larger product. The ability of being able to vary the pressure and temperature over a wide range is very important for several reasons: (1) we are able to choose a fluid density to make the best compromise between a range of low energy tracks long enough to measure, and higher density to minimize the detector size for a given rate; (2) we can identify the density the allows the avalanche rate that provides sufficient signal to noise for the low-energy tracks we need to measure in a given application; and (3) we can operate at the optimum density and hydrogen admixture for light production. A special cryostat was required to operate down to 1 K with pressures up to 40 Bar, well above the critical point of Neon.