PERDaix
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PERDaix (Proton Electron Radiation Detector Aix-la-Chapelle) is a novel, small and light weight
magnetic spectrometer A spectrometer () is a scientific instrument used to separate and measure spectral components of a physical phenomenon. Spectrometer is a broad term often used to describe instruments that measure a continuous variable of a phenomenon where the ...
to measure the charge and mass dependent solar modulation periodically for deeper understanding of
cosmic ray Cosmic rays are high-energy particles or clusters of particles (primarily represented by protons or atomic nuclei) that move through space at nearly the speed of light. They originate from the Sun, from outside of the Solar System in our own ...
s. For a better understanding of sources and acceleration of cosmic particles direct measurements of cosmic rays are necessary. Also for a better understanding of the solar modulation which is expected to follow the 22-year
solar cycle The solar cycle, also known as the solar magnetic activity cycle, sunspot cycle, or Schwabe cycle, is a nearly periodic 11-year change in the Sun's activity measured in terms of variations in the number of observed sunspots on the Sun's surfa ...
, time dependent measurements are needed. PERDaix is a newly designed detector which is constructed by the Department of Physics 1b, RWTH Aachen University. Being proposed to the
German Space Agency The German Aerospace Center (german: Deutsches Zentrum für Luft- und Raumfahrt e.V., abbreviated DLR, literally ''German Center for Air- and Space-flight'') is the national center for aerospace, energy and transportation research of Germany ...
in November 2009 for a participation in the BEXUS Program (Rocket and Balloon Experiments for University Students) after a first canceled flight attempt in October 2010 the actual flight took place as a post-BEXUS-campaign flight opportunity in November 2010. The detector is able to measure charged particles in the energy range of 0.5
GeV GEV may refer to: * ''G.E.V.'' (board game), a tabletop game by Steve Jackson Games * Ashe County Airport, in North Carolina, United States * Gällivare Lapland Airport, in Sweden * Generalized extreme value distribution * Gev Sella, Israeli-Sou ...
to 5 GeV. PERDaix uses a time of flight system, a scintillating fiber tracker with
silicon photomultiplier Silicon photomultipliers, often called "SiPM" in the literature, are solid-state single-photon-sensitive devices based on Single-photon avalanche diode (SPAD) implemented on common silicon substrate. The dimension of each single SPAD can vary fro ...
(SiPM) readout, and a
transition radiation detector A transition radiation detector (TRD) is a particle detector using the \gamma-dependent threshold of transition radiation in a stratified material. It contains many layers of materials with different indices of refraction. At each interface betwe ...
in combination with a permanent magnet to measure particle fluxes. The BEXUS balloons are launched at
Esrange Space Center Esrange Space Center (short form Esrange) is a rocket range and research centre located about 40 kilometers east of the town of Kiruna in northern Sweden. It is a base for scientific research with high-altitude balloons, investigation of the au ...
near Kiruna, Sweden. In November 2010 PERDaix reached a top altitude of 33.3 km at which it kept floating for 1.5 hours.


Sub-detectors


Time of flight system

The time of flight system (TOF) is the upper- and lowermost layer of the detector. It consists of scintillators with an SiPM readout. It is used as a trigger signal and to discriminate against particles entering the detector from below. With a design time resolution of approximately 300 picoseconds (ps) it can be used to distinguish between positrons and
electron The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have no ...
s in the momentum range below 1 GeV. Protons can be distinguished from positrons for momenta below 1 GeV if their velocity is lower than β = 1.http://www.srl.utu.fi/AuxDOC/kocharov/ICRC2009/pdf/icrc1099.pdf


Tracker

Perdaix will make use of a scintillating fiber tracking detector made up from 250 µm thin scintillating polystyrene fibers that emit light when traversed by a charged particle. The scintillating fibers are read out by silicon photomultiplier (SiPM) arrays which are structured semi-conductor photon detectors that offer high photon efficiencies of 50%, a high gain of 10^6 electrons / photon and that are very compact in size. One silicon photomultiplier array is 1.1mm by 8.0mm in size and has 32 channels. Twenty 32mm wide and 300mm long fiber modules are arranged in four layers around a hollow cylindrical permanent magnet array.


Magnet

The permanent magnet array is constructed as a Halbach-Ring and weighs 8 kg and produces a very high magnetic field of ~0.26 Tesla (T) inside an 80mm high and 213mm diameter magnet cylinder while producing only a negligible magnetic field outside the cylinder.


Transition radiation detector

Underneath the lowest tracker layer a
transition radiation Transition radiation (TR) is a form of electromagnetic radiation emitted when a charged particle passes through inhomogeneous media, such as a boundary between two different media. This is in contrast to Cherenkov radiation, which occurs when a ch ...
detector (TRD) is installed. The TRD detects transition radiation of
relativistic particle A relativistic particle is a particle which moves with a relativistic speed; that is, a speed comparable to the speed of light. This is achieved by photons to the extent that effects described by special relativity are able to describe those of su ...
s with a
Lorentz factor The Lorentz factor or Lorentz term is a quantity expressing how much the measurements of time, length, and other physical properties change for an object while that object is moving. The expression appears in several equations in special relativit ...
γ exceeding ≈ 1000. Particles crossing the interface of two media with different dielectric constant produce transition radiation. The energy loss at a boundary is proportional to the relativistic
gamma factor The Lorentz factor or Lorentz term is a quantity expressing how much the measurements of time, length, and other physical properties change for an object while that object is moving. The expression appears in several equations in special relativit ...
. A significant amount of TR is produced for a gamma greater than 1000. The gamma factor of protons is, up to a momentum of 5GeV, still in the order of 10, whereas the positron's gamma is greater than 1000, starting at 0.5GeV momentum. The detector is made up of 256 6mm thick straw tubes out of a 72 um thin multilayer
aluminium Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. I ...
- kapton foil, filled with an 80/20 mixture of
xenon Xenon is a chemical element with the symbol Xe and atomic number 54. It is a dense, colorless, odorless noble gas found in Earth's atmosphere in trace amounts. Although generally unreactive, it can undergo a few chemical reactions such as the ...
(Xe) and
carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...
(). It is used to measure the x-ray transition radiation produced by electrons in eight 20mm thick layers of an irregular fleece radiator. This leads to more than 100 material interfaces per radiator layer.


Launch in November 2010

Due to strong winds the launch campaign in October 2010 had to be canceled without a BEXUS-11 flight at first. Thanks to the support of German Space Agency ( DLR) and
Esrange Esrange Space Center (short form Esrange) is a rocket range and research centre located about 40 kilometers east of the town of Kiruna in northern Sweden. It is a base for scientific research with high-altitude balloons, investigation of the au ...
a second flight opportunity was provided in late November 2010. On 23 November a 100 000 m³ helium balloon was launched from Esrange carrying a payload of 334 kg containing the BEXUS student experiments including the PERDaix detector.


Sources

{{Reflist


External links


PERDaix Homepage



official BEXUS website
Spectrometers