 | Needs verification Some of these points are rough drafts and still need to be checked for accuracy at some point |
On this page you will find all kind of educational background on the working principles and devices related to the FELIX laser facility.
Follow the virtual tour
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In 2022 the entire building of HFML-FELIX became virtually available. You are kindly invited to have look [1] |
How does a klystron work?
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A klystron is used to amplify a electromagnetic wave. It converts the kinetic energy of an electron beam into electromagnetic wave energy, with it amplifying a radio frequency wave. The electromagnetic wave produced in the klystrons is used in the acceleration and bunching of the electrons.
FELIX's klystron creates waves of about 20 MW, equivalent to 20 000 magnetron ovens. Dr. Victor Claessen explains this in a YouTube movie [2] that can be found in our vitual tour [3]. If you are looking for more general information you can find a good explanation on Engineering 360 [[4]] The wave travels through a red rectangular tubing network, much like a sound wave would. The klystrons get there initial input from a capacitor bank hanging on the sealing. The laboratory has 3 klystrons, two used for the FELIX and FELICE lasers and one for the FLARE laser. |
How does an Electron Gun work?
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The electron gun used at FELIX is a thermionic triode gun (in 1996, stil the same?). It produces the free electrons used to make light in the undulator. The gun modulates at 1 GHz which generates electron bunches with 1 ns seperation. The bunches are about 200 ps in length and have a total charge of 200 pC. After passing through the prebuncher and a buncher devices, which shorten the bunch length, the bunches are injected into the first LINAC. (G. Knippels, "The short-pulse Free-electron laser: manipulation of the gain medium", 1996, page 9)
A interactive simulation of a electron gun, which explains the concept of an electron gun, can be found at this[5] website. |
How does a Liniar Accelerator (LINAC) work?
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In the LINAC the electrons gain energy which later is used to produce the right infrared laser light. FEL2 has 2 linacs, which result in a energy range of about 25 to 47 MeV. How this corrisponds to the spectrum produces can be seen at the page FEL2. FEL 1 uses one linac and has a different spectral range. A general explanation of a linac is explained on youtube [6]. When electron bunches enter the LINAC they are relativistic enough not to be influenced much by space-charge effects, about which you can learn more here[7]. |
How does a Steering magnet work?
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How do we monitor the electron bundle position?
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what happens inside the laser cavity, introducing Population inversion, Gain and Saturation mechanism? What are the consequences to engineering requirements?
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This is an introduction of the definitions in a non free electron laser: Population inversion, Gain and the Saturation mechanism. With population inversion atoms are brought into an exited state, from E1 to E2. (energy state 1 to the higher energy state 2). This is a complex process that involves more that 2 states and will not be explained here. We can say that a pumping process is responsible for creating this population inversion. When the atoms decay from exited state E2 to E1 they create a photon by spontaneous emission. Instead of spontaneous emission this decay can be induced by a existing photon that than will create a 'clone'. The 2 created photons can than create 4 and the 4 > 16 ect. This is called stimulated emission. In short Gain is the amount of amplification of one photon in multiple photons by stimulated emission. When one places this phenomenon between two mirrors, of which one has a hole, light can be build up. So pumping creates population inversion, population inversion is a starting state for photon creation, gain is the amount of amplification by stimulated emission, and now we have a cavity filled with light of with a part is lost through the hole in one of the mirrors. The amount of light in the cavity, the new photons made and the light lost will find a equilibrium. The mechanism describing this is called saturation mechanism; and is non-linear. The ration between pump energy and light output can be used to represent the machine efficiently.
Want to read more? ISBN 978-953-51-0279-3 (Free electron lasers edited by Sandor Varro) In short one can now also imagen that, choosing the hole size of the mirror is a important parameter in making light. The pumping mechanism for FELIX is different as electrons are wiggled in the undulator to create a photon rather than decaying from state E2 to E1. FELIX is a pulsed light source which creates an additional requirement; a photon bunch that is created in the cavity needs to intersect with the next one. Hence the distance between the cavity mirrors is of utmost importance if one wants to use the stimulated emission effect. Creating different frequencies of light involves changing the distance between the mirrors (continuously). This needs to be precise in a order of magnitude lower than the wavelength of the light. Around 200 nm, and with a range of +-3 mm. In 2022 a new undulator was installed what lowered the um range to 3 um. Subsequently a new mechanism was introduced to make the mirrors move: a compliant double-parallelogram translation stage made of a single block of titanium, carrying a 80 kg load. It removed traditional mechanical problems like backlash and friction and assembly. Next to this 2 large granite blocks were used underneath the cavity tanks to reduce the amplitude of vibrations in the system. |
How does a Undulator work?
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How is the laser light analysed?
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Each laser FELIX, FELICE, and FLARE have their own diagnostic stations. Here the light is analysed before giving it the a user. For FEL1 and FEL2, both FELIX laser the FELIX spectrum analyzer and FELIX power meter are important devices. |
How is light send to a user station?
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