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The GOLEM tokamak (formerly CASTOR) at Czech Technical University is demonstrated as an educational device for domestic and foreign students [bibref:GOLEM2007], [bibref:Svoboda2010]. The reinstalled tokamak (\(R = 0.4\) m, \(a = 0.1\) m) currently operates at a range of parameters (\(B_t < 0.8\) T, \(I_p < 10\) kA, pulse length \(< 15\) ms) which corresponds to a very small fusion triple product. Despite this fact, small tokamaks can produce edge plasma with similar characteristics to large tokamaks and so have general validity [bibref:VanOost2007]. Additionally the remote participation features could be applied to a tokamak of any size.

Plasma is generated using 4 basic electrical circuits. Each circuit is powered by charged capacitors connected to the coils through PC controlled thyristors. This enables the creation of the toroidal magnetic field \(B_t\), toroidal electric field \(E_t\) in two distinct phases (breakdown and current drive) and a vertical magnetic field \(B_{ST}\) providing basic plasma stabilization in the horizontal direction.

The tokamak is equipped with a basic diagnostic system for measuring key plasma parameters:

a single loop surrounding the transformer core measures the loop voltage \(U_{loop}\)
a Rogowski coil surrounding the tokamak chamber measures the sum of the plasma and chamber current \(I_{p+ch}\)
a small pick-up coil placed on the tokamak chamber detects the toroidal magnetic field \(B_t\)
a photocell which faces a glass port of the tokamak detects the plasma radiation from the emitted visible spectra

Additionally

a ’fast’ camera (1200 fps at a 336x96 resolution) is installed at a horizontal port to study the emission profile in the visible part of spectra
a set of 4 small Mirnov coils surrounding the plasma column in a poloidal cross section allowing local magnetic field measurement and finally
a linear array of 20 AXUV detectors (bolometers) positioned at a vertical port detecting plasma radiation emission profile in ultraviolet and soft X-rays part of the spectra

CASTOR is a small size tokamak. It does not enable reaching the temperature and confinement time high enough to ignite the fusion reactions. Nevertheless, for investigation the hot plasma, devices of CASTOR size have a capability of bringing a valuable contribution. The main advantage is their high flexibility. Testing new diagnostic tools is much more feasible and cheaper in these relatively simple facilities. Due to the low temperature, plasma enables us to immerse the diagnostic probes deep inside, thus a very detailed investigation of the edge plasma may be performed. The importance of such devices for education is also worth mentioning. A number of students of different degrees (bachelor, master, PhD) were gaining their experience with fusion facilities at the CASTOR tokamak department in the scope of their studies, several Summer schools for students and young scientists were organized by the CASTOR team.

The new location of the tokamak is just next to the old Prague Jewish cemetery where Rabi Loew (Golem builder) is burried, and that is why it was renamed GOLEM (and also for the symbol of potential power you get if you know the magic). Interestingly, here in Prague, where the Golem legend originated, Golem is not perceived as a symbol of evil, but rather as a symbol of power which might be useful but is very challenging to handle. To learn more of the Golem legend, see e.g. Wikipedia.

Credit:[Jana Brotankova PhD thesis]