27.10.2014

 

EMTEX for high FAIR intensities

Increase in output of GSI facility for FAIR


EMTEX setup (Photo: Gaby Otto for GSI)

It is intended to break a record with the new accelerator facility FAIR: More ions are to be accelerated at the same time than has ever before been achieved. The two existing GSI accelerators UNILAC and SIS18 are to be used for the first two stages of the acceleration at the new facility. So as to attain the high intensities, 10 to 20 times more ions will also have to be accelerated here than has been the case so far. This is a challenge for the particle physicists, and one which can only be overcome through improvements in many areas. With the emittance transfer experiment they have now tested an idea for improved beam guidance.

 

Experiments have been conducted at the GSI accelerator facility since 1969 with the linear accelerator UNILAC and since 1990 with the ring accelerator SIS18. The ions are sent through the accelerator facility in packages. To date a maximum of one billion uranium ions per package could be accelerated in the GSI ring accelerator. For the particle accelerator FAIR (Facility for Antiproton and Ion Research) which is currently under construction this figure will have to be around half a trillion. Scientists are now looking for possibilities to modify the existing facility so that it can accommodate so many ions – basic research at machine level therefore.

 

One starting point is the transition from the linear accelerator UNILAC to the ring accelerator SIS18. The opening to the SIS18 ring accelerator is narrow and tall. Yet like all linear accelerators the linear accelerator UNILAC provides quadratic ion packages. For this reason the package from the UNILAC has to date simply been trimmed at the sides when transferred to the SIS18 ring accelerator. This, however, meant that some of the ions were lost and the intensity was lower. At the same time space in the ring accelerator was not used.

 

So as to tap this potential, scientists at GSI developed the EMTEX setup in the transfer channel, the transition from the linear to the ring accelerator, therefore. This reshapes the packages with the aid of magnets. “Such reshaping has never been proposed with an ion LINAC, let alone attained,” says Lars Groening from the LINAC department. He explains how the concept functions: “Instead of simply cutting off the ions at the side of the package, we are stretching the packages upwards so as to utilize the space in the ring. At the same time we compress the packages laterally. Thus the density of the ions remains constant. This is decisive for ions cannot be packed more densely than they were initially created.” This compressing and stretching of the packages sounds simple at first. But it actually takes place in four dimensions. In addition to the width and height locations, the velocities of the ions to the right, left, up and down also play a role. “The vertical area which a particle beam occupies in the phase space (emittance) has to be around three times greater than the horizontal area,” says Groening. In two beam time periods the new concept was initially tested with light ions at low intensity.

 

“The experiments have functioned very well and correspond to the results attained in simulations. We now know, therefore, that the idea functions in principle. In the next stage we are further developing the setup so that the reshaping also functions with heavy ions at high intensity.” The project financing has just been extended by the Federal Ministry for Education and Research for this further development. Whether and in what form EMTEX will be used at FAIR has not yet been finally decided. Yet only with the aid of basic research in the field of acceleration physics can the high intensities be attained for FAIR. “The scientific community is greatly interested in this experiment,” adds Groening. “EMTEX could also be used with other ion accelerators.”

(taken and translated from GSI)




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