Theory, Design and Tests on a Prototype Module of a Compact ...

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84 5. RADIOFREQUENCY MEASUREMENT Figure 5.13. The particular realization of the bead pulling measurement for the LIBO module. 5.1. Preliminary considerations. In linear accelerators the level of the axial electric field in the accelerating cavities must be flat within a certain tolerance fixed by the dynamic of the beam. Usually, each cavity in LINACs has one or two tuners which are able to change the resonant frequency within 0.1% <strong>and</strong>, after that all the cavity are brazed together, these tuners are used for two important purposes: to make the whole resonant frequency at the value set by the power klystron, <strong>and</strong> to make the electric field level be flat in the cavities. The beam dynamic of LIBO is not stringent <strong>and</strong> requires a flat field within ±2.5% [20, 21]. We remember that one LIBO module has 4 tanks <strong>and</strong> 3 bridge couplers. Each tank has 13 accelerating cells <strong>and</strong> 12 coupling cells which are out of beam axis. Each bridge coupler is composed by 3 cavities: two coupling cells <strong>and</strong> a cell which is equivalent to an accelerating cell but, as the others two cells, it is displaced out of the beam axis, in order to leave space for the permanent quadrupole magnet, placed between each two tanks. It is worth remember that the resonant frequency of each cavity inside the four tanks ready for the bead pulling measurement has an error less than 500 kHz, respect to the π/2 frequency of the same tank. This result is obtained after the machining of the ring placed in each cavity, as it is explained in section 2.2. But this procedure does not leave out the possibility that the π/2 frequencies are different among the four tanks, in fact these were different within 500 kHz too. This means that we know that the tuners have to correct also this difference between the frequencies of the tanks. Another consideration has be done about the bridge couplers. The movable tuners of this cells were used before the bead pulling, in order
5. A TUNING PROCEDURE FOR THE LIBO MODULE 85 Figure 5.14. The bead pulling result after the bridge couplers tuning. to have the design values for the frequencies, <strong>and</strong>, more important, to have the frequencies of the coupling cells perfectly equals. This is important, because any difference in the coupling cells of a bridge coupler produces a step in the electric field of the adjacent tanks. 5.2. Bead pulling measurement. The first bead pulling of the whole structure gave the result shown in figure 5.14. The figure shows the normalized level of the squared electric field in all the accelerating cavities; the space between two cavities represents the coupling cells. The space between two tanks is the one of the bridge coupler which is out of axis <strong>and</strong> the bead does not pass through its cells. It is worth noting again that for the tuning procedure it is interesting only the relative levels between the tanks <strong>and</strong> not the absolute values, since this procedure is made at a low power level. For the measurement of figure 5.14, the π/2 frequency was 2996.99 MHz. Taking into account all the variations due to the real conditions 12 , the goal frequency should be 2997.10 MHz. The quality factor value was around 4500 which is a good value, but still far from the final 7200, this was due to the imperfect joints between the tanks <strong>and</strong> the bridge couplers, since they were not brazed together yet. Also, in that configuration <strong>and</strong> from a frequency measurement, it was possible to evaluate the stop-b<strong>and</strong> of the second nearest modes which was SBB = +216 kHz. This stop-b<strong>and</strong> is related to the bumplike behavior in the response of bead pulling measurement, its presence means that the second nearest modes in the dispersion diagram are excited <strong>and</strong> the behavior for these modes is just as a bump, having a minimum for the field (maximum) in the central bridge coupler cavity <strong>and</strong> a maximum field in the end cells (minimum). 12 Vacuum effect, temperature, final brazing, etc..
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UNIVERSITÀ DEGLI STUDI DI NAPOLI F
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ii CONTENTS List of Figures 105 Ack
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iv INTRODUCTION In the state of art
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2 1. INTRODUCTION TO THE HADRONTHER
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8 2. LINAC AND SCL ACCELERATORS par
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10 2. LINAC AND SCL ACCELERATORS wh
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12 2. LINAC AND SCL ACCELERATORS at
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14 2. LINAC AND SCL ACCELERATORS 2.
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16 2. LINAC AND SCL ACCELERATORS f
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18 2. LINAC AND SCL ACCELERATORS Fi
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20 2. LINAC AND SCL ACCELERATORS re
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CHAPTER 3 Design T
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1. GLOBAL PARAMETERS OF THE ACCELER
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2. ANALYSIS OF COUPLED CAVITIES 27
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3. SINGLE CAVITY DESIGN 29 Spice ha
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20mA 15mA 10mA 5mA 3. SINGLE CAVITY
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Page 43 and 44: 5. COUPLING BETWEEN WAVEGUIDE AND B
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Page 52 and 53: 46 4. CIRCUIT MODEL where the matri
Page 54 and 55: 48 4. CIRCUIT MODEL For the latest
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Page 62 and 63: 56 4. CIRCUIT MODEL matrix of the w
Page 64 and 65: 58 4. CIRCUIT MODEL For the derivat
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Page 68 and 69: 62 4. CIRCUIT MODEL the bars is pro
Page 70 and 71: 64 4. CIRCUIT MODEL is unitary, one
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Page 105 and 106: Conclusions and Ou
Page 107: CONCLUSIONS AND OUTLOOK 101 Finally
Page 110 and 111: 104 BIBLIOGRAPHY [23] U. Amaldi, B.
Page 112 and 113: 106 LIST OF FIGURES 2.12 Drawing of
Page 114 and 115: 108 LIST OF FIGURES methods, in add
Page 116: 110 ACKNOWLEDGEMENTS Naples, Italy
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