From microscopic to macroscopic dynamics of super-conducting accelerating cavities. Anirban Krishna Bhattacharyya

Transcription

1 From microscopic to macroscopic dynamics of super-conducting accelerating cavities Anirban Krishna Bhattacharyya

2 ESS Courtesy Matts Lindroos (ESS) 10/19/2017 Anirban Krishna Bhattacharyya 2

3 Outline 10/19/2017 Anirban Krishna Bhattacharyya 3

4 Outline Reflection 10/19/2017 Anirban Krishna Bhattacharyya 3

5 Outline Reflection Cavity Quality factor ( ) 10/19/2017 Anirban Krishna Bhattacharyya 3

6 Cavity Parameters 10/19/2017 Anirban Krishna Bhattacharyya 4

7 Step Charging RF Source Cavity Courtesy of P. Duthil Circulator Spoke Cavity (super - conducting) Load 10/19/2017 Anirban Krishna Bhattacharyya 5

8 RF Source Step Charging Circulator Cavity Courtesy of P. Duthil Beam injection Spoke Cavity (super - conducting) Load Charging time 10/19/2017 Anirban Krishna Bhattacharyya 6

9 Step Charging RF Source Circulator Cavity Courtesy of P. Duthil Spoke Cavity (super - conducting) Load 10/19/2017 Anirban Krishna Bhattacharyya 7

10 Step Charging (Frequency domain) (MHz) 10/19/2017 Anirban Krishna Bhattacharyya 8

11 Optimal Charging I g I b I r Instantaneous cavity voltage Filling time (Natural time scale) Loaded Quality factor Loaded cavity impedance Generator current (Nominal cavity voltage) 10/19/2017 Anirban Krishna Bhattacharyya 9

12 Optimal Charging Instantaneous cavity voltage I b I g I r Filling time (Natural time scale) Loaded Quality factor Loaded cavity impedance Generator current Reflected current External Quality factor Bare cavity Quality factor 10/19/2017 Anirban Krishna Bhattacharyya 10

13 Optimal Charging Instantaneous cavity voltage Filling time Loaded Q Loaded Generator impedance current Reflected current Reflected energy External Q Bare cavity Q 10/19/2017 Anirban Krishna Bhattacharyya 11

14 Minimum Action: Example from classical mechanics η... dt 10/19/2017 Anirban Krishna Bhattacharyya 12

15 Minimum Action: Example from classical mechanics η... dt 10/19/2017 Anirban Krishna Bhattacharyya 12

16 Optimal Charging The concept of minimum action, Find optimal and such that is minimum. Optimal charging profile 10/19/2017 Anirban Krishna Bhattacharyya 13

17 Optimal Charging The concept of minimum action, Optimal charging profile Free parameter 10/19/2017 Anirban Krishna Bhattacharyya 13

18 Effect of Optimal filling Step filling Optimal filling 10/19/2017 Anirban Krishna Bhattacharyya 14

19 Effect of Optimal filling No free lunch!!! Step filling Optimal filling 10/19/2017 Anirban Krishna Bhattacharyya 14

20 Effect of Optimal filling More power needed Step filling Optimal filling 10/19/2017 Anirban Krishna Bhattacharyya 14

21 Effect of charging time ( ) Relative reflected energy Peak generator power 10/19/2017 Anirban Krishna Bhattacharyya 15

22 Practical sources / IOT / IOT Gain characteristics Efficiency characteristics 10/19/2017 Anirban Krishna Bhattacharyya 16

23 Practical sources W. Doherty, A new high efficiency power amplifier for modulated waves, Radio Engineers, Proceedings of the Institute of 24 (9) (1936) doi: /jrproc B. Kim, J. Kim, I. Kim, J. Cha, The doherty power amplifier, Microwave Magazine, IEEE 7 (5) (2006) doi: /mw-m R. Pengelly, N-way rf power amplifier with increased backoff power and power added efficiency, wo Patent App. PCT/US2003/002,365 (Aug ). URL P. Colantonio, F. Giannini, R. Giofr, L. Piazzon, The doherty power ampli fier, INTERNATIONAL JOURNAL OF MICROWAVE AND OPTICAL TECHNOLOGY 5 (6) (2010) G. Ahn, M. su Kim, H. chul Park, S. chan Jung, J. ho Van, H. Cho, S. wook Kwon, J.-H. Jeong, K. hoon Lim, J. Y. Kim, S. C. Song, C.-S. Park, Y. Yang, Design of a high-efficiency and high-power inverted doherty amplifier, Microwave Theory and Techniques, IEEE Transactions on 55 (6) (2007) doi: /tmtt Klystron!!!! NXP Semiconductors, AN10967 BLF578 demo for 352 MHz 1kW CW power, 2nd Edition, application note (November 2012). D. Rees, D. Keffeler, W. Roybal, P. Tallerico, Characterization of a Klystrode as a RF Source for High-Average-Power Accelerators, Conf.Proc. C (1995) E. Montesinos, Tetrode power amplifiers, in: TIARA Workshop on RF Power Generation for Accelerators, Uppsala University, A ngstr om Laboratory, N. Pupeter, Significant increase of efficiency of solid state amplifiers due to improved ac/dc conversion and adaption of p1 point to actual operating power, in: EnEfficient RF Sources, Cockcroft Institute, / IOT Efficiency characteristics 10/19/2017 Anirban Krishna Bhattacharyya 16

24 Practical sources Source efficiency during filling 10/19/2017 Anirban Krishna Bhattacharyya RF Gain Source loss 17

25 Practical sources Tetrodes can be run in Doherty architecture 10/19/2017 Anirban Krishna Bhattacharyya 18

26 Effect of Transit time factor Variation Along Spoke LINAC 10/19/2017 Anirban Krishna Bhattacharyya 19

27 Effect of Transit time factor Beam injection time, Peak power Charging time 10/19/2017 Anirban Krishna Bhattacharyya 20

28 Effect of Transit time factor 10 J/pulse ESS operation: 14 Hz pulse rate 140 J/sec saved per cavity Assuming 8000 hours/year of operation 1.12 MWhrs saved per cavity 2 SEK/kWhr => 2240 SEK 26 Spoke cavities, 20 years of operation, => 1.16 MSEK 10/19/2017 Anirban Krishna Bhattacharyya 21

29 Cryogenic considerations Losses on cavity surface! "! $! #!, Ratio of energy loss () *! & ' #! 0 Intrinsic quality of the resonant structure 10/19/2017 Anirban Krishna Bhattacharyya 22

30 Cavity Quality factor To measure Quality factor of bare ESS superconducting spoke cavities Vertical tests in horizontal cryostat 10/19/2017 Anirban Krishna Bhattacharyya 23

31 Cavity resonator and self-excited loop / 0 ω ω 2 2ω 2 6/ : Self-excited loop θ 2 ω 0θ < ω 2=> 24

32 Reflection coefficient Γ δ κ10b κ01b δ δ :0 : tanθ 2 10/19/2017 Anirban Krishna Bhattacharyya 25

33 Reflection coefficient Γ G κ 0Γ GG κ 10κ κ 1 : 1 H 1 Γ GG under coupling κj1 Γ G critical coupling κ1 over coupling κi1 26

34 Superconducting cavity Γ G κ 0Γ GG κ 10κ κ : 27

35 Reflection co-efficient, Q-circle and surface Γ G κ 0Γ GG κ 10κ 28

36 Q-surface 29

37 Q-slope Double-spoke cavity 30

38 Q-slope 31

39 Effect of cooling rate on Residual resistance depends on trapped magnetic field Helmholtz Zentrum Berlin (HZB): magnetic field are generated by thermal currents. HZB & Cornell: Slow cooling to reduce thermal currents. Fermilab: Magnetic field (ambient) can be expelled by large temperature gradients creating a quick propagating super-conducting phase front. 10/19/2017 Anirban Krishna Bhattacharyya 32

40 Effect of cooling rate on 10/19/2017 Anirban Krishna Bhattacharyya 33

41 Ginzburg-Landau Equations 10/19/2017 Anirban Krishna Bhattacharyya 34

42 Conclusion Reflected energy and thus waste can be reduced by proposed filling profile. But physical factors provide constraints which require increased investigation to better understand the super-conducting cavity. The proposed measurement technique provides a means of accurately characterising the gradient dependent character of the superconducting cavities. The rate of cooling has been found to influence cavity and the G-L equations provide a means of theoretically explaining experimental observations. 10/19/2017 Anirban Krishna Bhattacharyya 35

43 Thank You 10/19/2017 Anirban Krishna Bhattacharyya 35

44 Experimental setup 29

45 Digital loop delay 30

46 Normal conducting cavity Γ GG Γ G 26

47 Cavity conditioning 31

48 Reflection coefficient Before cable compensation After cable compensation 32

49 Doherty Architecture 10/19/2017 Anirban Krishna Bhattacharyya 49