The 2008 SPS electron cloud transmission experiment: first results F. Caspers, E. Mahner, T. Kroyer B. Henrist, J.M. Jimenez Thanks to the SPSU study team members For helpful discussions Outline  Layout  Basics and history  First results during scrubbing run  Conclusion and outlook ILCDR 08 July 2008 Cornell

2F. Caspers, E. Mahner, T. KroyerILCDR 08 Cornell July 2008 Basic layout for microwave transmission setup (SPS 2008) Principle idea: “When electromagnetic waves are transmitted through a not too dense plasma, they experience a phase shift and possibly a small attenuation” Antenna1 Antenna m 33.1 m Antenna2 (excitation) dipole quad F. Caspers, T. Kroyer 2008 is similar to the 2004 setup

3F. Caspers, E. Mahner, T. KroyerILCDR 08 Cornell July 2008 Some basics and history (1)

4F. Caspers, E. Mahner, T. KroyerILCDR 08 Cornell July 2008 Some basics and history (2)

5F. Caspers, E. Mahner, T. KroyerILCDR 08 Cornell July 2008 Some basics and history (3)

6F. Caspers, E. Mahner, T. KroyerILCDR 08 Cornell July 2008 Some basics and history (4)

7F. Caspers, E. Mahner, T. KroyerILCDR 08 Cornell July 2008 Some basics and history (5)

8F. Caspers, E. Mahner, T. KroyerILCDR 08 Cornell July 2008 Some basics and history (6) The presently used setup in BA5 is rather similar, except that we have dedicated button like PU‘s and kickers with a circulator after the hybrid and rather narrow-band filters (40 MHz) with steep slopes. The filters are centered at 2.5 GHz. We used this time as receiver a conventional spectrum analyzer and a vector spectrum analyzer.

9F. Caspers, E. Mahner, T. KroyerILCDR 08 Cornell July 2008 Preliminary measurement results in scrubbing run (1) SPS super-cycle Display from a conventional spectrum analzyer. The phase modulation is in the small peaks, which are +/- 44 kHz away from the center. The beam induced signal are the two bigger peaks next to the center line.

10F. Caspers, E. Mahner, T. KroyerILCDR 08 Cornell July 2008 Preliminary measurement results in scrubbing run (2) Display from a conventional spectrum analzyer. The phase modulation is in the small peaks, which are +/- 44 kHz away from the center. The beam induced signal are the two bigger peaks next to the center line. In this display one can see the true width of the carrier, the modulation sideband and the beam signals. SPS super-cycle 17651

11F. Caspers, E. Mahner, T. KroyerILCDR 08 Cornell July 2008 Preliminary measurement results in scrubbing run (3) SPS super-cycle Time axis is from top to bottom, intensity is color coded. CW signal on

12F. Caspers, E. Mahner, T. KroyerILCDR 08 Cornell July 2008 Preliminary measurement results in scrubbing run (4) SPS super-cycle CW signal off-on-off-on

13F. Caspers, E. Mahner, T. KroyerILCDR 08 Cornell July 2008 Preliminary measurement results in scrubbing run (5) SPS super-cycle Shift of CW frequency

14F. Caspers, E. Mahner, T. KroyerILCDR 08 Cornell July 2008 Preliminary measurement results in scrubbing run (6) SPS super-cycle Higher harmonics of the modulation sidebands since the modulation is rather rectangular than sinewave

15F. Caspers, E. Mahner, T. KroyerILCDR 08 Cornell July 2008 Preliminary measurement results in scrubbing run (7) SPS super-cycle Expanded view of one modulation sideband vs time.

16F. Caspers, E. Mahner, T. KroyerILCDR 08 Cornell July 2008 Preliminary measurement results in scrubbing run (8) SPS super-cycle Intensity of the modulation sideband vs time in logarithmic scale

17F. Caspers, E. Mahner, T. KroyerILCDR 08 Cornell July 2008 Preliminary measurement results in scrubbing run (9) SPS super-cycle Intensity of the modulation sideband vs time in linear scale

18F. Caspers, E. Mahner, T. KroyerILCDR 08 Cornell July 2008 Preliminary measurement results in 2008 –AM contamination (1) SPS super-cycle 21196, July 9th 2008 How about AM contamination? Are we really sure that what we see on the green trace (upper half) is pure FM or PM At least in this case its pure AM since the demodulation function of the VSA tells us that there is NO FM or PM signal where we would expect it.(lower trace)

19F. Caspers, E. Mahner, T. KroyerILCDR 08 Cornell July 2008 Preliminary measurement results in 2008 –AM contamination (2) SPS super-cycle 21200, July 9th 2008 Here one can see a small assymetry in height of the modulation lines in the conventional SPA display which is ALWAYS a hint for superposition of AM and FM or PM AND we also see a very small FM –PM Linie in the lower half of the display where we expect it.

20F. Caspers, E. Mahner, T. KroyerILCDR 08 Cornell July 2008 Preliminary measurement results in 2008 –AM contamination (3) SPS super-cycle 17024, July 7th 2008 Another example Upper half: Conventional spectrum Lower half PM demodulation This shot was taken after acceleration at flattop where usually we observed the strongest PM signals 2 batches

21F. Caspers, E. Mahner, T. KroyerILCDR 08 Cornell July 2008 Preliminary measurement results in 2008 –AM contamination (4) SPS super-cycle 16972, July 7th 2008 Here we have in the upper half the conventional spectrum and in the lower half the PM demodulated part Obviously we cannot see anything during accerlation and a quantitative evaluation from this colour coded plot is not really possible.

22F. Caspers, E. Mahner, T. KroyerILCDR 08 Cornell July 2008 LHC beam in SPS, 25 ns bunch spacing, 72 bunches, 1 batch Preliminary measurement results in scrubbing run (10) PS-type shielded button pickup signals Yellow trace Yellow trace  stripline in stainless steel chamber #1 Blue trace Blue trace  pickup in chamber #1 containing enamel clearing electrode Magenta trace Magenta trace  pickup in stainless steel chamber #2 w/o enamel, for reference Note, that there is some (unexpected) low frequency ringing (EMI) in the blue and magenta trace We will try to understand its origin and get it removed in the future Note that depite EMI contamination one can clearly see (light blue trace) the buildup of the e-cloud related current over the duration of the batch

23F. Caspers, E. Mahner, T. KroyerILCDR 08 Cornell July 2008 Conclusion and Outlook The intermodulation problem observed in 2003 (experiments in BA2) has been considerably reduced using a proper RF setup with highly selective filters at the frontend, both, for excitation and on the pickup side. However the application of the phase demodulation function (using a vector spectrum analyzer) is strongly recommended for the elimination of residual AM contamination due to faint saturation effects [gain compression] (more than 50 dB below the carrier) caused by beam induced signals. First electron cloud transmission experiments performed during the 2008 SPS scrubbing run in June have shown very promising results in BA5. The presence of electron clouds was identified simultaneously with button pickups. Microwave transmission over a full LHC arc at cryogenic temperature has been already successfully demonstrated around 7 GHz. The technique discussed here can be directly applied for integral electron cloud diagnostics over a full arc in the LHC. For this purpose the installed in situ reflectometer couplers at the end of each arc could be used. Many thanks to Christian Carli for lending us the real-time spectrum analyzer and contributing during data taking.