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					805 MHz cavity TiN_Mo
     button test



                        1
• Cavity commissioning started in the early
  November, 2007
  – Abnormally high radiation background was observed
    with chipmunk detectors, ~100-1000 times higher than
    usual
• Calibrations were done on Nov 28th, 2007, with
  network analyzer
  – The signal on the scope actually needed to be
    multiplied by the scaling factor of 1.9 due to some
    connection problem on the 805MHz cavity RF pickup
    1
• The problem was fixed in the early Dec. 2007
• Data were taken in Dec. 2007
                                                          2
S21: The transmission coefficient from the RF input port on the waveguide to the
                                      s
805MHz cavity RF Pickup 1 : ~5.6dB’ difference between the loss factor on the
scope and the one we measured in May, 2007, means the actual signal is ~1.9
larger than the one we had seen on the oscilloscope




                                Res. frequency


                                                                                   3
Smith chart calibration: S11 (WG reflection)

                                                 inductance
                  resistance      resistance




     most reflection               least reflection




                               Res. frequency

                                                              4
       Up-limit of the on-axis accelerating gradient on button
                   surface at various magnetic field
                                                               45




             Maximal accelerating gradient on button surface
                                                               40                                                TiN_Mo 12/11-13/2007

                                                               35                                                Mo 06/2007

                                                               30                                                TiN_Mo 12/18/2007

                                                               25
                                (MV/m)


                                                               20


                                                               15


                                                               10


                                                                5

                                                                0
                                                                    0   0.5   1   1.5       2          2.5       3      3.5      4      4.5

                                                                                        Magnetic field (Tesla)

• Compared to bare Mo button, there is no significant improvement by TiN coating
• There is a balance between the field emitters generated and destroyed by the RF field. We
need to adjust the RF field very carefully to obtain the equilibrium; otherwise, either we cannot
reach the highest gradient, or break down the cavity. Each time we kept the gradient stable for
5-10 minutes
• The difference between the two curves of the TiN_Mo button is due to different surface
conditions
• Because the cavity had been subjected to the very high RF gradient up to 70MV/m due to the
wrong calibration in Nov, while we open up the cavity to change the button, we need to take a
close look at the TiN_Mo button surface to see if the TiN coating was seriously peeled off like
in the last May. Otherwise, we don’ know if the results are accurate
                                    t                                                             5
                             CENTER OF 805MHz
                             cavity TO DETECTOR 16
                             (NaI crystal): 6629mm

                             CENTER OF 805MHz
Det. 16                      cavity TO DETECTOR 8
NaI crystal                  (smaller scintillator
                             paddle): 5994MM

              Det. 8         RD46 CHIPMUNK
              Scintillator   DETECTOR IS AT
                             DOWNSTREAM BEHIND
                             THE 805 MHz CAVITY

    DOWNSTREAM




                                                     6
                                              Det. 16 NaI crystal 12/11-14/2007
                    1.00E+05
                                                                                   #16, B=0 12/11/07

                                                                                   #16, B=0.5T, 12/12/07
                    1.00E+04
                                                                                   #16, B=1T, 12/12/07
Counts in 100sec.




                                                                                   #16, B=1.5T, 12/12/07
                    1.00E+03
                                                                                   #16, B=2T, 12/13/07
                                                   Saturation ~ 27MV/m
                                                                                   #16, B=2.5T,12/14/07
                    1.00E+02
                                                                                   #16, B=3T, 12/14/07

                                                                                   #16, B=3.5T, 12/14/07

                    1.00E+01
                                               cosmic background


                    1.00E+00
                               10   15   20        25     30     35    40     45         50        55      60

                                                          Gradient (MV/m)
                       • Comparing the saturation points measured on the same day (the
                       surface conditions are about same), e.g., on 12/12/07, based on the
                       yellow, blue and purple curves, we can see that the magnetic field has
                       almost no influence on the detectors because of the enough long
                       distance between the cavity and detector.                                           7
                                              Det. 8 small scintillator paddle (12/11-14/2007)

                         1.00E+06



                         1.00E+05
                                                 No Saturation
C ou nts i n 10 0se c.




                                                                                          #8, B=0, 12/11/07
                         1.00E+04
                                                                                          #8, B=0.5T, 12/12/07
                                                                                          #8, B=1T, 12/12/07
                         1.00E+03
                                                                                          #8, B=1.5T, 12/12/07
                                                                                          #8, B=2T, 12/13/07
                         1.00E+02
                                                                                          #8, B=2.5T, 12/14/07
                                                                                          #8, B=3T, 12/14/07
                         1.00E+01
                                                                                          #8, B=3.5T, 12/14/07
                                                   cosmic background
                         1.00E+00
                                    10   15        20     25     30     35     40    45          50           55   60

                                                                 Gradient (MV/m)

                            No Saturation observed on yellow, blue and purple curves                                    8
                            RD46 chipmuk radiation detector readouts in Mili-Rad (12/11-
                                                      14/2007)
                 1.00E+04
                                                                                B=0, 12/11/07
                                                                                 B=0.5T, 12/12/07
                 1.00E+03
                                                                                 B=1T, 12/12/07
                                                                                 B=1.5T, 12/12/07
Readout (mrad)




                                                                                 B=2T, 12/13/07
                 1.00E+02
                                                                                B=2.5T, 12/14/07
                                                                                B=3T, 12/14/07
                 1.00E+01                                                        B=3.5T, 12/14/07



                 1.00E+00
                            10    15     20       25   30     35    40     45        50           55   60


                                              cosmic background
                 1.00E-01

                                                       Gradient (MV/m)

• Very sensitive to accelerating gradient, ~E14 . A small variation of
accelerating gradient can introduce large change of radiation background
• Therefore the signal cables from the RF pickups needs to be carefully
calibrated.
                                                                                                            9
             Future plans

•Open up the cavity, check out the TiN_Mo
 button to see the surface condition, and
 install the TiN_Cu for the next run
•May need to recalibrate the signal
 transmission cable from both RF pickup 1
 and 2 to make sure the calibration is
 accurate.


                                        10

				
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