Effect of 25ns, 50ns

1
Effect of 25ns, 50ns 75ns Beam Bunch Spacing
upon MKDV Kickers MD August 12th to 14th, 2008
M.J. BARNES, AB/BT Also on behalf of V. Senaj
L. Ducimetière
2
Principle of Beam Dumping
II.
3
MKDV Temperature Pressure on 12, 13 14th
August 2008
8s resolution
4
MKDV

• No measures taken to reduce beam coupling
  impedance to ferrite
• No transition pieces, between magnet tank and
  magnet frame, installed in LSS1 (now installed in
  spare MKDV1 magnet) ? 16cm gap at each end.

MKE magnet
5
MKDV Longitudinal Impedance

• Longitudinal Impedance (ZRL) Theoretical
  Calculation CERN-SL-2000-04 AP, by H. Tsutsui,
  pp7-10.
• MKDV1 theoretical ZRL fits baseline of
  measurement reasonably well.
• Cell length of 51cm ? (?/4) resonance, for open
  circuit, of 147MHz (assuming µr er of 1).
• Spikes may also be due to lack of transition
  pieces??

11.5MHz
6
MKDV Pressure on 14/08/2008, between 0120hrs
0210hrs.
1s resolution
Summary 50ns beam causes pressure rise high
pressure with 3 or 4 batches per shot.
7
MKDV Pressure on 14/08/2008, between 0500hrs
0700hrs.
1s resolution
8
MKDV Pressure on 14/08/2008, between 0549hrs
0550hrs.
Limited (1s) resolution for pressure May miss
peaks on graph (interlock requires few 10s of
ms) Fast pressure rise and fall due to surface
effect (e.g. electron cloud), or gauge
misreading??
Two shots of 4 batches of 50ns beam at 549hrs??
9
Misc. Longitudinal Impedance
(Note impedance data in following plot is scaled
according to length of tank rather than magnet
length therefore actual impedance per metre is
larger than shown in plot)

• For MKE
• Is frequency of onset of spikes dependent upon
  aperture size? e.g. (MKE-L9 MKE-S3)
• Serigraphy generally eliminates spikes up to and
  beyond 500MHz.

• Apertures (hap x vap)
• MKE-L 147.7 x 35mm
• MKE-S 135 x 32mm
• MKI 54 x 54mm
• MKDV1 56 x 75mm.
• Cell Length
• MKE 24cm
• MKDV1 51cm.

MKE no stripes
MKE (S6) stripes on 2 of 7 cells
MKE (L10) stripes on all cells
MKI no screen
MKDV1 no beam screen or transition pieces.
Spikes due to cell length ???
MKI 15 screen conductors
10
SPS Kickers Vacuum, August 14, 2008
1s resolution
11
SPS Kickers Vacuum, August 14, 2008
1s resolution
12
SPS Kickers Temperature, August 12-14, 2008
MKDV 75ns beam to 0130hrs, 50ns beam 0513 to
0700
MKDV 25ns beam
75ns beam
25ns beam
50ns beam
MKE6 75ns beam to 0130hrs, 50ns beam 0513 to
0700
MKE6 25ns beam
75ns beam
50ns beam
MKE6 temperature rise limited by serigraphy.
13
SPS Kickers Temperature, August 12-14, 2008
MKP temperature probes both on one magnet.
MKP temp. not overly sensitive to 50ns or 75
bunch spacing.
MKE4 temp. not overly sensitive to 50ns or 75
bunch spacing.
14
Summary Future Plans

• Spikes on measured MKDV1 longitudinal
  impedance, which are not present in analytical
  calculation, are probably attributable to magnet
  cell length, aperture dimensions and absence of
  transition pieces.
• An MKDV1 magnet is presently being HV conditioned
  (it has transition pieces). It is planned to make
  longitudinal impedance measurements on this
  magnet before installation (during the next
  shutdown) this will allow effect of transition
  pieces to be assessed.
• Impedance resonances of MKDV2 (not measured)
  probably cause heating of ferrite with 75ns bunch
  spacing.
• Shielding of MKE magnets eliminated high
  impedance resonances in longitudinal impedance
  and thus significantly reduces heating possible
  long-term solution for MKDV1 ?? (MKDV2 no-spare
  exists, so difficult to modify). Could MKDV1
  (H75mm) be used in place of MKDV2 (H83mm)?. But
  still see pressure rise with 50ns bunch
  spacing..
• 50ns bunch spacing causes immediate pressure rise
  (surface effect-e.g. electron cloud) for both
  MKDV1 MKDV2 but MKDV1 is more significant.
• MKE6, MKDH, MKDH MKQV kickers all show
  immediate pressure rise with 50ns bunch spacing
  .. But MKQH sensitive to 75ns bunch spacing
• Further MD with 50ns beam to confirm, with 3 or 4
  batches per shot, as cause of high pressure
  rise? electron cloud investigations ????.
• Log ion pump current?

15
Questions Comments
16
MKDH3 Longitudinal Impedance Measurements
MKDH3 no shielding or transition pieces.

• No temperature Probes on MKDH magnets
• MKDH3 length1.256m ? ?/4 resonance of 60MHz
• Transverse impedance measurements planned for
  MKDH3.

17
MKE Beam Coupling Impedance Reduction

• Beam coupling impedance is reduced using
  conductive stripes (serigraphy), i.e. interleaved
  comb structure, directly printed onto the
  ferrite blocks and a reliable contact to the
  metallic HV plates at either side
• Capacitive coupling between stripes (stripes
  carry beam image current).