Vasilis Vlachodimitropoulos Acknowledgements Mike Barnes Lorena Vega Cid 30052017 1 HLLHC WP14 Coordination Meeting Motivation 1 MKI overview given by Mike Circulating beam passes through Ushaped yokes ID: 793708
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Slide1
Study of an improved beam screen design for MKIs
Vasilis VlachodimitropoulosAcknowledgements: Mike Barnes, Lorena Vega Cid
30/05/2017
1
HL-LHC WP14 Coordination Meeting
Slide2Motivation (1)
MKI overview given by Mike
Circulating beam passes through U-shaped yokes
Beam-ferrite interaction → ferrites heat up → if above Tc
we cannot safely inject → wait to cool down → long turn around times → PROBLEM!
Solution: e/m shield the beam from the yoke (= beam screen)
Ferrite
Screen
Curie Temperature
Above the Curie Temperature the ferrite temporarily looses its permeability.
Courtesy: Lorena Vega
30/05/2017
2
HL-LHC WP14 Coordination Meeting
Slide3Motivation (2)
Beam screen upgraded during LS1 and as a result reduction of measured temperatures was observed
Observations during Run 2 are in agreement with predictions of existing models (see upcoming talk by Lorena)
Current MKI beam screen design is sufficient for Run 2
operation:
no heating issue is foreseen until the end of the run
E/m and thermal simulations predict that some yokes will exceed their Tc for HL-LHC beams
Further upgrades in the MKI beam screen design are necessary for HL-LHC!
30/05/2017
3
HL-LHC WP14 Coordination Meeting
Slide4The present MKI beam screen
24 conductive wires inside a ceramic tube
Fast rise time: wires grounded at one end (downstream) and
capacitively coupled to the other (upstream)
Arrangement and extra vacuum gap to deal with HV issues
2 sets of 9 ferrite rings to damp low frequency modes
Note: overlapping region between screen conductors and grounded metallic cylinder
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4
HL-LHC WP14 Coordination Meeting
Slide5Heating Process
Beam spectrum couples to real part of longitudinal impedance
R{Z
L}:
For MKI, Z
L
is now essentially geometric: overlapping region acts as
λ/2 cavity →
Beam looses energy primarily at the cavity’s resonant frequencies
Non uniform power distribution: ferrites (rings and yokes) close to the cavity are affected significantly more
30/05/2017
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HL-LHC WP14 Coordination Meeting
Courtesy: Mike Barnes
Slide6Solution we are looking into
Reduce overlap → upshift resonant frequencies to where the beam spectrum is reduced
Power loss estimates: depend on relative position of impedance peaks to beam harmonics
If overlap is reduced too much
→
beam screen is no longer effective: losses increase rapidly
Shorter cylinder + rings in the same position
→ part of power is dissipated in the rings before it reaches the yoke
30/05/2017
6
HL-LHC WP14 Coordination Meeting
Slide7New proposal for overlap
Mechanical constraints: 81mm-long cylinder
→ 56mm overlap
Ferrite rings are interchanged: 4B3 ↔ 4M2
Kapton
layer to support the last 5 upstream ferrite rings – temporary solution for measurements
C
oncentrate on power loss estimatesExpected temperatures will be presented by Lorena
30/05/2017
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HL-LHC WP14 Coordination Meeting
L
overlap
Exposed ferrite rings
Slide8Comparison 1: Impedance Simulations
Power Loss
†
(W)
Post-LS1
56mm
Run 2
37/27/9722/15/16
HL-LHC135/97/35079/54/58
Nominal
Beam Parameters
ppb (e+11)Nbt
b (ns)Run 21.15
28081HL-LHC
2.227481
30/05/2017
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HL-LHC WP14 Coordination Meeting†
PL was estimated in three ways:Directly from simulations (e.g. 380MHz for
post-LS1 design)With the first impedance peak at the frequency given by measurements (e.g. 420MHz)
With the first impedance peak at the lowest beam harmonic closest to the frequency given by measurements (e.g. 380MHz→ 400MHz)
Slide9Comparison 2: Impedance Measurements
Transmission wire method and resonant method
30/05/2017
9
HL-LHC WP14 Coordination Meeting
Slide10Comparison 3: Power
Distribution Simulations
% of total power
Post LS1
56mm
Upstream rings
43
90First 6 yokes23
4Most affected ring
927Most affected yoke8
1
Assume
HL-LHC: 120/80 Watt
+
Scaling factor: 4
Power (W)
Post LS156mm
Upstream rings205290
First 6 yokes11213
Most affected ring43
86Most affected yoke38.6
330/05/2017
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HL-LHC WP14 Coordination Meeting
Slide11Comparison 4: Power Distribution Measurements
Preliminary results
Probes at rings and yoke to measure received signal
Need to be repeated with probes in better locations
30/05/2017
11
HL-LHC WP14 Coordination Meeting
Slide12Summary
Upgrade of the MKI beam screen is necessary for HL-LHC
An easily implemented design was presented
Power loss reduction & redistribution to easier to cool areas
Preliminary measurements seem to verify expected behaviour
New beam screen design to be implemented in MKI prototype and tested with Run 2 beams:
provided ongoing thermal studies
ensure
that no heating issue is expected!30/05/2017
12
HL-LHC WP14 Coordination Meeting
Slide13Thank you for your attention!
30/05/2017
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HL-LHC WP14 Coordination Meeting
Slide14Questions?
Please, don’t ask me how hot we will get!
Lorena will come to that in a moment!
30/05/2017
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HL-LHC WP14 Coordination Meeting