Transcript The CLIC IP Kicker & QD0

The CLIC IP Kicker & QD0
A quick look to see if magnetic forces on IP feedback
kicker would be a significant design consideration.
For more details see: IP Kicker Supplementary Notes.pdf
C.Perry - Oxford - 21 April 2010
2: System Geometry
Magnetic field assumed axisymmetric about detector axis
- from the detector magnet & bucking coil cancelling field at QD0
- neglects fringing field from QD0: off-axis but should be negligible
- file: Magneticfield_aroundKickerBPM_CLIC.txt
- originally from H.Gerwig, 15mar2010
Kicker Position: from 325 to 350cm from IP - given
Angle from magnet axis to beam: 10mrad - half crossing angle
Horizontal displacement of kicker from axis: 338cm*10mrad ≈ 3.5cm
Length:
25cm - given
Gap:
1cm - reasonable given small beampipe diameter
Impedance:
120ohms - typical for an efficient stripline geometry
Orientation: kicker assumed parallel to the magnet axis
- for ease of analysis
- would actually be possible...
- forces little different if aligned to beam
C.Perry - Oxford - 21 April 2010
3: The Kicker
Geometry:
Type: stripline with strips in vacuum
Operating mode: shorted at far end (ie no electrostatic deflection)
Treat kicker as a single-turn rectangular coil in the vertical plane
Connections made at one point: can disregard feed currents
Short sides would be split to clear beam: little effect on forces
Deflection:
Assumed kicker current: 5A
Kicker L per unit length: Zo/c = 120/3E8 = 0.4uH/m
Coupled flux:
5A*0.4uH/m = 2uWb/m
For 1cm gap kicker, field: 2uWb/m / 0.01m = 200uT
For a uniform kicker field, this is also B near to the axis.
From :
p = 300 * B * r [MeV/c, T, m]
Curvature for 1.75TeV: 300 * 2E-4 / 1.75E6 = 3.4E-8 m-1
Angle for 0.25m kicker: 0.25 * 3.4E-8 = 8.5nrad
Displacement at IP:
3.4m * 8.5nrad = 29nm
==>So 5A drive is reasonable but generous
C.Perry - Oxford - 21 April 2010
4: Forces - 1
For 5A:
29nm at IP
Br = 72mT
Bz = 2.29T
Br mean = 58mT
z = 350cm
Bz = 3.12T
z = 325cm
Br = 45mT
3.5cm
NOT TO SCALE!
(Bz>>Br)
C.Perry - Oxford - 21 April 2010
5: Forces - 2
For 5A:
29nm at IP
Br = 72mT
73mN
Bz = 2.29T
Br mean = 58mT
156mN
112mN
z = 350cm
Bz = 3.12T
73mN
z = 325cm
Br = 45mT
3.5cm
C.Perry - Oxford - 21 April 2010
6: Forces - 3
For 5A:
29nm at IP
Br = 72mT
73mN
Bz = 2.29T
Transverse
force = 21mN
112mN
z = 350cm
Br mean = 58mT
156mN
10mN
10mN
Bz = 3.12T
73mN
z = 325cm
Br = 45mT
3.5cm
C.Perry - Oxford - 21 April 2010
7: Forces - 4
For 5A:
29nm at IP
Torque = 68mNm
Br = 72mT
73mN
Bz = 2.29T
Br mean = 58mT
Transverse
force = 21mN
112mN
z = 350cm
156mN
10mN
10mN
Bz = 3.12T
73mN
z = 325cm
Calculation from coupled flux:
force = work/ds = I*(dΦ/ds)
Mean dB/dr: 167 gauss/cm = 1.67T/m
Horizontal transverse force: dBr/dr*I*A = 0.021N
Vertical transverse force zero by symmetry
Br = 45mT
3.5cm
Axial forces (on short
sides) are negligble
C.Perry - Oxford - 21 April 2010
8: Motion
For single pulse:
If current is maximum for full 250ns, impulse: 0.021N * 250ns = 5.2nNs
Assume effective mass 100kg for kicker, QD0 and support structure.
Velocity: 5.2nNs / 100kg = 0.05nm/s
If resonant at 50Hz, amplitude: 0.05nm/s / (2π * 50Hz) = 0.15pm
For repetition at 50Hz:
Worst case: full impulse given & stays in phase with structural resonance.
If damping timeconstant 200ms, amplitude: 200ms * 50Hz * 0.15pm = 1.5pm
On more reasonable assumptions, under ~0.5pm peak.
Note:
Predicted motion is horizontal - but much could be converted to vertical.
C.Perry - Oxford - 21 April 2010
9: Frequency Domain View
System response is linear, so we can consider it in the frequency domain.
Only the low frequency (~50Hz) components of the drive current are significant.
Worst case:
Drive: 5A 0.25us pulses repeated at 50Hz
Spectrum roughly flat up to 2MHz
Amplitude of 50Hz component: 5A*50Hz/2MHz = 125uA
Force component at 50Hz: 0.021N*125uA/5A = 0.5uN
On a free 100kg mass, amplitude: 0.5uN/100kg*(2π*50Hz)**2 = 0.05pm
Resonance at 50Hz increases response
If Q=30 amplitude 0.05pm*30 = 1.5pm
==> *very* rough - but agrees with previous calculation
At LF induced currents in eg cable screens are insignificantly small so feed connections should be routed together.
We can remove LF components from drive: greatly reduces mechanical effects.
C.Perry - Oxford - 21 April 2010
10: Driving the Kicker
Example output stage performances possible with available MOSFETs:
1: Simple: +/-8A drive, +/-50nm, 7ns or better risetime
2: Maximum Kick: +/-30A to each segment, +/-160nm, 6ns or better risetime
Kicker divided into 4 segments each with own driver
Electronics plugged directly onto the kicker
3: Maximum Speed: +/-8A drive, +/-50nm, 3.5ns or better risetime
As 2, but with lower voltage, faster MOSFETs
Notes:
- no information on rad-hardness of devices
- magnetic field prohibits ferrite cores in amplifier: examples allow for this
- there are forces from currents in amplifier: can be kept negligible with care
C.Perry - Oxford - 21 April 2010