The AC Dipole system for LHC Technology and operational parameters
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Transcript of The AC Dipole system for LHC Technology and operational parameters
The AC Dipole system for LHCTechnology and operational parameters
Javier SerranoAB-CO-HT
LHCCWG 10 April 2007
10 April 2007 LHCCWG meeting 2 of 22
Outline
Introduction.Key stakeholders.Technical specifications.Proposed solution. Center frequency choices.Ongoing developments.Outstanding issues.Planning for the rest of 2007.
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Introduction
AC dipole: a dipole magnet excited with an oscillating current.
If the excitation frequency is close to the tune, a driven coherent oscillation of the beam results.
If the excitation amplitude is ramped up/down adiabatically, beam emittance is preserved.
In 2006 AB-BT agreed to let AB-CO use the MKQA magnets as AC Dipoles. A set of relays selects among three generators (Aperture, Q, AC Dipole) to drive one magnet.
The LHC AC Dipole project was endorsed by the LTC on 13/09/2006 with the goal of having a system ready for LHC commissioning.
(http://ab-div.web.cern.ch/ab-div/Meetings/ltc/ltc_2006-11.html)
10 April 2007 LHCCWG meeting 4 of 22
Key stakeholders
AB-ABP: will we have enough power in the AC Dipole to perform all the measurements we want? Contacts: Rogelio Tomás, Stéphane Fartoukh.
Machine protection: will the AC Dipole be properly designed so as to minimize the risks of machine damage? Contacts: Rüdiger Schmidt, Jörg Wenninger, Jan Uythoven.
AB-BT: will the Q and aperture generators be affected by the installation of the new AC Dipole generator in the same rack? Contacts: Gene Vossenberg, Etienne Carlier.
AB-OP: how will the AC Dipole system be operated? Contact: Jörg Wenninger.
US-LARP: can these developments benefit the existing AC Dipoles in FNAL and BNL? Contacts: Andreas Jansson, Ryoichi Miyamoto, Sacha Kopp, Mike Syphers (FNAL), Mei Bai, Rama Calaga, Peter Oddo (BNL).
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Technical Specifications (1/2)
z
BzBl
)(4
Integrated field strength necessary to generate a transverse displacement Δz using an AC-Dipole
Where:
• Bρ is the magnetic rigidity: 1501 Tm for LHC at 450 GeV.• δ is a relative measure of the distance in frequency between the B field and the tune: spec says 0.025.• βz is the value of the betatron function at the location of the AC-Dipole. In our case, of the four magnets the worst (lowest) case is 258.4 m. •Δz is specified as 7σ in the AC Dipole location at 450 GeV, i.e. 9.87 mm.
Bl(max) = 18.01 mT·m I(max) = 1733 A
I(rms) = 1225 A
NB1: in order to generate a displacement of 4 sigma at 7 TeV with δ=0.01 (previous spec) a Bl of 16.35 mT·m is enough. NB2: The specified Bl at injection corresponds to a “kick per turn” of 12 μrad.
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Technical specifications (2/2)
H tune foreseen between 0.28 (450 GeV) and 0.31 (7 TeV). V tune foreseen between 0.31 (450 GeV) and 0.32 (7 TeV). Total tunable range, including going to δ=0.025 on either side: 0.08 tune
units, i.e. 11245 * 0.08 = 900 Hz. We propose an RCL resonator (see next slides) with C chosen to set the
center frequency at 0.295 for the horizontal systems and at 0.315 for the vertical ones. Current at peak should be enough to guarantee 1225 A rms at ±450 Hz frequency offset.
If OP decides to work on other tunes, we have to go and change some caps. Special attention given to tune range 0.2-0.4.
Ongoing work at BNL to study variable capacitors and inductors (more on this later).
The specified excitation takes the shape of a sine wave with a trapezoidal envelope. To maintain adiabaticity, rise and fall times of 200 ms or longer are acceptable.
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Proposed solution (1/4): parallel RCL circuit
Rs
jXs
Rp jXp
Xs
RsXsXp
22
Rs
XsRsRp
22
22
2
XpRp
XpRpXs
22
2
XpRp
XpRpRs
This... ...is the same as this
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Proposed solution (2/4): quality factor definitions
Pr
P
L
RQ
ωωr
Z
BW
)(2 HzBWQ r
or
The current in LP is Q times the current in RP, i.e. this circuit works like a current amplifier. Note that Q is unchanged under series to parallel transformation, as long as it’s defined as ωrLS/RS for the series configuration.
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Proposed solution (3/4): audio amplifiers and transformers Switching (class D) audio amplifiers are available with several kW of power:
I-T8000 from Crown: 8kW amplifier used at FNAL and CERN. http://www.crownaudio.com/amp_htm/itech.htm
FP 13000 from Lab.Gruppen: 13 kW, being tested at CERN. http://www.labgruppen.com/Default.asp?Id=9024
DIGAM K18 from Powersoft, upcoming, not yet in their website: 18 kW. http://pro-audio.powersoft.it/an_series_list.php?use_in=53&id_menu=271&obj=12
These amplifiers are current-limited for low Rp and voltage limited for high Rp, i.e. they have a “preferred” Rp to deliver maximum power.
Transformers are needed to: Transform our initial Rp into the one the amplifier likes. Use the amplifiers in mono bridge mode (our magnet is returned to ground). Couple the power of more than one amplifier into the load (more on this later).
A transformer does not change the Q of the circuit. It just trades current for voltage, maintaining constant power (for a perfect transformer, that is).
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Proposed solution (4/4): design procedure
Assume you can match the load to the generators, so worry only about power needs and power ratings.
Measure RP and Q for the magnet at the desired frequency. If Imagnet is the specified rms current for the magnet, the needed power is P=(Imagnet/Q)2· RP
This is only a first estimate, because the resulting circuit will deliver Imagnet only at the frequency of the peak. We want Imagnet at ±450 Hz from the peak.
Choose the appropriate Cp to make the circuit resonate with Lp at the chosen frequency, and simulate.
Read the Imagnet current at ±450 Hz from the peak and scale the power requirement accordingly.
Choose amplifier(s) and transformer(s) to deliver enough power to the matched load.
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Center frequency choices
According to AC Dipole theory, and assuming a tune of 0.3 in the LHC, the AC Dipole generator can work at 4 different frequencies in the audio (0-20kHz) range:
f1 = 11245 * (0 + 0.3) = 3.37 kHz f2 = 11245 * (1 – 0.3) = 7.87 kHz f3 = 11245 * (1 + 0.3) = 14.62 kHz f4 = 11245 * (2 – 0.3) = 19.12 kHz
Q usually grows with frequency, although slower than ω due to skin effect. BW = (fR/Q) also grows, although again slower than ω.
However, the rise of Rs-RDC with sqrt(ω) (skin effect) means more losses at high frequencies.
The best thing is to test and simulate using test results. Tests are easier if we get higher currents by inserting a C in parallel to the
circuit under test, but our current choice for C values is limited...
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Test at f=2.9 kHz (close to f1)
C = 760μF (3*120μF + 4*100μF) Q(measured)=6.35 Rp(measured)=0.462 Ohm
Courtesy of Matthieu Cattin
CROWN I-T800 with 760uF capacitor
0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
f (kHz)
Imag
net
/Igen
0.000
0.050
0.100
0.150
0.200
0.250
0.300
0.350
0.400
0.450
0.500
Vm
agn
et/Im
agn
et (
Oh
m)
Imagnet/Igen
Vmagnet/Imagnet
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Test at f=8.2 kHz (close to f2)
C = 120μF (1*120μF) Q(measured)=10.2 Rp(measured)=1.677 Ohm
Courtesy of Matthieu Cattin
CROWN I-T8000 with 120uF capacitor
0.0
2.0
4.0
6.0
8.0
10.0
12.0
6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0
f (kHz)
Imag
net
/Igen
0.000
0.200
0.400
0.600
0.800
1.000
1.200
1.400
1.600
1.800
Vm
agn
et/Im
agn
et (
Oh
m)
Imagnet/Igen
Vmagnet/Imagnet
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AC Dipole Test Stand in building 867
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Coupling many amplifiers
This is the way they couple amplifiers in BNL, except they couple 24 250W amplifiers for a total power of 6kW.
FNAL is also working on this for their AC Dipole.
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Back to our measurements
f (kHz) 2.9 8.2
C (uF) (notice slight cheating to fit rest of data) 754.3169791 118.052011
Q 6.35 10.2
Rp (mOhm) 462 1677
Magnet current needed (A rms) 1225 1225
Power needed (kW) 17.19359539 24.1882749
Xp (mOhm) 72.75590551 164.411765
Lp (uH) 3.992917931 3.19109086
Rs (mOhm) 11.18034969 15.9653465
Xs (mOhm) 70.99522052 162.846535
Ls (uH) 3.896289752 3.16071109
Preferred load for the amp (Ohm) 4 4
Optimal N1/N2 for 2 transformer arrangement with secondaries in series 4.161251893 2.18412989
Impedance transformation ratio 17.31601732 4.77042338
Let’s take these numbers and simulate what two FP 13000 amplifiers can deliver to the magnet under these conditions.
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Simulation for f = 2.9 kHz caseBeam Excitation using two FP 13000 amplifiers
0
1
2
3
4
5
6
7
8
9
10
-0.025 -0.02 -0.015 -0.01 -0.005 0 0.005 0.01 0.015 0.02 0.025
Delta
Dis
pla
ce
me
nt
in s
igm
a
0
200
400
600
800
1000
1200
1400
1600
1800
2.637 2.737 2.837 2.937 3.037 3.137
Frequency (kHz)
Ma
gn
et
cu
rre
nt
rms
(A
)
Displacement in sigma at 450 GeV
Displacement in sigma at 7 Tev
Imagnet (rms)
NB: only 0.05 tune units shown
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Simulation for f = 8.2 kHz caseBeam excitation with two FP 13000 amplifiers at 8.2 kHz
0
1
2
3
4
5
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7
8
9
10
-0.025 -0.02 -0.015 -0.01 -0.005 0 0.005 0.01 0.015 0.02 0.025
Delta
Dis
pla
ce
me
nt
in s
igm
a
0
200
400
600
800
1000
1200
1400
Cu
rre
nt
in r
ms
am
ps
Displacement in sigma at 450 GeV
Displacement in sigma at 7 TeV
Imagnet rms (A)
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ComparisonBeam Excitation comparison
0
1
2
3
4
5
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9
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-0.025 -0.02 -0.015 -0.01 -0.005 0 0.005 0.01 0.015 0.02 0.025
Delta
Dis
pla
ce
me
nt
in s
igm
a
Displacement at 450 GeV exciting at 2.9 kHz
Displacement at 7 TeV exciting at 2.9 kHz
Displacement at 450 GeV exciting at 8.2 kHz
Displacement at 7 TeV exciting at 8.2 kHz
Near delta=0, lower losses favor f=2.9 kHz.Far away, the higher BW at f=8.2 kHz takes over.Tough choice!
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Ongoing developments
Coupling two amplifiers together and checking reality vs. simulations. Transformers should arrive at CERN anytime now. FNAL is also studying this.
Variable capacitors and inductors. Contact: Peter Oddo (BNL):
Variable capacitors: C in series with switch. Effective C depends on switch’s duty cycle.
Variable inductors (1): make a core saturate, therefore losing its inductance, a certain percentage of time, with the help of an auxiliary DC winding. This is ON/OFF control as with the capacitor.
Variable inductors (2): with an auxiliary winding carrying a DC current, go to a certain point in the core’s B-H curve. Incremental inductance can be controlled in this way.
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Outstanding issues
Test relay to verify it does not heat up too much (Ross model EA12-NO-20-2C-78A-BU). Have software avoid too frequent excitations if need be.
Measure magnetic field in the magnet to make sure our amps to T*m conversion factor is correct.
β-beating at injection can be ±15%. Adjust specs accordingly to meet 7σ spec for worst-case β at injection?
Organize cabling of AC Mains in UA43 (cable from AB-BT’s racks). Work on strategies to follow tune during LHC startup. Try to get hold of the new 18 kW amplifiers for test. Work with machine protection. Items for discussion include:
Constrain possible values of excitation by reading current Energy & Intensity in the front end.
Decide on final strategy for AC Dipole/Aperture/Q measurement selection button location(s).
Avoid collision with other interlocks (e.g. dump channel BPMs fire at Δz=3mm with unsafe beam).
Software could enforce a Q measurement before use.
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Planning: tentative dates
End of the year (2007) → have it ready, which means:
SW specs with OP, then find someone to develop, hopefully before beginning of Summer.
start working with MPWG right away.
Working prototype, with acceptable power, at the end of the Summer.
Installation in the four AB-BT generator racks in November.
HW/SW commissioning in December.
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Reserve slides
MKQA magnet parameters (courtesy of Gene Vossenberg).
FNAL system (courtesy of Andreas Jansson and Ryoichi Miyamoto).
BNL system (courtesy of Mei Bai).UA43 rack layout (courtesy of Etienne
Carlier).MKQA misc info, courtesy of Gene
Vossenberg.
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FNAL AC Dipole Generator
2.5μH 6μF 65mΩ8.3μH
8.2μF
Power Supply Magnet + Cables
20kHz
CT
Schematic Diagram and Picture of the Circuit
Ztot ≈ 10 Ω
R+XL = 1 Ω
Imagnet = Vamp / (R+XL) ≈ 100 A
Courtesy of A. Jansson and R. Miyamoto
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RHIC AC Dipole system
RR1, RR3, RR4, RR5, RR6open for series operation
Shorting
RR2 open for parallel operation
C1Bank
C2Bank
C1aBank
C2aBank
"C2" Buss bar
From Power Amp
RR1
RR2
RR3
RR4
RR5
Magnet "2"
Magnet "1"
Magnet "3"
Magnet Current - to scope
Magnet "4"
W1Andrew LDF4RN-50A
1 3
2
Current
T1Current Transformer
W2RG-58
1 3
2
bottom plate
RR7
Rd2
100
Rd1
100
Rd5
100
Rd4
100
Rd3
100
400300 500(60.84KHz ) (36.6KHz )
RR6
L1
L2
Magnet coils
Courtesy of M. Bai
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UA43 rack layout
10 April 2007 LHCCWG meeting 31
Misc info on MKQA
• Maximum flux in the steel tape cores of MKQA is 1100mT.
• Stacking factor is 0.88 and due to gap geometry 4% is lost.
• This means max. flux in gap is 930mT.
• With corresponding magnetic length of 0.614m, the max. kick is 571mT m.