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.


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)

http://ab-div.web.cern.ch/ab-div/Meetings/ltc/ltc_2006-11.html


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).


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.


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.


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


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.


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).

http://www.crownaudio.com/amp_htm/itech.htm

http://www.labgruppen.com/Default.asp?Id=9024

http://pro-audio.powersoft.it/an_series_list.php?use_in=53&id_menu=271&obj=12


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.


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...


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


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


AC Dipole Test Stand in building 867


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.


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.


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


Simulation for f = 8.2 kHz caseBeam excitation with two FP 13000 amplifiers at 8.2 kHz

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

Cu

rre

nt

in r

ms

am

ps

Displacement in sigma at 450 GeV

Displacement in sigma at 7 TeV

Imagnet rms (A)


ComparisonBeam Excitation comparison

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

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!


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.


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.


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.


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.





10 April 2007 LHCCWG meeting 28

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


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


UA43 rack layout


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.

Documents

The AC Dipole system for LHC Technology and operational parameters