APEX 2 Nov 06

the 60Hz Harmonics Problemthe 60Hz Harmonics Problem

Peter Cameron

APEX 2 Nov 06

OutlineOutline• Old Stuff – rehashing what almost everyone has

seen at least once– “tell them what you are going to tell them, then tell them,

then tell them what you told them”

• New stuff– another look at May APEX experiment data– harmonics beyond the betatron line

• Plans for Run 7– Common mode???– Ramping supply at injection – definitive?– Repeat the APEX of last May– DAQ

APEX 2 Nov 06

60Hz Harmonics60Hz Harmonics

• direct excitation of betatron resonance by high harmonics of power supply frequencies

• mechanism is not yet understood • large amplitude

– ~40dB above 3D AFE noise floor during injection and store (~1)– ~70dB above 3D AFE noise floor during ramping (~30)

• three definitive measurements– increase/decrease coincides with ramping supplies– coupling moves harmonics into vertical– main dipole 12 phase power supply tweak modifies spectrum

• Concerns– makes BBQ/TF system refinement at RHIC difficult– emittance growth???

APEX 2 Nov 06

the good news – if 60Hz harmonic are not blowing up emittance on the ramp (?), then BBQ certainly won’t

APEX 2 Nov 06

Effect of 60Hz Harmonics on BBQEffect of 60Hz Harmonics on BBQ

PLL locked on 60Hz harmonic

APEX 2 Nov 06

coupling variation shows coupling variation shows excitation is in horizontal planeexcitation is in horizontal plane

vertical

horizontal

APEX 2 Nov 06

12 phase 12 phase power power supply supply

balancingbalancing

• At injection, tweak one phase of 12 phase power supply• Causal relation was observed with pattern of 60Hz harmonics• The tweak was large – 150sec, or ~3 degrees at 60Hz• Pattern changed, but total 60Hz harmonics power remained constant

– not likely to be eliminated by better balancing?– problem is complex – 12 free parameters, not reasonable to expect improvement

from random tweaks– fact that line amplitudes decreased suggests there is no other comparable source

• This phenomenon is not understood

APEX 2 Nov 06

755am806am

807am

NI DSA

HP DSA

APEX 2 Nov 06

CorrelationsCorrelationscorrelation coefficients determination coefficients

• Coefficient of Determination– square of correlation coefficient– more intuitively meaningful than correlation coefficient– defined as ‘the proportion of variation in common between two

data sets’– with no noise, no machine drifts, perfect reproducibility of

magnets… would be “1” for 755am and 807am data sets

• Random probability of observed determination coefficients is < 1 part in 105

APEX 2 Nov 06

LOAD

A

B

=30 deg

1 3 5

4 6 2

1 3 5

4 6 2

firing order:A1, A2B1, B2A3, A4B3, B4A5, A6B5, B6

Phase between A and B bridges

depends on mains voltage (booster

on/off, ???...)

With phase shift between A and B

bridges, this reproduces the

pattern used in the simulation.

RHIC 6 phase 12 pulseRHIC 6 phase 12 pulse

APEX 2 Nov 06

3D AFE

M Turn BPM

Simulation

APEX 2 Nov 06

DC to 20KHz on the rampDC to 20KHz on the ramp

only 720Hz lines high-lighted position of minimum

determined by amount of SCR

overlap

note – amplitude at betatron line ~ amplitude at 720Hz according to million turn BPM

APEX 2 Nov 06

OutlineOutline• Old Stuff – rehashing what almost everyone has

seen at least once– “tell them what you are going to tell them, then tell them,

then tell them what you told them”

• New stuff– another look at May APEX experiment data– harmonics beyond the betatron line

• Plans for Run 7– Common mode???– Ramping supply at injection – definitive?– Repeat APEX of last May– DAQ

APEX 2 Nov 06

Baseband data from Carl SchultheissBaseband data from Carl Schultheiss

APEX 2 Nov 06

•APEX experiment baseline

•baseband data arbitrarily ‘renormalized’ for display, ‘renormalization’ the same for all graphs

•60Hz harmonics at betatron line (h~340) aligned with main dipole PS baseband spectrum

•spectra are quite different

•APEX experiment – one phase tweaked

•power in betatron spectrum remains ~constant

•power in baseband spectrum goes up a lot (~15dB on average)

APEX 2 Nov 06

•baseband data arbitrarily ‘renormalized’ for display, ‘renormalization’ the same for all graphs

•difference between spectra at baseband and betatron line with one phase tweaked

•‘baseline’ difference between spectra at baseband and betatron line

•difference between tweaked and baseline spectra at baseband

• power goes up a lot (~15dB on average)

•difference between tweaked and baseline spectra at the betatron line

APEX 2 Nov 06

Conclusions – May APEX experimentConclusions – May APEX experiment

• clear causal relation between main dipole PS phasing and 60Hz harmonics

• Simulation of 12 phase power supply and Comparison with Data– imbalance between the two 6-phase bridges reproduces one

observed spectral pattern– overlap between phases reproduces observed null at

~10KHz

• Comparison of baseband and betatron spectra– they are quite different - what does this imply about the

source? also see following slides– power in baseband goes up a lot with single (large) tweak

APEX 2 Nov 06

span 50KHzadditional ‘resonances in yellow,

not at the betatron line?

Blue horiz

Yellow horiz

Yellow horiz

Yellow vert

span 5KHz60Hz harmonics evident at

~31KHz

APEX 2 Nov 06

spectral pattern a function of frequencyoverlaps of 12 phase power supply?

Blue horiz – span 39KHz, center 21KHz

20dB enhancement at betatron line – effective Q of betatron resonance is ~100?

proposed new p-p working pt

APEX 2 Nov 06

OutlineOutline• Old Stuff – rehashing what almost everyone has

seen at least once– “tell them what you are going to tell them, then tell them,

then tell them what you told them”

• New stuff– another look at May APEX experiment data– harmonics beyond the betatron line

• Plans for Run 7– Common mode???– Ramping supply at injection – definitive?– Repeat the APEX of last May– DAQ

APEX 2 Nov 06

Plans for Run 7Plans for Run 7• Carl – additional filtering, gain ~5dB • Fritz Caspers - Common mode excitation??? will check

(also capacitance to ground)• Eduard - measure PS ripple – AC couple, no magnetic

core • Ramping supply at injection – definitive?

– George Ganetis/Kevin Brown – trivial to switch to ramping supply while at injection

– look for changes in spectral pattern, amplitudes,…

• Repeat last May’s APEX with more refinement, systematic attempt to tune out harmonics

• additional DAQ helpful – presently just FFT

APEX 2 Nov 06

Bunch-by-bunch turn-by-turn system for Run 7

14 bit A/Dch1ch2

clock/3

triggerWindows PC

running LabVIEW

Control System

GPMs, archiving,…

SNAP

local 1TB hard drive(archiving)

HP VME Mux

28MHz RF

1m Stripline

BH inBH outBV up

BV downYH in

YH outYV up

YV down

optional ext trigger (Artus,…)

hybrid

s

(Tom Russo’s talk tomorrow)

APEX 2 Nov 06

Bunch-by-bunch turn-by-turn system for Run 7modified to be sampling synchronous to selectable 60Hz

harmonicboxcar average the data to improve S/N

idea is to be able to observe effect of phase tweaks in time domain14 bit

A/Dch1

ch2

clock/n

triggerWindows PC

running LabVIEW

Control System

GPMs, archiving,…

SNAP

local 1TB hard drive(archiving)

60Hz

optional ext trigger

3D AFEBHBVYHYV

1m Striplin

eBHBVYHYV

n x h x PLL