Transcript the 60Hz Harmonics Problem Peter Cameron

the 60Hz Harmonics Problem
Peter Cameron
APEX
2 Nov 06
Outline
• 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 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 (~1m)
– ~70dB above 3D AFE noise floor during ramping (~30m)
• 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 BBQ
PLL locked on
60Hz harmonic
APEX
2 Nov 06
coupling variation shows
excitation is in horizontal plane
horizontal
vertical
APEX
2 Nov 06
12 phase
power
supply
balancing
•
•
•
•
At injection, tweak one phase of 12 phase power supply
Causal relation was observed with pattern of 60Hz harmonics
The tweak was large – 150msec, 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
NI DSA
755am
806am
HP DSA
807am
APEX
2 Nov 06
Correlations
correlation 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
RHIC 6 phase 12 pulse
1
3
5
4
6
2
3
5
A
Df=30 deg
1
B
4
6
APEX
2
2 Nov 06
firing order:
A1, A2
B1, B2
A3, A4
B3, B4
A5, A6
B5, B6
Phase between A
and B bridges
depends on mains
LOAD
voltage (booster
on/off, ???...)
With phase shift
between A and B
bridges, this
reproduces the
pattern used in the
simulation.
3D AFE
M Turn
BPM
Simulation
APEX
2 Nov 06
DC 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
Outline
• 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 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 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
Yellow horiz
span 5KHz
60Hz harmonics evident at ~31KHz
Blue horiz
span 50KHz
additional ‘resonances in yellow,
not at the betatron line?
Yellow horiz
Yellow vert
APEX
2 Nov 06
spectral pattern a function of frequency
overlaps of 12 phase power supply?
proposed new p-p working pt
20dB enhancement at
betatron line – effective
Q of betatron resonance
is ~100?
Blue horiz – span 39KHz, center 21KHz
APEX
2 Nov 06
Outline
• 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 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
(Tom Russo’s talk tomorrow)
1m
Stripline
BH in
BH out
BV up
BV down
YH in
YH out
YV up
YV down
D
hybrids
14 bit A/D
ch1
ch2
HP
VME
Mux
28MHz RF
optional ext trigger (Artus,…)
clock/3
trigger
Windows PC
running
LabVIEW
APEX
2 Nov 06
SNAP
Control
System
GPMs,
archiving,…
local 1TB
hard drive
(archiving)
Bunch-by-bunch turn-by-turn system for Run 7
modified to be sampling synchronous to selectable 60Hz harmonic
boxcar average the data to improve S/N
idea is to be able to observe effect of phase tweaks in time domain
1m
Stripline
BH
BV
YH
YV
60Hz
3D AFE
BH
BV
YH
YV
n x h x PLL
14 bit A/D
ch1
ch2
clock/n
trigger
optional ext trigger
Windows PC
running
LabVIEW
APEX
2 Nov 06
SNAP
Control
System
GPMs,
archiving,…
local 1TB
hard drive
(archiving)