Development of a New Beam-Energy-Spread
Monitor Using Multi-Stripline Electrodes

Tsuyoshi Suwada (e-mail:tsuyoshi.suwada@kek.jp),
Masanori Satoh and Kazuro Furukawa,Accelerator Laboratory,
High Energy Accelerator Research Organization (KEK),
1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan

Tsuyoshi Suwada/KEKB Injector Linac

PAC2003, May 12-16 @ Portland,
U.S.A.

1KEKB Accelerator Complexe-e+Ee+=3.5GeV
Ee-=8GeV

e+e-

Tsuyoshi Suwada/KEKB Injector Linac

PAC2003, May 12-16 @ Portland,
U.S.A.

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Introduction
PurposeWell-controlled operation of the KEKB injector linac is strongly required• for keeping the injection rate as high as possible,• and for maintaining stable operation.

Beam Feedback Controls• Beam position feedback [LINAC2000, pp.633-635]• Beam energy feedback [ICALEPCS’99, pp.248-250]• Beam energy-spread feedback

Motivation• A nondestructive energy-spread monitor contributes toward further stable
operation/injection of the linac.
à We developed a new beam energy-spread monitor with multi-striplineelectrodes.

Tsuyoshi Suwada/KEKB Injector Linac

PAC2003, May 12-16 @ Portland,U.S.A.

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Beam Energy-Spread Monitor with Eight
Stripline-Type Electrodes• This work was strongly motivated bya pioneering work of R. H. Miller, et al.
[HEAC’83, pp.602-605].
à They showed that a stripline-type BPM
with four pickups could be utilized as anonintercepting emittance monitor.

• Also our previous work using similar
stripline-type BPMs [Jpn.J.App.Phys.
40 (2001), pp.890-897] demonstrated
that the higher-order (second- and thirdorder) moments of an electron beam weredirectly measured depending upon thetransverse beam sizes.

Tsuyoshi Suwada/KEKB Injector Linac

PAC2003, May 12-16 @ Portland,U.S.A.

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Multi-Stripline Energy-Spread Monitor:
Mechanical Design Parameters

Tsuyoshi Suwada/KEKB Injector Linac

PAC2003, May 12-16 @ Portland,U.S.A.

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Multipole Analysis of the Electromagnetic
Field Generated by a Charged Beam
• The image charge density distribution by a line
charge for a conducting round duct is formulated by,• Assuming the transverse r-distribution r(r) of a travelingcharged beam, the total image charge J is formulated by,• It is easily expanded by the power series,

Tsuyoshi Suwada/KEKB Injector Linac

PAC2003, May 12-16 @ Portland,
U.S.A.

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Multipole Analysis of 8-Electrode BESM
The multipole moments are defined by using the pickup voltages(Vi)• for the 1st-order (dipole) moments,• the skew angle (x-y coupling) of thebeam is formulated by• and the beam energy spread is also
formulated using the optics parameters
and transverse emittances by• and for the 2nd-order (quadrupole andskew) moments,

Tsuyoshi Suwada/KEKB Injector Linac

PAC2003, May 12-16 @ Portland,
U.S.A.

where g is the parameter due tothe gain imbalance and thegeometrical errors of the pickups.

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Beam Test at the 180-degree J-arc
section of the injector linac

Tsuyoshi Suwada/KEKB Injector Linac

PAC2003, May 12-16 @ Portland,U.S.A.

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Beam Test:Experiment and beam condition
1. Beam Conditions:•single bunch (KEKB) electron and high-current e-/e+ production
beam (bunch width=12ps, bunch charge=0.9 and 8nC, repetition
rate=25Hz)•beam energies (Eb=1.7GeV) at the linac J-arc.
2. Second-order moments (quadrupole and skew moments) were measured
by the BESM depending upon the rf phase of the booster klystronand the transverse beam positions.
3. Beam-size calibration was performed by a fluorescent screen monitor
with a high-resolution image processing system.
4. Data-acquisition system of the BESM comprises a signal-digitizing
system of a fast oscilloscope(LeCroy WavePro 950) with a sampling
rate of 8-GS/s (BW=1GHz) and a PC/Linux-based computer with aPentium IV microprocessor at 2.2GHz.

Tsuyoshi Suwada/KEKB Injector Linac

PAC2003, May 12-16 @ Portland,
U.S.A.

9Experimental Results:
Variations of the horizontal and verticalbeam-position dependence of Jquad
Horizontal
Vertical
X position

Position-corrected Jquad

Position-corrected Jquad

Jquad

Jquad

Tsuyoshi Suwada/KEKB Injector Linac

Y position

PAC2003, May 12-16 @ Portland,
U.S.A.

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Experimental Results:
Variations of Jquad and the energy spread dependingon the rf phase (0.9 and 8-nC e- beams)
Variations of Jquad
Energy Spread
Gaussian distribution

DE/E(%)

8-nC e-0.9-nC e-

8-nC e0.9-nC e-

SC data

0.264±0.004% 0.150±0.007%

Parabolic distribution
Tsuyoshi Suwada/KEKB Injector Linac

PAC2003, May 12-16 @ Portland,U.S.A.

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Experimental Results:
Time trend of the quadrupole moment and the rf
phase of the booster klystron

Jq~6hours

rf phase

Tsuyoshi Suwada/KEKB Injector Linac

PAC2003, May 12-16 @ Portland,
U.S.A.

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Conclusions•Result of the beam-size measurement by the BESM is•

consistent well with that obtained by the fluorescent screen monitor
system, and the 2nd-order moments need to be corrected with thetransverse beam positions.

•Beam energy spreads were••0.150±0.007% for the 0.9-nC electron beam,and 0.264±0.004% for the 8-nC e- beam, and the resolution is on theorder of 10-3 depending upon the beam charge and the rf phase.

•Good agreement between the rf phase of the booster klystron and the 2ndorder moment by the BESM for the variation of the time trend is a clear
demonstration of the principal function of the BESM, and it is an
important step towards the stable operation of the injector linac.

•We have a plan to investigate beam characteristics of two beam bunches inthe two-bunch injection scheme.

Tsuyoshi Suwada/KEKB Injector Linac

PAC2003, May 12-16 @ Portland,
U.S.A.

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Multipole Analysis of the Electromagnetic
Field Generated by a Charged Beam:

Wall current formula and its multipole expansion(cont’d)
The multipole moments are definedfor the 1st-order moment,

for the 2nd-order moment,

and for the xy coupling term,

Tsuyoshi Suwada/KEKB Injector Linac

PAC2003, May 12-16 @ Portland,
U.S.A.

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Multipole Analysis of the Electromagnetic
Field Generated by a Charged Beam:

Wall current formula and its multipole expansion(cont’d)Assuming a gaussian function for the transverse charge distribution, thetotal image charge is formulated by,

Tsuyoshi Suwada/KEKB Injector Linac

PAC2003, May 12-16 @ Portland,
U.S.A.

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Multi-Stripline Energy Spread Monitor:
Charge Simulation Method

Tsuyoshi Suwada/KEKB Injector Linac

PAC2003, May 12-16 @ Portland,
U.S.A.

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Multi-Stripline Energy Spread Monitor:
Jquad-Sensitivity Calculation

Tsuyoshi Suwada/KEKB Injector Linac

PAC2003, May 12-16 @ Portland,
U.S.A.

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Experimental Results:
phase=0deg (0.9-nC e- beam)Tsuyoshi Suwada/KEKB Injector Linac

PAC2003, May 12-16 @ Portland,
U.S.A.

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Experimental Results:
phase=+3deg (0.9-nC e- beam)Tsuyoshi Suwada/KEKB Injector Linac

PAC2003, May 12-16 @ Portland,
U.S.A.

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Experimental Results:
Beam-size measurement by the screen monitor
system depending on the rf phase (0.9-nC e- beam)Tsuyoshi Suwada/KEKB Injector Linac

PAC2003, May 12-16 @ Portland,
U.S.A.

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Experimental Results:
Variations of the skew angles depending upon the rf
phase (0.9 and 8-nC e- beams)
The obtained skew angles inaverage are• 21 and 20 mrad for the
0.9- and 8-nC e- beamover the measured
region of the rf phase.

Tsuyoshi Suwada/KEKB Injector Linac

PAC2003, May 12-16 @ Portland,U.S.A.

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Experimental Results:
Variations of Jquad and the rf phase resolution
depending on the rf phase(0.9 and 8-nC e- beams)
Variations of Jquad

Tsuyoshi Suwada/KEKB Injector Linacrf phase resolution

PAC2003, May 12-16 @ Portland,
U.S.A.

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Experimental Results:
Variations of the beam energy spread depending
upon the rf phase▲

The obtained beam energyspreads were• 0.150±0.007% for the 0.9nC e-,• and 0.264±0.004% for the8-nC e-/e+ production at therf phase of the energyspread minimum
The resolution of themeasurement is on the order of10-3 depending upon the beam
charge and the rf phase.

Tsuyoshi Suwada/KEKB Injector Linac

PAC2003, May 12-16 @ Portland,
U.S.A.

23

Conclusions•Result of the beam-size measurement by the BESM is consistent well with thatobtained by the fluorescent screen monitor system, where the 2nd-order moments
need to be corrected with the transverse beam positions.
•RF phase resolutions were•less than 1 deg. for the high-current primarly electron(8-nC) beam,and less than 1 deg. over the region of ±1 deg. apart from the rf phase at the energyspread minimum.

•Beam energy spreads were••0.150±0.007% for the 0.9-nC electron beam,and 0.264±0.004% for the 8-nC e- beam, and the resolution is on the order of 10-3
depending upon the beam charge and the rf phase.

•Skew angles of the electron beam were•

21 and 20 mrad in average over the measured region of the rf phase for the 0.9- and 8nC electron beam, respectively.

Tsuyoshi Suwada/KEKB Injector Linac

PAC2003, May 12-16 @ Portland,
U.S.A.

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