Proceedings of the 5th Annual Meeting of Particle Accelerator Society of Japanand the 33rd Linear Accelerator Meeting in Japan (August 6-8, 2008, Higashihiroshima, Japan)

TRANSVERSE BEAM TUNING AND INJECTION TO RCSAT J-PARC LINAC
H. Sako#, A. Ueno, T. Morishita, Japan Atomic Energy Agency (JAEA), Tokai, Japan
M. Ikegami, High Energy Accelerator Research Organization (KEK), Tsukuba, Japan
calculations are done by the Newton-Raphson methodwith a response matrix calculated from the XAL model[2].

AbstractSince December 2006, LINAC commissioning has
been performed. Transverse beam matching has been
carried out every time when a beam condition has beenchanged, which is essential to suppress beam loss in
LINAC. We show reproducibility of the tuning
procedure and show the resulting beam emittance.
LINAC beam injected to RCS reflects performance ofRCS beam at various modes. We have established amethod to determine field of quadrupole magnets in
L3BT injection region to set Twiss parameters anddispersions to designed values at the RCS injection point.
We have defined sets of quadrupole field, applied them,and observed that the designed Twiss parameters anddispersions have been actually achieved.

Matching Results
Comparison of beam profiles at beam current of 10mA
is shown in Fig. 1. It is clearly seen that the tail part isenhanced between SDTL and A0BT sections both inhorizontal and vertical profiles. The source of tailenhancement might be in beam acceleration at SDTLtanks.

INTRODUCTION
As shown in Refs. [1,2], there are seven matching
sections where wire scanners are installed; MEBT1,SDTL, A0BT, L3BT straight section, L3BT arc section,L3BT collimator section, and L3BT injection section.
Each section consists of 4 or more knob quadrupole
magnets (QM’s) each of which has an individual power
supply, and 4 wire scanners (WS’s) with an exception of
8 WS’s at the L3BT collimator section. Except for
MEBT1 and L3BT injection sections, the lattice isperiodic at each wire scanner, where matching condition
is to have an identical Twiss parameters (αx, αy, βx, βy) at
all wire scanners. MEBT1 and L3BT injection sections
have no periodic lattice. MEBT1 section is for beamtuning between RFQ and DTL1, and L3BT injectionsection is for beam tuning to the RCS injection point.

Fig. 1: Horizontal (top) and vertical (bottom) beamprofiles measured at SDTL (green), A0BT (blue), andL3BT (magenta) matching sections. Note that horizontal
coordinates are not corrected for beam energy.
Therefore an apparent larger width is seen for SDTL
(βγ~0.33) compared to A0BT and L3BT (βγ~0.65).

TRANSVERSE MATCHING IN LINAC
Matching Method
The matching procedure is described in detail in Ref.
[2]. Here only the outline is described. An initial QM
field is calculated with TRACE3D model. Except for
matching sections, field of QM’s is fixed. At eachmatching section, beam profiles are first measured withwire scanners. For a measured beam profile distribution,
we subtract baseline then fit the distribution with aGaussian. We define the beam width as a sigma of the fit.
Then, we fit the sigmas at 4 WS’s to the XAL model [3]with fit parameters of Twiss parameters and emittance(αx, αy, βx, βy, εx, εy) at an upstream position of thesection. Then, field of 4 QM’s are calculated so that (αx,αy, βx, βy) at 4 WS’s agree to each other. TheseFig. 2 shows normalized 1σ emittance of beamprofiles (πmmmrad) obtained by fit to beam widths ateach section at beam current of 5mA and 30mA, where
the beam width is defined as a sigma of a Gaussian fit toa profile distribution. Emittance at 30mA is larger thanthat at 5mA by about 50~60%. Both at 5mA and 30mA,emittance at SDTL section is larger than other sections
by about 50~70%. This might be due beam mismatch
between MEBT1 and SDTL sections. Emittance obtainedwith the standard deviation of the profile distribution has,on the other hand, no significant enhancement at SDTL,
but it is similar to the emittance at downstream sections.
Therefore the apparent emittance decrease from SDTL toA0BT with the Gaussian sigma may be due to dramatic___________________________________________#sako.hiroyuki@jaea.go.jp-491-

Proceedings of the 5th Annual Meeting of Particle Accelerator Society of Japanand the 33rd Linear Accelerator Meeting in Japan (August 6-8, 2008, Higashihiroshima, Japan)enhancement of the profile tails between SDTL andA0BT.
Blue and red lines in Fig. 2 show data at two timeseparated commissioning runs. The difference ofemittance at two runs reflects reproducibility of thetransverse matching procedure. It is seen the emittanceagrees very well at the two runs, which proves good
reproducibility of the matching procedure. The mismatch
factor, defined as M=(σmax-σmin)/(σmax+σmin) whereσmax and σ min are maximum and minimum standard
deviations of 4 WS’s, are compared also at two runs. At
both runs mismatch factors of less than 4% have beenachieved, which shows an excellent matching power ofthe present method.

This is done by constructing a response matrix with QM
field as input parameters and difference between Twiss
parameters of the model to goal Twiss parameters at thefoil position as output parameters. In case dispersion
matching is required, dispersion difference is also
included as output parameters. Then, by calculating a
pseudo-inverse matrix through SVD (Singular Value
Decomposition), and multiplying it with the difference
between current Twiss parameters (and dispersion) andtheir goal values, corrections to QM field are derived.
Ideally the whole procedure should be iterated until thegoal values are reproduced. Due to limited time for beam
experiments, however, iteration of this procedure has notbeen done.

Tuning Method for RCS Injection
We have calculated three sets of QM field. The
following 3 sets of parameters are defined;
1. “Matched” setting where (αx, αy, βx, βy) arematched with those of RCS circulating beam at
the foil.
2. “Dispersion matched” setting where Dx=0, andD’x=0 at the foil.
3. “Half-matched” setting” which is a default settingwith Twiss parameters and dispersions between“Matched” and “Dispersion matched” settings.
We applied them and measured beam profiles withWS’s and MWPM’s. The resulting envelopes fit tomeasured Gaussian sigma of profiles and dispersions
calculated with the model are shown in Fig. 3.

Fig. 2: Normalized one sigma emittance at 5mA (firstrow) and 30mA (second row) in horizontal (left) andvertical (right) directions. Mismatch factors at 5mA(third row) and 30mA (fourth row) in horizontal (left)
and vertical directions (right).

TUNING OF RCS INJECTION
Tuning Method for RCS Injection
There are 18 QM magnets after the L3BT collimator
section which can be used as knobs to set Twiss
parameters and dispersion at RCS injection point at thecharge exchange foil.
The procedure of tuning RCS Twiss parameters anddispersion is as follows. Beam profiles of L3BT
collimator sections, L3BT injection sections aremeasured with WS’s, and downstream profiles to theRCS injection point are measured with MWPM’s (MultiWire Profile Monitors). Sigmas of Gaussian fit to theseprofiles are fit to the XAL model by varying (αx, αy, βx,βy, εx, εy) at the beginning of L3BT with a similar
response matrix method as the matching procedure. Thenfixing the parameters, optimum QM fields are calculated.
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Proceedings of the 5th Annual Meeting of Particle Accelerator Society of Japanand the 33rd Linear Accelerator Meeting in Japan (August 6-8, 2008, Higashihiroshima, Japan)

Fig. 4: Top: Horizontal (left) and vertical (right) phase
ellipses of LINAC beam at the charge exchange foil at5mA and 30mA with “Half-matched” setting; compared
to RCS circulating beam. Bottom: Horizontal (left) andvertical (right) LINAC beam for “Matched”,“Dispersion-matched”, and “Half-matched” settings.

SUMMARY
In summary, we have developed a procedure fortransverse matching at LINAC matching sections withperiodic lattice from SDTL to L3BT collimator sections
with a response matrix calculated from a model. The
matching results are reproduced at two time separated
runs, and excellent mismatch factors less than 4% havebeen achieved. Measured emittance is larger at 30mA
than that at 5mA by about 50~60%. Apparent emittanceenhancement by about 50~70% compared to othersections has been observed with fit of profiles at eachsection. This effect may be due to uncertainties ofacceleration electric field or magnetic field in MEBT1,DTL, and SDTL, are going to be investigated in detailutilizing muli-particle simulations. We also tuned
LINAC beam injected to RCS, with varying quadrupole
magnets after L3BT collimator section. The method tocalculate quadrupole field setting for designed Twiss
parameters and dispersions at the injection point hasbeen developed, with a response matrix calculated with amodel, similarly to the transverse matching procedure.
We have applied 3 sets of Twiss parameters at theinjection point, and measured resulting beam profiles.
Expected Twiss parameters have been obtained from themeasurements. To study the optimum beam parameters
for RCS, data analysis of orbit and beam profiles in theRCS ring is planned.

Fig. 3: Envelopes (mm) in horizontal (red line) andvertical (blue line) directions fit to profile widths (points)
and dispersions (m) (black line) calculated by the modelat different sets of QM field; First row: 5mA Matched,second row: 5mA Dispersion-matched, third row: 5mA
Half-matched, fourth row: 30mA Half-matched. The RCS
injection point at the charge exchange foil corresponds tothe z position of about 190 m.
We have then calculated Twiss parameters at the foil andcompared phase ellipse with RCS as in Fig. 4 for “Halfmatched” settings at 5 and 30mA. At both current, very
similar ellipse has been obtained. Fig. 4 also shows
comparison of LINAC ellipse for all settings. Theemittance of the LINAC ellipse in the figure is with
5σ of the Gaussian fit of a beam profile, which is 1.6πmmmrad at 5mA and 2.0 πmmmrad at 30mA as
unnormalized emittance, which corresponds to thefraction of the about 85% of the total beam.

REFERENCES[1] M. Ikegami, et. al, “Transverse Tuning Scheme for
J-PARC LINAC”, PAC’05, Knoxville, USA, May
2005, FRE043.
[2] H. Sako, et. al, “Transverse Matching in J-PARC
LINAC Commissioning”, 4th Annual Meeting ofParticle Accelerator Society of Japan, Wako, Aug.
2007, TP61.
[3] J. Galambos, et al, “XAL Application Programming
Framework”, ICALEPCS 2003, Gyeongju, Korea.

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