THE NAL BOOSTER-TO-MAIN RING BEAM TRANSFER SYSTEM

A. W. Maschke and L. W. Oleksiuk National Ac ce l e rator Labo r a t ory

Batavia-, Illinois A~s tr ;. r- t

The process of transferring the 8 GeV proton beam from the rapid cycling booster synchrotron to the main accelerator at NAL is described in terms of overall system features and optical parameters. Recent tests of the transfer system, using a 1 GeV booster beam, have yielded successful beam extraction from the boost­er synchrotron of close to 100% efficiency, at low beam intensities (~1 ma). Injection into the main accelera­tor has been accomplished with indications of good transverse matching and good overall control system stability.

General Description The booster-to-main ring transfer process can be

decomposed into three natural divisions: (i) the boost­er extraction section, (ii) the beam transport and matching section, and (iii) the main ring inflection section.

These three subsystems together carry the booster beam approximately 240 meters (800 feet) horizontally and through a vertical rise and fall of about+ 1.5 ft to the end of the injection-extraction long straight section of the 500 GeV main synchrotron, where the 8 GeV beam arrives matched to the transverse phase space and momentum dispersion characteristics of the main synchrotron.

I Booster Extraction In order to fill the M.R. (main ring) circumfer­

ence, approximately twelve booster pulses will be re­quired. Each pulse must be extracted via a fast ex­traction process. Booster beam extraction is accom­plished using the vertical plane since the booster magnet geometries and a vertical beta maximum in the booster long straight sections have been combined to yield a more favorable design problem in this plane.

The booster beam is bumped by a fast rectangular SO ohm transmission-line kicker magnet 1 designed to rise between 25 ns - 30 ns. An empty RF bucket will be produced near injection to provide the necessary notch for this kicker. Four 1 meter kicker modules are situ­ated one cell upstream of the extraction straight sec­tion. With a vertical phase shift per cell of ~101° and a ✓8 1 8 2 = ~20 meters, the kicked beam receives about 20 mm/mrad kick. The vertical half gap of 32 mm in the booster D-magnets allows a 1 cm vertical diameter beam to nicely clear the D-magnet pole tips with a 20 mm de­flection, and enter the pulsed septum ejector. This ejector magnet deflects the beam vertically through 44 mrads, allowing it to clear the downstream booster mag­net. The design of this pulsed magnet 2 utilizes an eddy current shielding effect which allows the magnet to re­semble a one-turn thin septum magnet during the ejec­tion period (L 6 µsec) even though the D. C. character­istics of the module resemble those of a C-magnet, with its associated undesirable fringe field.

Measured fringe fields of ~3 gauss at extraction time on the booster side of the septum sandwich carry­ing currents of 18,000 amperes result in no significant beam losses during its 220 µs rise. In order to ease the ejector current regulation requirements, the down­stream vertical pitching magnet that flattens the ex­tracted booster beam was built as a one-turn magnet connected in series with the booster ejector. This fea­ture relaxes the current stability requirements to ±_ .1% for a 10% vertical emittance dilution.

A half-wavelength orbit bump magnet system will be utilized to allow vertical trimming of the booster equilibrium orbit in the extraction region . This trim­ming may be useful when high booster beam intensities (~200 ma) are reached via multiturn injection. Bumps of

the order of 0 .5 to 1.0 cm vertically in the extraction section will be required at injection since the extrac­tion septum may lie within beam occupied vertical aper­ture, at high current intensities.

.II Transport And Matching The beam transport system must provide a link be­

tween the two different accelerator lattice structures lying at either end of the transport section such that the beam enters the M.R. structure properly matched in the transverse planes, including the matching of the momentum dispersion functions. In order to provide some degree of tuning, the optical system has been designed in three sections: (i) a momentum recombining section that momentum recombines the booster beam, (ii) a dis­persion free section resembling an accelerator straight section to allow some beta function tuning without per­turbing the momentum match, and (iii) a momentum match­ing section to allow the beam to assume the required horizontal momentum dispersion required by the M.R. lattice.

A tabulation of the transverse optical parameters existing at bo.oster and M. R. ends of the transport sys­tem is given in Table A. Figure 1 shows the plot of (8x)l/2 & (8y)l/2 (ml/2) and the dispersion functions Xp, Yp (cm/%) along tJ-,e optical axis of the system. Some of the design constraints were as follows: (i) The Xp function at the booster extraction station was nega­tive with respect to the M.R. radial direction, neces­sitating a momentum ray crossover before recombination could be accomplished. (ii) Because of requirement (i) a horizontally highly diverging beam is produced near the first horizontal bend, necessitating a rather dense distribution of quadrupoles initially to keep the beam sizes within reasonable limits. (iii) Both momentum-ray crossovers were utilized in order to provide extra beta function tuning wi~hout perturbing the momentum match. (iv) The long dispersion-free second section must pro­vide a good phase space match in both transverse planes and simultaneously keep the maximum beta values within about 200 mas the optical elements are all derived ! from M.R. laminations. (v) The use of vertical extrac­tion and injection introduces dispersion in the verti­cal plane. This dispersion must be held to tolerable limits to check vertical betatron oscillations in the M.R. (vi) The entire quadrupole array was composed of M.R. 4-foot modules and was to be driven in series with tuning to be accomplished by means of a few small power supplies paralleling chosen tuning quadrupoles.

A tabulation of the pertinent optical parameters for the transport elements is given in Table B. Basic computer codes have been designed to generate useful tuning algorithms for the matching sectton.

III Main Ring Injection The injection of the transferred beam into the M.R.

acceptance is accomplished by a three stage injection process. After the beam has passed through the transport section it is traveling about 16 inches directly above the M. R. beam centerline. It then enters the first s tage of injection. Two vertical series- connected dipoles pitch it down and then flatten the descending beam to within 11. mrads of the horizontal.

989

A pu l sed one-turn s ep tum magne t s imilar in de s i gn to the booster extractor provides the second stage of injection. This module flattens the descending beam t o about 1 mrad u tilizing a hal f sine 2.1 kc 15, 000 amp peak pu lsed current drive t o pr ovide the eddy-current­shie l ded magnet i c f i eld . This s eptun lies en t i r ely out of the M.R. aperture and so provides extra disp lacement be t ween the M. R. beam and the septum since the M. R. beam

Summary will see some fringe fields on the descending portion of the current drive when the eddy current shieldi ng begins to diminish .

The final process of i nj ection is provide'd by t he ~. R. fast k i cker inflec t or, cons i stiG~ of t wo o~e- ~e te r long, rectangular 25 ohm transmission-line modules that provide about 0.7 mrads vertical deflection 1 for the beam insertion. These units have rise-time requirements of about ~80-100 ns, the beam time between batches in the M.R., since about 4-5 empty R.F. buckets can be provided.

Recent tests of t he boos ter-to- main ring tr ans fer sys tem using the 1 GeV booste r beAm have indicated that e xcellent extraction effici. e nc , · , . ~~ ,".u• h i Pved using lo~: intensi t y beams. Successful beam transport and main ring injection tests have been accomplished with indi­cations of good transverse matching and excellent over­all control system stability3. References

1. J. D. McCarthy, NAL, Private Communication 2. A. T. Visser and R. F. Nissen, These Proceedings 3. R. E. Daniels, NAL, Private Communication

TABLE A· BEAM OPTICS BOUNDARY CONDITIONS FOR THE BOOSTER-TO-MAIN RING TRANSFER SYSTEM cm/% m/% cm/%

REFERENCE POSITION f3x(m) Clx f3y(m) Cly Xp Xpl Yp

Entrance of Booster 7.59 .4901 20.45 .1499 -1.841 0 . 0 0.0 Innut Extraction Section

Center of M.R. Long 70 .26 -.7506 70.10 .747 2.85 .0337 o.o Output Straight (Station

AO) Typical Center of M.R. Long 60.1 -.7363 68.66 .1831 2.57 .0307 -.275 Calculated Straight (Station Match (AO)

TABLE B· 8 GEV TRA..~SPORT SECTION ELEMENT PARAMETERS ELEMENT TOTAL NO. NOMINAL FIELD PARAMETER TYPICAL CURRENT AMPS TOTAL POWER REQUIRED CURRENT

4 Ft MR Ouadrunoles 18 s ft Bl Dipoles 4

1 DC MR Inflectors 2

· 2.0

·2.0

.41 kg/cm 10 kg

4 kg 4.3 6.1 kg

8 GEV 800STER-MAIN RING TRANSFER MOMENTUM OISPEIISION

~ut-

8 GEV BOOSTER·MAIN RING TRANSFER ,: A- TRANSVERSE BEAM RADII

·-~ .. {"4) 2

! '~ ( ... ~\'2

,co ♦ F([T-20

20

f~(M)..,

l~"'>'• I 400 FEET-20 I

Figure

990

733 30 KW +.5% 790 80 KW ±.01 - .02% 330 4 KW +.OS% 600 35 KW +.1%

200 .be I I

AO

AO

""'

I ~/ 200 lOO

'

AO

AO

.25F"'!'O ,,..f'LECTION ll1C•( II'

' ' ,00 I,()()

I I

1.

mr/% Ypl

0.0

0 .0

.03

STABIL.