Johnstone C

Muratori Bruno

Smith Susan Louise

Tzenov Stephan Ivanov

English

ePubs: the open archive for STFC research publications

INJECTION AND EXTRACTION FOR THE EMMA NS-FFAGB.D. Muratori, S.L. Smith, S.I. Tzenov STFC Daresbury Laboratory and Cockcroft Institute, UKC. Johnstone Fermilab, Batavia, Illinois, USAAbstractEMMA (Electron Machine with Many Applications) isa prototype non-scaling FFAG to be hosted at DaresburyLaboratory. NS-FFAGs related to EMMA have an unprece-dented potential for medical accelerators for carbon andproton hadron therapy. It also represents a possible activeelement for an ADSR (Accelerator Driven Sub-critical re-actor). This paper will summarize the design of the extrac-tion and injection transfer lines of the NS-FFAG. In orderto operate EMMA, the ALICE (Accelerators and Lasers InCombined Experiments) machine shall be used as an injec-tor and the energy will range from 10 to 20 MeV. Becausethis would be the first non-scaling FFAG, it is importantthat as many of the bunch properties are studied as feasi-ble, both at injection and extraction. To do this, a complexinjection line was designed consisting of a dogleg to ex-tract the beam from ALICE, a matching section, a tomog-raphy section and some additional dipoles and quadrupolesto transport the beam to the entrance of EMMA. Further, anequivalent tomography module was placed in the extractionline together with several other diagnostic devices includ-ing the possibility of using a transverse deflecting cavity.INTRODUCTIONThe ALICE accelerator is used as an injector to theEMMA ring. The energy delivered by this injector can varyfrom a 10 to 20 MeV single bunch train with a bunch chargeof 16 to 32 pC at a rate of 1 to 20 Hz. ALICE is presentlydesigned to deliver bunches which are around 4 ps and 8.35MeV from the exit of the booster of its injector line. Theseare then accelerated to 10 or 20 MeV in the main ALICElinac after which they are sent to the EMMA injection line.The EMMA injection line ends with a 70◦ septum for in-jection into the EMMA ring itself followed by two kickersso as to direct the beam onto the correct, energy dependent,trajectory.After circulation in the EMMA ring, the electronbunches are extracted using what is almost a mirror imageof the injection set-up with two kickers followed by a 65◦extraction septum. The beam is then transported to a diag-nostic line whose purpose it is to analyse in as much detailas possible the effect the NS-FFAG has had on the bunch.The paper is divided according to injection and extrac-tion, going through each in some detail, but shall not men-tion the injection and extraction kickers and septa as theseare covered in [1, 2].INJECTIONThe entire EMMA layout is shown in Fig. 1 togetherwith all the diagnostics described below for both the injec-tion and extraction lines. The EMMA injection line con-OTR / YAGTransverse EMMA quadrupolesFaraday cupEMMAdeflectingcavity (TDC)SRS quadrupolesALICEquadrupolesALICEscreensFigure 1: EMMA layout.sists of a symmetric 30◦ dogleg whose first dipole extractsthe beam from the ALICE accelerator and second dipolecloses the dispersion with the help of three quadrupoles. Itis possible to make energy, energy spread and bunch lengthmeasurements using either the first dogleg extraction dipoleand the screen in the dogleg as shown, or with a similar setup, but going straight ahead and using the ALICE outwardarc dipole and subsequent screen. Bunch charge is mea-sured with the Faraday cup as shown in Fig. 1. After thedogleg, some quadrupoles are used to match the beam intoa tomography section. This tomography section consistsof three screens with 60 degrees of phase advance betweenthem to allow for projected transverse emittance measure-ments. Further, this tomography section has the dual pur-pose of keeping the beam small at an early stage because ofthe very stringent requirements, in terms of Twiss parame-ters and dispersion, of the EMMA machine. Subsequently,the beam enters into a dispersive section consisting of two30◦ dipoles and a septum, with six quadrupoles and twoscreens as shown in Fig. 1 (bending magnets not shown).At the first screen is also a vertical slit with which the mea-THPP006 Proceedings of EPAC08, Genoa, Italy03 Linear Colliders, Lepton Accelerators and New Acceleration Techniques3386A12 FFAG, Cyclotronssurement of energy and energy spread is done on the sec-ond screen. In the last leg of the dispersive section are alsosteerers, both vertical and horizontal and placed roughlyπ/2 phase advance apart in both planes, so as to be able toexactly centre the beam with the correct position and angle,at the entrance of the EMMA ring. The steerers also havethe additional purpose giving an offset to the bunch whenwe wish to do phase space painting. Phase space paintingconsists in the exploration of the entire acceptance of theEMMA ring which should be based on a normalised emit-tance of 3 mm rad as opposed to the ALICE probe beamwhich has a 3 mm mrad emittance. Phase space paintingin the vertical plane is done with the steerers whereas thehorizontal one is done with the kickers inside the EMMAring. Finally, in order to steer the beam appropriately beamposition monitors are located at the entrance of all dipolesthroughout the injection line.The modelling of the ALICE to EMMA injection linewas done with MAD8 and the results are summarized inFig. 2 for the entire line with details shown in Fig. 3 forthe tomography section and in Fig. 4 for the last dispersivestraight before the EMMA ring. Not all the quadrupolesand dipoles were new and it was possible to re-use SRSones where space was not restricted. Despite the fact thatthe requirements on the Twiss and dispersion parameterswere very stringent, those achieved were remarkably closeto those requested (to within < 0.1%) in the model. How-ever, because this is a new machine and there is a consider-able degree of uncertainty, a large contingency was allowedfor in the quadrupole strengths and these are therefore spec-ified at 8.5 T/m.0.0 2. 4. 6. 8. 10. 12. 14. 16.s (m)δ E/ p 0c = 0 .Table name = ALLalice2emma bm & stWindows NT 4.0 version 8.23dl 26/05/08  19.43.000.05.10.15.20.25.30.35.40.45.50.β(m) β x β yFigure 2: βx,y for the ALICE to EMMA injection line.EXTRACTIONThe extraction line from the EMMA ring consists ofan extraction septum with the dispersion closed by somequadrupoles and an additional dipole forming an irregu-lar dogleg set-up as shown in Fig. 1. This irregular dog-leg shall also be equipped with steerers operating in both0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6s (m)δ E/ p 0c = 0 .Table name = TOMOGRAPHYalice2emma bm & stWindows NT 4.0 version 8.23dl 26/05/08  19.43.000.40.50.60.70.80.91.01.11.21.3β(m) β xβ yFigure 3: βx,y for the tomography section of the ALICE toEMMA injection line.planes to aid with the extraction process. The extractionseptum bends 65◦ and the subsequent dipole used to closethe dispersion only by 10◦. This makes this line challeng-ing due to the difference between the two bend angles. Thisstill has to be investigated because the available settings sofar give a beam size which is slightly too big and thereforemore quadrupoles are likely to be required. As a result,only the following dispersion-free diagnostic straight shallbe considered in this present paper.As part of this irregular dogleg, there is a screen whosefunction it is to measure the energy, together with an ad-ditional screen in the following dispersion-free straight.In the straight following the dogleg are some matchingquadrupoles to match the beam either directly into a tomog-raphy section or into a transverse deflecting cavity. Thetomography section is identical to the one in the injectionline. The idea is to be able to make direct comparisons with0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0s (m)δ E/ p 0c = 0 .0 0 0 0 0Table name = INJalice2emma bm & stWindows version 8.51/14 30/05/08  18.16.330.00.51.01.52.02.53.03.54.04.55.05.5β(m) β x β yFigure 4: βx,y in the last dispersive section of the ALICEto EMMA injection line before entrance into the EMMAring.Proceedings of EPAC08, Genoa, Italy THPP00603 Linear Colliders, Lepton Accelerators and New Acceleration Techniques A12 FFAG, Cyclotrons3387the measurements made earlier (projected transverse emit-tance), thereby quantifying the exact effect the non-scalingFFAG has had on the bunch. Further measurements can bedone with the transverse deflecting cavity, such as bunchlength and projected transverse slice emittance to try to seethe profiles of the bunch as much as possible. After the to-mography section there is a spectrometer dipole as shown.This allows us to measure the energy and energy spread ofthe beam in the usual way. Further, if we streak the bunch,with the deflecting cavity, at the same time then we are ableto measure the slice energy spread of the beam as well. Be-tween the tomography section and the spectrometer dipole,there will also be an EO section to measure bunch lengthand longitudinal profiles via electro-optic techniques. Thematching for the later part of the extraction line is shownin Fig 5 where some reasonable initial assumptions weremade about the Twiss parameters and the transverse de-flecting cavity is not shown. In the first instance and de-0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0s (m)δ E/ p 0c = 0 .0 0 0 0 0Table name = F3emma2ext bm & stWindows version 8.51/14 08/06/08  09.07.040.05.10.15.20.25.30.35.40.45.50.β(m) β x β yFigure 5: βx,y for EMMA extraction line.pending on availability, a reduced version of the extractionline is also planned. This would be the same as that shownin Fig. 1 but reduced in length and without the tomographysection or the transverse deflecting cavity. This is why anEO section is also planned as this would give some of themeasurements planned with the deflecting cavity.An updated version of all the proposed measurements,diagnostics and their location and number for the EMMAcomplex, from [3], is shown in Table 1 below, where theabreviations for transverse deflecting cavity (TDC) and re-sistive wall monitor (RWM) have been used as well as themore standard ones.As a result of the phase space painting described ear-lier, it was found [4] that the beam decoheres and, insteadof having a well defined probe beam, one ends up with aring in the vertical or horizontal phase space. This makesextraction difficult and, as a result, it is proposed [5] to sim-ply extract a portion of the beam. Therefore, collimation isrequired in order to have a known and well-defined trans-verse phase space area that can be measured and looked at.Table 1: Diagnostics summary for the EMMA injection andextraction / diagnostic lines.Measurement Device NumberBeam position BPMs 2/plane/cell4 inj. & ext.Beam profile OTR / YAG 6 inj. & ext.1 in ringWire scanner 4 in ringBeam current RWMs / F. cup 1 inj. & ext.Transmission RWMs / F. cup 1 inj. & ext.Beam Loss BLM 4 in ringMomentum BPMs & 82 in ringRWMs 1 in ringEmittance OTR / YAG 3 inj. & ext.Slice emittance TDC & 1 at ext.OTR / YAG 3 at ext.Extracted momentum Spectrometer 1 at ext.Longitudinal Profile TDC & 1 at ext.OTR / YAG 3 at ext.Energy spread Spectrometer 1 at ext.Slice energy spread TDC & 1 at ext.Spectrometer 1 at ext.This could be achieved through a combined function OTR(or YAG) screen and collimator object so that the screencould be lowered when required and otherwise one wouldhave the jaws of the collimators. This is possible becausetomography is not required at the same time as painting andhence collimation.CONCLUSIONSA short description of the injection and extraction linesof the EMMA machine was given. Diagnostics for bothwere briefly described together with those of the EMMAring itself. Some work remains to be done on the extractionline but, otherwise, the components are specified.REFERENCES[1] B.D. Muratori, S.L. Smith and S.I. Tzenov (2008). ’Hamil-tonian approach to the dynamics of particles in non-scalingFFAG accelerators’. These proceedings.[2] B.D. Muratori, S.L. Smith and S.I. Tzenov (2008). ’Injectionand extraction orbits and Twiss parameters for the EMMAring’. These proceedings.[3] S.R. Koscielniak (2007). ’Diagnostic requirements for theEMMA machine’. Private communication.[4] S. Machida (2008). Private communication.[5] J.S. Berg (2008). Private communication.THPP006 Proceedings of EPAC08, Genoa, Italy03 Linear Colliders, Lepton Accelerators and New Acceleration Techniques3388A12 FFAG, Cyclotrons

Diagnostic requirements for the EMMA machine’. Private communication.

Hamiltonian approach to the dynamics of particles in non-scaling FFAG accelerators’. These proceedings.

Injection and extraction orbits and Twiss parameters for the EMMA ring’. These proceedings.

Private communication.

Injection and Extraction for the EMMA NS-FFAG

Injection and Extraction for the EMMA NS-FFAG

Abstract

Similar works

Full text

Available Versions

ePubs: the open archive for STFC research publications