the electron beam diagnostics," and some of the

The Los Alamos free -electron laser laser oscillator oscillator experiment: experiment: free-electron

status and present status plans and

Swann, A. Swann, T. A. Winston, T. G. Winston, J. G. Stein, J. E. Stein, Eraser, W. E. S. Fraser, J. S. R. W. R. W. Warren, Warren, J. A. Lumpkin, Lumpkin, R. R. L. L. Sheffield, Sheffield, J. J. E. E. Sollid, Sollid, B. B. E. E. Newnam, Newnam, C. C. A. A. Brau, Brau, and and J. J. M. M. Watson Watson A. Los Alamos National Laboratory Los AT -7, MS MS H825, H825, Los Los Alamos, Alamos, New New Mexico AT-7,

87545

Abstract experiment amplifier experiment free-electron ALamos free Los Alamos the Los modify the to modify Plans Plans have have been been made to -electron laser laser amplifier required, were required, microns. Several 10.6 microns. at 10.6 oscillator at an oscillator as an its use as allow its to allow to Several major major changes were as are discussed as is discussed these changes for these completed. The been completed. all of which which have have now been The necessity necessity for changes is all of we where we point where the point the details of In some some cases cases we we have progressed to the have progressed fulfillment. In their fulfillment. of their described. is described. status is systems. The present status new systems. the new of the the performance of report on can can report on the Introduction 1982, and in 1982, The Los Alamos free -electron laser laser (FEL) (FEL) amplifier amplifier experiment experiment was was completed completed in and free-electron results. optical 2 results. the optical2 and the its were published beam 1 and electron beam' parts: the two parts: in two published in findings were its findings the electron experimental predictions. The experimental theoretical predictions. with theoretical agreement with excellent agreement in excellent These results are in These results be techniques techniques and and equipment equipment designed designed to to produce produce these these results results were were found, found, in in general, general, to to be purpose. flexible and and well well suited suited to their purpose. flexible techniques are The The next next step step will will be be an an experiment experiment in in which which the the same same apparatus apparatus and and techniques are used used amplifier our amplifier with our performed with be performed not be could not step could it. This amplify it. to This step light, not amplify generate light, to generate the in the resulted in changes resulted it. These changes to it. equipment until equipment until several several major major changes changes had had been made to following:

-5 5 66 -1 1 2 2 3 3 44

current beam current electron beam achievement of a higher peak electron achievement longer current pulse provision for for aa longer provision of an optical cavity construction of provision provision for for radiation protection construction of additional wigglers provision provision for for more more extensive diagnostics

to made to and, in made and, been made now been in most most cases, cases, measurements measurements have have been been made have now changes have These These changes equipment. new equipment. the new of the performance of the performance and the techniques and of the new techniques judge judge the the success success of experioscillator experithe oscillator for the It It is is the the purpose purpose of of this this paper paper to to present present our our current current plans plans for have we have equipment we new equipment the new performance of possible, the wherever possible, ment and the performance of the describe, wherever to describe, and to ment of areas of six areas the six a discussion of the occupied with is occupied installed. The major major part part of of this this paper paper is with a experiamplifier experithe amplifier in the techniques used in the techniques cases the In many above. In presented above. major change presented many cases major for discuspapers 1 ' 2 for earlier papers';2 refer you to the earlier We refer ment will be used without modification. sysbuncher sysdetail the buncher in more techniques. Three of these techniques. sions of sions Three companion companion papers papers present present in more detail our which our on which work 5 on theoretical works the theoretical ** and electron beam tem, tem,33 the the electron beam diagnostics, diagnostics," and some some of of the this of this parameters of important parameters most important the most many of the presents many 1 presents Table 1 based. Table understandings are based. understandings experiment. Equipment modifications

Higher Higher electron electron beam current it and it was 11 AA and gun was electron gun the electron from the drawn from experiment, the peak current drawn the amplifier In the In amplifier experiment, the wiggler. With and wiggler. accelerator and the accelerator into the introduced into ^5 AA before to 1,5 bunched to was bunched was before being being introduced With the ^1% energy) 1,1% beam energy) in beam current (1% spread in this current at this energy) at wiggler (7% taper in in energy) tapered tapered wiggler be cannot be Clearly, aa reliable, oscillation cannot growing oscillation reliable, rapidly achieved. optical was achieved. optical gain was rapidly growing gain. low gain. such aa low developed with such that aa 11-A so that system so bunching system the bunching improved the we improved experiment, we For the oscillator experiment, For -A gun gun current current the gun from the accomplish this, To 100-A gives aa 100 -A wiggler wiggler current. To accomplish this, the the current current pulse pulse emitted emitted from gun subsystemofoftwotwo usinga asystem widthusing ps width 30 ps to aa 30 bunched to then bunched for 55 ns and then is is collected collected for 108108-MHz -MHz sub in presents in Fraser 3 presents of Erasers paper of The paper buncher. The fundamental buncher. 1.3-GHz one 1.3 and one bunchers and harmonic bunchers harmonic -GHz fundamental performance. system performance. and system detail the design considerations and Longcurrent macropulse macropulse Long-current

micropulses few micropulses of aa few consisted of beam macropulse consisted experiment, the electron beam In the amplifier experiment, the amplifier interacted (FWHM). This wide (FWHM). ns wide spaced by spaced by 0.7 0.7 ns ns and and enclosed enclosed by an envelope 33 ns This macropulse interacted energy single-pass the single produced the and produced length, 55 ns, same length, the same about the of about pulse of laser pulse with a laser with ns, and -pass energy 130 130

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1. Table 1.

Design Parameters

Optical 10% ym ±± 10% 10.6 pm

Wavelength in cavity Optical power in Pulse length Rayleigh length Mirror Mirror reflectivities Input Input mirror mirror Output mirror Mirror separation separation of Precision of control of separation mirror separation

1,1 GW ^1 GW

30 ps

0.4 to 0.6 0.6 m 99.5% 99.5-90.0% 99.5-90.0$ 6.923 m 6.923

±1 um ym

Electron Beam 21 MeV ±± 5% 5% 21 ±0.5% 2i\ 2n mm'mrad mmmrad 100 100 A 30 ps 46.15 ns 2000

Energy Energy Energy spread Emittance Peak Peak current Micropulse Micropulse length Micropulse separation Micropulse/macropulse Micropulse /macropulse

Spread 40-A at 40 Performance at Wiggler Performance -A Current Current and and No Energy Spread taper 12% taper Standard 12% Small signal gain power Saturated power Time to saturation

15% 1,1 GW GW ^1 ys 70 ps

No taper Small signal gain Saturated Power Time to saturation

100%

^0.25 GW %0.25 ys 25 ps

For the oscillator experiment, the gain 2 that we measured. optical gain2 and optical extraction extraction'1 and optical signal signal must must be be given given aa chance chance to to grow grow by by means means of of repeated repeated passes passes through through the the wigwigoptical to needed to are needed thousand passes Some micropulse. beam micropulse. Some thousand passes are electron beam an electron of an the company of in the gler gler in satiswhich satisexperiment, which our experiment, of our structure of time structure level. The time noise level. the noise reach saturation saturation from the reach the loading of requirements and reduces power fies fies this this requirement requirement and and at at the the same same time time reduces power requirements and loading of the 1. Figure 1. in Figure shown in is shown bunchers, is accelerator accelerator and bunchers,

s. 10 s. to 10 from 11 to in from is performed 1, aa complete Figure 1, of Figure top of the top As complete experiment experiment is performed in As shown at the Next, each macro macro^100 ys. occupying 1,100 macropulse occupying of a macropulse us. consists of experiment consists each each experiment optical an optical of an round-trip the round ns, the ^50 ns, by %50 spaced by micropulses, spaced 2000 micropulses, of 2000 pulse -trip time time of consists of pulse consists V30 ps is 1,30 ps wide wide and and 100 A high. micropulse is each micropulse Finally, each resonator. Finally, in our signal signal in our resonator. Then,

It It is is no no trivial trivial matter matter to to develop develop aa macropulse macropulse of of uniformly uniformly shaped shaped and and uniformly uniformly spaced spaced the in the and in gun and driving the gun electronics driving are found mainly in in the electronics found mainly problems are The problems micropulses. The gun's the gun's with the achieved with success achieved The accelerators. and accelerators. bunchers and the bunchers driving the systems driving rf rf systems The success micropulse, typical micropulse, shape of aa typical electronics are demonstrated demonstrated in in Figure Figure 2, 2, which which shows shows the the shape electronics are illustration, this illustration, For this gun. For the gun. from the emitted from as emitted macropulse as shows aa macropulse 3, which shows and in Figure and Figure 3, micropulse to variations from micropulse the variations the macropulse 200 micropulses only 200 only micropulses are are shown shown in in the macropulse so so that that the to and aa cent and amplitude variation an amplitude measured an have measured seen. We micropulse can be seen. We have variation of of aa few few per per cent micropulse ns. fieldofof1 1-2 accelerator's rfrf field the accelerator's to the relative to error relative maximum timing error -2 ns. their perto their into the introduced into is introduced When the the macropulse macropulse is the bunchers, bunchers, aa major major perturbation perturbation to perWhen the produced by the field, produced rf field, the gross shows the 4 shows noted. Figure formance is noted. formance Figure 4 gross perturbation perturbation in in the the rf cavities the cavities like the much like bunchers act buncher. The subharmonic buncher. first subharmonic the first electron electron beam beam in the The bunchers act much extract and extract down and slow down that slow fields that beam, fields the beam, by the in aa klystron in klystron where where large fields are excited by to detect fields, using undesired fields, these undesired control these electrons. We control energy from the electrons. using probes probes to detect their their signal being presence and feedback feedback systems systems to to adjust adjust the the phase phase and and amplitude amplitude of of the the rf rf signal being fed fed presence and kept be kept can be fields can buncher fields measures, the buncher these control measures, to the bunchers. By correct use of these of beginning of the beginning ys) at interval (10 short interval for aa short except for amplitude except and amplitude in phase (10 ps) at the constant in constant phase and of The cost of achieved. The be achieved. can be that can control that of control degree of Figure 5 the degree shows the 5 shows the macropulse. Figure is fields is undesired fields the undesired control the to control needed to power needed rf power however. The high, however. these measures measures is The rf is high, these For example, large. very large. be very can be and can current and beam current the beam proportional to proportional to the the square square of of the 131


-l-IOs- -.-4--1-10s

lOOu ss ————>• IOOp,

'I997 ^1997

--1998 ^1998

^1999 -*1999

*2000 4 2000

.4---50ns 50 ns

100amp lOOamp

30 ps p

Figure 1. 1.

pulses, Time dependence of current pulses. Time

in aa Figure 3. 3. Two hundred micropulses One division repreOne division macropulse. sents 11 us ys horizontally and 11 A vertically.

from current from Figure 2. 2. Single Single micropulse micropulse of of current Figure ns One division represents represents 22 ns gun. One vertically. horizontally and 11 AA vertically.

132


A

B

A

Figure 4. 4. The The rf rf field in subharmonic buncher. The electron beam beam is The electron is introintroduced duced at at AA and and ends ends at at B. One division represents 20 ps lis horizontally and is uncalibrated uncalibrated verzontally and is vertically.

B

Figure 5. 5. The rf field field with feedback feedback control control on. Same sensitivities as as in in on. Figure 4. 4.

^1 titkWkWisis needed needed to to excite excite an an empty empty buncher buncher cavity cavity to to the the fields fields needed needed for for bunching. bunching. A 1-A-Agun 1 guncurrent current induces induces undesirable undesirable fields fields that that require require another another 1 kW kW to to cancel. cancel. AA 22-A -A curcurrent excitation plus 44 kW rent needs needs 11 kW kW for for the the desired desired excitation kW for for cancellation, cancellation r etc. etc. Being limited limited to 5 kW to 5 kW by by our our rf rf supply, supply, we cannot successfully bunch bunch gun gun currents currents of of more more than than 22 A. A. The accelerators accelerators have the same kind kind of of beam beam-loading The have the -loading problem problem as as the the bunchers, bunchers, but but the the problem is eased considerably considerably by problem is by two two factors: factors: the the phase phase of the the induced induced fields fields differ differ by by 90° and handle for 90° and are are therefore therefore easier easier to handle for accelerators accelerators compared compared to to bunchers; bunchers; and, and, the the rf rf field field or, or, equivalently, equivalently, the the energy energy density is is much higher higher in in accelerators accelerators compared compared to to that that in bunchers. Therefore, if the the same same energy were delivered to Therefore, if were delivered to an an accelerator accelerator and and a buncher buncher by the electron electron beam, beam, the the percentage percentage loading loading of the by the the accelerator accelerator would would be be much much less, less, thus thus easier to handle. easier AA final final concern concern introduced introduced by by the the long long macropulse macropulse is is its its rf rf energy energy and and power power requirerequireThe oscillator experiment experiment needs needs somewhat somewhat more more peak peak power power and and several several thousand thousand times times more average average rf rf power power then then the the previous more previous amplifier amplifier experiment. experiment. We revised our our rf rf system system We revised accordingly. Most difficult difficult was the provision provision of Most was the of an an rf rf klystron klystron able able to to handle handle this this increased power other requirements increased power and and the the other requirements of the the pulse pulse scenario. scenario. We We settled settled on on using using two two klystrons klystrons and and split split the the accelerator accelerator into into two two sections, sections, each each to to be be supplied supplied by by a a single single klystron. This arrangement arrangement has has the the advantage advantage that that the the separate separate phase This phase and and amplitude amplitude concontrols trols needed needed for the the two two sections sections afford afford useful useful flexibility flexibility (as (as with with the the subharmonic bunchers) to accommodate space and other other problems bunchers) to accommodate space charge charge and problems that that may may be be encountered encountered in in the the beam -transport system. beam-transport ments.

Optical cavity

The optical optical cavity cavity is is adjusted adjusted in in length length so so that The -trip time that the the round round-trip time for for an optical optical pulse is ',50 ^50 ns, pulse is ns, that that is, is, the the 60th 60th subharmonic subharmonic of of the the accelerator accelerator frequency frequency and and the the frefrequency at at which which gun pulses quency pulses are are emitted. emitted. The cavity cavity mirrors mirrors are The are composed composed of of multilayer multilayer coatings on ZnSe coatings on ZnSe substrates substrates so so that that the the mirror mirror on on one one end end essentially essentially is is completely reflective at 10 microns, that on on the reflective at 10 microns, whereas whereas that the other other end can be be selected selected to to have have from from 0.5 0.5 to 5% 5% transmission. transmission. The to The mirrors mirrors can can be be tilted tilted remotely remotely with with piezoelectric piezoelectric actuators actuators and and separation adjusted adjusted with with aa computer their separation -controlled dc computer-controlled dc motor. motor. The The computer computer is is interfaced interfaced interferometer, mounted mounted on on the the mirrors mirrors so with aa HeNe interferometer, so that that the the mirror mirror spacing spacing can can be be held held constant face of of ambient ambient temperature temperature variations constant in in the the face variations or or moved moved in in aa flexible manner to flexible manner to satisfy our our other other requirements. requirements. The mirrors satisfy mirrors are are mounted mounted external external to to the the wiggler's wiggler's vacuum vacuum system, thus thus two two BrewsterBrewster-mounted system, mounted NaCl NaCl vacuum vacuum windows windows are are aa part of the the optical optical cavity. cavity. Careful alignment is essential essential so so that that the Careful alignment of of the the cavity cavity is the mode mode that that begins begins to to oscillate oscillate is centered on the wiggler and is centered and electron electron beam beam axes. axes. This is is accomplished accomplished with with an an auxiliary auxiliary 133


HeNe laser laser that injected into HeNe that is is injected into the the cavity cavity through through one one of of the the mirrors mirrors and and exits exits from the other end. end. The and substrates substrates used allow a a considerable considerable transmission transmission at at 0.633 0.633 nm The coatings coatings and used allow and still still provide provide sufficient sufficient reflectivity reflectivity to and to partially partially trap trap the the HeNe HeNe radiation within the radiation within the cavity. The consequence of this trapping, trapping, that that is, is, multiple reflections from the the mirrors, mirrors, The consequence of this multiple reflections can can be seen seen in in the the beam beam leaving leaving the the cavity. cavity. When the injected injected beam beam lies lies on on the the cavity's cavity's When the optical is circiroptical axis, axis, the the multiple multiple reflections reflections are are superimposed superimposed so so that that the the exiting exiting beam beam is and bright. bright. When cular and the injected injected beam is is even even slightly slightly off off-axis, When the -axis, the the exiting exiting beam beam is is out and and weak. weak. spread out Once the HeNe Once the HeNe beam beam is is aligned aligned with with the the optical optical axis, axis, it it is is next next used used to to test test the the wiggler wiggler alignment by alignment by illuminating illuminating two two cross cross hairs hairs mounted mounted at at opposite opposite ends ends of of the the wiggler wiggler and and exactly on on its its magnetic magnetic axis. axis. Images Images of hairs appear appear in of the the cross cross hairs in the the "bright "bright spot" spot" menmenabove. When When each each cross cross hair hair is tioned above. is centered centered in in the the bright bright spot, spot, the the optical optical axis axis and and axis are are superimposed. superimposed. wiggler axis Finally, the the same same HeNe HeNe beam beam is is used used to to align align the the electron electron beam beam by by allowing Finally, allowing both both beams beams to strike strike one three fluorescent fluorescent screens to one of of three screens that that are are mounted mounted in in the the wiggler wiggler and and can can be be inserted into into the the beams. beams. Both Both an an electron electron beam inserted laser spot spot are are seen seen on beam spot spot and and aa laser on the the screens. When these these spots spots are superimposed superimposed on on all all three three screens screens by by adjusting adjusting the the beam's beam's steering, all all three axes are superimposed. superimposed. steering,

Adjustment of length initially initially will Adjustment of the the cavity cavity length will be be guided guided by by monitoring monitoring the pulsed pulsed sponspontaneous from the the electrons. electrons. If is correct, pulses produced produced taneous emission from If the the length length is correct, the optical pulses by by all all of of the the electron electron micropulses micropulses in in aa macropulse macropulse and and their their echoes echoes from from the the mirrors mirrors will will be superimposed in in a special special way. way. For of the the 1st be superimposed 1st micropulse micropulse will will For example, example, the the 30th 30th echo echo of fall exactly on top top of of the the 29th 29th echo echo of of the the 2nd 2nd micropulse, micropulse, the the28th 28thecho echoofofthe fall the3rd 3rdmicro microThe pulses observed observed will, pulse, etc. be a will, therefore, therefore, be a combination The pulses combination of of many many individual individual pulses. An An incorrect incorrect cavity length will cause the the individual cavity length will cause individual pulses pulses to to be be spaced spaced apart, apart, producing producing an an exponentially exponentially enveloped enveloped group group whose whose shape shape indicates indicates the the sense sense and and amount amount of of error length. error in the length. Provisions various kinds kinds within within the the Provisions have have been been made made to to attach attach apertures apertures and and filters filters of of various cavity mirrors. Apertures will will be be used used to to control control the the transverse transverse mode mode content content of of the the beam, beam, whereas whereas sharp sharp cutoff cutoff filters filters will will be be used used to to modify modify the the growth growth of of sidebands of the sidebands of the main main oscillating oscillations or or other other similar similar effects. effects. oscillating frequency due to synchrotron oscillations Radiation Radiation problems The major major facilities facilities change change required required for for the the oscillator oscillator experiment experiment was was aa transfer transfer of of The all new underground underground vault. vault. This This move was required required because because of of the the roughly roughly all equipment equipment to to a new 10,000-fold neu10,000 -foldincrease increaseininaverage averagecurrent currentand and the the concomitant concomitant increase increase in in xx rays rays and and neutrons. The and the the use use of concrete shield shield blocks blocks at at strastraThe underground underground nature nature of of the the vault vault and tegic levels outside outside the the vault vault negligible. negligible. Within, Within, however, however, the the tegic positions positions make make radiation levels radiation is much too high for occupancy when beam beam current current is is on. on. In radiation level level is In addition, addition, there is concern is concern over over the the effects effects of the radiation radiation on on optical optical detectors detectors and and other other sensitive sensitive comcomponents. Most these effects effects can be reduced reduced by local local shielding, shielding, but but radiation radiation damage to to Most of of these the the many many fluorescent fluorescent screens screens by direct electron electron bombardment bombardment cannot cannot be be avoided. avoided. We plan to to replace conventional phosphors thin, high high-purity replace our our conventional phosphors with with thin, -purity quartz quartz wafers wafers and and to to view view the the Cerenkov radiation from from these these targets. Quartz has high energy radiatargets. Quartz high resistance resistance to to highhigh-energy radiaCerenkov radiation tion, this approach approach has has the the additional additional advantage advantage that that Cerenkov Cerenkov radiation radiation is is emitted emitted tion, and and this no delay. delay. Thus, radiation observed with no Thus, the the time time structure structure of of the the radiation observed can can be be used to used directly directly to infer the of the electron beam. infer the time time structure of beam. Wiggler designs

As discussed discussed above, our major major tasks tasks is is to to provide provide an electron electron beam beam current As above, one one of of our current of of 100 that our our standard standard tapered tapered wiggler oscillate strongly strongly and and achieve achieve saturated saturated 100 AA so so that wiggler will will oscillate 100 -us macropulse. An untapered wiggler, on the other hand, should power during aa 100-ys untapered wiggler, accomplish this this at a current of 10 10 A. A. To be safe, safe, we plan to to begin begin our our experiment experiment with an an untapered wiggler. After laser oscillations it, we shall insert After laser oscillations are are seen seen with with it, we shall insert wigglers wigglers of of progressively more extreme tapers progressively more extreme tapers until until oscillation oscillation cannot cannot be be achieved. achieved. Accordingly, Accordingly, we have built second untapered untapered wiggler technique for for "wedging" "wedging" either either have built aa second wiggler and and have have developed developed aa technique of our wigglers wigglers so so as as to to increase increase or or decrease decrease its its effective effective taper. taper. Wedging of our involves Wedging involves placing a series series of of spacers spacers of of varying varying thickness thickness between between the the half half-wiggler placing a -wiggler containing containing the the "top" magnets and and the the half half-wiggler "top" -wiggler containing the the "bottom" "bottom" magnets. magnets. In In this this way the the field field strengths reduced gradually down the the wiggler's wiggler's axis. axis. Using aa 11-mm-maximum strengths can can be be reduced -mm- maximum spacer, we can can alter alter the the effective effective taper taper by by 66%, thus we will achieve achieve effective effective tapers tapers in in wavewavewe %, thus we will length of 12, and 18% with only two two different basic basic wigglers. wigglers. length of 0, 0, 6, 6, 12, To provide provide aa more more fundamental To fundamental variation in in wiggler design, design, we we shall shall make make aa minor minor change change in the the wiggler wiggler cartridges cartridges so so that that they they can in can be be inserted inserted backward backward in in the the beamline. beamline. The wiggler then will will operate operate in the phasephase-displacement wiggler then in Ref. Ref. 6. in the displacement manner manner described described in 6. Our 134 134


as same as the same nearly the is nearly configuration is reversed configuration such aa reversed of such gain of the gain that the show that calculations 7 show calculations less is less builds up is field builds optical field the optical as the frequency chirp that frequency but that one f but direct one, the direct that of the chirp as that of the in the interest in main interest Our main suppressed. Our substantially suppressed. be substantially may be sidebands may growth of sidebands the growth and and the control. sideband control. and sideband is chirp and reversed configuration is taper has yet its taper although its third wiggler, Finally, we Finally, we are are in in the the process process of of building building aa third wiggler, although gain signal gain small signal between small compromise between better compromise find a better to find defined. Our Our major major goals goals are are to to be defined. performnow performWe are now growth. We sideband growth. eliminate sideband to eliminate and to reduce chirp and and and saturated saturated power power to to reduce followsmoothly followvary smoothly that vary tapers that with tapers of wigglers with ing ing computer computer simulations simulations of the behavior of are end. We are the end. at the tapered at strongly tapered to strongly beginning to ing some ing some power power law law from from untapered untapered at the beginning tapers. exotic tapers. more exotic of more also examining the behavior of Augmented Augmented diagnostics beam-diagnostic electron beam main electron the main experiment, the In -diagnostic apparatus apparatus consisted consisted of of aa amplifier experiment, the amplifier In the vidicon spectrometer to disperse disperse the the beam, beam, aa fluorescent fluorescent screen screen target target for for the the beam, beam, and and aa vidicon spectrometer to that we except that experiment, except this experiment, in this approach in same approach the same use the screen. We use TV camera viewing the screen. times during now use now use aa means means for for separating separating the the images images produced produced on on the the screen screen at at different different times during TV the TV "on" the gating "on" by gating ways: by different ways: two different in two this in accomplish this We accomplish 100-ys the the 100 -as macropulse. macropulse. micropulse single micropulse by aa single produced by image produced the image camera for such such aa short only the sees only it sees that it time that short time camera for perpendicuand and by by deflecting deflecting the the electron electron beam beam after after it it leaves leaves the the wiggler wiggler in in aa direction direction perpendicurepresents aa screen represents the screen on the produced on image produced The image spectrometer. The the spectrometer. by the produced by that produced lar lar to to that techtwo techmacropulse. The The two 3-D 3 -Dplot plotofofelectron electron current current versus versus beam beam energy energy and and time time in in aa macropulse. paper. 1* companion paper." in aa companion further in discussed further are discussed advantages are their relative advantages and their niques niques and amplifier the amplifier in the employed in that employed than that extensive than more extensive The optical optical diagnostic system is much more is much The instruments: following instruments: It includes the following experiment. It A liquid-helium-cooled, (1) 10 -um radiation. liquid- helium -cooled, mercury-doped-germanium mercury- doped -germanium detector for 10-ym (1) electhe elecemission from the spontaneous emission measure spontaneous enough to measure sensitive enough is sensitive This This detector detector is this use this will use We will ^200 ps. is, 1,200 that is, fast, that very fast, is very response is its response tron beam beam and and its We tron in particular initial setup instrument to to assist assist in in the the initial setup of of the the oscillator oscillator cavity, cavity, in particular instrument above. discussed above. as discussed mirrors as the mirrors of the separation of to to determine the correct separation be detectors can where detectors stations where many stations have many The first can be will have first will The Two spectrometers. spectrometers. Two (2) (2) macropulse. the macropulse. during the placed to -up of of fields fields at at chosen wavelengths during build-up the build view the to view difat difrates at growth rates relative growth monitor relative to monitor Multiple Multiple detectors detectors can can be be placed placed so so as as to time. versus time. growth versus sideband growth and sideband chirp and reveal chirp to reveal example, to for example, ferent ferent wavelengths, wavelengths, for "on" for The second second spectrometer will use use aa Pockels Pockels cell cell and and can can be be gated gated "on" for aa single single spectrometer will The provide is aa multielement Its micropulse. Its detector detector is multielement pyroelectric pyroelectric device device that that will will provide aa measurement measurement of of the the optical optical signal's signal's wavelength wavelength content content at at the the chosen chosen time time during during time and spectrometer systems the spectrometer of the systems produce produce both both time and wavelength wavelength the the macropulse. Both of both use both to use plan to information. We plan redundant information. give redundant should give thus, should and, thus, information and, information reproducibility of systems because because of of concern concern over over the the reproducibility of successive successive macropulses macropulses and and systems wavelength the the desirability desirability of of acquiring acquiring complete complete information information concerning concerning time time and and wavelength macropulse. behavior behavior on on a single macropulse. devices, apparatus. These devices, far-field and far Near(3) (3) Near- and -field pattern pattern and and focusability focusability measuring measuring apparatus. detectors, auxiliary detectors, and auxiliary infrared-imaging an infrared -imaging vidicon vidicon camera camera and and various various pinholes and from the the optical of the optical beam extracted extracted from the will be used to measure the spatial pattern of the infer the measurements we these measurements dependence. From time dependence. its time and its laser laser cavity cavity and From these we can infer its of its motion of longitudinal motion or longitudinal transverse or any transverse detect any and detect beam and mode content content of of the beam mode macropulse to macropulse measured from macropulse to kind will be measured this kind focal point. of this point. Motions Motions of and during aa macropulse. that show that above show (3) above in (3) If the Wavefront-measuring (4) (4) Wavefrontmeasuring devices. If the measurements discussed in wavethe wave of the shape of the shape measure the will measure we will stable, we sufficiently stable, is sufficiently the the optical optical beam is Smartt using aa Smartt done using be done This focus. its focus. near its beam near optical beam the optical of the fronts of fronts This will will be reference both aa reference produces both manner, produces simple manner, in a simple interferometer,8 that, in device that, a device interferometer, 8 a waves these waves treated. The being treated. beam being the beam from the and sample wave from The interference between these vidicon. The infrared-imaging viewed bybyananinfrared be viewed will be that will pattern that fringe pattern produces aa fringe -imaging vidicon. is it is desirable, it Although desirable, fringes. Although these fringes. from these reconstructed from wavefronts can can be be reconstructed wavefronts distorting seriously distorting without seriously system without this system gate this to gate cell to Pockels cell use aa Pockels difficult to use difficult upon depends upon measurements depends Thus, the wavefrpnt measurements these wavefront of these success of the success wavefronts. Thus, the wavefronts. macropulse. A significant complete macropulse. during aa complete wavefronts during the wavefronts of the the the reproducibility of pattern. fringe pattern. the fringe destroy the or sideband growth may destroy frequency chirp or frequency Present Present status are parts are All All components components of of the the oscillator oscillator system system have have been been constructed constructed and and the the major major parts sub-emittance. The sub good emittance. The gun has ^5 AA with good to 1,5 up to currents up delivered currents has delivered assembled. The now assembled. MeV. Atten21 MeV. of 21 energy of beam energy achieved aa beam well. The accelerator has achieved harmonic bunchers work well. associsystems associcontrol systems feedback control five feedback the five of the adjustment of the adjustment tion presently tion presently is is centered centered on the systems optical systems and optical accelerator and other accelerator the other All of the accelerators. All and accelerators. the bunchers and ated ated with with the tested. to be tested. are ready to 135


Acknowledgment

Projects Agency and was carried Advanced Research Projects Defense Advanced This work was supported by the Defense Energy. of Energy. Department of States Department the United States the auspices of the out out under under the References

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