Allison, R.W.

Beal, J.W.

Everett, W.L.

Guggemos, J.R.

Lamb, W.A.S.

Richter, R.M.

Sherwood, W.A.

Spoerlein, R.L.

Tanabe, J.

Wright, R.E.

Zajec, E.

eScholarship - University of California

Lawrence Berkeley National LaboratoryRecent WorkTitleMEASUREMENT AND OPTIMIZATION OF THE EMITTANCE OF A 300-ns 250-A 3.4-MeV ELECTRON BEAMPermalinkhttps://escholarship.org/uc/item/68c5000sAuthorsAllison, R.W.Beal, J.W.Everett, W.L.et al.Publication Date1969-02-20eScholarship.org Powered by the California Digital LibraryUniversity of CaliforniaUCRL-18522 RECEIVED LAWRENCE RADIATION LABORAlOR.Y MAR 18 '\~69 LIBRARY AND DOCUMENTS:rvf.t~SWEMENT AND OPTIMIZATION OF THE EMITTANCE OF A 300-ns 250-A 3.4-MeV ELECTRON BEAM R. W. Allison, Jr., J. W. Beal, W. L. Everette, J. R. Guggelllos, W. A.' So Lalllb, R. Mo Richter, W. A. Sherwood, Ro L. Spoerlein, J. Tanabe, R. E. Wright, and Eo Zajec February 20, 1969 TWO-WEEK LOAN COpy This is a library Circulating Copy which may be borrowed for two ·weeks. For a personal retention copg', call Tech. Info. Diuisio". Ext. 5545 c::; (} LAWRENCE RADKATION 1LABORATOR~~ ~ \ I . .... UNIVER§KTY Df CALIFORNKA BERI{ELEy}f ~ N DISCLAIMER This document was prepared as an account of work sponsored by the United States Government. While this document is believed to contain COlTect information, neither the United States Government nor any agency thereof, nor the Regents of the University of California, nor any of their employees, makes any walTanty, express or implied, or assumes any legal responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by its trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof, or the Regents of the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof or the Regents of the University of California. \ \'( Presented at the National Particle Acc~lerator Conference, Washington, D. C., March 1969 UNIVERSITY OF CALIFORNIA Lawrence Radiation Laboratory Berkeley, California AEC Contract No. W -7405-eng-48 UCRL-18522. Prepdnt MEASUREM,ENT AND OPTIMIZATION OF THE EMITTANCE OF A 300-ns 250-A 3.4-MeV ELECTRON BEAM R. W. Allison, Jr., J. W. Beal, W. L. Ev~rette, J. R. Guggem.os, W. A. S. Lam.b, R.· M. Richter, W.A. Sherwood, R. L. Spoerlein, J: Tanabe, R. E. Wright, and E. Zajec February 20, 1969 () MEASUREMENT AND OPTIMIZATION OF THE EMITTANCE OF A 300-ns 250-A 3.4-MeV ELECTRON BEAM* R. W. Allison, Jr., J. W. Beal, W. L. _Everette, J. R. Guggemos, W. A. S. Lamb, R. M. Richter, W. A. Sherwood, R. L. Spoerlein, J. Tanabe, R. E. Wright, and E. Zajec Lawrence Radiation Laboratory University of California Berkeley, California The two-dimensional emittance of the 3.4-MeV 250-A beam produced by the Astron linear induction accelerator has been measured. The measurement utilized a slit plate and a glass slide. A densi-tometer scan of the slit pattern formed on the glass by irradiation was analyzed and emittance contours drawn. Substitution of a radiation-resistant Cr3+_ activated A1203 scintillator permitted observation of the slit pattern of each pulse by using tele-v~s~on. This equipment allowed the induction accelerator to be tuned for minimum emittance without excessive beam loss. Ninety percent of the beam was within a phase-plane area of 0.17 cm-radian. Data on the two-dimensional phase-space density are also presented. Introduction In order to obtain data for the design of the transport system used in the recent electron ring experiment at LRL,l the two-dimensional emittance of the beam produced by the Astron·linear in-duction accelerator2 has been measured. The measurement technique used a slit plate3 -and a glass slide. A densitometer scan of the pattern formed on the glass by irradiation was analyzed and emittance contours drawn. The current within each contour and the maximum density in the phase space has also been computed. A radiation-resistant A1203(cr3+) scintillator permitted observation of the slit pattern during each pulse by using television. This eqUipment allowed the induction accelerator to be tuned for minimum emittance without excessive beam transmission loss. Experimental Setup A sketch of the experimental equipment is shown in Fig. 1. A beam transport system with five solenoid focusing magnets was used to trans-port the beam from the linear induction accelerator, past the Astron experimental tank, to the diagnos-tic box. The total transport distance was 4.7 meters, and the acceptance of the beam line was 0.5 cm-radian. *Work done under auspices of the U. S. Atomic Energy Commission. Near the exit of the induction accelerator were located a beam toroid (BTl) and a set of magnetic induction position detectors (6Xl,6Yl). Downstream from these devices four steering coils (DM1, DM2) were located, inside solenoids S2 and S3, respectively. A water-cooled aluminum target (Tl) was located at the entrance of the beam diagnostic box. The diagnostic box contained a beam toroid (BT2), a slit plate with 10 slits, an aluminum oxide scintillator, and a glass slide holder. The slits, scintillator, and glass slide were mounted on motor-driven probes. The slide probe retracted into an air lock, which allowed removal of the glass slide after each irradiation. The diagnostic box had a view window through which the scintillator was viewed by using a Vidicon. The slit plate dimensions are sketched in Fig. lAo Each slit was 0.38 mm Wide, the slit separation was 6.25 mm. The slit plate was constructed of carbon and was 1.25 cm thick. The spacing between the slit and slide was 14.5 cm. A deep Faraday cup terminated the beam line. This cup had an aperture of 2.54 cm and was 47 cm deep. Experimental Procedure Before exposing each glass plate, the in-duction accelerator and transport system were tuned for minimum emittance at the desired current. This was done in the following way: (a) Tl was inserted in the beam and the induction accelerator tuned for optimum beam transmission and minimum position sweep at BTl and 6Xl, 6Yl • (b) Tl was then removed and the beam maximized on BT2 and the Faraday cup by tuning the beam transport system. (c) The emittance slits and scintillator were then inserted in the beam and the accelerator and transport system fine-tuned for minimum emittance by observing the slit pattern on each pulse. Typically the beam transmission from the accel-erator electron gun to BTl was 80%; at BT2, 70 to 75% was usually achieved. The exposure of the glass slide was made by inserting Tl, retracting the scintillator, and inserting the glass slide; Tl was then removed and seven pulses of beam were received by the slide. At the end of the exposure the slide was removed from the vacuum through the air Lock. Use of the technique described above,permitted ex-posure of each slide without shutdown of the accelerator, and thus ensured that the measurement took place while the output beam was stable. Measurements were made over a current range of 100 to 250 A at BT2. The beam energy was 3.4 MeV, the energy spread about ±1.5%. The beam pulse (with the exception of one measurement) was 300 ns. The accelerator was operated at a PRF of 2 pulses/so The accelerator core voltages were held constant at 28 kV. The gun cores were operated at 26 kV to ensure maximum stability. (This voltage limited the maximum current obtained.) A typical slit pattern is shown in Fig. 2. Data Reduction The pattern formed on each slide was scanned by use of a densitometer. The effective slit width in the scan direction was 18~, the slit height was 1.5 cm. Background from x rays and low-energy electrons was minimized by adjusting the densitometer zero. Two of the density scans are shown in Fig. 3a,b. At the ith slit the profile peak represents the phase-space density p(XiX') at Xl = O. The width of the ith profile represents the divergence of the beam-at Xi' If Po is the peak density (the maximum of the envelope about alL the profiles) then a line of constant relative density, Ej = p/po' is represented by a horizontal line. The divergence of the beam at the ith slit is computed from the intercept of this line with bhe ~th density profile: 8 = (Xr - Xi - ;)/L, lfhere L = separation of slit and slide, w = slit 'Tidth, Xi = slit location, and Xr = intercept location. (We have taken the edge of the first slit as the coordinate system zero.) The beam aurrent within an emittance contour was obtained ~rom Ic = It Ac/At J where At is the total area of the density profiles and Ac is the total pro-~ile area within the divergence intercepts. This area is shaded in Fig. 3a,b. The total current, It, was taken to be the current read on BT2. Divergences and currents within a constant density were computed for Ej = 0.1, 0.3, 0.5, 0.8, and 0.9. The emittance contours that correspond to the density profiles of Fig. 3a,b are shown in Fig. 4a,b. Each contour was formed by connecting adjacent (X,X·) pOints with straight lines. For convenience the coordinate system used in reducing the densitometer scans was transformed to a coordinate system in (X,X·) with a zero which was the center of gravity of Ej = 0.9. In all the data the emittance numbers are the actual phase-plane area in cm-radians, at 3.4 MeV. For comparison of different exposures we have plotted (Fig. 5) the current within each con-tour against the two-dimensional phase-space area within each contour. In addition, the maximum - 2 -density of the phase space was computed from Po = It/J(p/po)dxdxJ = ItiJ(p/po)dA, where the integral in the denominator was numerically evaluated from plots of €j vs the two-dimensional emittance A. The results of this computation are plotted in Fig. 6. An examination of Figs. 3 and 4 indicates that changes in beam divergence are readily de-termined. Low-energy electrons scattered from the slits apparently do not seriously affect the measurement. _We did not adjust the diver-gence for space-charge effects, since only 5 A total beam is transmitted by the slits, and this produces a negligible change in the beam diver-gence at 3.4 MeV. EXperimental Results An examination of Fig. 5 indicates that as the total beam current increases more current appears at larger emittances. This effect is especially apparent when the 200- and 250-A runs are compared. In addition the peak density in phase space (Fig. 6) rises to a maximum at 190 A and then flattens out at higher current. At 190 A 90% of the current is cent'ered wi thin a phase-plane area of 0.17 cm-radian, 50% of the current within an area of 0.037 cm-radian. At 250 A the areas are 0.215 and 0.049 cm-radian respectively. The maximum phase-space density at 190 A is 2990 A/cm-radian, at 250 A it is 2669 A/cm-radian. This saturation of the central core of the beam indicates that for this par-ticular electron gun a limit has been reached, and that any additional increase in output current results in an increase in the beam emittance. An emittance measurement of a 20-ns portion of the 300-ns beam pulse has been made and also plotted in Figs. 5 and 6. It is obvious that this short beam pulse has a higher phase-space density (po = 3860 A/cm-radian) than that of the 300-ns pulse. Thus it is possible that the limit reached in the long-pulse-beam phase-space density is due to some time-dependent parameter such as emission variation or beam sweeping due to accel-erator voltage variations. We have taken the 190-A measurement and, using an impulse approximation for space charge, obtained the location of the apparent 3.lI-MeV object produced by the induction accelerator. It is located 31 cm inside the last accelerating section, and has a beam width of 2.9 cm and a divergence of ±.038 radian. References 1. R. W. ALLison et al., UCRL-18498, 1 Oct. 1968, to be published in Proceedings of National Accelerator Conference, Moscow, USSR, Oct. 1968. D. Keefe et al., UCRL-18671., Dec. 1968. t, " i \ ' .. ' 2. J. W. Beal, The Astron Linear Accelerator, in Proceedings of the 1968 Linear Accelerator Conference, P713, 1968. 3. B. Vosicki, in Proceedings of the 1966 Linear Accelerator Conference, 344, 1966. Astron linac H. Wroe, Nucl. Instr. Methods 58, 213 (1968). I Valve & beam toroid L I 6X!.6Y!. BTl ; i--14.60cm Astron linear induction £J. accelerator V;a;con f-----464.82cm ----~.'----~ Fig. 1. Experimental setup, showing beam line and diagnostic equipment. Fig. Z. Photograph of irradiated slide (Figures " 3B and 4B are obtained from this slide). l.°r;--:----r----~r_---~--_____.~___,----__r----~-_,...._......., (a) .9 .8 Typical of method used to sum up all Ic in contour( Ej = 0.5) >- .7 Ej = 0.5 ~ .6 ~.5r------l---------------t~~~~~~~~~~--~~~---------------------~ g;.4 ~ .3 Q) a:: 6 cm 10~----~r------'r-~----,~-----.----r--~-~ (b) >- 0.9 Typical of method used +-' 0.8 to sum up all Ic in contour <fl c 0.7 (Ej =0.5) Q) -00.6 ~ Q5~-~--L~~----1~----~~~--~~----~~---~-----~-~ :,:; 0.4 ~ 0.3 ~0.2 Q1 0. 1 2 3 4 5 em Fig. 3. Density scan of (a) ZOO-A, (b) 190-A, 3. 4-MeV beam. - 3 -·30 +24 +18 +12 <fl C +6 ro "'0 0 ro '-I E -6 X -12 (a) ... 18 Ej.O,1{.14~km.rad) j=03(07rcm.rad) "'" 1 2 ·,,_o.5C050cm-rad j~OB(02, em-rad j.09COll em-rad -lBL-~~ __ ~ __ ~~~L-__ ~ __ ~ __ ~ __ ~ __ ~ -4.0 -3.2 -24 ~1.6 +1.6 +2.4 +3.2 Fig. 4. (a) ZOO-A, (b) 190-A emittance contours. .. -18 4000r----------r--~------r_-~------_, l b\ -24 -30 -;32 -24 -1.6 -.80 0 +.BO +1.6 +24 +3.2 ,-.. 3000 "'0 ro x<cm) '-E u ....... <fl 2000 c.> '-c.> 0-E ::5 c:r 1000 Fig. 6. Plot of the maxirrlUm phase space density Po as a function of the beam current, It. 100 I ..... -~hort Pulse po I 200 It (amperes) 2S0r_---,-----,----,-----~--_,----_,----_r----,_----r_--_,----_r----,_----r_--_,----~ ,.......240 (/) 0... E 200 ro '-' -+--' C 160 ~ "-"-::l U 120 "-::l B so c o U 40 Ie Vs Ac 20 n sec 1.100 amps· o 0!-----0.:-::-2----. ."-0-,4----. ..l0-,6----.-:l0c:S=-----.1LO-----.1L2-----. .L14-----.-L16------1.1S----. ..l2-0---l2L2---. 2L4---. .L2-6--. .L2-S-~. 30 Area (contour) eM -Radians Fig. 5. Ic (current within a contour) as a function of the two-dimensional phase-space area. -4-300 ~) iJ • LEGAL NOTICE This report was prepared as an account,of Government sponsored work. Neither the United States, nor the Commission, nor any person acting on behalf of the Commission: A. Makes any warranty or representation, expressed or implied, with respect to the accuracy, completeness, or usefulness of the informa-tion contained in this report, or that the use of any information, apparatus,method, or process disclosed in this report may not in-fringe privately owned rights; or B. Assumes any liabilities with respect to the use of, or for damages resulting from the use of any information, apparatus, method, or process disclosed in this report. As used in the above, "person acting on behalf of the Commission" includes any employee or contractor of the Commission, or employee of such contractor, to the extent that such employee or contractor of the Commission, or employee of such contractor prepares, disseminates, or pro-vides access to, any information pursuant to his employment or contract with the Commission, or his employment with such contractor. '~, ~, ..oAJ~,~" TECHNICAL INFORMA TION DIVISION LAWRENCE RADIA TION LABORATORY UNIVERSITY OF CALIFORNIA BERKELEY, CALIFORNIA 94720 ... !<;,7~ !9~~ 

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MEASUREMENT AND OPTIMIZATION OF THE EMITTANCE OF A 300-ns 250-A 3.4-MeV ELECTRON BEAM

https://escholarship.org/uc/item/68c5000s

MEASUREMENT AND OPTIMIZATION OF THE EMITTANCE OF A 300-ns 250-A 3.4-MeV ELECTRON BEAM

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