The Next Linear Collider Test Accelerator (NLCTA) being built at SLAC will integrate the new technologies of X-band Accelerator structures and RF systems for the Next Linear Collider, demonstrate multibunch beam-loading energy compensation and suppression of higher-order deflecting modes, and measure the dark current generated b

A. D. Yeremian

R. H. Miller

The Next Linear Collider Test Accelerator (NLCTA) being built at SLAC will integrate the new technologies of X-band Accelerator structures and RF systems for the Next Linear Collider, demonstrate multibunch beam-loading energy compensation and suppression of higher-order deflecting modes, and measure the dark current generated by RF field emission in the accelerator. The current injector being constructed for phase 1 of the NLCTA tests is a simple injector consisting of a gun with a 150 ns long pulse and X-band bunching and accelerating system. While the injector will provide average currents comparable to what is needed for NLC it will not provide the bunch structure since every X-band RF bucket will be filled. The injector upgrade will produce a similar bunch train as planned for NLC mainly a train of bunches 1.4 ns apart with 3 nC in each bunch up to 50 to 60 MeV. The bunching system for the upgrade is more elaborate than the current injector and the plan is to produce a bunch train right at the gun. The difference between the NLCTA injector upgrade and the planned injector for NLC is that the NLCTA injector will not have polarized beam and the accelerator sections are X-band rather than S-band. If the authors are able to produce beams comparable to the NLC requirements with the X-band injector then it should be easier to do with the S-band

Yeremian, A. D.

Miller, R. H.

UNT Digital Library

SLAC-PUB-95-6980 August 1995 NEXT LINEAR COLLiDER TEST ACCELERATOR INJECTOR UPGRADE k D. Yeremian, R H. Miller Stanford Linear Accelerator Center, Stanford University, Stanford, CA 94039, USA Introduction: The Next Linear Collider Test Accelerator (NLCTA) being built at SLAC will integrate the new technologies of X-band Accelerator structures and RF systems for the Next Linear Collider, demonstrate multibunch beam-loading energy compensation and suppression of higher-order deflecting modes, and measure the dark current generated by RF field emission in the accelerator [I]. The current injector being constructed for phase 1 of the NLCTA tests is a simple injector consisting of a gun with a 150 ns long pulse and X-band bunching and accelerating system [2]. While the injector will provide average 4 currents comparable to what is needed for NLC it will not provide the bunch structure since every X-band RF bucket will be filled. The injector upgrade will produce a similar bunch train as planned for NLC mainly a train of bunches 1.4 ns apart with 3 nC in each bunch up to 50 to 60 MeV. The bunching system for the upgrade is more elaborate than the current injector and the plan is to produce a bunch train right at the gun. The difference between the NLCTA injector upgrade and the planned injector for NLC is tha t the NLCTA injector will not have polarized beam and the accelerator sections are X-band rather than S-band. If we are able to produce beams comparable to the NLC requirements with the X-band injector then it should be easier to do with the S-band. Work supported by Department of Energy contract DE-AC03-76SF00515 Gun Design. The NLCTA upgrade will have a thermionic gun which produces pulse trains of bunches 1.4 ns apart, 380 ps wide, and 4.8 nC in each bunch for 150 ns at 10 Hz repetition rate. The plan is to use a 714 MHZ resonant pulser with a bias to generate the desired bunch train format at the gun. The gun used for the upgrade will have a 35 mm gap between the anode and the cathode to achieve the required 12.6 A of current near the space charge limited flow at 150 KeV. The rms emittance at the gun is about 5 mm-mad, about a factor of 10 lower than after bunching. Bunching and Beam Transport System Figure 1 shows the schematic of the NLCTA injector upgrade. The bunching system consists oftwo 714 MHz subharmonic bunchers, a two cell S-band traveling wave buncher with p = 0.6 and 0.7, and the first few cells of the first X-band accelerator section. The S-band buncher requires about 5 MW of power to achieve the 6.7 and 9 MV/m gradients in each of the cells. The two X-band accelerating sections following are identical to and in fact are the same ones used for the first phase of the NLCTA injector. The same solenoid magnets but in slightly different configuration will be used for the upgrade as are being used for the current injector. PARMELA simulation show that at the end of the injector at 56 MeV, 63% of the charge from the gun is captured in 15" of X- band producing bunches with 3 nC in 3.6 ps at 56 MeV. The energy spread is t2% and the normalized rms emittance is 40mm-mrad. Figure 2 shows the beam parameters at the b Presented at the 17th International Free Electron Laser Conference and 2nd International end of the injector as simulated with PARMELA. Table 1 shows the simulation results as compared to the requirements for the  NLCTA injector upgrade. Conclusion The NLCTA injector upgrade will produce a bunch train similar to that required from the NLC injector. Producing this train in an X-band injector is more difficult than in the S- band and thus we have confidence that the S-band injector planned for NLC will also meet the requirements. Construction of the NLCTA injector upgrade will allow us to study some of the single bunch effects in the X-band accelerator sections that we would not be able to study with the simple injector planned for the first phase. References [l] NLC Test Accelerator Conceptual Design Report, SLAC Report-411, August 1993 [Z] A. D. Yeremian, R. H. Miller, J. W. Wan& proceeding ofLINAC 94 conf., Tsukuba Japan, 1994, p89 I 1 I Y ;  3Table,k.! :,; , l.. Electron Beam Requirements and Simulation Results for the NLCTA Injector Upgrade Parameter Total transmission gun to end of injector Capture in 15" X-band ("h) Charge in 15' X-band (nC) pbunch width F W H M  ("X-band) I* due to charge in 1 So X-band (A) + (In-rad) Requirement Simulation 80% - 63% - 2.5 3 10 5 1.8 2.1 <5 1 0 5  4 10-5 4 3 DISCLAIMER Portions of this document may be illegible in electronic image products. Images are produced from the best available original document. n B E z E h 4 td f B I- ? er i U. 0 NLCTA Injector Upgrade s-band Buncher p=O.7, 9 MV/m p = 0.6, 6.7 MVlm x-band Buncher Accelerator p = 0.6,0.7,1 E = 50 MVlm t 17 MVlm (beam loading for 3 A) x-band Buncher Accelerator p = 1 E = 50 MVIm -17 MVlm (beam loading for 3 A) Anode I 1 i I I Y Y Y L  44.8 76.8 cm cm 150 130 124 296 30.5 55f1 keV keV keV keV MeV MeV I I I I I I I  1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 I I I I 1 I l r l l I I I 1  I I I  0 100 200 300 400 cm At Gun q = 4.8 nc 2 ~ H M  = 380 PS Ip = 12.6 A IA =3.4 A 8.95 Bo2iAi At the end of the injector 63 % (3 nc) capture in 15" 57 % (2.7 nc) capture 10" 2 W H M  - 5"= 1.2 PS Ip =: 2.2 KA IA = 1.9 A (including only q in IO")  IA = 3.7 ncl1.4 ns = 2.7 A (including all q) E rMz= 4 x m-rad 1%5 % (-lnc in the tail > IO") 2 % (-O.lnc adjasent buckets) 22 % (-lnc lost) Fig 1 N Element 252 Run 200 48 I I 1 .  I 36 c 12 241 n .,-20 0 20 -0.8 0 0.8 h -500 15 -1 000 i -1 -500 0-20 0 20 0 40 80 120 160 p bunch Length ("X-band) Energy Spectrum a-95 8021A3 es = 56.170 MV z = 431.5 cm Fig. 2 DISCLAIMER This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsi- bility 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. Refer- ence herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement. recom- mendation, or favoring by the United States Government or any agency thereof. The Views and opinions of authors expressed herein do not necxssady state or reflect those of the United States Government or any agency thereof. 7 

NEXT LINEAR COLLIDER TEST ACCELERATOR INJECTOR UPGRADE

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