.2 MW KLYSTRON FOR ASYMMETRC STORAGE RNG B FACTORY W. R. Fowkes, G. Caryotakis, E. Doye, E. Jongewaard, C. Pearson, R. Phiips, J. Sackett, E. Wright Stanford Linear Acceerator Center, Stanford University, CA 94309 USA Fj p Fj & r p 4 and v z :,& 9.b H. Bohen, G. Huffman, S. Lenci, E. Lien, E. McCune and G. Miram Varian Associates, Pao Ato, CA 94304 USA E Abstract A cw kystron operating at 476 MHz has been deveoped jointy by SLAC and Varian Associates. The unique set of characteristics of this tube were strongy guided by requirements of the fast feedback necessary to prevent osciations of the storage ring beams caused by the detuned acceerating cavity. This requires a combination of bandwidth and short group deay within the kystron. The RF feedback stabiization scheme aso requires ampitude moduation making it necessary to operate the kystron about 0% beow saturation. Performance specifications and initia operating resuts are presented.. NTRODUCTON SLAC and Varian have joined efforts under a Cooperative Research and Deveopment Agreement (CRADA) to deveop and test a new UHF super power kystron as a prototype 476 MHz RF source for the Asymmetric Storage Ring B Factory under construction at SLAC. This kystron was originay designed to produce.6 MW CW saturated to be operated at 90 KV, 27 amperes. After the kystron deveopment was we underway, some of the requirements were reaxed as a resut of further study in the acceerator physics aspects of the machine. As a resut, the kystron wi be operated conservativey at 83.5 KV and woud deiver.2 MW if saturated. The kystron wi be operated 0% beow saturation and must be abe to respond to fast feedback *Work supported by Department of Energy contract DEAC0376SF0055 ~~~~~~~~~~ ip. correction in both ampitude and phase in acceerating cavity osciations induced storage ring beams. This feedback scheme requires the kystron to have very short group deay (d$/do) and wide bandwidth. When this deveopment effort began neither of these features were avaiabe off the shef in commercia tubes of simiar power and frequency such as those used at LEP and TRSTAN storage rings. A mutistage depressed coector, designed by Varian was very seriousy pursued because much of the efficiency that is given up running underdriven is recovered. The operating cost savings woud have been substantia but the manufacturing risks and additiona upfront costs were considered too great to continue aong the MSDC path. The "headroom" needed for ampitude moduation was reduced from 25% to 0%. The design parameters for this tube are isted in the tabe beow. DESGN PARAMETERS Operating Frequency (MHz) Output Power at Saturation (KW) Operating Point Beow Saturation (KW) Beam Votage (KV) Beam Current (A) Efficiency (%) Saturated Gain (db) db Bandwidth (MHz) Group Deay at k0.5 MHz (nanosec.) OF WS D O C U M M 0s ~L~~~ BS 476 200 00 83.5 24. >60 >43 f 3.O 00 Presented at the 6th EEE Partice Acceerator Conference (PAC 95) and nternationa Conference on High Energy Acceerators, Daas, TX, May 5, 995
. ELECTRCAL DESGN The Varian eectron gun design has a peak cathode oading of 0.3 N c m 2 and a maximum surface gradient of 50 KVcm. Computer simuation predicts a beam diameter of 4.5 cm with a 5.8% scaop in a 7 cm tunne diameter. The mechanica design was borrowed from the SLAC 5045 gun which aows adjustment of the radia and axia position of the cathode and focus eectrode with respect to the anode. The aignment must be preserved whie operating horizontay. t is primariy radiativey cooed to the anode housing. An interna copper web conducts heat from the region of the focus eectrode adjacent to the cathode out to the arge outside diameter where it is radiated away to the anode housing. 55 3 z..c d ( ( 50 a 00 45 40 2 00n 495 0 20 30 40 nput Power (W) 50 7949A2 Figure 3. Predicted Output Power versus Drive at 90 KV. MECHANCAL DESGN 2
DSCLAMER Portions of this document may be iegibe in eectronic image products. mages are produced from the best avaiabe origina document.
the tube is operating. Each cavity except the output cavity has its own diagnostic RF monitor oop. The noses of a cavities except the prepenutimate and the second harmonic were coated with TiN to hep suppress mutipactor. n addition the input cavity drive oop, the output couping oop and the vacuum side of the output window were aso coated for the same reason. The output couping oop and a cavities are water cooed to stabiize their operating temperature and hence frequency. A drift tubes are aso water cooed as protection against eectron beam interception. The imited bakeout station cearance required optimization of the coector design to minimize the tube ength. The interior is contoured to have neary constant fux for highest surface cooing efficiency. The arge inside diameter of the coector necessitated a departure from standard coector designs where there is an inner coector with mied cooing channes and an outer, separabe water jacket. This is to avoid excessivey high stresses in the coector wa due to the pressure of the cooing water. This construction technique aows optima design of the cooing channes and wa thickness for best cooing performance. n addition, onepiece construction aows the monitoring of beam deposition by measuring temperatures on the outer jacket. The coaxia output window has matching choke hubs in 50 ohm 6.25 " diameter coax ine. Air cooing of the inner conductor and window face is accompished by ducting air (approximatey 50 scfm dry air) through the T bar couper into the inner conductor and across the window through jets at the bottom of the inner conductor matching choke. The air exits to the atmosphere via hoes at the bottom of the outer conductor choke hub. The inner and outer conductors are water cooed on the vacuum side ony. The Tbar coax to WR200 waveguide transition was preferred over the doorknob type because of its good bandwidth and the configuration aows access to the inner conductor for bowing air and pacing window temperature monitoring thermocoupes. t aso aows compiant couping between the inner conductor and the Tbar to prevent excessive mechanica oading on the output window. A compiant membrane is aso designed into the vacuum side output coax center conductor. The support structure under the magnet frame has both heavy duty casters and jack screws so that the entire assemby incuding gun oi tank can be roed into pace in the fina operating position in the BFactory kystron housing. V. TEST RESULTS The kystron went into test in midfebruary and processed ceany up to 60 KV. At this point the 2.6 MW dc power suppy faied, putting an end to pubishing any test resuts in time for this conference. The measured RF output power the ower votages showed good agreement with simuation predictions where the efficiency is expected to be ow. As of this printing the kystron is awaiting the repair of the power suppy so that testing may continue. There is every indication that the kystron wi meet a of the performance predictions. V. ACKNOWLEDGMENTS The authors wish to thank the many members of both Varian and SLAC for their vauabe contributions to this deveopment and manufacturing effort. G. Hu, F. Friedander, L. ves, R. Vranas of Varian provided much of the computer simuation work on the gun, output window coector and RF interaction region. Many vauabe engineering contributions, advice and technica support were provided by severa departments and shops at SLAC. These efforts wi continue through the testing and instaation of this tube. V. REFERENCES [ E. L. Lien, "High Efficiency Kystron Ampifier", Pubication OF Eight nt Conf. on M/W and Optica Generation and Ampification, Sept. 970 [2] E. L. Lien, US Patent #3,8,065 May 4, 974 [3] W. R. Fowkes et a., "PEP Prototype Kystron", Proceedings of the 993 Partice Acceerator Conference, Wash. D. C. Vo. 2, p. 259 The magnet consists of tweve individua convection cooed cois that are airspaced with approximatey a 45% fi factor to aow access to the tube body for tuning. The magnet return path is formed by four symmetricay paced four inch diameter stee pipes that run the ength of the kystron between the gun end and coector end poepieces. The magnet return path aso serves to support and space the cois as we as to support the kystron in the horizonta position. Rais attached to the kystron body engage support shoes on each magnet coi support aowing transverse support and ongitudina freedom to aow differentia therma expansion between the kystron body and the magnet support structure. 3
DSCLAMER 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 empoyees, makes any warranty, express or impied, or assumes any ega iabiity or responsibiity for the accuracy, competeness, or usefuness of any information, apparatus, product, or process discosed, or represents that its use woud not infringe privatey owned rights. Reference herein to any specific commercia product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessariy constitute or impy its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessariy state or refect those of the United States Government or any agency thereof.