M-257

HIGH-POWER SWITCHING BY MPULTI-GRID IGNITRONS

BY T. F. Turner

and H. S. Butler

Internal Memorandum M Report No. 257

March 1961

PROJECT M STANFORD UNIVERSITY STANFORD, CALIFORNIA

HIGH-PWER SWITCHING BY

MULTI-GRID IGNITRONS

T. F. Turner

and

H. S. But ler

In t e rna l Memorandum M Report No. 257

March 1961

Project M Stanford University Stanford, Cal i fornia

SUMMARY

This report describes an investigation which had as its major pur-

pose the development of a high-power switch for use in the modulators

for the proposed Stanford two-mile linear electron accelerator. It has

been found that existing ignitron tubes can be used to switch current

pulses of thousands of amperes and several microseconds duration at

repetition frequencies of hundreds per second while holding off voltages

of tens of kilovolts. The performance of a typical switch is described

in detail with regard to:

(2) maximum peak current capability, (3) maximum peak power capability,

(4) average power capability, (3) pulse-time jitter and anode delay, and

(6) effective deionization time.

(1) maximum reliable hold-off voltage,

Several additional experimental observations are reported here

which provide some insight into the pulsed operation of the ignitron

and which were used as guideposts in the design of an ignitron specifi-

cally for high-power switching purposes.

A complete schematic for an 87 Mw, 110 kw modulator is also included.

TABLE OF C(lNTEXPS Page

I. Introduction . . . . . . . . . . . . . . . . . . . . . . . 1

11. Description of ignitrons . . . . . . . . . . . . . . . . . 2

111. Typical switch performance . . . . . . . . . . . . . . . . 9

1. Maximum reliable hold-off voltage . . . . . . . . . . 9

10 2. Maximum peak current capability . . . . . . . . . . . 11 3. Maximum peak power capability . . . . . . . . . . . . 11 4. Average power capability . . . . . . . . . . . . . . . 11 5. Pulse-time jitter and anode delay . . . . . . . . . . 11 6. Effective deionization time . . . . . . . . . . . . .

IV. Discussion of pulsed ignitron operation . . . . . . . . . 13

1. Hold-off period . . . . . . . . . . . . . . . . . . . 13

2. Post-pulse period . . . . . . . . . . . . . . . . . . 15

3. Pulseperiod.. 20 . . . . . . . . . . . . . . . . . . . V. Conclusions . . . . . . . . . . . . . . . . . . . . . . . 25

List of references . . . . . . . . . . . . . . . . . . . . . . 29

1.

2.

3.

4.

5.

6.

7.

8a.

8b.

9.

10.

11.

12

LIST OF FIGURES Page

Internal structure of type 5630 ignitron . . . . . . . . . . 3

Internal structure of type 6228 ignitron I . . a a a . e . . 4

Internal structure of type 25233 ignitron . . . . . . 5

Internal structure of type 25234 ignitron . . . . . . . . 6

Typical ignitor voltage and current characteristics . . . . 8

Typical pulse service voltage distribution (solid line) compared to recommended rectifier service voltage distribution (dashed line) for tube type GL-6228 . . . . . . 14

Shield grid voltage as a function of time for three values ofpeakcurrent . . . . . . . . . + . . . . . . . . . . . . 17

Deionization time in the cathode-shield grid region vs peak arc current for two cooling-water temperatures . . . 18

Deionization time in the control grid region vs peak arc current for two cooling-water temperatures . . . . . . . . 19

Effect of cooling-water temperature on deionization time . 21

Deionization time at the control grid vs peak current for two pulse repetition rates . . . . . . . e . . . 22

Circuit diagram for 87 M w , 110 kw modulator e . . . . . . 26

Ignitor voltage (bottom curve) and holding anode current for GL-6228 operated in circuit of Fig. 11 . . . . . . 27

Ignitron assembly--experimental design #1 . . . . a 28

- iv -

I. INTRODUCTION

Since the Spring of 1959 an e f f o r t has been made t o f ind a device

t o serve as the high-power switch f o r use i n the modulators f o r t h e pro-

posed Stanford two-mile l i n e a r e lectron accelerator . ' switch had t o make possible t h e development of modulators having t h e

following pr inc ipa l specif icat ions:

Brief ly , t h e

Peak power output (max)

Average power output (max)

64 MW

74 kw

Output pulse voltage range 158-248 kv

Output pulse current range 120-258 amps

Load impedance range 1320-962 ohms

Pulse length ( f l a t - top ) 2.50 psec

Rise and f a l l times (m O-lOO$) 0.7 psec

Pulse r epe t i t i on rate 60, 120.. .360/sec

Pulse height deviation from f l a tnes s (max) +_ 0.5%

Pulse t i m e j i t t e r (max) 5 10 apsec

Pulse-to-pulse amplitude j i t t e r (max) f 0.25%

In addition, t h e modulator had t o be the design t h a t would be most

economical when maintenance and operating costs over a ten-year period

were taken in to account.

The first pa r t of t he switch invest igat ion led t o the conclusion

t h a t the spark-gap devices and hydrogen thyratrons then i n existence or

under development were not capable of meeting a l l of t h e switch require-

ments. We therefore undertook, more o r less as a last hope, an invest i -

gation of t he performance of igni t rons as high-power switches.

1. All references appear a t the end of t h e t ex t .

- 1 -

11. DESCRIFTION OF IGNITRONS

For the most part, the ignitron tubes tested at Stanford have been

of the multi-grid sealed-off design,

several descriptions of ignitron^,^'^ a brief review of the tube struc- ture and processing is given here for convenience. Figures 1 through 4

illustrate the internal structure of several specific designs.

Although the literature contains

The conventional ignitron consists of a sealed envelope containing

a mercury-pool cathode, one or more ignitors, an anode, and one or more

grids used for various purposes.

external integral water jacket which allows reasonably close but not

complete control of the internal mercury-vapor temperature and pressure.

(It is known that under operating conditions the mercury-vapor pressure

is somewhat higher than that associated with the water in the external

jacket.)

cases e

An important part of the tube is its

Auxiliary anodes near the mercury pool may be included in some

The tubes discussed in this paper are processed much like high-

vacuum tubes during manufacture, i.eo, all but the glass seal is baked

at a temperature of approximately TOO C for a period of about eight

hours. While baking, the tqbes are pumped with high-quality mercury

diffusion pumps.

fied mercury is admitted and the tube is sealed off.

0

After evacuation a metered amount of specially puri-

Typical ignitors are made of a refractory material. The material

used varies from manufacturer to manufacturer, as does the processing of

the material during manufacture. In general, the materials are mixed,

extruded to cylindrical shape, and fired to a high temperature in a

disposable graphite crucible under pressure, The completed ignitor rod

- 2 -

W A T

FIG. I INTERNAL STRUCTURE OF TYPE 5630 IGNITRON

- 3 -

ANODE 1

GRADIENT GRID - CONTROL GRID 1

SHIELD G R I D 1

I

3! I . D. 20 CM.-

WATER JACKET 1

BAFFLE-

FIG, 2 INTERNAL STRUCTURE OF TYPE 6228 IGNITRON

5 CM. I CM. I CM.

1 CM. SPAC E"A"

SPACE SPACE SPACE

- 4 -

GRADIENT GRID

WATER JACKET

I 3 I

1 I CM. I CM. ICM.

16 CM.

I! FIG.3 INTERNAL STRUCTURE

OF TYPE 25233 IGNITRON

- 5 -

ANODE

GRADIENT G R I D

C O N T R O L GRID

SHIELD GRID

1.D.30 CM.

B A F F L E

WATER J A C K ET

!

FIG. 4 INTERNAL STRUCTURE OF TYPE 25234 IGNITRON

I I CM. I I CM. I I CM.

- 6 -

is pointed by grinding and is mounted on a molybdenum or Kovar rod in

as s embly

While the exact mechanism of cathode formation by ignitor firing

is not known to the authors at this time, several observations can be

made which may be helpful in tube application.

First, the ignitor appears as a nonlinear circuit element. This

behavior is illustrated by the typical voltage and current curves shown

in Fig. 50 In addition, it is an experimental fact that the ignitor

appears to de or a very slowly changing voltage as though it were a low

resistance (of the order of 5 0 - l O O ohms) which itself is a slowly vary-

Ing function of the applied dc voltage.

4 A photographic examination of ignitor operation by Cummings has

shown that the spot of cathode activity surrounding the ignitor propa-

gates rapidly out over the surface of the cathode pool after breakdown.

The velocity of propagation inferred by Cmings is about 2 x 10

2 x 10 cm/sec.

must be regarded as approximate.)

2 microseconds after application of the ignitor pulse before the applica-

tion of the grid pulse, there is reasonable assurance that the main pulse

current discharge will come from the central region of the cathode pool

and not from the ignitor stub itself, thus prolonging the life of the

ignitor

.5 to 6 (This value is dependent on total cathode current and

Therefore, by waiting a period of

- 7 -

I

Lo

2

200

150

100

50

0

psec

400

300

200

100

0 2 4 6 8 io

psec

FIG. 5--Typical i gn i to r voltage and current characteristics.

- 8 -

111. TYPICAL SWITCH PERFORMANCE

I To date, only two types of gridded ignitrons have been extensively

For our pur- tested in this laboratory, namely, the GL-6228 and 25233.

poses, the GL-6228 performs more satisfactorily than the 25233.

presently in progress on the type 25234 have not shown any advantages

over the GL-6228 for our work,

be confined to the performance of the GI,-6228.

Tests

The following discussion will therefore

The GL-6228 has been tested in various circuit configurations to

allow independent measurement of the following parameters:

1. Maximum reliable hold-off voltage

2 0 Maximum peak current capability

3. Maximum peak power capability

4. Average power capability

5.

6. Effective deionization time

Pulse-time jitter and anode delay

These tests will be described in order and the results of each will be

given below

1 a Maximum Reliable Hold-Of f Voltage

The reliable hold-off voltage is a function of the water jacket

temperature, the method of biasing the tube, and the average power

dissipation. For the purposes of this paper, maximum hold-off voltage

is defined as the highest anode voltage that can be applied for a period

of 30 minutes without tube malfunction.

results of this test for the GL-6228 with optimum bias.

The following table gives the

- 9 -

Average Power Outlet Water Temp. vIIELX

- < 10 kw 30 < t < 45OC 60 kv

60 kVn 0 25 kw t = 4 5 * 1 c

55 kw t = 40°C 50 kv

75 kw t = 36Oc 45 kv

110 kw t = 36Oc 45 kv

*The data on l i n e two were obtained inde- 6 pendently by Craggs and Meek a t prf = 750 cps.

i s t h e network 'n Here, average power = 1/2 C p r f , where

t o t a l capacity,

pulse r epe t i t i on frequency.

Vmax i s t h e maximum hold-off voltage, and prf i s the

These measurements were made a t various

r epe t i t i on frequencies a t o r below 360 pps.

2. Maximum Peak Current C a D a b i 1 i t - v

Tests t o determine an absolute peak current capabi l i ty i n modulator

service serve very l i t t l e purpose. However, an attempt w a s made t o f ind

a reasonable upper l i m i t by connecting the tube under tes t i n a Blumlein

c i r c u i t and running a t optimum bias and optimum w a t e r temperature a t a

prf of 120 cps.

conditions, we observed s t ab le operation as follows:

A t our f u l l power-supply capabi l i ty , under the above

Pulse length = 3.7 microseconds

Peak current = 8600 amperes

Peak power = 144 Mw

Average power = 64 kw

= 33.6 kv

- 10 -

These tests and much of t he information gleaned from various appli-

cat ions of igni t rons i n crowbar service7 indicate tha t there i s v i r t u a l l y

no l i m i t t o cathode emission capabi l i ty i n igni t rons of t h i s type.

3. Maximum Peak Power Capability

To date, 144 Mw i s t h e maximum peak power switched with the GL-6228.

A s noted i n t h e discussion of peak current capabi l i ty , t h i s value w a s

l i m i t e d by t h e r a t ing of our power supply and should not be taken as an

upper l i m i t on t h e performance capabi l i ty of t he igni t ron as a switch.

4. Average Power Capabili ty

W e have successfully operated the tube f o r a period of 48 hours a t

110 kw average. Testing a t high average power l eve l s w i l l continue as

soon as p rac t i ca l circumstances make it possible; we have been ab le t o

operate f o r short periods of time (15-20 minutes) a t average powers of'

150 kw. The l imi t ing f ac to r i n high average power t e s t i n g has thus far

been the auxi l ia ry apparatus and not t he switch tube.

5. Pulse Time J i t ter and Anode Delay

Under optimum bias conditions, as discussed below, and a t an average

powep of 64 kw, t h e pulse-time j i t t e r has been shown t o be less than

4.0 millimicroseconds.

sophis t icated c i r c u i t problem when these power l eve l s are involved

(because of cross- ta lk , e tc . ).

measurement techniques t o t h e point where it i s possible t o present more

accurate information. Anode delay seem t o be of t h e order of one-half

Measurement of j i t t e r t o high accuracy i s a

Time has not permitted us t o r e f ine our

microsecond and s table .

6. Effect ive Deionization Time

We are primarily in te res ted

which t h e tube can be operated,

i n t h e maximum repe t i t i on frequency at

r a the r than the deionization t i m e a s such.

- 11 -

Because various regions of t h e mercury-vapor space within t h e tube take

r ad ica l ly d i f f e ren t times t o deionize, it i s d i f f i c u l t t o define a

spec i f ic deionization t i m e . Suff ice it t o say here t h a t without delayed

charging c i r c u i t r y the tube w i l l operate s a t i s f a c t o r i l y a t 110 kw aver-

age power a t 360 pps. Craggs and Meek report operating a t 23 kw aver-

age and 750 pps. A s of t h i s wri t ing w e bel ieve tha t operation a t pulse

r epe t i t i on rates of 1000 or even 2000 per second would be possible a t

75 kw average power, but w e do not; have t h e f a c i l i t i e s t o test t h i s

supposition.

8

- 12 -

IV. DISCUSSION OF PULSED IGNITRON OPERATION

During the course of t h i s invest igat ion a nurriber of experimental

observations were recorded which appear t o have an important bearing on

the theory of t he pulsed operation of igni t rons. Since no quant i ta t ive

theory dealing with t h e subject i s known t o t he authors, it seems

desirable t o recount these findings i n the hope t h a t they w i l l contr i -

bute t o an increased understanding of ign i t ron operation,

A convenient way t o discuss the pulsed operation of igni t rons i s

t o divide the pulse cycle in to three periods, which w e s h a l l discuss i n

the following order:

and (3) the pulse period.

seconds long; w e s h a l l consider t h e condition of t he tube j u s t before

f i r i n g . The post-pulse period of i n t e r e s t i s about two milliseconds.

The pulse period, during which the pulse current i s flowing, i s of t h e

order of a few (say th ree ) microseconds.

any one of the periods a f f e c t behavior i n t h e succeeding period w i l l be

(1) t h e hold-off period, (2 ) t h e post-pulse period,

The hold-off period i s of t h e order of m i l l i -

The way i n which the events i n

discussed below.

1. Hold-Off Period

During the hold-off period the poten t ia l d i s t r ibu t ion within the

tube must be such t h a t no conduction can occur. Generally speaking,

Paschen's l a w 9 i s expected t o d i c t a t e t he correct voltage d is t r ibu t ion ,

s ince it relates t h e poten t ia l t h a t can ex i s t perpendicular t o a gap

without breakdown t o t h e gas pressure within the gap. Figure 6 shows

t h e experimentally derived voltage d i s t r ibu t ion within t h e tube which

w a s found t o be the most s a t i s f ac to ry one f o r pulsed operation. Insofar

as hold-off i s concerned, t he most c r i t i c a l space i s t h a t between the

- 13 -

0- cu

0- d

0 3

f’ S * o c o c L n l r rl I I

k 0 0

q 4 - I

- 14 -

anode and the gradient gr id , across which 50 kv i s dropped.

l y no r e l i a b l e Paschen's breakdown curve (sparking poten t ia l vs reduced

electrode dis tance) is avai lable f o r t he range of reduced electrode dis-

tances per t inent t o the GL-6228; experimental work i n t h i s range i s

qui te d i f f i c u l t .

possible t o ass ign a r e l i a b l e value t o the ion density i n t h e anode-

gradient g r i d region because the high operating temperature of t h e anode

Introduces a density gradient i n t h i s region whose e f f ec t i s d i f f i c u l t

t o assess , Thus a cor re la t ion d i r ec t with Paschen's l a w i s not possible

a t present, although t h i s l a w did influence t h e direct ion of our experi-

mentation, Nevertheless, two important points can be made. (1) When

t h e ign i t ron i s used i n pulsed operation t h e voltage dis tpibut ion must

be a l t e r ed from t h a t associated with non-pulsed operation (e. g. , high-

po ten t i a l t e s t i n g ) because t h e space between t h e mercury pool and t h e

sh ie ld g r i d s tays ionized, as w i l l be discussed i n the next section.

For comparison purposes the recommended voltage d i s t r ibu t ion f o r t he

GL-6228 when used i n conventional r e c t i f i e r operation i s included i n

Fig. 6. (2) The voltage d i s t r ibu t ion shown i n Fig. 6 i s the f i n a l

r e s u l t of an exhaustive program of experiments t o derive the d is t r ibu-

t i o n t h a t provided the most s t ab le and r e l i a b l e operation and t h a t re-

duced the spurious currents inherent i n t h e post-pulse period t o a mini-

mum. Variations from t h i s d i s t r ibu t ion of only a few percent reduce the

tube performance below i t s optimum.

2 0 Post-Pulse Period

Unfortunate-

Even i f such a curve were avai lable , it i s almost i m -

This period w i l l be considered next because it provides some ins ight

i n to what occurs during t h e pulse period, Following the end of t h e

- 15 -

I

current pulse, it was found experimentally that the shield grid-cathode

voltage drop remained constant for a time which may exceed two milli-

seconds at high peak currents.

shown in Fig. 7.

increases with increasing current.

in terms of residual ionization.

period require a finite time to decay.

the deionization time.

ion density, created initially by the current pulse, has decayed to a

certain minimum ion density below which full conduction cannot be sup-

ported.

Curves typical of this performance are

Note that the time corresponding to the break-point

These curves have been interpreted

The ions formed during the pulse

This time will be referred to as

The break-point on each curve implies that the

This minimum ion density is fixed by the tube geometry.

Figure 8a shows the deionization time in the shield grid-cathode

region as a function of peak current for two different values of the

cooling-water temperature.

region around the control grid. Note the much shorter deionization

times associated with the control grid region.

surface ratio is much smaller in this area than in the area between the

cathode and the shield grid, the deionization time is correspondingly

shorter, because the major deionization process is recombination at the

wall. The most notable feature of these graphs is the fact that the

deionization time approaches a maximum value. This tmplies that the

ion density created initially by the current pulse approaches a maximum

value and that this maximum value can only correspond to lo@ ionization

of the mercury vapor. Thus, the deionization time is intimately associ-

ated with the degree of ionization.

Figure 8b shows the analogous data for the

Since the volume-to-

Two additional observations relating to the deionization time were

made. A s is apparent from Figs. 8a and 8b the deionization times in

- 16 -

t m

E-I r B" ,; V

r( H

m

- 17 -

..

u 0 In

II

R

0

> > \ u

3 3 3 u

3 3 -I n

0 0 0 A

0 0 In

0 0

- 18 -

c) 0 R II

E-l

9 u

\n M 0

\

h 0 0 0 0 c-7 cu rl

0 0 O e \c) In 3 0 0

03

(spuoaaso~aym) auqq uoyq'ezyuoyaa

0

cu R

0 0 0 (u

0 0 Ln rl

0 0 0 r l

0 0 In

0

- 19 -

both regions increased with increasing cooling water temperature. This

is simply a reflection of the fact that at the higher temperature the

pressure and gas density are higher and more atoms are available for

point ionization.

the deionization time plotted versus cooling-water temperature for fixed

arc current and fixed pulsed repetition frequency. The deionization

time increases steadily with temperature, The variation of the points

from the expected straight line is ascribed to experimental uncertainties.

This conclusion is emphasized by Fig. 9, which shows

The deionization time is also found to vary with pulse repetition

frequency, as shown by Fig. 10.

that the mercury vapor pressure that exists in the ignitron during opera-

tion corresponds to a temperature in excess of the cooling-water tempera-

ture.

per hundred ampere seconds.

greater the amount of mercury evaporated into the body of the tube,

Some but not all of the excess condenses out. A steady statedis reached

in which there exists an effective vapor pressure corresponding to a

temperature in excess of the temperature of the cooling-water.

3. Pulse Period

This is a reflection of the known fact

With each pulse mercury is boiled off at the rate of 0.75 grams

The longer and more frequent the pulse, the

As previously noted, Figs. 8a and 8b suggest that for peak currents

in excess of 2,000 amperes one is dealing with an essentially fully

ionized plasma. A complete qualitative theory for the pulse period

cannot be presented at this time. At higher peak currents one would

expect some form of a "pinch"" in which the radius of the discharge

column would contract due to the self-magnetic field of the current

being carried by the column, Cummings observed and photographed some

pinches at arc currents of 10,000 amperes.

4

However, under our operating

- 20 -

I

0 L n

0 0 m cu 0 r i

=t =t

0 f

\ D U m o B

f cu

0 cu 0

- 21 -

m g: 0 ul M

0

0 0 0 cu

0 0 Ln r(

0 0 0 rl

0 0 co

0 0 ul

0 0 f

0 0 cv

0 0

F (spuoaasozarm) J,

k u

-P cd

I 0 d

- 22 -

conditions it seems certain that the plasma is not pinching.

One interesting observation relates to an oscillation noted in the

arc current pulse waveform.

constant of 0.6 x 10 sec-l and a frequency of 5 Mc/sec. The ampli-

tude was solely a function of the cooling-water temperature, increasing

with increasing temperature.

was quite prominent at

by noting that the amplitude is a function of the initial time rate of

increase of arc current. At the higher cooling-water temperatures

dI/dt is larger because of the higher residual ionization left in the

cathode-shield grid region as a result of the increased vapor pressure

and particle density,

did not change with pressure suggests that the origin of the oscillation

is in the ignitron tube itself and not in the plasma column. Efforts

are being made to isolate the source of this oscillation.

It was a damped oscillation with a time 6

It was barely noticeable at T = 3 6 O c , but

This characteristic can be understood T = 5OoC.

The fact that the frequency and damping factor

We conclude this section by summarizing the order of events in the

ignitron, beginning at the end of the hold-off period with the tube in

an essentially quiescent condition.

The ignitor fires and forms a cathode spot.

The tube is switched on. The electrons from the cathode spot are

accelerated toward the anode, the arc discharge forms, and the current

pulse begins. The degree of ionization and the electron and ion temper-

atures quickly reach their steady-state values.

When the pulse network is discharged, the tube is switched off.

The plasma in the space between the grids begins to deionize. Simul-

taneously, the arc column expands toward the water-cooled walls of the

- 23 -

tube by ambipolar diffusion.

gr id region begins.

There deionization of the cathode-shield

The external circuit recovers and begins to build up voltage for

the next pulse.

are built up.

grid space but, because this space does not have to hold off any voltage,

no breakdown occurs.

The inter-grid plasma decays before appreciable voltages

Deionization proceeds more slowly in the cathode-shield

The hold-off voltage reaches its maximum value. Deionization is

The tube is essentially complete in the cathode-shield grid space.

again ready for firing.

3

- 24 -

V. CONCLUSIONS

A s the result of an extensive program of experimentation we have

concluded that commercially available ignitron tubes can be used success-

fully as high-power switches. Specifically they make possible the de-

velopment of modulators which satisfy the requirements outlined in the

Introduction for the modulators in the proposed Stanford two-mile linear

electron accelerator. However, in many ways they

surpass these specifications and offer promise f o r providing an order of

magnitude advance in high-power switch capabilities plus very long

switch-tube lifetimes. They should be especially useful in boosting the

power output potentials of land-based radar installations.

(See Figs, 11 and 12.)

An additional outgrowth of our experiments was a collection of

observations that contributed to our understanding of the pulsed opera-

tion of ignitrons. Based on these observations we designed an ignitron

specifically for high-power switching purposes. (See Fig. 13,) Its per-

formance is currently being evaluated,

I - 23 -

l l-71

- 26 -

Scale: 5 psec/cm

Fig. 12--Ignitor voltage (bottom curve) and holding anode current f o r GL-6228 operated i n c i r c u i t of Fig. 11. holding anode current i s 225 amperes. voltage is 400 vol t s . holding anode current maximum.

The peak The peak i g n i t o r

The control gr id i s f i r e d a t

- 27 -

- 28 -

LIST OF REFERENCES

1. I n i t s first phase of operation, t he two-mile acce lera tor would

produce a maximum electron energy of 20 Bev with an average beam

current of 30 pamps a t t h a t energy.

supplied by 240 klystron amplif iers , each del iver ing up t o 24 mega-

w a t t s of peak power a t the design frequency of 2856 Mc/sec.

Radiofrequency power would be

B c h

klystron would have i t s own modulator. By increasing t h e complement

of klystrons t o 960, it would be possible t o increase the beam ener-

gy t o 40 Bev and the average beam current t o 60 pamps. For a gener-

a l descr ipt ion of t h e proposed Stanford machine, see R. B. Neal and

W.K.H. Panofsky, "Progress Report on Proposed Stanford Two-Mile

Linear Electron Accelerator," Proceedings of CERN Conference on

High Eaergy Accelerators, CERN, Geneva, 1959.

2. H.C. S te iner , J .L. Zehner, and H.E. Zuvers, Trans. Am. I n s t . R e c .

mrs., 63 (1944).

3. M. J. Mulhern, Trans. Am. I n s t . Elec. EZtgrs., 69 (1950).

4. D. B. Cummings, UCRL Report No. 5687, Electronic Engineering

Department, Radiation Laboratory, University of California,

Livermore, Cal i fornia (June 3, 1960).

5. For an indicat ion of t he mercury ion bombardment damage possible t o

the ign i to r s t ruc ture , see D. B. Cummings , UCRL Report No. 5411,

Electronic Engineering Department, Radiation Laboratory, University

of Cal i fornia , Livermore, Cal i fornia (November 1958).

6. J. 0. Craggs and J. M. Meek, - High Voltage Laboratory Technique

(Butterworth Pub. Co., London, 1934), p. 204.

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7. See, for example: Internal Report No. LE 306-1, Electronic Engi-

neering Department, Radiation Laboratory, University of California,

Livermore, California (March 25 , 1959 ) . 8. Craggs and Meek, op. cit. , p. 204.

9. See, for example:

Oxford, 1955) pp. 169-173.

A. Von Ehgel, Ionized Gasses (Clarendon Press,

10. This topic is discussed in almost any book on plasma physics,

for example:

L. Spitzer, Physics -- of Fully Ionized Gasses (Interscience

Publishers, Inc., New York, 1956), pp. 41-43.

A. S. Bishop, Project Sherwood (Addison-Wesley Publishing

Co., Reading, Massachusetts, 1958), p. 24.

An especially clear exposition is in

S. Glasstone and R. H. Lovberg, Controlled Thermonuclear

Reactions (D. Van Nostrand Co. , Inc., Princeton, New Jersey,

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