RUTGERS 12-inch cyclotron For Students

Timothy W. Koeth Spring, 2006

The Rutgers 12 Inch Cyclotron

- What is a cyclotron ?

- A little cyclotron History - Who built the Rutgers Cyclotron ?

- How we did it - It works !

- Future Plans - Acknowledgements

“Start the Ball Rolling”

1927: Lord Rutherford requested a “copious supply” of projectiles more energetic than natural alpha and beta particles. At the opening of the resulting High Tension Laboratory, Rutherford went on to reiterate the goal:

What we require is an apparatus to give us a potential of the order of 10 million volts which can be safely accommodated in a reasonably sized room and operated by a few kilowatts of power.

We require too an exhausted tube capable of withstanding this voltage … I see no reason why such a requirement cannot be made practical.

MANY FAILED ATTEMPTS

Just one example:

1928: Curt Urban, Arno Brasch, and Fritz Lange successfully achieved 15 MV by harnessing lightning in the Italian Alps !

The two who survived the experiment went on to design an accelerator tube capable of withstanding that voltage.

Cyclotron History

1929: Rolf Wideroe R. Wideroe proposed an accelerator by using an alternating voltage across many alternating “gaps.” It was not without a myriad of problems - Focusing of beam - Vacuum leaks - Oscillating high voltages - Imagination His professor refused any further work because it was “sure to fail.” Never the less, Wideroe still published his idea in

Archiv fur Electrotechnic

Ernest Orlando Lawrence (EOL)

In April 1929, UC Berkley’s youngest Physics professor happened across

Archiv fur Electrotechnic

.

Not able to read German he just looked at the diagrams and pictures of the journal.

Immediately after seeing Wideroe’s schematic, Ernest fully comprehended it’s implications.

Cyclotron History

Lawrence quickly jotted down: F r



mV

2

r and equated with F B



qVB and solved for r: r



mV qB and substituted V in terms of

  2 

f



V r “R cancels R !” f



qB

2 

m The Cyclotron Frequency

Cyclotron History

& It worked : EOL was awarded the 1939 Nobel Prize for the invention of the cyclotron.

Beam plot from 4”

Cyclotron History

The Cyclotron evolved quickly at Berkeley: 4” (80keV protons) 11” (1MeV protons) 1931 1932 27” (5.5MeV Deuterons) 1937 37” (8.0MeV Deuterons) 1938 60” (16MeV Deuterons) 184” … 1939 1945

How the Cyclotron Works

Major Components of a Cyclotron

How the Cyclotron Works

A Mechanical Analog to the Cyclotron:

The Rutgers 12-inch Cyclotron

Who Built It ? And Why ?

Tim Koeth

Cyclotron “Staff”

Stuart Hanebuth Bill Schneider Dan Hoffman

The Cyclotron Students (9 so far):

Carolyn & Liam 2002 Rob & John 2003 Kent 2001 Doug & Mike 2004 Alex & Anthony 2006

The Rutgers 12-inch Cyclotron

FAQ: How long did it take ?

I got the “bug” in 1995 from Tom Devlin’s Class First beam detected 1999 It is now 2006 and I’m still partially involved… FAQ: How much did it cost ?

About $15,000 / 10 years between Tim & Stu ~ equal to smoking a pack of cigarettes/day FAQ: Why ? Initially to personally have the experience of replicating EOL & MS Livingston 1.2MeV Cyclotron, but then to share accelerator physics with other students.

The Cyclotron Chamber

1997 The SS Chamber started out as a 2” x 4” bar that was rolled, welded, and machined down. The lids are ¼ inch Aluminum and are sealed with Viton o-rings The SS was a donation from Alloy Fab of S. Plainfield NJ The machining costs were about $500 at the Rutgers Phys & Chem Shop Vacuum hardware purchased from KJL

The Cyclotron Chamber

2006

9-Inch Cyclotron Prototype

$50 and a case of beer to the guys at Rutgers surplus: A 9 Inch 1960’s vintage Varian NMR Magnet ~2000 LBS, 40Volts, 170Amps, Peak field: 1.2 Tesla

9-Inch Cyclotron Prototype

9-Inch Cyclotron Prototype

Early Ion Source: Negatively biased hot filament located near the top of the chamber between the DEEs emits electrons that follow the B-field, ionizing Hydrogen on the way down Top View In operation seen through view port.

9-Inch Cyclotron Prototype

1 st successful operation was recorded by slowly sweeping B-field to located resonance condition. September 16, 1999: Faraday cup insertion set to intercept beam at 300keV.

1

st

Detected Beam September ‘99

After parameters were adjusted for peak beam intensity (ion source, RF, magnetic field, etc) the florescent screen was inserted. A tall narrow beam spot was observed: Then the spot abruptly extinguished, but the electrometer said otherwise.… After some thought, and 2 hours in the sputtering lab, I tried again. This time with 50 Å of gold coated on the screen with a path to ground. The spot never extinguished again !

The Rutgers 12-inch Cyclotron

Since I initially set forth the goal of generating 1.2 MeV Protons to duplicate E.O.L. and M. Stanley Livingstons 1MeV experiment, I was not satisfied with the 9-inch magnet setup.

EOL’s 1.2 MeV Cyclotron - 1932 Tim’s 1.2 MeV Cyclotron - 2006 We needed a 12” inch magnet…

The Rutgers 12-inch Cyclotron: The Magnet I had read that ANL had a 60 inch cyclotron. 1950s 1998 A 12” magnet While at FNAL in 1998 I arranged a tour of the machine. I was amazed to find out that the machine was scheduled for demolition in a few months time.. I asked if I could have it… They said “sure…”

The Rutgers 12-inch Cyclotron: The Magnet ANL Building 211’s loading dock – Oct ‘98 Bare Metal New coils (Low Z) Back at RU

Nice paint job The Rutgers 12-inch Cyclotron: The Magnet Stu making the table 1 st electrical test 12” Magnet 5500 lbs (1600 in Cu) Gap ~ 2” 80V 50 Amps 1.21 Tesla

Magnet Studies: Weak Focusing

Flat pole tips profile – no focusing !

Intentionally introduce radial B-field component: New pole tips with radial slope !

Magnet Studies: Weak Focusing

Poisson Superfish (PSF) modeling of tapered pole tips 1.2

1 0.8

0.6

0.4

0.2

Measured Vs. Modeled Field Profile 0 0 1 2 3 4 5 Radius [inches] 6 7 8 9 10 1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0.0

0

Theoretical Field Inex

n

 

r B dB dr

There are three possible cases: 1.

n

< 0 the field increases with

r

2.

n

= 0 the field is uniform 3.

n

> 0 the field decreases with

r

5 10 Radius [cm] 15

Magnet Studies: 2D field Mapping

Due to the non-azimuthal symmetry of the magnet’s construction (i.e. the left right return yokes) there may be an azimuthal variation in the magnetic field. An azimuthal variation with a periodicity of 2 is radially unstable (periodicities of 3 or more are stable).

Tesla Two students set forth to design a 2 dimension “robot” to map the magnetic field in the median plane. The were only able to build the unit, write the control software but did not have enough time to take data or analyze… We are still awaiting for this project to be revisited ( x y  B ) X Trial run of 2-D Mapper Y

The Vacuum System

CHAMBER MV LN2 TRA P WATER COOLED BAFFELS ROUGH VALVE ROUGH PUMP WATER COOLING DIFF PUMP SAFETY VALVE IONIZATION GAUGE FORE PUMP PIRANI GAUGE PIRANI GAUGE

The Vacuum System

Chamber pumps down to 5x10 -7 Torr ~ 2 hours We operate fine at 1x10 -5 Torr 2 Thermocouple Gauges ,1 ion gauge Diff Pump ion gauge Mass flow controller interface (student project)

New Ion Source:

PSF model of early Ion Source Present Ion Source with Chimney

New Ion Source

Chimney installed in between DEE (l) and Dummy DEE. Top of Chimney in thermal contact with Dummy DEE and chamber. Filament requires ~ 22A, 5 Volts (~110 Watts), bias -200 V, up to 50mA

x y

of emission.

  

qE

2

m qE m

2

m

 2

m

 2 {  {  sin( 

t

0 ) sin( 

t

) cos( 

t

0 ) sin( 

t

)   

t

sin( 

t

2 sin( 

t

0 )[ 1   Ion Source as seen in operation though view port. Hydrogen plasma “sprays” into DEE aperture. Needs characterization – another student project.



t

0 )} cos( 

t

)]  

t

cos( 

t

 

t

0 )} Assumes electric field of DEE Dummy DEE gap spacing of ½ inch/DEE V peak

Early Ion Paths at Several DEE Voltages

Scale : inches 1.0

1.0

1.0

First Ions Clear Chimney 0.5

0.5

0.5

-1.0

-0.5

0.0

0.0

0.5

-0.5

-1.0

1.3KV

peak 1.0

-1.0

-0.5

0.0

0.0

0.5

-0.5

-1.0

1.9KV

peak 1.0

-1.0

-0.5

0.0

0.0

0.5

-0.5

-1.0

2.5KV

peak 1.0

1.0

0.5

-1.0

-0.5

0.0

0.0

0.5

-0.5

-1.0

2.7KV

peak 1.0

1.0

0.5

-1.0

-0.5

0.0

0.0

0.5

-0.5

-1.0

3.8KV

peak 1.0

1.0

0.5

-1.0

-0.5

0.0

0.0

0.5

-0.5

-1.0

5.9KV

peak 1.0

The Cyclotron RF System

f cyc



qB

2 

m

 ~ 15

MHz f o

 2  1

LC C

 78 .

1

pF

L

L

 1 .

1 

H

C

The Cyclotron RF System

Record Input Power 2kW: 8.4 kV peak

How Much RF power is needed ?

V p



p

 2 2

PL R AC C

18000 16000 14000 12000 10000 (the ion energy gained in one revolution) Comparison of Measurements and Theory

R AC

 0 .

80  8000 6000 4000 2000 0 0 200 400 600 800 Forward Power [watts] 1000 Series3 Series4 Series5 Series1 Series2 1200 1400 RF Pickup -0.5

-0.3

0.5

-0.1

0.0

0.1

0.3

0.5

-0.5

inches

12000 10000 8000 6000 4000 2000 DEE V to Pickup Corellation y = 3710.1x

R 2 = 0.9938

0 0 0.5

1 1.5

2 Pickup Vp-p 2.5

3 3.5

Calculation showing first ions squeak by at 165 Watts of RF into the cyclotron at 14.8640MHz. This was verified by starting with beam at 300Watts and reducing RF power while watching beam current. Beam intensity decreases with RF power.

Beam current abruptly dropped to zero at 170 watts !

12 Inch Cyclotron Controls:

Operator’s Position: LabView VI display

Lets make beam !

• Vacuum: √ • Magnet: √ • Ion Source: √ • RF Power: √ • Controls: √ Observed beam spot above median plane.

Observed Betatron Motion

r o r 1 r 2

f = 14.864 MHz B o = 0.977 Tesla RF Power: 300 W (7,500 V p-p )

r 0 =8.6 cm (338keV) r 1 =9.2 cm (387keV) r 2 =9.6 cm (421keV) radius

15 second exposure while positioner was slid in and out.

Expected Betatron Motion

Ion Energy [eV]: Take derivative: Turns spacing:

E



r



E



r

   

qB

2 2

m r

2  1   

E



E

2 

E E

 2  1

E

where Or since E(r): 

r

 2 

qB

2 2

m

 

Em qB

2

r

r [cm] 8.6

8.7

n(r) 0.025

0.026

Fraction of Betatron Period 0 0.2

8.8

0.026

0.3

where 

E

is energy gained per rev, or just DEE V p-p 8.9

0.027

0.5

Using our operating values: 

r

 7500

eV

 1 .

6

E

  1 .

67 27

E

  0 .

977  27 2  1

r

or 

r

 8 .

2

E

 5 

r

1 9.0

9.1

0.028

0.030

0.6

0.8

9.2

0.031

1.0

Caclulated n values

Calculated

n

(r) Vertical Betatron Relationship: 6.00E-02 9.2

0.033

1.2

9.3

0.034

1.3

5.00E-02

f

 

vert



T

 

vert



n f

0 1

n T

0 1

n

4.00E-02 3.00E-02 2.00E-02 1.00E-02 y = -0.0008x

4 + 0.0354x

3 - 0.5587x

2 + 3.7821x - 9.3651

R 2 = 0.9997

0.00E+00 8 8.2

8.4

8.6

8.8

9

radius [cm]

9.2

9.4

9.6

9.8

10 9.4

9.5

9.6

9.7

0.037

0.039

0.041

0.042

1.5

1.7

1.9

2.1

Almost a Perfect Match !

Future Projects:

2D Magnetic field mapping (?) Auto-tuner for Cyclotron RF tank (present student work) Characterize Ion Source Experiments: Cyclotron Magnetic Resonance Condition Reducing Betatron Oscillations E X B spectrometer (septum & deflector) Run with Deuterium Ions: neutron production & Activation expt’s Proton-Deuteron Mass difference (?) Make a new chamber to extract beam

“Brag & Brag Shamelessly”

- Tom Devlin

Acknowledgements

Tom Devlin

: Inspired me to build the cyclotron during one of his Modern Physics Lectures in 1995.

Mohan Kalelkar

: Undergraduate chairman.

Always

finds the needed funds and other support to make with work possible ever since I “loaned” the cyclotron to the lab course in 2001 The Senior (Modern Physics) Lab Course Instructors: M. Gershenson G. Thomson H. Kojima