EXPERIENCE WITH THE CONSTRUCTION ANDOPERATION WITH THE MAGIC TELESCOPE

E. Lorenz, MPI Munich

WILL CONCENTRATE ON ISSUES RELEVANT FOR THE CONSTRUCTION OF POSSIBLEFUTURE LARGE IACTS

A FEW COMMENTS ON THE PAST:IDEA FOR MAGIC WAS ‘BORN’ IN 1994/5

LARGE MIRROR INSPIRED BY A 17 m Ø SOLAR MIRROR OF THE DLR CONSTRUCTEDIN LAMPOLDSHAUSENMECHANICS INSPIRED BY THE DESIGN OF SCHLAICH, BERGEMAN AND SONS

SOON OBVIOUS THAT THE ORIGINAL MIRROR CONCEPT UNSUITED FOR THEREQUIRED PRECISION OF AN IACT (FOCAL SPOT MUCH TOO LARGE)

FUNDING AGENCY SET TIGHT PRICE LIMIT OF 5 MDM (=2.5 M€) IN 1996

SOME ORIGINAL GOALS

• CLOSE THE ENERGY GAP BETWEEN 2. GENERATION IACTS AND EGRET-> THRESHOLD 15 GEV ?NOT POSSIBLE WITH CLASSICAL PMTS ->NEW DEVELOPMENT OF HIGH QE PMTSLOTS OF NEW PHYSICS EXPECTED IN THE ENERGY DOMAIN < 300(150) GEV

• RECOMMENDATION FROM REVIEW COMMITTEE: BUILD MAGIC FIRST WITHCLASSICAL PMTS

ALLOW FAST ROTATION FOR GRB OBSERVATIONS -> LIGHT WEIGHT CONSTRUCTION, RIGID CONSTRUCTION

ALLOW OBSERVATIONS DURING PARTIAL MOON SHINE-> USE PMTS WITH LOW GAIN + VERY GOOD AC COUPLED PREAMPS

INCREASE DAQ RATE TO 500-1000 HZ

BUILD A NEW TECHNOLOGY TELESCOPE, AFTER SUCCESSFUL DEMONSTRATION-> MULTIPLE TELESCOPE (STEREO OR MULTIPLE PARALLEL OBSERVATIONS)

WHY NOT A STEREO SYSTEM FROM THE BEGINNING ?

NO FUNDING AGENCY WOULD HAVE GIVEN MONEY FOR 3-4 NEW TECHNOLOGY TELESCOPES WITHOUT TESTING A LARGE PROTOTYPE

FUNDING AGENCIES WOULD FIRST REQUIRE 1 DEMO AND THAN DECIDE ON THE NEXT ONES.

EVEN IF WE HAD APPLIED FOR NOVEL TELESCOPES WE COULD, WITHIN THE FINANCIAL LIMITS, ASK ONLY FOR SMALL TELESCOPES

ADVANTAGE OF ONE LARGE TELESCOPE FIRST: LOWER THRESHOLDDISADVANTAGE: LOWER SENSITIVITY IN OVERLAP REGION

LESSON TO BE LEARNED: IF THE CONSTRUCTION WILL BE TOO AMBITIOUSONE WILL HAVE TROUBLE TO GET FULL SUPPORT FROM THE COMMUNITY(BMBF WAS MORE POSITIVE ABOUT NEW IDEAS AND NEW TECHNOLOGIESTHAN COMMUNITY)

THE MAGIC I TELESCOPE

17 mtr

NOVEL OR UNCONVENTIONAL TECHNICAL COMPONENTS

ITEM WHY .

17 m DIAMETER MORE LIGHT -OPTICAL DISTORTIONS

SPACE FRAME - CARBON FIBER-EPOXY TUBES LOW WEIGHT, SEE LIST

SINGLE MAST CAMERA SUPPORT LESS OBSCURATION, WEIGHT

NEW MIRRORS LOW WEIGHT, CHEAPER, SEE LIST

ACTIVE MIRROR CONTROL CHEAPER SPACE FRAME

SPECIAL PMTS MORE SIGNAL, SEE LIST

ANALOG SIGNAL TRANSMISSION OF PMT SIGNALS NO BULKY CABLES, SEE LIST

300 MHZ FADC NSB REDUCTION, NOW STANDARD OR EVEN OUTDATED

MULTI-LEVEL TRIGGERS HIGHER TRIGGER SELECTIVITY

NEW TECHNOLOGIES HAVE ALWAYS SOME RISK. GENERAL: 1 DEVELOPMENT ≈ BREAK EVEN OR FAILURE 2. PRODUCTION: REAL BREAKTHROUGH 3. PRODUCTION: SETS NEW STANDARD

SOME TECHNICAL DETAILS I:

CONCRETE FOUNDATION: CONVENTIONAL, WEIGHT >> TELESCOPE WEIGHT FOR STABILITY REASON: WIND, VIBRATIONS GOOD FOR 15 Y LIFETIME, BUT NOT FOR>>15 Y WE HAVE TO BUILD IN EASY DISMOUNTING

KNOWN PROBLEMS: SHOULD BE WHITE TO PREVENT SUN HEATUP SHOULD BE BLACK TO SUPPRESS NSB REFLECTION

DOME ?? TO EXPENSIVE BUT MAY BE NEW IDEAS AROUND TO COVER ONLY MIRROR

RAIL: SIMPLE RAILWAY RAIL WITH < 1 mm VARIATION IN HEIGHT CURRENT SYSTEM CAN MOVE UNDER THERMAL EXPANSION SLIGHT DEFORMATION -> LIMITED TRACKING PRECISION RAIL SUPPORTED EVERY 60 cm -> SLIGHT DEFORMATION UNDER TELESCOPE LOAD (2 BOGEY WHEELS ≈ 210 CM APART->SOME EQUALIZING OF DEFORMATION BUT NOT ALL FOR 6 BOGEYS)

NOTE: WITH 6 BOGEYS SYSTEM OVERDETERMINED_> SOME INTERNALDEFORMATION OF SUBSTRUCTURE ->NO PERFECT SHAFTENCODERS NEEDED <-> PRECISE TELESCOPE AXIS POSITION MEASUREMENTS IMPOSSIBLE -> 13 BIT ENCODERS OK 0.02° LSB

ALSO AFFECTING TRACKING:WE USE CHAINS LIKE IN A BICYCLE- SOME PLAYNOT PERFECTLY ROUND -> SOFTWARE CORRECTIONSNOT PERFECTLY SMOOTH (LINEAR) -ALSO A REASON WHY A PERFECT HIGH RESOLUTION SHAFTENCODER DOES NOT HELP

NOTE: WE HAVE 1 SHAFTENCODER FOR AZIMUTH POSITION, 2 FORDECLINATION (DEVIATE FROM EACH OTHER- MIRROR DISH DEFORMATIONPROBLEM WITH CULMINATION-> SEPARATE TALK)TELESCOPE CAN TURN > 450° IN AZIMUTH -> MULTITURN SHAFTENCODER

ENCODERS ARE ABSOLUTE ENCODERS -> NO CHANGE AFTER POWER FAILUREENCODER ARE THE HIGHEST MECHANICAL PRECISION ITEMS OF DETECTOR

DRIVE MOTORS: 11 KW SYNCHRO-MOTORS (CURRENTLY LIMITED TO ≈ 70%OF PEAK POWER)MAX TURNING OF TELESCOPE->CAN REACH 180° IN AZIMUTH IN ≈ 20 SEC2 MOTORS FOR AZIMUTH (HAVE TO MOVE 64 TONS)1 MOTOR FOR DECLINATION (HAS TO MOVE 22 TONS

WEIGHT OF TELESCOPE ELEMENTS•BOGEYS 25.2 T•LOWER STRUCTURE 15.8 T•CAMERA 0.75 T•CAMERA MAST RING 1.2 T•MIRRORS 12. T•SPACE FRAME 5.6 T•COUNTER WEIGHT 2. T•AUXILIAR ELEMENTS 1.4 T

•SUM ≈ 65 T

LESSON TO BE LEARNED: BOGEYS ARE UNNECESSARY HEAVY, IF A BETTER SOLUTION FOR PROTECTION AGAINST STRONG WINDS CAN BE FOUND(SEE ALSO LATER COMMENT ON ADVERSE ATMOSPHERIC CONDITIONS)

WHY DID WE CHOOSE A SPACE FRAME MADE FROM CARBON FIBER-EOPXY TUBES

•LOW WEIGHT (5.4 TONS FOR MAGIC)•LESS DEFORMATION THAN STEEL OR ALUMINUM (17 MØ DISH QUITE DIFFERENT TO 10 MØ DISH )•SAGGING ABOUT 1/2 OF SAME STEEL CONSTRUCTION•WEIGHT 1/3 OF STEEL CONSTRUCTION•THERMAL EXPANSION NEARLY ZERO•(STEEL EXPANDS BY 3 cm BETWEEN DAY-NIGHT TEMPERATURE CHANGE OF 50°C), WE SEE EFFECT VERY CLEARLY DURING DAY-TIME•HIGH OSCILLATION DAMPING•NO CORROSION-RUST

DISADVANTAGES•HIGHER DEVELOPMENT COSTS (NOT MORE IN FUTURE)•HIGHER PRODUCTIOPN COSTS( NOW MARGINALLY HIGHER)•ORIGINALLY NO LONGTERM EXPERIENCE

•LESSON TO BE LEARNED: RAPID PROGRESS IN CFRP CONSTRUCTION COMPONENTS. ENORMOUS PROGRESS IN YOUNGS MODULUS, MAX BREAKING LIMITS EPOXY MATERIALS

MIRRORSALL ALUMINIUM SANDWICH CONSTRUCTION WITH INTERNAL HEATINGDIAMOND TURNED SURFACES, 10 DIFFERENT RADII (-> APPROXIMATION OF PARABOLA-> ISOCHRONOUS -> NO ADDITIONAL TIME SPREAD FOR SIGNALS - STAGGERING- TIME SPREAD < 0.4 nsec)

WE HAVE 49.5X 49.5 cm MIRROR ELEMENTS (DIAMOND TURNING TECHNIQUE 2000, OPTICALDISTORTIONS SMALL)4 MIRRORS MOUNTED ON A PANELPANELS MOUNTED TO SPACE FRAM VIA AMC TOTAL MIRROR AREA 236m**2MIRRORS HAVE QUARTZ COATING FOR PROTECTION

ADVANTAGES:LESS WEIGHT THAN GLASS MIRRORSCHEAPER (WHEN USING WESTERN PRODUCTION COSTS)CAN HAVE NON-CIRCULAR SHAPE : SQUARES WITH ROUNDED EDGES…LESS DAMAGE DUE TO CORROSIONEASIER TO PRODUCE WITH DIFFERENT RADIIWILL NOT BREAK

DISADVANTAGESSLIGHTLY LESS REFLECTIVITYCAN HAVE AGEING DEFORMATIONS DUE TO SLOW CONTINUING PLASTIC POLYMERISATION (MPI MIRRORS)CAN HAVE WATER LEAKS (DELAMINATION WHEN FREEZING)

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Mirrors quartz coated

THE MIRRORCOMPOSED OF 940 ELEMENTALL ALUMINIUM CONSTRUCTIONMANY DIFFERENT RADII (PARABOLIC PROFILE)

M. GARCZARZYK, USING METHOD PROPOSED. BY RAZMIK MIRZOYAN IN 2003 (SEE ALSO CONTR, PALAUSEAU CHERENKOV MEETING): OBSERVE DIRECT STAR + REFLECTED IMAGE ON CAMERA COVER

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VEGA, OBSERVED BOTH DIECTLY BY STARGUIDER CAMERA AND OVER CAMERA COVER(IMAGES OF VEGA COMPLETELY OVEREXPOSED)

THE ACTIVE MIRROR CONTROL

FOR LARGE DISHES DEFORMATIONS A PROBLEM

A)EITHER BILD A STIFF BUT HEAVY CONSTRUCTIONB) OR A LOW WEIGHT CONSTRUCTION AND CORRECTION OF BENDING EFFECTS

LARGE MODERN OPTICAL TELESCOPES FOLLOW B)

MAGIC: THE FIRST TEST OF AMC FOR IACTS NO PREVIOUS EXPERIENCE INDUSTRY HAD NO SUITABLE UNITS AND WE HAD TO DEVELOP IT INHOUSE HARD ROAD TO GET IT WORKING PROBLEMS TO UNDERSTAND THE PRINCIPLE HARDWARE PROBLEMS WITH WATER TIGHTNESS IP67 NOT ENOUGH MONEY TO EQUIPP EVERY MIRROR WITH AMCBUT FINALLY IT WORKED WELL

THE ACTIVE MIRROR CONTROLCOUNTERACTS SOME SMALL DEFORMATIONS OF MIRROR SUPPORT FRAME

EXAMPLE OF MIRROR FOCUSSED TO A LIGHTSOURCE 1000mtr AWAY

PSF 0.03° AFTER MANUALADJUSTMENT (0.02° POSSIBLE)WILL DEGRADE DURINGRUNS IF NOT FREQUENTLYREADJUSTED

0.1°

pedestal

Slide 3

Lasers of the Automatic Mirror Control on a foggy evening …Lasers of the Automatic Mirror Control on a foggy evening …

The camera

Two sections: Inner part: 0.10 PMTs Outer part: 0.20 PMTs

Plate of Winston conesPlate of Winston cones Active camera area Active camera area 100%100%

Matrix of 577 PMTsMatrix of 577 PMTs

SEE SEPARATE TALK FLORIAN GOEBEL

A FREQUENTLY ASKED QUESTION

WHY DID WE NOT BUILD A UNIFORM CAMERA

TWO DIFFERENT SIZES OF PIXELS VERY INCONVENIENT MC, CALIBRATION, UNIFORMITY

MAIN REASON WAS COSTS

1 PIXEL PRICE ≈ 2000€

AN ALL FINE PIXEL CAMERA WOULD BE NEARLY TWICE AS EXPENSIVE

FINE PIXELS NOT JUSTIFIED FOR OUTER AREA DUE TO ABERRATIONS

-> A POINT IMAGE BLURRED BY ABOUT 0.2° DUE TO f/D ≈ 1 + ALSO PARABOLIC PROFILE

LESSON TO BE LEARNED: USE f/D > 1.2 AND AT LEAST 5° FOW CAMERA WITH

UNIFORM PIXELS IF MONEY IS NOT THE MAJOR CONSTRAINT

A PARABOLIC PROFILE IS NEARLY A MUST

WE USE HEMISPHERICAL PMTS WITH 6 DYNODES

ADVANTAGES•BETTER TRANSIT TIME SPREAD•OPTIMAL FOR LIGHT CATCHERS•SOME DOUBLE CHANCE OF PHOTON-PHOTOELECTRON CONVERSION•LOW GAIN-> LOW ANODE CURRENT DUE TO NSB, MOON SHINE->•LESS AGING, LESS DAMAGE, CAN WORK DURING MOON SHINE•LESS POWER FOR HT, LOWER HT, LESS BLEEDER CURRENT-LOWER HEATING IN CAMERA•FASTER•HIGHER GAIN FOR PANEQUE LACQUER ->ABOUT 13-15% PHOTON-PHOTOELECTRON CONVERSION POSSIBLE

DISADVANTAGESHIGH QUALITY PREAMP NEEDEDCAN HAVE MORE PICKUP, NOISE ON SIGNAL

OTHER DISADVANTAGE SPECIFIC TO SELECTED PMTHIGH AFTERPULSE RATE AND LARGE AFTERPULSES FOR HIGH PE COLLECTION EFF.TUBE VACUUM

WE HAVE A CAMERA WINDOW THAT CAUSES 8% LIGHT LOSSWE HAVE SOME PROBLEMS WITH TEMPERATURE STABILIZATION, HUMIDITY

ONE GENERAL ISSUE IF ONE USES PMTS:WHAT IS THE PHOTOELECTRON COLLECTION EFF.

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AREA RATIO OFWinston Cone/PMT=1.91

PM GAIN ≈ 10 000PM type 9116ANOTE: NON-NEGL. SENSITIVITY TO NSBLIGHT SCATTERED FROM GROUNG

0

0,5

1

1,5

2

2,5

3

-60 -40 -20 0 20 40 60

Gain: Wiston cone + Laquer coating

RELATIVE GAIN/cos

Θ

, 0° NORMALIZED TO INCIDENCE OF PLAIN PMT

ANGLE OF INCIDENCE

----- 3 + cone lined with M dielectric foil laquer coating----- + cone lined with aluminised Mylar laquer coating----- , 22 plain PMT diaphragm mm

<- ->LIMIT ANGULAR ACCEPTANCE

CAMERA

CONNECTION BETWEEN CAMERA AND DAQ

MAGIC USES OPTICAL FIBERS FOR THE ANALOG SIGNAL TRANSFERFROM CAMERA PMTS TO THE 100 M AWAY COUNTING HOUSE

PROS: LOW WEIGHT OF CAMERA (OSCILLATIONS REDUCED) REDUCED ELECTRONICS IN CAMERA -> LESS DOWNTIME DUE TO DEFECTS LOW POWER CONSUMPTION IN CAMERA EASIER TO MODIFY ELECTRONICS (TRIGGER…) EASIER TO IMPLEMENT TRIGGER FOR MULTITELESCOPESYSTEM

CONS: NEW PRINCIPLE, NO EXPERIENCE EXTRA COSTS

USE OF VCSELS AS LIGHT EMITTER (CAN DRIVE TO 200 MA PULSE CURRENT FORLOW DUTY CYCLE. HIGH BANDWIDTH (> 1 GHZ POSSIBLE, NOW 230 MHZ BW)NO ATTENUATION OVER 165 M LENGTH

ACHIEVED DYNAMIC RANGE ≈ 800 (LINEAR), > 1000 WITH SOME NONLINEARITY

WE ARE WORKING ON NEXT GENERATION ‚MONOMODE‘ VCSELS. -> HIGHER STABILITY, LOWER NOISE, LOWER POWER

EXPERIENCE WITH ADVERSE ATMOSPHERIC CONDITIONSHIGH WIND SPEED, GUSTY WINDS

•NO PROBLEM TO OBSERVE AT WINDSPEEDS > 10, BUT < 15 m/SEC WIND•CAMERA OSCILLATIONS VERY SMALL•CFRP TUBES HIGH OSCILLATION DAMPING (PROBLEMS WITH LONG METAL TUBES)•USE OF HEAVY BOGEYS: A SAFETY ISSUE BUT BETTER SOLUTIONS WITH MUCH LESS WEIGHT POSSIBLE•HIGHEST WIND SPEED AT SITE UP TO NOW ≈ 140 KMH -> NO PROBLEMS

HUMIDITY: SERIOUS PROBLEMS BECAUSE NOW MORE ELECTRONICS, ELECTRICAL COMPONENTS… A LESSON TO BE LEARNED: COMPONENTS MUST BE IP67 TESTED FOR LONG DURATION AND STRONG SUN LIGHT EXPOSURE

ICE, DEW: LESS SERIOUS THAN ANTICIPATED: HEATING OF MIRRORS WORKS BUTPOWER CONSUMPTION MIGHT BE A PROBLEM

UV-LIGHT OF SUN (CAN BE VERY DESTRUCTIVE AT HIGH ALTITUDE FOR PLASTICS)NO SERIOUS PROBLEMS ENCOUNTERED (EX CABLE BINDERS…)

FAILURES OF ELECTRICAL POWER CAN BE A PROBLEM

FOREST FIRES CAN BE A SERIOUS PROBLEMLIGHTNING PROTECTION

PM, 6 DYNODES

PREAMP

OPTICAL FIBER160 mtr

PIN PHOTODIODE

AMPL.

FAST PM SIGNAL TRANSMISSION BY OPTICAL FIBER SYSTEMWORKING IN ANALOG MODE

VCSEL Input pulse ≈ 2.5 nsecOutput pulse at optical fiber system, 160mtrOutput pulse after RG 58C cable, 156 mtr

•VERY LOW FAILURE RATE AFTER ≈ 1 YEAR

•VERY LOW CROSSTALK, NO PICKUP

•LARGE DYNAMIC RANGE (>60 db)

•SOME NONLINEARITY

•SOME GAIN SHIFT AND MODE HOPPING

•NEEDED TO SELECT VCSELS

TO TRIGGER LOGIC

TO FADC

SUMMARY

MANY TECHNOLOGIES USED IN MAGIC WERE VERY AMBITIOUS IN 2000 BUT NOW NEARLY ‘CONSERVATIVE ‘

CAMERA AND ELECTRONICS ARE OUTDATED MOSTLY AFTER 4-6 YEARS(WE HAVE PROBLEMS TO GET SOME SPARE ELECTRONICS CHIPS)EXAMPLES 300 MHZ FADCs, FAST COMPARATORS

THERE ARE ALSO NEW SOLUTIONS FOR HARDWARE STRUCTURE AVAILABLEFOR LARGE DISHES FOR REASONABLE COSTS

HIGH WIND SPEED MIGHT BECOME A PROBLEM

MORE AND MORE ELECTRONICS COMPONENTS - PROBLEMS WITH WATERTIGHTNESSERVICING AND REPAIR

VERY GOOD EXPERIENCE (EXCEPTIONS CONFIRM THE RULES) WITH DIAMOND TURNED MIRRORS

AMC A VIABLE SOLUTION TO BUILD LOW WEIGHT DISHES

The Calibration: hardware

• Nishia single quantum-well LEDs • Light pulses in 3 colors (UV, blue and green)• Different intensities over dynamic range of factor 300 • Match pulse width of cosmics• Trigger available over wide range of frequences: E.g.: - Calibration run: 500 Hz - Data run with interlaced calibration events: 50Hz - Test runs up to: 4 KHz

WE HAVE A TEMPERATURE

STABILITY PROBLEM

SOME KEY MAGIC PARAMETERS:•MIRROR AREA 242 m2 f/D = 1 MIRROR Ø: 17 m MIRROR PROFILE: PARABOLIC (ISOCHRONOUS)

•MAIN MIRROR COMPOSED OF 940 ELEMENTS,

•ALL ALUMINIUM SANDWICH UNITS, DIAMOND TURNED, LIGHTWEIGHT, HEATEABLE

•ACTIVE MIRROR CONTROL TO COUNTERACT SMALL DISH DEFORMATIONS

•574 PIXEL CAMERA, 3.5 ° Ø, INNER PIXELS 0.1°Ø, OUTER PIXELS 0.2° Ø, SPECIAL LIGHT CATCHERS

•HEMISPHERICAL PMTS (ET 9116,9117, 6 STAGTES) TREATED FOR ENHANCED QE (30-34% AT PEAK )

• LOW LOSS, HIGH BW (> 250 MHz) SIGNAL TRANSMISSION BY OPTICAL FIBER SYSTEM

•THREE LEVEL TRIGGER (REJECTS ALREADY A FRACTION OF HADRONS ON TRIGGER LEVEL)

•TRIGGER AREA ≈ 2° Ø, TRIGGER RATE 250-300 Hz ( TECHNICAL LIMIT 1 KHz)

•SIGNAL DIGITISATION: DUAL RANGE FADC (≈ 58 dB DYN. RANGE) , DIGITISATION FREQUENCY 300

MHz

•MAX ROTATION SPEED: 23(20) sec FOR 180° TURN -> FOR RAPID RESPONSE TO GRBS(CONTROLLED

•TESTS), CURRENTLY NO REVERSE MODE -> SOMETIMES 360° TURNS NECESSARY, ALSO SLOWER

•BECAUSE OF SAFETY REASONS

SOME KEY MAGIC PARAMETERS II:

TRACKING PRECISION ≈ 0.02 (WITHOUT STARGUIDER CAMERA) EXPECT TO REACH 0.005 WITH STAR GUIDER CAMERA

PSF: 0.03° EXPECT TO REACH 0.02° FOR OPTIMISED AMC

CURRENT THRESHOLD: AROUND 50 GeV (TRIGGER) AROUND 80-90 GEV FOR PHYSICS ANALYSIS

->30-40 GEV FOR SPECIAL PULSAR TRIGGER

CURRENT SENSITIVITY: STILL ABOUT FACTOR 2-3 WORSE THAN PREDICTED (USE OF CLASSICAL IMAGE ANALYSIS NOT SO EFFICIENT < 150 GeV)

PMT

Maximizing Double-Hits in a PMT

Not yet optimized for the milky PMT coating

Significant additional improvements to come

PHOTOCATHODE

OLD TRICK OF ASTRONOMERS TO INCREASE QE

SMALL PRISM

FRACTION OF LIGHT SCATTERED OUT

MOST LIGHT TRAPPEDINSIDE HIGH n MATEREIAL

GRADED DIFUSSE SCATTER LAYERWITH MICROSCOPICVOIDS

PHOTOCATHODE

A TOY MODEL